Aneka Teknik Listrik - Electrical, by ATC Automation

Exploring Current Transformer Applications (Part 2)

2011-09-30T23:10:00.000+07:00

When choosing the burden resistor, the engineer can create any output voltage per amp, as long as it doesn't saturate the core. Core saturation level is an important consideration when specifying current transformers. The maximum volt-microsecond product specifies what the core can handle without saturating. The burden resistor is one of the factors controlling the output voltage. There's a limit to the amount of voltage that can be achieved at a given frequency. Since frequency = 1/cycle period, if the frequency is too low (cycle period too long) so that voltage-time product exceeds the core's flux capacity, saturation will occur. The flux that exists in a core is proportional to the voltage times cycle period. Most specifications provide a maximum volt-microsecond product that the current transformer can provide across the burden resistor. Exceeding this voltage with too large a burden resistor will saturate the transformer and limit the voltage.

What happens if the burden resistor is left off or opens during operation? The output voltage will rise trying to develop current until it reaches the saturation voltage of the coil at that frequency. At that point, the voltage will cease to rise and the transformer will add no additional impedance to the driving current. Therefore, without a burden resistor, the output voltage of a current transformer will be its saturation voltage at the operating frequency.

There are factors in the current transformer that affect efficiency. For complete accuracy, the output current must be the input current divided by the turns ratio. Unfortunately, not all the current is transferred. Some of the current isn't transformed to the secondary, but is instead shunted by the inductance of the transformer and the core loss resistance. Generally, it's the inductance of the transformer that contributes the majority of the current shunting that detracts from the output current. This is why it's important to use a high-permeability core to achieve the maximum inductance and minimize the inductance current. Accurate turns ratio must be maintained to produce the expected secondary current and the expected accuracy. Fig. 2 shows the current transformed is smaller than the input current by:

ITRANSFORMED=IINPUT-ICORE-jIMAG (1)

What about the effect the transformer will have on the current it's monitoring? This is where the term burden enters the picture. Any measuring device alters the circuit in which it measures. For instance, connecting a voltmeter to a circuit causes the voltage to change from what it was before the meter was attached. However minuscule this effect may or may not be, the voltage you read isn't the voltage that existed before attaching the meter. This is also true with a current transformer. The burden resistor on the secondary is reflected to the primary by (1/N2), which provides a resistance in series with the current on the primary. This usually has minimal effect and is usually only important when you are concerned about the current that would exist when the transformer isn't in the circuit, such as when it's used as a temporary measuring device.

Notice the four loss components in the circuit of Fig. 2. The resistance of the primary loop (PRIDCR), the core loss resistance (RCORE), the secondary DCR (RDCR) is reduced by 1/N2, and the secondary burden resistor RBURDEN is also reduced by a factor of N2. These are losses that affect current source (I). The resistances have an indirect effect on the current transformer accuracy. It's their effect on the circuit that they are monitoring that alters its current. The primary dc resistance (PRIdcr) and the secondary DCR/N2 (RDCR/N2) don't detract from the Iinput that is read or is affecting the accuracy of the actual current reading. Rather, they alter the current from what it would be if the current transformer weren't in the circuit. With the exception of the burden resistor, these loss resistors are the components that contribute to the loss in the transformer and heating.

This wasted energy is usually small compared with the power in the circuit it's monitoring. Usually, the design of the transformer and choice of the burden resistor will be within the maximum energy loss the end user can allow. As battery-operated devices come into wider use and power consumption contributes to the energy crisis — even this power may be of concern. Under these circumstances, it may require special design attention to power consumption.

Current transformers are an efficient way to measure current. Since the burden resistor is reflected to the primary by 1/N2, the resistance seen in the circuit being monitored can be very small. This allows a larger voltage to be created on the output with minimal effect on the circuit being measured. A simpler and lower-cost method to measure current is to use a sense resistor connected in series with the current. However, this method can only be used when power consumption is of secondary concern. With the more frequent use of battery-powered devices and the prevailing need to reduce power consumption, the extra expense of a current transformer can soon be recovered with use. Also, with high current or when a voltage of any magnitude is required, a sense resistor would be impractical.

Exploring Current Transformer Applications (Part 1)

2011-09-30T23:06:00.000+07:00

For a variety of applications, using current transformers is an efficient way to sense current with minimum insertion loss.

Current transformers can perform circuit control, measure current for power measurement and control, and perform roles for safety protection and current limiting. They can also cause circuit events to occur when the monitored current reaches a specified level. Current monitoring is necessary at frequencies from the 50 Hz/60 Hz power line to the higher frequencies of switchmode transformers that range into the hundreds of kilohertz.

The object with current transformers is to think in terms of current transformation rather than voltage ratios. Current ratios are the inverse of voltage ratios. The thing to remember about transformers is that Pout = (Pin — transformer power losses). With this in mind, let's assume we had an ideal loss-less transformer in which Pout = Pin. Since power is voltage times current, this product must be the same on the output as it is on the input. This implies that a 1:10 step-up transformer with the voltage stepped up by a factor of 10 results in an output current reduced by a factor of 10. This is what happens on a current transformer. If a transformer had a one-turn primary and a ten-turn secondary, each amp in the primary results in 0.1A in the secondary, or a 10:1 current ratio. It's exactly the inverse of the voltage ratio — preserving volt times current product.

How can we use this transformer and knowledge to produce something useful? Normally, an engineer wants to produce an output on the secondary proportional to the primary current. Quite often, this output is in volts output per amp of primary current. The device that monitors this output voltage can be calibrated to produce the desired results when the voltage reaches a specified level.

A burden resistor connected across the secondary produces an output voltage proportional to the resistor value, based on the amount of current flowing through it. With our 1:10 turns ratio transformer that produces a 10:1 current ratio, a burden resistor can be selected to produce the voltage we want. If 1A on the primary produces 0.1A on the secondary, then by Ohm's law, 0.1 times the burden resistor will result in an output voltage per amp.

Many voltage transformers have adjusted ratios that produce the desired output voltage and compensate for losses. The turns-ratios or actual turns aren't the primary concern of the end-user. Only the voltage output and possibly regulation and other loss parameters may be of concern. With current transformers, the user must know the current ratio to use the transformer. The knowledge of amps in per amps out is the basis for use of the current transformer. Quite often, the end users provide the primary with a wire through the center of the transformer. They must know what secondary turns are to determine what their output current will be. Generally, in catalogues, the turns of the transformers are provided as a specification for use.

With this knowledge, the user can choose the burden resistor to produce their desired output voltage. The output current of 0.1A for a 1A primary on the 1:10 turns ratio transformer will produce 0.1 V/A across a 1Ω burden resistor, 1V per amp across a 10Ω burden and 10V per amp across a 100Ω burden resistor.

Fig. 1 shows an ideal transformation ratio. In this analysis, the secondary dc resistance (RDCR) doesn't become part of the calculation. When considering the secondary current, only the actual current affects V. How well that current can be determined controls the accuracy of the prediction of V. The secondary dc resistance is best analyzed by reflecting it to the primary by RDCR/N2.

Current Tranformers (Part-3 Finish)

2011-09-29T20:36:00.000+07:00

Note:

General

CTs should be specified as follows:

RATIO: input / output current ratio

VA: total burden including pilot wires.

CLASS: Accuracy required for operation

DIMENSIONS: maximum & minimum limits

Metering CTs In general, the following applies:
CLASS • 0.1 or 0.2 for precision measurements
• 0.5 for high grade kilowatt hour meters for commercial grade kilowatt hour meters
• 3 for general industrial measurements
• 3 or 5 for approximate measurements
BURDEN (depending on pilot lead length) • Moving iron ammeter 1-2VA
• Moving coil rectifier ammeter 1-2.5VA
• Electrodynamic instrument 2.5-5VA
• Maximum demand ammeter 3-6VA
• Recording ammeter or transducer 1-2.5VA

Protection CTs In addition to the general specification required for CT design, protection CT’s require an Accuracy Limit Factor (ALF). This is the multiple of rated current up to which the CT will operate while complying with the accuracy class requirements.
In general the following applies:
• Instantaneous overcurrent relays & trip coils - 2.5VA Class 10P5
• Thermal inverse time relays - 7.5VA Class 10P10
• Low consumption Relay - 2.5VA Class 10P10
• Inverse definite min. time relays (IDMT) overcurrent - 15VA Class 10P10/15
• IDMT Earth fault relays with approximate time grading - 15VA Class 10P10
• IDMT Earth fault relays with phase fault stability or accurate time grading required - 15VA Class 5P10

Class X CTs Class X CTs are special CTs used mainly in balanced protection systems (including restricted earth fault) where the system is sensitively dependent on CT accuracy. Further to the general CT specifications, the manufacturer needs to know:
• Vkp - Voltage knee point
• Io - Maximum magnetising current at Vkp
• Rs - Maximum resistance of the secondary winding

Current Tranformers (Part-2)

2011-09-29T20:29:00.000+07:00

Preferred primary and secondary current ratings [and therefore ratios], classes, burdens and accuracy limit factors are defined in BS3938 and other comparable national standards, together with other minimum performance requirements, physical construction requirements, etc.

It should be remembered when using a CT that where there are two or more devices to be operated by the secondary winding, they must be connected in series across the winding. This is exactly the opposite of the method used to connect two or more loads to be supplied by a voltage or power transformer where the devices are paralleled across the secondary winding.

With a CT, an increase in the burden will result in an increase in the CT secondary output voltage. This is automatic and necessary to maintain the current to the correct magnitude. Conversely, a reduction in the burden will result in a reduction in the CT secondary output voltage.
This rise in secondary voltage output with an increase in burden means that, theoretically, with infinite burden as is the case with the secondary load open circuit, an infinitely high voltage appears across the secondary terminals. For practical reasons this voltage is not infinitely high, but can be high enough to cause a breakdown in the insulation between primary and secondary windings or between either or both windings and the core.
For this reason, primary current should never be allowed to flow with no load or with a high resistance load connected across the secondary winding. When considering the application of a CT it should be remembered that the total burden imposed on the secondary winding is not only the sum of the burden(s) of the individual device(s) connected to the winding but that it also includes the burden imposed by the connecting cable and the resistance of the connections.
If, for example, the resistance of the connecting cable and the connections is 0.1 ohm and the secondary rating of the CT is 5A, the burden of the cable and connections (RI2) is 0.1 x 5 x 5 = 2.5VA. This must be added to the burden(s) of the connected device(s) when determining whether the CT has an adequately large burden rating to supply the required device(s) and the burden imposed by the connections.
Should the burden imposed on the CT secondary winding by the connected device(s) and the connections exceed the rated burden of the CT the CT may partly or fully saturate and therefore not have a secondary current adequately linear with the primary current.
The burden imposed by a given resistance in ohms [such as the resistance of a connecting cable] is proportional to the square of the rated secondary current. Therefore, where long runs of cable between CT and the connected device(s) are involved, the use of a 1A secondary CT and a 1A device rather than 5A will result in a 25-fold reduction in the burden of the connecting cables and connections.
All burden ratings and calculations are at rated secondary current. Because of the foregoing, when a relatively long [more than a very few metres] cable run is required to connect a CT to its burden [such as a remote ammeter] a calculation should be made to determine the cable burden. This is proportional to the “round trip” resistance, i.e. twice the resistance of the length of twin cable used. Cable tables provide information on the resistance values of different sizes of conductors at 20o C per unit length. The calculated resistance is then multiplied by the square of the CT secondary current rating [25 for 5A, 1 for 1A]. If the VA burden as calculated by this method and added to the rated burden(s) of the device(s) to be driven by the CT exceeds the CT burden rating, the cable size must be increased [to reduce the resistance and thus the burden] or a CT with a higher VA burden rating must be used, or a lower CT secondary current rating [with matching change in the current rating of the device(s) to be driven] should be substituted.

Current Tranformers (Part-1)

2011-09-29T20:26:00.000+07:00

A current transformer is a transformer, which produces in its secondary winding a current, which is proportional to the current flowing in its primary winding. The secondary current is usually smaller in magnitude than the primary current.

The principal function of a CT is to produce a proportional current at a level of magnitude, which is suitable for the operation of measuring or protective devices such as indicating or recording instruments and relays.

The rated secondary current is commonly 5A or 1A, though lower currents such as 0.5A are not uncommon. It flows in the rated secondary load, usually called the burden, when the rated primary current flows in the primary winding.
The primary winding can consist merely of the primary current conductor passing once through an aperture in the current transformer core or it may consist of two or more turns wound on the core together with the secondary winding.
These are two basic CT types. The first is commonly called a “ring” type CT as the core is usually annular, but in some cases it may be square or rectangular in shape. The second is usually known as a “wound primary” type CT.
The primary and secondary currents are expressed as a ratio such as 100/5. With a 100/5 ratio CT, 100A flowing in the primary winding will result in 5A flowing in the secondary winding, provided the correct rated burden is connected to the secondary winding. Similarly, for lesser primary currents, the secondary currents are proportionately lower.
It should be noted that a 100/5 CT would not fulfil the function of a 20/1 or a 10/0.5 CT as the ratio expresses the current rating of the CT, not merely the ratio of the primary to the secondary currents.
The extent to which the secondary current magnitude differs from the calculated value expected by virtue of the CT ratio is defined by the [accuracy] “Class” of the CT. The greater the number used to define the class, the greater the permissible “current error” [the deviation in the secondary current from the calculated value].
Except for the least accurate classes, the accuracy class also defines the permissible phase angle displacement between primary and secondary currents. This latter point is important with measuring instruments influenced both by magnitude of current and by the phase angle difference between the supply voltage and the load current, such as kWh meters, wattmeter’s, var meters and power factor meters.
Common burden ratings are 2.5, 5, 10, 15 and 30VA.
Current transformers are usually either “measuring” or “protective” types, these descriptions being indicative of their functions. The principal requirements of a measuring CT are that, for primary currents up to 120% or 125% of the rated current, its secondary current is proportional to its primary current to a degree of accuracy as defined by its “Class” and, in the case of the more accurate types, that a specified maximum phase angle displacement is not exceeded.
A desirable characteristic of a measuring CT is that it should “saturate” when the primary current exceeds the percentage of rated current specified as the upper limit to which the accuracy provisions apply. This means that at these higher levels of primary current the secondary current is less than proportionate. The effect of this is to reduce the extent to which any measuring device connected to the CT secondary is subjected to current overload.
On the other hand the reverse is required of the protective type CT, the principal purpose of which is to provide a secondary current proportional to the primary current when it is several, or many, times the rated primary current. The measure of this characteristic is known as the “Accuracy Limit Factor” (A.L.F.). A protection type CT with an A.L.F. of 10 will produce a proportional current in the secondary winding [subject to the allowable current error] with primary currents up to a maximum of 10 times the rated current.

DETERMINING BURDEN FOR CURRENT TRANSFORMERS

2011-09-23T19:50:00.000+07:00

CT SECONDARY WIRE SIZING EXAMPLE

A Watt Transducer (0.75 VA burden) is to be used with three 1200:5 current transformers. The CT secondary is 30 ft. one way. To maintain the maximum CT accuracy (0.6%), the total burden must be kept below 2.5 VA as seen on the current transformer specification sheet.

If 2.5 VA total is available then 2.5 - 0.75 = 1.75 VA is available for the wire. Assuming the maximum 5 amp secondary current, on Nomogram No. 1, align a straightedge on 5 amps (left hand column) and 1.75 VA (center column). Read the impedance in ohms (right hand column). This should read 0.07 ohms.

Now go to Nomogram No. 2. Place a straightedge on 0.07 ohms (center column) and 30 ft. cable length one way (right hand column). Read the cable size (left hand column), which should read #10 AWG copper cable or larger.

With the above conditions, #10 wire or larger will keep the current transformer within its best accuracy limit.

Slip Ring Induction Motors Basics (3)

2011-08-28T18:11:00.000+07:00

What happens when external resistance is added?

In case of squirrel cage induction motor, the rotor resistance is very low, so that the current in the rotor is so high; which makes its starting torque poor. But adding external resistance in case of a slip ring induction motor, makes the rotor resistance high during starting, thus the rotor current is low, thus the starting torque is maximum. Also the slip necessary to generate maximum torque is directly proportional to the rotor resistance. In slip ring motors, the rotor resistance is increased by adding external resistance, thus the slip is increased. Since the rotor resistance is high, the slip is more, thus possible to achieve “pull-out” torque even at low speeds. As the motor reaches its base speed (full rated speed), after the removal of external resistance, under normal running conditions, it behaves in the same way as squirrel cage induction motor.

Thus these motors are best suited for very high inertia loads, which requires a pull-out torque at almost zero speed and accelerate to full speed with minimum current drawn in a very short time period.

Advantages of slip ring induction motors

•The main advantage of slip ring induction motor is that its speed can be controlled easily.
•"Pull-out torque" can be achieved even from zero r.p.m
•High starting torque when compared to squirrel cage induction motor. Approximately 200 - 250% of its full-load torque.
•A squirrel cage induction motor takes 600% to 700% of the full load current. But a slip ring induction motor takes a very low starting current approximately 250% to 350% of the full load current.

What happens if the motor is started as a normal induction motor?
If the slip motor is started with all the slip rings or the rotor terminals shorted, like a normal induction motor, then it suffers extremely high locked rotor current, ranging up to 1400%, accompanied with very low locked rotor torque as low as 60%. So, it is not advised to start a slip ring induction motor with its rotor terminals shorted.

In my next article, lets discuss on various starting methods & speed control of a slip ring induction motors.

Slip Ring Induction Motors Basics (2)

2011-08-28T18:05:00.000+07:00

Construction

Stator:
The stator construction is same for both squirrel cage & slip ring induction motor. The main difference in slip ring induction motor is on the rotor construction and usage. Some changes in the stator may be encountered when a slip ring motor is used in a cascaded system, as the supply for the slave motor is controlled by the supply from rotor of other slip ring motor with external resistance mounted on its rotor.

Rotor:
The slip ring induction motors usually have “Phase-Wound” rotor. This type of rotor is provided with a 3-phase, double-layer, distributed winding consisting of coils used in alternators. The rotor core is made up of steel laminations which has slots to accommodate formed 3-single phase windings. These windings are placed 120 degrees electrically apart.
The rotor is wound for as many poles as the number of poles in the stator and is always 3-phase, even though the stator is wound for 2-phase. These three windings are “starred” internally and other end of these three windings are brought out and connected to three insulated slip-rings mounted on the rotor shaft itself. The three terminal ends touch these three slip rings with the help of carbon brushes which are held against the rings with the help of spring assembly.

These three carbon brushes are further connected externally to a 3-phase start connected rheostat. Thus these slip ring and external rheostat makes the slip ring induction motors possible to add external resistance to the rotor circuit, thus enabling them to have a higher resistance during starting and thus higher starting torque.
When running during normal condition, the slip rings are automatically short-circuited by means of a metal collar, which is pushed along the shaft, thus making the three rings touching each other. Also, the brushes are automatically lifted from the slip-rings to avoid frictional losses, wear and tear. Hence, under normal running conditions, the wound rotor is acting as same as the squirrel cage rotor.

Slip Ring Induction Motors Basics (1)

2011-08-28T17:58:00.000+07:00

The slip ring motors usually have “Phase-Wound” rotor. This type of rotor is provided with a 3-phase, double-layer, distributed winding consisting of coils used in alternators. The rotor core is made up of steel laminations which has slots to accommodate formed 3-single phase windings.

Introduction
We have seen the construction, operation, starting, speed control & classes of squirrel cage induction motors. In this article, we will discuss on slip ring induction motors. As discussed earlier, a slip ring induction motor is an asynchronous motor, as the rotor never runs in synchronous speed with the stator poles. Lets understand the construction and operation of slip ring induction motor.

Tujuan Pentanahan Logam Instalasi

2011-05-07T20:52:00.000+07:00

Tujuan Pentanahan Titik Netral

2011-05-07T20:49:00.000+07:00

Sistem Tenaga Listrik

2011-05-07T20:44:00.001+07:00

Proses Penyediaan Tenaga Listrik

2011-05-07T20:37:00.002+07:00

BUS-BAR DESIGN(3)

2011-04-08T17:54:00.000+07:00

The insulators are selected by considering mechanical bending load occurring at that instant of peak short circuit current. During short circuit the insulators supporting the bus-bars experience a bending force and unless these insulators have enough cantilever strength to withstand the dynamic force occurring during short circuits they will fail.

Bolting and clamping should be done by proper grades of steel or of alumimium alloy.

Typical properties for recommended material are

Tensile strength = 71 Kg/Sq. mm.

0.2 % Proof stress (minimum) = 52 Kg/Sq. mm.

Hardness = Brinell 200 minimum Rockwell B 93 minimum

Also absolute minimum contact pressure should be taken as 28 Kg/Sq. cm. and a desirable minimum should be 56 Kg/Sq. cms.

The washers (Plain and spring) should also be used. They should be aluminized or electrogalvanised.

The following sizes are recommended :

BUS-BAR DESIGN (2)

2011-04-08T17:48:00.000+07:00

After calculating the overall derating factor, the required current rating is obtained by dividing the normal current rating by the overall derating factor. According to the requires current rating we note down the cross-section of the conductor. Suitability of this conductor depends upon the minimum size of the conductor required to withstand the short circuit current within permissible temperature rise for the given duration. Suppose the cross-sectional area obtained on the basis of derating factor is a Sq. cms. and obtained on the basis of derating factor is a Sq. cms. and that on the basis of short circuit withstand capacity be A Sq. cms. Obviously we are to select the cross-sectional area which is nearer to the greater of the two (i.e. between a and A). Now we are required to calculate the cross-sectional area of the conductor to withstand short circuit current for a given duration within permissible temperature rise. Basic assumption made here is that the heat produced due to a through short circuit current raises the temperature of the conductor and none escapes by convection or radiation in the very short time of

the fault.

By equating the heat produced and the heat stored it follows that for aluminium alloy busbar.

BUS-BAR DESIGN (1)

2011-04-08T17:43:00.000+07:00

Bus-bars are current carrying conductors. They are designed to carry certain normal current continuously.

The bus-bars are designed to carry certain rated normal current continuously within the permissible rise in temperature. The value of cross-section so obtained is verified for temperature rise under short time short-circuit current. This figure is further used from the protection point of view while considering the relay setting. In fact, the relay should be set such that under fault condition no damage is caused to these bus-bars.

Bus-bar conductors are separated on post insulators or strain insulators. These insulators experience electrodynamics forces depending upon the current being handled. these forces produce bending moments on the insulators. These bending moments, therefore, become the ruling factor to decide the spacing between insulators (span).

The following factors are taken into consideration while designing a bus-bar :
(i) Bus-bar material,
(iii) Cross-section of conductors,
(iii) Temperature rise during continuous normal current,
(iv) Temperature rise during short circuit current of 1 sec. of 3 sec.
(v) Design of insulator creepage distance and clearance,
(vi) Distance between phase conductors,
(vii) Force on insulators during peak short circuit current,
(viii) Span of insulators support, and
(ix) Enclosure design.

Copper and Aluminum are two preferred materials for electrical conductors. Considering certain advantages of lightness, cost, resistance to corrosion, temperature coefficient of resistance etc. Aluminum has got an edge cover copper. As such, most of the bus-bar conductors now-a-days are of Aluminum (E 91-EWP Class).
Though a table has been prepared keeping certain parameter fixed (sec table-3) but to select the cross-section of the bus-bar we may first have to find out the derating factors.
Derating factors depend on :
(i) Allowable bar temperature over an ambient of 35 C,
(ii) Enclosure of the bus-bar.

Derations for these two factors are obtained from the table 1 & 2 given below and multiplied to get the overall derating factors.

Panel Capacitor Bank / Automatic Power Factor

2011-01-15T19:12:00.000+07:00

PLN akan membebankan biaya kelebihan pemakaian KVARH pada pelanggan, jika rata-rata factor dayanya (Cos phi) kurang dari 0.85. Disinilah fungsi dari Pemasangan Panel Capacitor Bank yaitu Untuk memperbaiki factor daya (Cos phi) sehingga biaya denda akibat kelebihan pemakaian KVARH dapat diminimalkan / dihilangkan.

Selain itu fungsi lain dari pemasangan Panel capacitor Bank :Menghilangkan Denda / Kelebihan Biaya (kVARh)

Menghindari kelebihan beban transformer / trafo over load
Menghindari kenaikan Arus / Suhu pada kabel,
Memaksimalkan Pemakaian Daya yang terpasang (kVA),
Menghindari voltage drop pada Line end,
Meningkatkan kualitas sumber daya listrik,
Memelihara peralatan / perangkat electric yang terpasang.

Hubungi kami jika anda memerlukan capacitor bank.

Apakah yang dimaksud dengan Ats Amf

2011-01-15T19:07:00.000+07:00

PLN Padam? Operasikan Genset secara Otomatis!

ATS adalah singkatan dari Automatic Transfer Switch, yaitu proses pemindahan penyulang dari penyulang/sumber listrik yang satu ke sumber listrik yang lain secara bergantian sesuai perintah pemrograman, ATS adalah pengembangan dari COS atau yang biasa disebut secara jelas sebagai Change Over Switch, beda keduanya adalah terletak pada sistim kerjanya, untuk ATS kendali kerja dilakukan secara otomatis, sedangkan COS dikendalikan atau dioperasikan secara manual.

AMF adalah singkatan dalam istilah kelistrikan dari Automatic Main Failure yang maksudnya menjelaskan cara kerja otomatisasi terhadap sistem terhadap sistem kelistrikan cadangan apabila terjadi gangguan pada sumber/penyulang listrik utama (Main), istilah ini secara umum sering dijabarkan sebagai sistim kendali start dan stop genset, baik itu diesel generator, genset gas maupun turbin.

Sistim kerja panel ATS dan AMF yang sering kita temukan adalah kombinasi untuk pertukaran sumber baik dari genset ke pln maupun sebaliknya, bilamana suatu saat sumber listrik dari PLN tiba-tiba padam, maka AMF bertugas untuk menjalankan diesel genset sekaligus memberikan proteksi terhadap sistim genset, baik proteksi terhadap unit mesin/engine yang berupa pengamanan terhadap gangguan rendahnya tekanan minyak pelumas (Low Oil Pressure) maupun kondisi temperatur mesin serta media pendinginannya, dan juga memberikan perlindungan terhadap unit Generatornya. baik berupa pengamanan terhadap beban pemakaian yang berlebih maupun perlindungan terhadap karakterlistrik lain seperti tegangan maupun frequensi genset, apabila parameter yang diamankan melebihi batasannormal/setting maka tugas ATS adalah melepas hubungan arus listrik ke beban sedangkan AMF bertugas untuk memberhentikan kerja mesin.

Apabila generator yang dijalankan beroperasi dengan baik, berikutnya ATS bertugas memindahkan sambungan dari sebelumnya yang tersambung dengan pln dipindahkan secara otomatis ke sisi generator sehingga aliran listrik bisa tersambung ke sisi pengguna.

Apabila kemudian pln kembali normal, selanjutnya ATS bertugas untuk mengembalikan jalurnya dengan memindahkan switch kembali ke sisi utama dan untuk kemudian disusul dengan tugas AMF untuk memberhentikan kerja mesin diesel tersebut, demikian seterusnya semua sistim kontrol dikendalikan secara otomatis berjalan dengan sendirinya.

Pemakaian sistim otomatisasi ini memiliki beberapa keuntungan antara lain :1. Sistim perpindahan dari pln ke genset dan sebaliknya hanya perlu waktu yang sangat singkat, hanya dengan hitungan detik saja setelah pln padam, genset langsung start dan listrik segera dapat di 'nikmati' kembali oleh pengguna.

2. Meringankan tugas tehnisi listrik yang bisa sangat banyak sekali, bahkan gedung perkantoran sering tidak memiliki tehnisi listrik, dengan panel ATS-AMF ini semuanya menjadi mudah, listrik padam okey, genset langsung start sendiri, pln nyala kembali...okey...genset stop sendiri, tehnisi tak perlu berlari-lari karena panik hanya untuk cepat-cepat men-start genset dan mengoper switch supaya roda aktifitas tak terganggu, yang paling penting genset tetap harus dipelihara agar sistim bisa bekerja secara maksimal, merawat genset sama mudahnya dengan merawat mobil, asal air accu berada di levelnya,bahan bakar tersedia cukup, air radiator normal, oli normal..., sudah.., hanya begitu saja, untuk pemanasan genset sebaiknya cari saja panel ats amf yang sudah dilengkapi dengan fasilitas pemanasan secara otomatis, genset akan melakukan pemanasan sendiri secara terjadwal tanpa harus mematikan listrik pln, tanpa mengganggu sistim dan roda aktifitas kantor, tanpa perlu operator 'dadakan' yang takut dengan suara genset untuk memanaskan genset, semuanya menjadi mudah.

3. Memberi perlindungan terhadap alat kantor seperti komputer, AC , peralatan pabrik maupun laboratorium, seringkali terjadi tegangan listrik pln maupun genset tiba-tiba anjlok atau bahkan tiba-tiba naik sampai jauh diluar batas toleransi normal untuk keamanan alat-alat elektronik, bahkan sering pula ada salah satu fasa listrik yang hilang (untuk sistim 3 fasa), turun dan naiknya tegangan, maupun hilangnya tegangan ini kadang tak terdeteksi dengan kasat mata, tiba-tiba saja muncul aroma hangus ada peralatan yang terbakar, nah... tambah lagi permasalahan baru, tanpa AC bisa saja pakai kertas untuk kipas-kipas, tetapi apa yang harus dihadapi bila yang rusak adalah komputer atau media program lainnya, bisa-bisa data ikutan hilang, masalah lagi...., apalagi bila yang mengalami kerusakan adalah peralatan laboratorium atau peralatan yang menggunakan sistim pemrograman plc, tegangan over voltage bisa merusak alat, perlu waktu yang lama untuk memperbaikinya, bahkan kadang terpaksa harus inden 3-4 bulan hanya untuk menunggu kedatangan spare part atau tehnisi 'impor'. Dengan panel ats amf ini maka semuanya bisa menjadi mudah lagi, over voltage? under voltage? over frequency? under frequency? fasa hilang? bukan masalah, sistim ats dan amf yang akan melakukan tugas yang harus diembannya.

Hubungi kami untuk detailnya.

Harmonic Distortion , What you need to know.

2011-01-03T16:04:00.000+07:00

With the release of the G5/4-1 SYSTEM PLANNING LEVELS FOR HARMONIC DISTORTION which supersedes document G5/4 we thought it would be a good idea to put this information together as a general reference and put to bed some of the misconceptions regarding this subject. As you will appreciate it is quite a far reaching subject with many twists and turns eg; we found that as you answer one question, another question manifests itself but, we have tried to keep the subject as brief and simple as possible.

In years past, most electrical equipment operated on an ideal voltage and current waveform. However, in the past 25 years (particularly since the late 1980's) there has been an explosion in the use of solid-state electronic technology. This new, highly efficient, electronic technology provides improved product quality with increased productivity by the use of smaller and lighter electrical components. Today we are able to produce products that costs less than in years past, but this new technology requires clean electric power and is highly sensitive to power distortions.

Electronic devices convert 50 Hz alternating current to direct current by the use of switching power supplies that contain rectifiers and often capacitors. In addition to converting alternating current to direct current, sometimes the current is converted back to alternating current but into a different frequency.

Electronic equipment (switching power supplies) draws current differently than non-electronic equipment. Instead of a load having a constant impedance drawing current in proportion to the sinusoidal voltage, electronic devices change their impedance by switching on and off near the peak of the voltage waveform.

Switching loads on and off during part of the waveform results in short, abrupt, nonsinusoidal current pulses during a controlled portion of the incoming peak voltage waveform. These abrupt pulsating current pulses introduce unanticipated reflective currents (harmonics) back into the power distribution system. The currents operate at frequencies other than the fundamental 50 Hz. Harmonic currents can be likened to the vibration of water in a water line when a valve is open and closed suddenly.

Harmonics affect us all; from the secretary operating a computer, to the engineer trouble shooting equipment failure, the electrical contractor having to absorb the cost of equipment replacement, the inspector who must investigate the cause of electric fires, to the facilities management interested in effective and efficient equipment operation and the avoidance of down time. The scope of harmonics impacts consultants, engineers, designers, suppliers, equipment manufactures, and, of course your plant operation.

What types of equipment loads can cause the problem?

For example the largest contributor of reflective harmonic currents for commercial buildings is the personal computer. There are, however, as we know in our industry other large contributors too, such as:

Variable Speed Drives (VSD)
Arc Equipment
Battery Chargers
Computer Power Units (CPU)
Discharge Lighting (fluorescent, mercury, sodium, etc.)
Electronic Ballasts
Personal Computers (PC)
Rectifiers
Uninterrupted Power Supplies (UPS)

Clean power is required for today's equipment

Electronic microprocessor PLC equipment requires clean power. This type of equipment needs undistorted voltage to function properly, and it is particularly sensitive to voltage transients (notches or spikes) and flat topping of the voltage waveform caused by the large pulsating currents. High frequency harmonic currents can introduce voltage (noise) in electronic cables or components.

Electronic equipment installation manuals often require the total voltage distortion to be no more than 10%. Voltage distortion can cause poor product performance, but in general, it is not a safety hazard. Strangely, electronic equipment requires clean power, but its power supplies generate the reflective harmonic currents that cause the voltage distortions!!!!

Exactly what is the problem?

The actual problems of any Project will vary, depending on the types and number of installed harmonic producing loads. Most Projects can withstand nonlinear loads of up to 15% of the total electrical system capacity without concern, but, when the nonlinear loads exceed 15% some non-apparent negative consequences can be expected. For Projects that have nonlinear loading of more than 25%, particular problems can be become apparent. The following is a short summary of most, but not all of the problems caused by harmonics:

Capacitor Failure - Harmonic Resonance
Circuit Breakers Tripping - Inductive Heating and Overload
Computer Malfunction or Lockup - Voltage Distortion
Conductor Failure - Inductive Heating
Electronic Equipment Shutting down - Voltage Distortion
Flickering of Fluorescent Lights - Transformer Ballast Saturation
Fuses Blowing for No Apparent Reason - Inductive Heating and Overload
Motor Failures (overheating) - Voltage Drop
Neutral Conductor and Terminal Failures - Additive Currents
Overheating of Metal Enclosures - Inductive Heating
Power Interference on Voice Communication - Harmonic Noise
Transformer Failures - Inductive Heating

The heating effects of harmonic currents can cause destruction of equipment, conductors, and fires. The results can be unpredictable legal and financial ramifications. Voltage distortions can lead to overheating of equipment, electronic equipment failure, expensive downtime, and maintenance difficulties. Harmonic currents and voltage distortion are becoming the most severe and complex electrical challenge for the electrical industry. The problems associated with nonlinear loads were once limited to isolated devices and computer rooms, but now the problem can appear throughout the power and utility system.

Past, present, and future trends

In the past, most electric power was consumed by "linear loads." Reflective harmonic currents from nonlinear loads (fluorescent lighting) were a relatively minor component of the total Project power usage. In 1992, 15 to 20% of the total load was nonlinear, and by this year (2007) it is expected that 50 to 70% of all loads will be nonlinear. As we can see from the projection, the problems (or opportunities) of harmonics will be growing with the expanded used or electronics. With this information we hope to inform the engineers as we have found many people in the electrical industry as yet do not fully understand the basics of harmonics; much less have a working knowledge of the problems.

Is there anything we can do?

Be sure that the Project Team has been made aware of the causes, the effects, and the solutions of harmonic currents. Because harmonics are here to stay, we must adjust our thinking on electrical system design, installation, inspection, and maintenance. We must anticipate the non-apparent overload of the electrical system and the associated distortions to the voltage waveforms. Think of harmonic currents as the symptoms of the common cold; there is no cure, but we can treat the symptoms. Before we apply any treatments or preventive measures, we must understand the symptoms and their cause.

What types of loads cause harmonic currents?

Let's understand the difference between linear and nonlinear loads. A linear load is a load that opposes the applied voltage with constant impedance resulting in a current waveform that changes in direct proportion to the change in the applied voltage. Examples of these loads are resistance heating, incandescent lighting, motors, etc. If the impedance is constant, then the applied voltage is sinusoidal, and the current waveform will also be sinusoidal.

A nonlinear load, on the other hand, is a load that does not oppose the applied voltage with constant impedance. The result is a nonsinusoidal current waveform that does not conform to the waveform of the applied voltage. Nonlinear loads have high impedance during part of the voltage waveform, and when the voltage is at or near the peak the impedance is suddenly reduced.

The reduced impedance at the peak voltage results in a large, sudden, rise in current flow until the impedance is suddenly increased resulting in a sudden drop in current. Because the voltage and current waveforms are no longer related, they are said to be "nonlinear." Nonlinear loads are loads that have diode-capacitor power supplies such as: computers; laser printers; welders; Variable Speed Drives; UPS systems; fluorescent lighting; etc., which draw current in short pulses during the peak of the line voltage. These nonsinusoidal current pulses introduce unanticipated reflective currents back into the power distribution system, and the currents operate at frequencies other than the fundamental 50 Hz. Harmonic is a term that describes sinusoidal waveforms that operate at a frequency that is a multiple of the fundamental 50 Hz frequency.

When a current, or voltage, operates at other than the fundamental 50 Hz frequency it is said to operate at a specific harmonic order (3rd harmonics operate at 150 Hz; 5th harmonics operate at 250 Hz). Because reflective harmonic currents operate at frequencies higher than the fundamental, we must be concerned with their effect in the electrical distribution system.

The most significant effects of high frequency harmonic currents are as follows: Inductive heating of transformers, generators, and other electromagnetic devices such as motors, relays, and coils (due to the inductive heating effects of eddy currents, skin effect, and hysteresis). Inductive heating of conductors, breakers, fuses, and all other devices that carry current (because of eddy currents, skin effect, and hysteresis).

Inductive heating of metal parts such as cable ways, metal enclosures, and other ferrous (iron or steel) metal parts (because of eddy currents and hysteresis). Voltage distortion resulting in unpredictable equipment operation because of harmonics. Excessive neutral current resulting in equipment overheating or failure because of additive harmonic currents, excessive voltage drop, and distortion.

Finally, how serious Is this problem?

The effects of harmonic currents on electrical distribution systems are not understood by most in the electrical industry. The number one hazard with harmonic currents is equipment failure because of current overload that result in fires. In addition to the electrical safety aspects, harmonics cause voltage waveform distortions that affect many different types of loads in different ways.

Engineering research on the problems and solutions is still in its infancy; solutions recommended today may not be viewed as correct further down the line.

CHF100A series High Performance Universal Inverter

2010-12-25T14:47:00.000+07:00

CHF100A series high performance universal inverter is the enhanced edition of CHF series, which is combined the advantage of CHF100 & CHE100. It adopts the DSP control system supplies sensorless vector control and V/f control. The performance is more perfect and stable. It is widely applied in Pump & Fan and some applications with high speed control accuracy, rapid torque response and high performance at low frequency.

Features
HF100A series high performance universal inverter is the enhanced edition of CHF series, which is combined the advantage of CHF100 & CHE100. It adopts the DSP control system supplies sensorless vector control and V/f control. The performance is more perfect and stable. It is widely applied in Pump & Fan and some applications with high speed control accuracy, rapid torque response and high performance at low frequency.

Technical
. Control mode: Sensorless vector control, V/f control, torque control
. Start-up torque: 0.5Hz/150%(SVC)
. Built-in DC reactor (from 18.5kW to 90 kW) to improve power factor and efficiency.
. Built-in breaking units (from 1.5kW to 11kW). If need to stop rapidly，please connect the brake resistance directly.
. Multi-step speed control: 16 steps can be set; PID control; Simple PLC.
. Offer 8 multi-functional digital inputs (PNP&NPN),2 analog inputs,2 relay output,2 analog output,1 open-collector output.
. Can check the actual parameters by the .
. AVR: Can output constant voltage automatically when input voltage is fluctuating. QUICK/JOG function.
. Offer RS485 serial communication interface, adopts standard Modbus-RTU communication protocol.
. Oscillation suppression function.
. Over-torque detection function.
. Multiple frequency upper limit setting source.
. Dormancy and wake-up function.
. Speed Tracing Function: Smoothly start the running motor.
. Up to 23 fault protections: Protect from over current, over voltage, under voltage, over temperature, phase failure, over load etc.

Application
* Fans & pumps
* Energy saving renovation of Central Air-conditioning System
* Water flood pump & fuel supply pump
* Energy saving renovation of air compressor
* Circular-water pump, constant water supply
* Musical Fountain

Contact us for special price !

High Performance Inverter

2010-11-01T17:30:00.002+07:00

Untuk memenuhi kebutuhan Anda dalam penggunaan inverter untuk pengaturan speed, energy saving dsb, kami, Crescendo Teknik, menyediakan inverter merk Invt (China), dengan kualitas terbaik, sanggup bersaing dengan merk-merk lain yang sudah terlebih dahulu ada, baik dari Eropa, Amerika, Jepang dan Korea. Dan tentu saja dengan harga lebih ekonomis. Bergaransi.

CHF100A series High Performance Universal InverterSpecial Inverter for Synchronous Control

http://www.invt.com.cn/detail.aspx?cid=1021

Modification Star Delta to Inverter

2010-09-19T20:17:00.001+07:00

How Solar hot water panels work?

2010-09-19T20:10:00.000+07:00

Solar hot water panels are a means to harness the sun's energy in a unique way. Like traditional solar panels, solar hot water panels are placed in direct sunlight, oftentimes arrayed on rooftops, like in the photograph below: A solar hot water array, often referred to as a solar hot water heater, uses the energy from the sun to heat a fluid, which is in turn used to move heat generated in the array to a heat storage vessel. The process starts by heating a body of sanitized water and storing it in a hot water cylinder. Next, solar hot water panels would be installed on the rooftop, each with a darkly-coated absorber plate complete with water circulation tubes.

The tubes carray the heated water from the solar water heater to a place where it can be used or stored. A heat exchanger released heat and circulates the cooled water back to the solar hot water array to be reheated. This cycle of heating, energy utilization, and cooling is begun anew with each sunrise and lasts throughout the day for the effective life of the solar hot water heater. These arrays are especially useful for businesses that utilize large quantities of hot water, such as the pictured laudromat.

Solar hot water heaters are composed of a several hot water panel units, and can be fully automated systems.

How are solar panels made?

2010-09-19T20:07:00.000+07:00

Making solar panels is a delicate process, and it is for this reason that major solar advances did not come into play until the lattermost quarter of the last century, when advances in semiconductors and photovoltaic design allowed increasingly efficient and affordable solar cells to be developed.

Crystalline Silicon Solar Panels

The creation of solar panels typically involves cutting crystalline silicon into tiny disks less than a centimeter thick. These thin, wafer-like disks are then carefully polished and treated to repair and gloss any damage from the slicing process. After polishing, dopants (materials added to alter an electrical charge in a semiconductor or photovoltaic solar cell) and metal conductors are spread across each disk. The conductors are aligned in a thin, grid-like matrix on the top of the solar panel, and are spread in a flat, thin sheet on the side facing the earth.

To protect the solar panels after processing, a thin layer of cover glass is then bonded to the top of the photovoltaic cell. After the bonding of protective glass, the nearly-finished panel is attached to a subtrate by an expensive, thermally conductive cement. The thermally conductive property of the cement keep the solar panel from becoming overheated; any leftover energy that the solar panel is unable to convert to electricity would otherwise overheat the unit and reduce the efficiency of the solar cells.

Despite these protective measures against the tendancy of solar panels to overheat, it is vital that when installing a solar panel, additional steps should be taken to ensure the solar panel is kept cool. Elevating the solar panel above ground to let the airflow underneath cool the device.

Amorphous Silicon Solar Panels

Amorphous silicon solar panels are a powerful, emerging line of photovoltaics, that differ in output, structure, and manufacture than traditional photovoltaics which use crystalline silicon. Amorphous silicon solar cells, or A-si cells, are developed in a continuous roll-to-roll process by vapor-depositing silicon alloys in multiple layers, with each extremely thin layer specializing in the absorption of different parts of the solar spectrum. The result is record-breaking efficiency and reduced materials cost (A-si solar cells are typically thinner than their crystalline counterparts).

Some Amorphous Solar Panels also come with shade-resistant technology or multiple circuits within the cells, so that if an entire row of cells is subject to complete shading, the circuit won't be completely broken and some output can still be gained. This is especially useful when installing solar panels on a boat.

The development process of Amorphous Silicon solar panels also renders them much less susceptible to breakage during transport or installation. This can help reduce the risk of damaging your significant investment in a photovoltaic system.

How Solar Cells Work?

2010-09-19T20:00:00.000+07:00

Working of solar cells is based on photovoltaic effect. What is photovoltaic effect? It is a direct conversion of light into electricity at atomic level. This effect was first observed in 1839 by Edmund Bequerel, a French physicist. He had observed that certain materials produced small amounts of electrical energy on being exposed to light. This theory was further studied by Albert Einstein who came up with the theory of photoelectric effect after studying the behavior of light closely. So, now that you know a brief history on solar cells, how they work will be our next subject of study. A solar cell is usually made of a semiconductor material like silicon (most commonly used). In the functioning of a solar cell, it is important to understand as to why silicon is used as a semiconductor material in a solar cell and what is its significance in generating the electrical energy in a solar cell.

Silicon is a non metal with some special chemical properties. If we observe the atomic structure of silicon, it has 14 electrons arranged in three shells. The first two inner shells have 2 and 8 electrons respectively. The outer shell has 4 electrons. As per the atomic structure of any element, the outer shell must contain 8 electrons to achieve a neutrality. So, the silicon atom will devise ways to fill the outer shell with the remaining 4 electrons. Once it bonds with neighboring atoms to complete its outer shell, it gets a crystalline structure. This pure crystalline structure of silicon is such that the electrons are not free to move about. Hence, silicon in pure form is a poor conductor of electricity. So, impurities or other elements like phosphorous are added to it in such a way, that there remain a few electrons which are free to move. The process of adding impurities to silicon is often known as doping. This is because phosphorus has 5 electrons in its outer shell of atomic structure of which 1 electron will be left free. When sun light strikes the silicon semiconductor, the alignment of the atoms is disturbed due to the heat energy of the light. The free electrons present in the semiconductor due to the impurities, break free and move in a particular direction trying to fill in into the holes of crystal lattice structure, thereby generating an electric current. Silicon which is fused with phosphorous to produce this photoelectric effect is also called 'n type semiconductor'.

A solar cell is constituted of two silicon pieces, of which one is the p type semiconductor (the silicon doped with boron) and the n type silicon (the silicon doped with phosphorus). So, when the sun light falls on this solar cell, the p type semiconductor and the n type semiconductor come in contact with each other. In the process, the free electrons in the n type semiconductor rush to fill in the holes in the p type semiconductor. This flow creates the requisite electric current in a solar cell. The electric field produced in the solar cell causes a voltage. Product of the voltage and current is what gives solar power. Voila! That's how a solar cell works.

Toshiba PLC program save/load/monitor

2010-09-17T10:30:00.004+07:00

Software Name : TPDS.EXE

How to save program:

Hubungkan kabel interface antara computer (COM 1) dengan CPU PLC.
Buka directory C:\TPDS.
Ketik TPDS, tekan . Maka akan muncul tampilan pembuka dari program TPDS.
Tekan atau tombol lain sesuai dengan pesan yang ditampilkan pada tampilan pembuka yaitu “Press any key to start T-PDS”. Maka akan muncul “T-PDS MODE MENU”.
Jika pada menu tersebut muncul pesan “PLC RUN”, maka program TPDS sudah dalam mode online. Tetapi jika muncul pesan “Offline:C”, berarti program TPDS masih dalam mode Offline, maka arahkan kursor ke “L: Online/Offline”, tekan , maka akan muncul pilihan “Select mode”. Pilih “N: Online”, tekan , maka akan muncul pesan “Cable connection ready ?”, pilih “Y: Yes”, tekan . Beberapa saat kemudian akan muncul pesan “Save settings into disk ?”, pilih “Y: Yes”, tekan . Setelah itu akan muncul pesan “PLC RUN”.
Pada “T-PDS MODE MENU”, pilih “O: Setup Options”, tekan , maka akan muncul menu “.
Tekan F1 (Edit), maka kursor akan muncul pada “Layer1station No.[ ]”.
Ketik nomor sesuai dengan Station No. yang diinginkan.
Pindahkan kursor ke pilihan directory untuk “Register/device”, pilih directory yang sesuai dengan Station No. tersebut.
Tekan F1 (Set), maka akan muncul pesan “Change settings ?”, pilih “Y: Yes”, tekan , tunggu sampai muncul pesan “Connection completed”.
Tekan F10 (Cancel), maka akan kembali ke “T-PDS MODE MENU”.
Pilih “T: Load/Save/Compare”, tekan , maka akan muncul menu “”.
Pilih “D: PLC-Disk”, tekan , maka akan muncul menu “”.
Pilih “S: Save(PLC-Disk)”, tekan , maka akan muncul menu “”.
Pilih “A: All”, tekan , maka akan muncul menu “”.
Pilih directory dan file yang diinginkan, tekan , maka akan muncul pesan “Execute ?”, pilih “Y: Yes”, maka proses save to file dimulai.
Setelah proses save to file selesai, maka akan muncul pesan “complete”. Setelah itu tekan F10 (Cancel) beberapa kali sampai kembali ke “T-PDS MODE MENU”.
Untuk keluar dari program TPDS, pilih “Q: Quit”, tekan , maka akan kembali ke DOS prompt.
Lepaskan kabel interface antara computer dan PLC.
Selesai.

How to load program

Hubungkan kabel interface antara computer (COM 1) dengan CPU PLC.
Buka directory C:\TPDS.
Ketik TPDS, tekan . Maka akan muncul tampilan pembuka dari program TPDS.
Tekan atau tombol lain sesuai dengan pesan yang ditampilkan pada tampilan pembuka yaitu “Press any key to start T-PDS”. Maka akan muncul “T-PDS MODE MENU”.
Jika pada menu tersebut muncul pesan “PLC RUN”, maka program TPDS sudah dalam mode online. Tetapi jika muncul pesan “Offline:C”, berarti program TPDS masih dalam mode Offline, maka arahkan kursor ke “L: Online/Offline”, tekan , maka akan muncul pilihan “Select mode”. Pilih “N: Online”, tekan , maka akan muncul pesan “Cable connection ready ?”, pilih “Y: Yes”, tekan . Beberapa saat kemudian akan muncul pesan “Save settings into disk ?”, pilih “Y: Yes”, tekan . Setelah itu akan muncul pesan “PLC RUN”.
Pada “T-PDS MODE MENU”, pilih “O: Setup Options”, tekan , maka akan muncul menu “.
Tekan F1 (Edit), maka kursor akan muncul pada “Layer1station No.[ ]”.
Ketik nomor sesuai dengan Station No. yang diinginkan.
Pindahkan kursor ke pilihan directory untuk “Register/device”, pilih directory yang sesuai dengan Station No. tersebut.
Tekan F1 (Set), maka akan muncul pesan “Change settings ?”, pilih “Y: Yes”, tekan , tunggu sampai muncul pesan “Connection completed”.
Tekan F10 (Cancel), maka akan kembali ke “T-PDS MODE MENU”.
CPU PLC harus dalam keadaan “Halt”. Ada dua cara untuk mengubah mode PLC dari “Run” ke “Halt”, yaitu pertama: pindahkan kunci pada CPU PLC dari posisi “Run” ke “Halt”, maka akan muncul pesan “PLC HALT”, yang kedua: tekan tombol F9 (Control), maka akan muncul menu pilihan “Select command”, pilih “H: HALT”, tekan , maka akan muncul pesan pilihan “Execute command ?”, pilih “Y: Yes”, tekan , maka akan muncul pesan “PLC HALT”.
Pada menu “” pilih “L: Load (Disk-PLC)”, tekan , maka akan muncul menu “Load(disk-plc)”.
14. Pilih “A: All”, tekan , maka akan muncul menu “Load(Disk-PLC)/All”.
Pilih directory dan file name yang akan di transfer ke PLC, tekan , maka akan muncul pesan “Execute ?”. Pilih “Y: Yes”, maka proses load program dimulai.
Setelah proses transfer selesai, maka akan muncul pesan “Complete”. Kemudian tekan F10 (Cancel) beberapa kali sampai kembali ke “T-PDS MODE MENU”.
Kembalikan mode PLC dari “Halt” ke “Run”, yaitu pindahkan kunci yang ada pada CPU PLC dari posisi “Halt” ke “Run” atau dengan menggunakan tobol F9 (Control) dan pilih “R: RUN” sampai muncul pesan “PLC RUN”.
Untuk keluar dari program TPDS, pilih “Q: Quit”, tekan , maka akan kembali ke DOS prompt.
Lepaskan kabel interface antara computer dan PLC.
Selesai.

How to enter program for monitoring

Hubungkan kabel interface antara computer (COM 1) dengan CPU PLC.
Buka directory C:\TPDS.
Ketik TPDS, tekan . Maka akan muncul tampilan pembuka dari program TPDS.
Tekan atau tombol lain sesuai dengan pesan yang ditampilkan pada tampilan pembuka yaitu “Press any key to start T-PDS”. Maka akan muncul “T-PDS MODE MENU”.
Jika pada menu tersebut muncul pesan “PLC RUN”, maka program TPDS sudah dalam mode online. Tetapi jika muncul pesan “Offline:C”, berarti program TPDS masih dalam mode Offline, maka arahkan kursor ke “L: Online/Offline”, tekan , maka akan muncul pilihan “Select mode”. Pilih “N: Online”, tekan , maka akan muncul pesan “Cable connection ready ?”, pilih “Y: Yes”, tekan . Beberapa saat kemudian akan muncul pesan “Save settings into disk ?”, pilih “Y: Yes”, tekan . Setelah itu akan muncul pesan “PLC RUN”.
Pada “T-PDS MODE MENU”, pilih “O: Setup Options”, tekan , maka akan muncul menu “.
Tekan F1 (Edit), maka kursor akan muncul pada “Layer1station No.[ ]”.
Ketik nomor sesuai dengan Station No. yang diinginkan.
Pindahkan kursor ke pilihan directory untuk “Register/device”, pilih directory yang sesuai dengan Station No. tersebut.
Tekan F1 (Set), maka akan muncul pesan “Change settings ?”, pilih “Y: Yes”, tekan , tunggu sampai muncul pesan “Connection completed”.
Tekan F10 (Cancel), maka akan kembali ke “T-PDS MODE MENU”.
Pada “T-PDS MODE MENU”, pilih “P: Program”, tekan , maka akan muncul program PLC pada Block:M 1.
Untuk pindah ke lain Block, tekan F2 (Read), maka akan muncul pilihan untuk “Select program type”.
Pilih “M: Main program”, tekan , maka akan muncul pilihan untuk “Select read method”.
Pilih “B: Block number”, tekan , maka akan muncul kolom untuk “Enter block number”. Isi dengan angka sesuai dengan Block yang akan ditampilkan, tekan , maka akan ditampilkan program PLC pada block tersebut.
Selesai.

Toshiba AC Drive parameter save/load/monitor

2010-09-17T10:04:00.000+07:00

Software name: STOOL.EXE

How to save parameter:
1. Hubungkan kabel interface antara computer (COM 1) dengan AC Drive.
2. Buka directory C:\STOOL.
3. Ketik STOOL, tekan .
4. Beberapa saat kemudian akan muncul “Main Menu”. Pilih “F•Function”, tekan , pilih “M. file management”, tekan , maka akan muncul menu “file management”.
5. Pilih “S. setting”, tekan , pilih “S. load/save”, tekan , maka akan muncul menu pilihan untuk “SOURCE” dan “DEST.” (destination).
6. Pada kolom “SOURCE” pilih “RAM”, sedangkan pada kolom “DEST.” Pilih “MS-DOS FILE”, tekan .
7. Maka akan muncul kolom isian untuk “TITLE =________”, tekan , kemudian pilih nama file untuk parameter yang akan di-save, tekan . Tetapi jika nama file belum ada, yaitu merupakan file baru, maka tekan tombol
dan isi “FILE NAME =________” dengan nama file yang diinginkan, tekan . Selanjutnya akan muncul kolom isian “MEMO =________”, isi dengan keterangan untuk file tersebut, kemudian tekan .
8. Setelah itu akan muncul pesan “Parameter load/save start ?”, pilih “Yes” dengan cara menekan huruf “Y”, maka proses save parameter dimulai.
9. Setelah proses save parameter selesai, tekan tombol sampai kembali ke menu “file management”. Pilih “M. menu”, tekan , maka akan muncul pesan “return to main menu ?”, pilih “Yes” dengan cara menekan huruf “Y”, maka akan kembali ke Main Menu.
10. Pada ”Main Menu”, pilih “Q•Quit”, tekan , maka akan muncul pesan “Quit ? (y/n)”, tekan huruf “Y”, maka program akan kembali ke DOS prompt.
11. Selesai.

How to load parameter:

1. Hubungkan kabel interface antara computer (COM 1) dengan AC Drive.
2. Buka directory C:\STOOL.
3. Ketik STOOL, tekan .
4. Beberapa saat kemudian akan muncul “Main Menu”. Pilih “F•Function”, tekan , pilih “M. file management”, tekan , maka akan muncul menu “file management”.
5. Pilih “S. setting”, tekan , pilih “S. load/save”, tekan , maka akan muncul menu pilihan untuk “SOURCE” dan “DEST.” (destination).
6. Pada kolom “SOURCE” pilih “MS-DOS FILE”, sedangkan pada kolom “DEST.” Pilih “RAM”, tekan .
7. Pilih nama file yang akan di-load, tekan , maka akan muncul pesan “Parameter load/save start ?”, pilih “Yes” dengan cara menekan huruf “Y”, maka proses load parameter dimulai.
8. Setelah proses load parameter selesai, tekan tombol sampai kembali ke menu “file management”. Pilih “M. menu”, tekan , maka akan muncul pesan “return to main menu ?”, pilih “Yes” dengan cara menekan huruf “Y”, maka akan kembali ke Main Menu.
9. Pada ”Main Menu”, pilih “Q•Quit”, tekan , maka akan muncul pesan “Quit ? (y/n)”, tekan huruf “Y”, maka program akan kembali ke DOS prompt.
10. Selesai.

How to enter program for monitoring:

1. Hubungkan kabel interface antara computer (COM 1) dengan AC Drive.
2. Buka directory C:\STOOL.
3. Ketik STOOL, tekan .
4. Beberapa saat kemudian akan muncul “Main Menu”. Pilih “F•Function”, tekan , pilih “S. data Set & read”, tekan , maka akan muncul menu “data Set & read”.
5. Pilih “C.change”, tekan , maka kursor akan pindah ke kolom “SYMBOL NAME”. Selanjutnya tekan , maka akan muncul kolom isian untuk “SYMBOL =________”, isi dengan parameter yang diinginkan, tekan , maka nilai parameter tersebut akan ditampilkan pada kolom “DATA” disebelah kanan kolom “SYMBOL NAME”.
6. Jika parameter list sudah tersimpan dalam file tertentu, maka file tersebut dapat langsung dipanggil yaitu dengan cara memilih “D.display”, tekan , pilih “R.read”, tekan , maka akan muncul menu pilihan untuk memilih nama file yang diinginkan. Pilih file, tekan , maka semua parameter yang telah di-save pada file tersebut akan ditampilkan pada menu ini.
7. Selesai.

SIEMENS S5 PLC program save/load/monitor

2010-09-17T09:42:00.000+07:00

Software name: STEP5.EXE

How to save program:Hubungkan kabel interface antara computer (COM 1) dengan CPU PLC.

Cari file S5.BAT, kemudian ketik S5, tekan , maka akan muncul menu “File > Project > Set F4”.
Pada menu tersebut tekan atau tekan tombol F4, maka akan muncul menu pilihan untuk “1. PLC”.
Pada menu tersebut terdapat kolom pilihan “Mode:”. Jika pada pada kolom tersebut berisi “Offline”, maka tekan tombol F3 agar berganti menjadi “Online”. Setelah itu tekan agar kembali ke menu “File > Project > Set F4”.
Pada menu File, pilih “File > Blocks > Transfer . . . F5”, tekan atau tekan tombol F5, maka akan muncul menu “Transfer Block(s)”.
Pada menu tersebut terdapat sub-menu yaitu “Transfer from”, pilih “PLC” dengan cara menggeser kursor kearah “PLC”, sehingga pada kolom disebelah kiri “PLC” terdapat tanda (X).
Setelah itu pilih directory dan file yang akan di-save dengan cara memindah kursor pada “Program file” dari sub-menu “Transfer to” sehingga disebelah kiri kolom “Program file” terdapat tanda (X). Setelah itu arahkan kursor ke kolom yang ada disebelah kanan “Program file”, kemudian tekan tombol F3, maka akan muncul menu “Select file”.
Pada menu tersebut pilih directory dan file yang diinginkan, kemudian tekan , maka akan kembali ke menu “Transfer block(s)”.
Arahkan kursor ke kolom “Block list” dari sub-menu “Selection”, sehingga pada kolom sebelah kiri “Block list” terdapat tanda (X).
Arahkan kursor kekolom disebelah kanan “Block list”, kemudian ketik huruf “A” yang berarti “All”. Setelah itu tekan , maka proses save to file dimulai.
Setelah proses selesai tekan tombol beberapa kali sampai kembali ke menu “File”.
Untuk keluar dari program Step 5, arahkan kursor ke “Exit”, tekan , maka akan muncul “Message”. Kemudian tekan pada “Exit”, maka akan kembali ke DOS prompt.
Lepaskan kabel interface antara computer dan PLC.
Selesai

How to load program:

Hubungkan kabel interface antara computer (COM 1) dengan CPU PLC.
Cari file S5.BAT, kemudian ketik S5, tekan , maka akan muncul menu “File > Project > Set F4”.
Pada menu tersebut tekan atau tekan tombol F4, maka akan muncul menu pilihan untuk “1. PLC”.
Pada menu tersebut terdapat kolom pilihan “Mode:”. Jika pada pada kolom tersebut berisi “Offline”, maka tekan tombol F3 agar berganti menjadi “Online”. Setelah itu tekan agar kembali ke menu “File > Project > Set F4”.
Pada menu File, pilih “File > Blocks > Transfer . . . F5”, tekan atau tekan tombol F5, maka akan muncul menu “Transfer Block(s)”.
Pada menu tersebut terdapat sub-menu yaitu “Transfer from”, pilih “Program file” untuk memilih directory dan file yang akan di-transfer dengan cara menggeser kursor kearah “Program file”, sehingga pada kolom disebelah kiri “Program file” terdapat tanda (X). Setelah itu arahkan kursor ke kolom yang ada disebelah kanan “Program file”, kemudian tekan tombol F3, maka akan muncul menu “Select file”.
Pada menu tersebut pilih directory dan file yang diinginkan, kemudian tekan , maka akan kembali ke menu “Transfer block(s)”.
Setelah itu pilih “PLC” dengan cara memindah kursor pada “PLC” dari sub-menu “Transfer to” sehingga disebelah kiri kolom “PLC” terdapat tanda (X).
Arahkan kursor ke kolom “Block list” dari sub-menu “Selection”, sehingga pada kolom sebelah kiri “Block list” terdapat tanda (X).
Arahkan kursor kekolom disebelah kanan “Block list”, kemudian ketik huruf “A” yang berarti “All”. Setelah itu tekan , maka proses load program dimulai.
Setelah proses selesai tekan tombol beberapa kali sampai kembali ke menu “File”.
Biasanya setelah proses down load program selesai, CPU PLC dalam keadaan “STOP”, maka harus dikembalikan ke mode “RUN” yaitu dengan cara me-reset switch yang ada pada CPU PLC, caranya adalah: pindahkan switch dari posisi “RUN” ke “STOP”, kemudian arahkan switch reset keatas yaitu posisi “RESET” (Jangan diarahkan ke kebawah ke posisi “OVERALL RESET”, program bisa hilang) dan tahan. Pada saat itu pindahkan switch yang pertama ke posisi “RUN” dan lepaskan switch reset. Cara yang kedua adalah melalui software, yaitu pada menu utama, pindahkan ke menu “PLC”, pilih “Start PLC Shift+F11”, tekan , maka akan muncul pilihan antara “Cold start” dan “Warm start”, pilih salah satu, tekan , sampai CPU PLC dalam keadaan “RUN”.
Untuk keluar dari program Step 5, arahkan kursor ke “Exit”, tekan , maka akan muncul “Message”. Kemudian tekan pada “Exit”, maka akan kembali ke DOS prompt.
Lepaskan kabel interface antara computer dan PLC.
Selesai

How to enter program for monitoring:

Hubungkan kabel interface antara computer (COM 1) dengan CPU PLC.
Cari file S5.BAT, kemudian ketik S5, tekan , maka akan muncul menu “File > Project > Set F4”.
Pada menu tersebut tekan atau tekan tombol F4, maka akan muncul menu pilihan untuk “1. PLC”.
Pada menu tersebut terdapat kolom pilihan “Mode:”. Jika pada pada kolom tersebut berisi “Offline”, maka tekan tombol F3 agar berganti menjadi “Online”.
Pindahkan ke menu “2. Blocks” untuk memilih file *ST.S5D dan *XR.INI, yaitu dengan cara menekan tombol dan “2”, maka kursor akan berada pada kolom pilihan untuk “Program file”. Tekan tombol F3 maka akan muncul menu “Select file”, pilih directory dan file yang diinginkan, kemudian tekan , maka akan kembali ke menu “2. Blocks”.
Pindahkan ke menu “3. Symbols” untuk memilih file *Z0.INI dan *Z0.SEQ, yaitu dengan cara menekan tombol dan “3”, maka kursor akan berada pada kolom pilihan untuk “Symbols file”. Tekan tombol F3 maka akan muncul menu “Select file”, pilih directory dan file yang diinginkan, kemudian tekan , maka akan kembali ke menu “3. Symbols”. Kemudian tekan untuk kembali ke menu “File > Project > Set F4”.
Pindahkan kursor ke menu “Test > Block Status . . . Shift+F6”, kemudian tekan , maka akan muncul menu “Block status”.
Pada kolom “Block list” tekan tombol F3, maka akan muncul menu pilihan “Block status”. Kemudian pada kolom “Block” pilih block yang diinginkan, tekan , maka akan kembali ke menu sebelumnya.
Tekan sekali lagi maka akan muncul program PLC beserta statusnya sesuai dengan block yang telah dipilih.
Selesai

Toshiba CPE & DC Drive parameter save/load

2010-09-17T09:36:00.000+07:00

Software name: IS10.EXE

How to save parameter:Hubungkan kabel interface antara computer (COM 1) dengan CPE.

Buka directory C:\IS10CPE atau C:\IS10.
Ketik IS10, tekan , maka akan muncul tampilan pembuka dari program ini.
Tekan sembarang tombol, maka akan muncul menu pilihan “INTERFACE SELECTION”, Pilih “RS232C”, dengan cara menekan tombol F2, maka akan muncul menu berikutnya.
Selanjutnya tekan sembarang tombol, maka akan ditampilkan nama identitas dari CPE tersebut. Kemudian tekan sembarang tombol.
Tekan F7 (Setting Data Control), tekan F1 (Save RS-232C Data into Floppy Disk), kemudian isi nama file yang diinginkan, tekan .
Selesai.

How to load parameter:

Hubungkan kabel interface antara computer (COM 1) dengan CPE.
Buka directory C:\IS10CPE atau C:\IS10.
Ketik IS10, tekan , maka akan muncul tampilan pembuka dari program ini.
Tekan sembarang tombol, maka akan muncul menu pilihan “INTERFACE SELECTION”, Pilih “RS232C”, dengan cara menekan tombol F2, maka akan muncul menu berikutnya.
Selanjutnya tekan sembarang tombol, maka akan ditampilkan nama identitas dari CPE tersebut. Kemudian tekan sembarang tombol.
Tekan F7 (Setting Data Control), tekan F5 (Write Floppy Disk Data into RS-232C).
Posisi protection switch dicard MCU-7B8A (dibelakang pintu CPE) harus pada posisi “Non-Prot”.
Isi nama file yang akan di-load ke CPE, tekan .
Selesai

GPPRO2 Software Quick Start

2010-09-17T09:32:00.000+07:00

Software Name : GPPRO2.EXE

How to save program:

Hubungkan kabel interface antara computer (COM 1) dengan Touch screen.
Buka directory C:\GPPRO2.
Ketik GP, tekan , maka akan muncul menu pilihan untuk “Open file”.
Dengan menggunakan mouse, klik “Cancel” agar kembali ke menu utama.
Klik “F7-Setup”, klik “Comm. Port”, maka akan muncul pilihan Comm. Port. Pilih “[0] COM1”, klik “OK”.
Klik “F7-Setup”, klik “PLC”, maka akan muncul menu pilihan macam-macam type PLC yang dapat dihubungkan dengan touch screen ini. Pilih type PLC yang sesuai, kemudian klik “OK”.
Klik “F7-Setup”, klik “GP Type”, maka akan muncul menu pilihan macam-macam type touch screen, yaitu GP-250, GP-450 dan GP-550. Pilih salah satu yang sesuai, kemudian klik “OK”.
Klik “F2-File”, klik “Transfer”, maka akan muncul menu pilihan untuk “Transfer file”. Pilih “[1] Receive Scrn file”, klik “OK”, maka akan muncul menu pilihan “Receive Scrn file”. Klik pada kolom disebelah kanan dari “Dir” untuk menentukan directory yang digunakan untuk save program. Setelah diklik, ketik directory yang diinginkan.
Pastikan ada tanda “*” disebelah kanan kolom “Start file”, jika bukan, maka pilih tanda “*” dengan cara meng-klik tanda tersebut dan klik tanda “*”, dan setelah itu klik “OK”, maka akan muncul pesan untuk konfirmasi, kemudian klik “OK” sekali lagi, maka proses save program dimulai.
Setelah proses tersebut selesai, maka akan muncul pesan “File Transfer Complete!”, kemudian klik “OK”. Setelah itu klik “Cancel” untuk kembali ke menu utama.
Lepas kabel interface antara computer dengan touch screen.
Klik “F2-File”, klik “Quit”, maka program akan kembali ke DOS prompt.
Selesai.

How to load program:

Hubungkan kabel interface antara computer (COM 1) dengan Touch screen.
Buka directory C:\GPPRO2.
Ketik GP, tekan , maka akan muncul menu pilihan untuk “Open file”.
Dengan menggunakan mouse, klik “Cancel” agar kembali ke menu utama.
Klik “F7-Setup”, klik “Comm. Port”, maka akan muncul pilihan Comm. Port. Pilih “[0] COM1”, klik "OK”.
Klik “F7-Setup”, klik “PLC”, maka akan muncul menu pilihan macam-macam type PLC yang dapat dihubungkan dengan touch screen ini. Pilih type PLC yang sesuai, kemudian klik “OK”.
Klik “F7-Setup”, klik “GP Type”, maka akan muncul menu pilihan macam-macam type touch screen, yaitu GP-250, GP-450 dan GP-550. Pilih salah satu yang sesuai, kemudian klik “OK”.
Klik “F2-File”, klik “Transfer”, maka akan muncul menu pilihan untuk “Transfer file”. Pilih “[0] Send Scrn file”, klik “OK”, maka akan muncul menu pilihan “Send Scrn file”. Klik pada kolom disebelah kanan dari “Dir” untuk menentukan directory yang digunakan untuk save program. Setelah diklik, ketik directory yang diinginkan.
Pastikan ada tanda “*” disebelah kanan kolom “Start file”, jika bukan, maka pilih tanda “*” dengan cara meng-klik tanda tersebut dan klik tanda “*”, dan setelah itu klik “OK”, maka akan muncul pesan untuk konfirmasi, kemudian klik “OK” sekali lagi, maka proses load program dimulai.
Setelah proses tersebut selesai, maka akan muncul pesan “File Transfer Complete!”, kemudian klik “OK”. Setelah itu klik “Cancel” untuk kembali ke menu utama.
Lepas kabel interface antara computer dengan touch screen.
Klik “F2-File”, klik “Quit”, maka program akan kembali ke DOS prompt.
Selesai.

Safe Meter Usage

2010-09-15T20:07:00.004+07:00

Using an electrical meter safely and efficiently is perhaps the most valuable skill an electronics technician can master, both for the sake of their own personal safety and for proficiency at their trade. It can be daunting at first to use a meter, knowing that you are connecting it to live circuits which may harbor life-threatening levels of voltage and current. This concern is not unfounded, and it is always best to proceed cautiously when using meters. Carelessness more than any other factor is what causes experienced technicians to have electrical accidents.

The most common piece of electrical test equipment is a meter called the multimeter. Multimeters are so named because they have the ability to measure a multiple of variables: voltage, current, resistance, and often many others, some of which cannot be explained here due to their complexity. In the hands of a trained technician, the multimeter is both an efficient work tool and a safety device. In the hands of someone ignorant and/or careless, however, the multimeter may become a source of danger when connected to a "live" circuit.

There are many different brands of multimeters, with multiple models made by each manufacturer sporting different sets of features. The multimeter shown here in the following illustrations is a "generic" design, not specific to any manufacturer, but general enough to teach the basic principles of use:

You will notice that the display of this meter is of the "digital" type: showing numerical values using four digits in a manner similar to a digital clock. The rotary selector switch (now set in the Off position) has five different measurement positions it can be set in: two "V" settings, two "A" settings, and one setting in the middle with a funny-looking "horseshoe" symbol on it representing "resistance." The "horseshoe" symbol is the Greek letter "Omega" (Ω), which is the common symbol for the electrical unit of ohms.
Of the two "V" settings and two "A" settings, you will notice that each pair is divided into unique markers with either a pair of horizontal lines (one solid, one dashed), or a dashed line with a squiggly curve over it. The parallel lines represent "DC" while the squiggly curve represents "AC." The "V" of course stands for "voltage" while the "A" stands for "amperage" (current). The meter uses different techniques, internally, to measure DC than it uses to measure AC, and so it requires the user to select which type of voltage (V) or current (A) is to be measured. Although we haven't discussed alternating current (AC) in any technical detail, this distinction in meter settings is an important one to bear in mind.
There are three different sockets on the multimeter face into which we can plug our test leads. Test leads are nothing more than specially-prepared wires used to connect the meter to the circuit under test. The wires are coated in a color-coded (either black or red) flexible insulation to prevent the user's hands from contacting the bare conductors, and the tips of the probes are sharp, stiff pieces of wire:

The black test lead always plugs into the black socket on the multimeter: the one marked "COM" for "common." The red test lead plugs into either the red socket marked for voltage and resistance, or the red socket marked for current, depending on which quantity you intend to measure with the multimeter.
To see how this works, let's look at a couple of examples showing the meter in use. First, we'll set up the meter to measure DC voltage from a battery:

Note that the two test leads are plugged into the appropriate sockets on the meter for voltage, and the selector switch has been set for DC "V". Now, we'll take a look at an example of using the multimeter to measure AC voltage from a household electrical power receptacle (wall socket):

The only difference in the setup of the meter is the placement of the selector switch: it is now turned to AC "V". Since we're still measuring voltage, the test leads will remain plugged in the same sockets. In both of these examples, it is imperative that you not let the probe tips come in contact with one another while they are both in contact with their respective points on the circuit. If this happens, a short-circuit will be formed, creating a spark and perhaps even a ball of flame if the voltage source is capable of supplying enough current! The following image illustrates the potential for hazard:

This is just one of the ways that a meter can become a source of hazard if used improperly.
Voltage measurement is perhaps the most common function a multimeter is used for. It is certainly the primary measurement taken for safety purposes (part of the lock-out/tag-out procedure), and it should be well understood by the operator of the meter. Being that voltage is always relative between two points, the meter must be firmly connected to two points in a circuit before it will provide a reliable measurement. That usually means both probes must be grasped by the user's hands and held against the proper contact points of a voltage source or circuit while measuring.
Because a hand-to-hand shock current path is the most dangerous, holding the meter probes on two points in a high-voltage circuit in this manner is always a potential hazard. If the protective insulation on the probes is worn or cracked, it is possible for the user's fingers to come into contact with the probe conductors during the time of test, causing a bad shock to occur. If it is possible to use only one hand to grasp the probes, that is a safer option. Sometimes it is possible to "latch" one probe tip onto the circuit test point so that it can be let go of and the other probe set in place, using only one hand. Special probe tip accessories such as spring clips can be attached to help facilitate this.
Remember that meter test leads are part of the whole equipment package, and that they should be treated with the same care and respect that the meter itself is. If you need a special accessory for your test leads, such as a spring clip or other special probe tip, consult the product catalog of the meter manufacturer or other test equipment manufacturer. Do not try to be creative and make your own test probes, as you may end up placing yourself in danger the next time you use them on a live circuit.
Also, it must be remembered that digital multimeters usually do a good job of discriminating between AC and DC measurements, as they are set for one or the other when checking for voltage or current. As we have seen earlier, both AC and DC voltages and currents can be deadly, so when using a multimeter as a safety check device you should always check for the presence of both AC and DC, even if you're not expecting to find both! Also, when checking for the presence of hazardous voltage, you should be sure to check all pairs of points in question.
For example, suppose that you opened up an electrical wiring cabinet to find three large conductors supplying AC power to a load. The circuit breaker feeding these wires (supposedly) has been shut off, locked, and tagged. You double-checked the absence of power by pressing the Start button for the load. Nothing happened, so now you move on to the third phase of your safety check: the meter test for voltage.

First, you check your meter on a known source of voltage to see that its working properly. Any nearby power receptacle should provide a convenient source of AC voltage for a test. You do so and find that the meter indicates as it should. Next, you need to check for voltage among these three wires in the cabinet. But voltage is measured between two points, so where do you check?

The answer is to check between all combinations of those three points. As you can see, the points are labeled "A", "B", and "C" in the illustration, so you would need to take your multimeter (set in the voltmeter mode) and check between points A & B, B & C, and A & C. If you find voltage between any of those pairs, the circuit is not in a Zero Energy State. But wait! Remember that a multimeter will not register DC voltage when its in the AC voltage mode and vice versa, so you need to check those three pairs of points in each mode for a total of six voltage checks in order to be complete!

However, even with all that checking, we still haven't covered all possibilities yet. Remember that hazardous voltage can appear between a single wire and ground (in this case, the metal frame of the cabinet would be a good ground reference point) in a power system. So, to be perfectly safe, we not only have to check between A & B, B & C, and A & C (in both AC and DC modes), but we also have to check between A & ground, B & ground, and C & ground (in both AC and DC modes)! This makes for a grand total of twelve voltage checks for this seemingly simple scenario of only three wires. Then, of course, after we've completed all these checks, we need to take our multimeter and re-test it against a known source of voltage such as a power receptacle to ensure that its still in good working order.
Using a multimeter to check for resistance is a much simpler task. The test leads will be kept plugged in the same sockets as for the voltage checks, but the selector switch will need to be turned until it points to the "horseshoe" resistance symbol. Touching the probes across the device whose resistance is to be measured, the meter should properly display the resistance in ohms:

One very important thing to remember about measuring resistance is that it must only be done on de-energized components! When the meter is in "resistance" mode, it uses a small internal battery to generate a tiny current through the component to be measured. By sensing how difficult it is to move this current through the component, the resistance of that component can be determined and displayed. If there is any additional source of voltage in the meter-lead-component-lead-meter loop to either aid or oppose the resistance-measuring current produced by the meter, faulty readings will result. In a worse-case situation, the meter may even be damaged by the external voltage.
The "resistance" mode of a multimeter is very useful in determining wire continuity as well as making precise measurements of resistance. When there is a good, solid connection between the probe tips (simulated by touching them together), the meter shows almost zero Ω. If the test leads had no resistance in them, it would read exactly zero:

If the leads are not in contact with each other, or touching opposite ends of a broken wire, the meter will indicate infinite resistance (usually by displaying dashed lines or the abbreviation "O.L." which stands for "open loop"):

By far the most hazardous and complex application of the multimeter is in the measurement of current. The reason for this is quite simple: in order for the meter to measure current, the current to be measured must be forced to go through the meter. This means that the meter must be made part of the current path of the circuit rather than just be connected off to the side somewhere as is the case when measuring voltage. In order to make the meter part of the current path of the circuit, the original circuit must be "broken" and the meter connected across the two points of the open break. To set the meter up for this, the selector switch must point to either AC or DC "A" and the red test lead must be plugged in the red socket marked "A". The following illustration shows a meter all ready to measure current and a circuit to be tested:

Now, the circuit is broken in preparation for the meter to be connected:

The next step is to insert the meter in-line with the circuit by connecting the two probe tips to the broken ends of the circuit, the black probe to the negative (-) terminal of the 9-volt battery and the red probe to the loose wire end leading to the lamp:

This example shows a very safe circuit to work with. 9 volts hardly constitutes a shock hazard, and so there is little to fear in breaking this circuit open (bare handed, no less!) and connecting the meter in-line with the flow of electrons. However, with higher power circuits, this could be a hazardous endeavor indeed. Even if the circuit voltage was low, the normal current could be high enough that an injurious spark would result the moment the last meter probe connection was established.
Another potential hazard of using a multimeter in its current-measuring ("ammeter") mode is failure to properly put it back into a voltage-measuring configuration before measuring voltage with it. The reasons for this are specific to ammeter design and operation. When measuring circuit current by placing the meter directly in the path of current, it is best to have the meter offer little or no resistance against the flow of electrons. Otherwise, any additional resistance offered by the meter would impede the electron flow and alter the circuits operation. Thus, the multimeter is designed to have practically zero ohms of resistance between the test probe tips when the red probe has been plugged into the red "A" (current-measuring) socket. In the voltage-measuring mode (red lead plugged into the red "V" socket), there are many mega-ohms of resistance between the test probe tips, because voltmeters are designed to have close to infinite resistance (so that they don't draw any appreciable current from the circuit under test).
When switching a multimeter from current- to voltage-measuring mode, its easy to spin the selector switch from the "A" to the "V" position and forget to correspondingly switch the position of the red test lead plug from "A" to "V". The result -- if the meter is then connected across a source of substantial voltage -- will be a short-circuit through the meter!

To help prevent this, most multimeters have a warning feature by which they beep if ever there's a lead plugged in the "A" socket and the selector switch is set to "V". As convenient as features like these are, though, they are still no substitute for clear thinking and caution when using a multimeter.
All good-quality multimeters contain fuses inside that are engineered to "blow" in the event of excessive current through them, such as in the case illustrated in the last image. Like all overcurrent protection devices, these fuses are primarily designed to protect the equipment (in this case, the meter itself) from excessive damage, and only secondarily to protect the user from harm. A multimeter can be used to check its own current fuse by setting the selector switch to the resistance position and creating a connection between the two red sockets like this:

A good fuse will indicate very little resistance while a blown fuse will always show "O.L." (or whatever indication that model of multimeter uses to indicate no continuity). The actual number of ohms displayed for a good fuse is of little consequence, so long as its an arbitrarily low figure.
So now that we've seen how to use a multimeter to measure voltage, resistance, and current, what more is there to know? Plenty! The value and capabilities of this versatile test instrument will become more evident as you gain skill and familiarity using it. There is no substitute for regular practice with complex instruments such as these, so feel free to experiment on safe, battery-powered circuits.

REVIEW:

A meter capable of checking for voltage, current, and resistance is called a multimeter.
As voltage is always relative between two points, a voltage-measuring meter ("voltmeter") must be connected to two points in a circuit in order to obtain a good reading. Be careful not to touch the bare probe tips together while measuring voltage, as this will create a short-circuit!
Remember to always check for both AC and DC voltage when using a multimeter to check for the presence of hazardous voltage on a circuit. Make sure you check for voltage between all pair-combinations of conductors, including between the individual conductors and ground!
When in the voltage-measuring ("voltmeter") mode, multimeters have very high resistance between their leads.
Never try to read resistance or continuity with a multimeter on a circuit that is energized. At best, the resistance readings you obtain from the meter will be inaccurate, and at worst the meter may be damaged and you may be injured.
Current measuring meters ("ammeters") are always connected in a circuit so the electrons have to flow through the meter.
When in the current-measuring ("ammeter") mode, multimeters have practically no resistance between their leads. This is intended to allow electrons to flow through the meter with the least possible difficulty. If this were not the case, the meter would add extra resistance in the circuit, thereby affecting the current.

Common Causes of High Bills

2010-09-09T18:41:00.000+07:00

To gain control over your energy consumption, it’s helpful to understand the most common causes of high bills. They are:

1.Weather – Weather is the No. 1 cause of high bills.
◦Hot weather – Even if you never change your thermostat, cooling can account for half or more of your electric bill during hotter weather. When you lower your thermostat to stay comfortable in humid weather, it causes your A/C to run longer, which increases energy use. To save energy, cool your home at 78 degrees or warmer with the thermostat fan switch on "auto." For additional savings, raise your thermostat to 82 degrees or warmer when you're away from home. Also, clean or replace your air conditioner's filter every month to trim your cooling costs and help your unit run more efficiently.
◦Cold weather – During periods of cold weather, strip heating and portable heaters are among the highest sources of electric demand. In fact, strip or electric resistance-based heating requires two to three times more energy than air conditioning. That is why for every two degrees you lower your thermostat, i.e. setting your thermostat from 68 degrees to 66 degrees, we estimate you will save approximately 20 percent on the heating portion of your bill. Also, people tend to take longer showers in colder weather, which increases water heating costs. View more cold weather tips.

2.Electronics and appliances* – Many electronic devices continue to draw power even when they are not in use. So, consider either plugging these devices into a power strip with an on/off button or unplugging items when not in use. This includes:
◦TVs (Larger and plasma TVs use more electricity and produce more heat, which makes your A/C operate more.)
◦Stereos
◦DVDs and DVRs
◦Cell phone or battery chargers
*Caution: Shutting some items off may require reprogramming.

3.Household – House guests, including kids home from college, can use a lot more electricity — more showers, laundry, cooking and dishes, all of which use hot water. In addition, the size, age and type of house you live in can impact the amount of energy you consume.

4.Length of billing cycle – A billing cycle is the number of days in each bill. Normally, your meter is read on the same day every month, but some months are longer than others and weekends and holidays can sometimes get in the way. Occasionally, an FPL employee can't get to your meter because a gate is locked or a dog is in the backyard, and it’s not safe to enter. As a result, some monthly bills cover as few as 25 days and some as many as 35 days.

Energy Conservation Measures for Commercial

2010-09-09T18:32:00.000+07:00

Office Equipment Tips

• Turn off all office equipment and lights every night and weekend. If you can't turn off the whole computer, turn off the monitor and the printer.

• When purchasing PCs, monitors, printers, fax machines and copiers, consider ENERGY STAR® models that "power down" after a user-specified period of inactivity.

• Install free software from the Environmental Protection Agency that puts monitors in sleep mode when not in use. This can save $0.085/kWh of power used by networks.

• If appropriate, use laptop computers and inkjet printers — they consume 90 percent less energy than standard desktop computers.

• Use e-mail instead of sending memos and faxing documents.

• If you need to print, consider double-sided printing and reusing paper.

Lighting Tips
• Retrofit T12 lights with magnetic ballasts to T8 lights with electronic ballasts.
• Replace incandescent light lamps with compact fluorescent lamps (CFLs), wherever appropriate. CFLs use at least 66% less energy and last an average of 10 times longer.
• Consider removing excess fluorescent lights and installing reflectors. Lighter colored walls need less light.
• Install motion detectors to control lighting in frequently unoccupied areas, such as restrooms.
• Retrofit incandescent or fluorescent exit signs with long-lasting, low-energy LED exit signs.
• Clean dusty diffusers and lamps every 6-12 months for improved lumen output.
• Turn off the lights when not needed. It is a myth that leaving them on uses less energy than turning them off. Turn off signage and other lights not necessary for security and safety.
• Open blinds and shades. Turn off lights in unoccupied areas or in spaces with sufficient natural lighting.
• Use teamwork to reduce lighting loads. Cleaning staff can work in teams (instead of different areas simultaneously) to reduce lighting usage. This can save up to 20% in lighting energy.

HVAC Tips
• Set thermostats at 78 degrees F for cooling in the summer when the workplace is occupied, and 85 F or off after business hours. During the winter, set the thermostat to 68°F when the work place is occupied and 63°F after business hours. The energy savings can be as much as 2% of your air conditioning costs for each one degree that you raise the thermostat.
• Install electronic time clocks or setback-programmable thermostats to maximize efficiency.
• Install locking covers on your thermostats to prevent employee tampering with temperature settings.
• Regularly clean condenser coils, replace air filters, and check ducts and pipe insulation for damage.
• Consider installing an air conditioning economizer to bring in outside air when cool outside.
• Consider replacing old HVAC systems with new energy-efficient systems.
• Install ceiling fans.
• Install blinds or solar screen shades. Use reflective window film or awnings on all south-facing windows. Consider solar control window films applied to existing glass in windows and doors to reduce peak demand during hot months and conserve energy anytime air conditioning might be required. These films can also reduce exposure to ultraviolet radiation and reduce glare. Save 5 to 10%.
• Perform regular maintenance to keep heating, ventilation and air conditioning (HVAC) systems running more efficiently. Maintenance activities can save up to 30% of fan energy and up to 10% of space conditioning energy use.
• Install ceiling and wall insulation.
• Insulate water heaters and supply pipes.

Refrigeration Tips
• Perform scheduled maintenance on units, especially keeping evaporator coils clean and free of ice build-up.
• Adjust door latches, replace worn door gaskets, install autoclosers, and add strip curtains to walkin doors.
• Use night covers on both vertical and horizontal display cases.
• Disconnect anti-condensate heaters.
• Keep refrigerators full (water jugs make good fillers).
• Turn off and recycle your second refrigerator. Many of these secondary units (usually older and less energy efficient) use as much as 40% more energy than a new model.

Food Service Equipment Tips
• Consider replacing some or all electric cooking equipment with comparably sized gas-fired equipment.
• Purchase insulated cooking equipment whenever possible (e.g., fryers, ovens, coffee machines).
• Preheat cooking equipment no longer and at no higher setting than the manufacturer's recommendation.
• Use cooking equipment to capacity. Fully loaded equipment utilizes energy more efficiently. Turn off unused and backup equipment during low production periods.
• Filter fryer oil at least once a day to extend the oil life.
• Don't overload fryer baskets beyond the recommended capacity. Overloading increases cook time.
• Where applicable, replace broilers with grooved or smooth griddles to significantly reduce the associated energy consumption.
• Make sure oven doors fit tightly and gaskets are in good condition.
Other Energy Savings Tips for Commercial Sector:
• Implement a dress code for warm weather. Allow employees to wear comfortable clothing during warm or hot weather. It makes little sense to keep a room cold enough that workers must wear suits and coats.
• Adjust workplace schedules to reduce energy use during the "peak" hours when there is most demand for electricity, typically noon to 7 p.m.

Sources:

http://www.pge.com/biz/energy_tools_resources/small_biz/
http://www.fypower.org/inst/tools/energy_tips.html

Function of Capacitors

2010-09-06T21:08:00.000+07:00

Electric power has two components:

Active power, which produces work.

Reactive power, which is needed to generate magnetic fields required for operation of inductive electrical equipment, but performs no useful work.

Active power is measured in KW (1000 Watts)

Reactive power is measured in KVAR (1000 Volt-Amperes Reactive)

Total power is measured in KVA (1000 Volts-Amperes)

The ratio of working power to total power is called Power Factor.

The function of Power Factor Correction Capacitors is to increase the power factor by supplying the reactive power when installed at or near inductive electrical equipment.

Peranan Kapasitor dalam Penggunaan Energi Listrik

2010-09-06T16:17:00.000+07:00

Kehidupan modern salah satu cirinya adalah pemakaian energi listrik yang besar. Besarnya energi atau beban listrik yang dipakai ditentukan oleh reaktansi (R), induktansi (L) dan capasitansi (C). Besarnya pemakaian energi listrik itu disebabkan karena banyak dan beraneka ragam peralatan (beban) listrik yang digunakan. Sedangkan beban listrik yang digunakan umumnya bersifat induktif dan kapasitif. Di mana beban induktif (positif) membutuhkan daya reaktif seperti trafo pada rectifier, motor induksi (AC) dan lampu TL, sedang beban kapasitif (negatif) mengeluarkan daya reaktif. Daya reaktif itu merupakan daya tidak berguna sehingga tidak dapat dirubah menjadi tenaga akan tetapi diperlukan untuk proses transmisi energi listrik pada beban. Jadi yang menyebabkan pemborosan energi listrik adalah banyaknya peralatan yang bersifat induktif. Berarti dalam menggunakan energi listrik ternyata pelanggan tidak hanya dibebani oleh daya aktif (kW) saja tetapi juga daya reaktif (kVAR). Penjumlahan kedua daya itu akan menghasilkan daya nyata yang merupakan daya yang disuplai oleh PLN. Jika nilai daya itu diperbesar yang biasanya dilakukan oleh pelanggan industri maka rugi-rugi daya menjadi besar sedang daya aktif (kW) dan tegangan yang sampai ke konsumen berkurang. Dengan demikian produksi pada industri itu akan menurun hal ini tentunya tidak boleh terjadi untuk itu suplai daya dari PLN harus ditambah berarti penambahan biaya. Karena daya itu P = V.I, maka dengan bertambah besarnya daya berarti terjadi penurunan harga V dan naiknya harga I. Dengan demikian daya aktif, daya reaktif dan daya nyata merupakan suatu kesatuan yang kalau digambarkan seperti segi tiga siku-siku.

Perbandingan daya aktif (kW) dengan daya nyata (kVA) dapat didefinisikan sebagai faktor daya (pf) atau cos phi.

cos phi = pf = P (kW) / S (kVA) ........(1) P (kW) = S (kVA) . cos phi................(2)

Seperti kita ketahui bahwa harga cos phi adalah mulai dari 0 s/d 1. Berarti kondisi terbaik yaitu pada saat harga P (kW) maksimum [ P (kW)=S (kVA) ] atau harga cos phi = 1 dan ini disebut juga dengan cos phi yang terbaik. Namun dalam kenyataannya harga cos phi yang ditentukan oleh PLN sebagai pihak yang mensuplai daya adalah sebesar 0,8. Jadi untuk harga cos phi = 0,8 berarti pf dikatakan jelek. Jika pf pelanggan jelek (rendah) maka kapasitas daya aktif (kW) yang dapat digunakan pelanggan akan berkurang. Kapasitas itu akan terus menurun seiring dengan semakin menurunnya pf sistem kelistrikan pelanggan. Akibat menurunnya pf itu maka akan muncul beberapa persoalan sbb:

a. Membesarnya penggunaan daya listrik kWH karena rugi-rugi.

b. Membesarnya penggunaan daya listrik kVAR.

c. Mutu listrik menjadi rendah karena jatuh tegangan.

Secara teoritis sistem dengan pf yang rendah tentunya akan menyebabkan arus yang dibutuhkan dari pensuplai menjadi besar. Hal ini akan menyebabkan rugi-rugi daya (daya reaktif) dan jatuh tegangan menjadi besar. Dengan demikian denda harus dibayar sebabpemakaian daya reaktif meningkat menjadi besar. Denda atau biaya kelebihan daya reaktif dikenakan apabila jumlah pemakaian kVARH yang tercata dalam sebulan lebih tinggi dari 0,62 jumlah kWH pada bulan yang bersangkutan sehingga pf rata-rata kurang dari 0,85. Sedangkan perhitungan kelebihan pemakaian kVARH dalam rupiah menggunakan rumus sbb:

[ B - 0,62 ( A1 + A2 ) ] Hk

Dimana :

B = pemakaian kVARH

A1 = pemakaian kWH WPB

A2 = pemakaian kWH LWBP

Hk = harga kelebihan pemakaian kVARH

Untuk memperbesar harga cos phi (pf) yang rendah hal yang mudah dilakukan adalah memperkecil sudut phi. Sedang untuk memperkecil sudut phi itu hal yang mungkin dilakukan adalah memperkecil komponen daya reaktif (kVAR). Berarti komponen daya reaktif yang ada bersifat induktif harus dikurangi dan pengurangan itu bisa dilakukan dengan menambah suatu sumber daya reaktif yaitu berupa kapasitor.

Proses pengurangan itu bisa terjadi karena kedua beban (induktor dan kapasitor) arahnya berlawanan akibatnya daya reaktif menjadi kecil. Bila daya reaktif menjadi kecil sementara daya aktif tetap maka harga pf menjadi besar akibatnya daya nyata (kVA) menjadi kecil sehingga rekening listrik menjadi berkurang. Sedangkan keuntungan lain dengan mengecilnya daya reaktif adalah :

Mengurangi rugi-rugi daya pada sistem.
Adanya peningkatan tegangan karena daya meningkat.

Proses Kerja Kapasitor
Kapasitor yang akan digunakan untuk meperbesar pf dipasang paralel dengan rangkaian beban. Bila rangkaian itu diberi tegangan maka elektron akan mengalir masuk ke kapasitor. Pada saat kapasitor penuh dengan muatan elektron maka tegangan akan berubah. Kemudian elektron akan ke luar dari kapasitor dan mengalir ke dalam rangkaian yang memerlukannya dengan demikian pada saaat itu kapasitor membangkitkan daya reaktif. Bila tegangan yang berubah itu kembali normal (tetap) maka kapasitor akan menyimpan kembali elektron. Pada saat kapasitor mengeluarkan elektron (Ic) berarti sama juga kapasitor menyuplai daya treaktif ke beban. Keran beban bersifat induktif (+) sedangkan daya reaktif bersifat kapasitor (-) akibatnya daya reaktif yang berlaku menjadi kecil.

Rugi-rugi daya sebelum dipasang kapasitor :
Rugi daya aktif = I2 R Watt .............(5)
Rugi daya reaktif = I2 x VAR.........(6)

Rugi-rugi daya sesudah dipasang kapasitor :
Rugi daya aktif = (I2 - Ic2) R Watt ...(7)
Rugi daya reaktif = (I2 - Ic2) x VAR (8)

Pemasangan Kapasitor
Kapasitor yang akan digunakan untuk memperkecil atau memperbaiki pf penempatannya ada dua cara :
1. Terpusat kapasitor ditempatkan pada:
a. Sisi primer dan sekunder transformator
b. Pada bus pusat pengontrol
2. Cara terbatas kapasitor ditempatkan
a. Feeder kecil
b. Pada rangkaian cabang
c. Langsung pada beban

Perawatan Kapasitor
Kapasitor yang digunakan untuk memperbaiki pf supaya tahan lama tentunya harus dirawat secara teratur. Dalam perawatan itu perhatian harus dilakukan pada tempat yang lembab yang tidak terlindungi dari debu dan kotoran. Sebelum melakukan pemeriksaan pastikan bahwa kapasitor tidak terhubung lagi dengan sumber. Kemudian karena kapasitor ini masih mengandung muatan berarti masih ada arus/tegangan listrik maka kapasitor itu harus dihubung singkatkan supaya muatannya hilang. Adapun jenis pemeriksaan yang harus dilakukan meliputi :

Selain komponen induktor pemborosan pemakaian listrik bisa juga terjadi karena:

Tegangan tidak stabil Ketidak stabilan tegangan bisa menyebabkan terjadinya pemborosan energi listrik. Ketidakstabilan itu dapat diartikan tegangan pada suatu fase lebih besar, lebih kecil atau berfluktuasi terhadap teganga standar. Sedangkan akibat pembrosan energi listrik itu maka timbul panas sehingga bisa menyebabkan pertama kerusakan isolator peralatan yang dipakai. Ke dua memperpendek daya isolasi pada lilitan. Sementara itu dengan ketidakseimbangan sebesar 3% saja dapat memperbesar suhu motor yang sedang beroperasi sebesar 18% dari keadaan semula. Hal ini tentunya akan menimbulkan suara bising pada motor dengan kecepatan tinggi.

Harmonik
Harmonik itu bisa menimbulkan panas, hal ini terjadi karena adanya energi listrik yang berlebihan. Harmonik itu bisa muncul karena peralatan seperti komputer, kontrol motor dll. Harmonik merupakan suatu keadaan timbulnya tegangan yang periodenya berbeda dengan periode tegangan standar. Periode itu bisa 180 Hz (harmonik ke-3), 300 Hz (harmonik ke-5) dan seterusnya. Harmonik pada transformator lebih berbahaya, hal ini karena adanya sisrkulasi arus akibat panas yang berlebih. Sehingga hal ini bisa mengurangi kemampuan peralatan proteksi yang menggunakan power line carrier sebagai detektor kondisi normal.

Untuk mengoptimalkan pemakaian energi listrik bisa digunakan beban-beban tiruan berupa LC yang dilengkapi dengan teknologi mikroprosesor. Sehingga ketepatan dan keandalan dalam mendeteksi kualitas daya listrik bisa diperoleh. Mikroprosesor itu berfungsi untuk mengolah komponen-komponen yang menentukan kualitas tenaga listrik. Seperti keseimbangan beban antar fasa, harmonik dan surja. Apabila terdapat ketidakseimbangan antara fasa satu dengan fasa yang lainnya, maka mikroprosesor akan memerintahkan beban-beban LC untuk membuka atau menutup agar arus disuplai ke fasa satu sehingga selisih arus antara fasa satu dengan fasa yang lainnya tidak ada. Banyaknya L atau C yang dibuka atau ditutup tergantung dari kondisi ketidakseimbangan beban yang terdeteksi oleh mikroprosesor. Kondisi harmonik yang terdeteksi bisa dihilangkan dengan menggunakan filter LC.

Keuntungan alat ini adalah :
Mampu mereduksi daya sampai 30%.
Meningkatkan pf antara 95-100%
Dapat mengeliminasi terjadinya harmonik.
Dengan demikian pemakaian energi listrik bisa dihemat yaitu dengan cara mengoptimalkan konsumsi energi masing-masing peralatan yang digunakan, memperkecil gejala harmonik dan menstabilkan tegangan. Sehingga energi tersisa bisa dimanfaatkan untuk sektor lain yang lebih membutuhkan. Sedang dampak negatif dari pemborosan energi listrik itu pertama menciptakan ketidakseimbangan beban fasa-fasa listrik yang pada gilirannya akan mempengaruhi over heating pada motor dan penurunan life isolator. Ke dua bagi PLN sebagai penyuplai energi listrik tentunya harus menyediakan energi listrik yang lebih besar lagi.

Life time capacitor bank

2010-09-06T14:14:00.001+07:00

Beberapa hal dapat mempengaruhi usia dari capacitor bank, antara lain : temperature, tegangan yang masuk ke capacitor, frekuensi, juga kualitas power (THD = Total Harmonic Distortion).

THD (Total Harmonic Distortion) > 5% bisa membuat capacitor meledak. Yang menyebabkan harmonic tinggi adalah beban non linear, seperti rectifier, ups, batetry charge, inverter, lampu hemat energi, arc furnaces dsb.
Ada 2 macam THD, yaitu THDv dan THDi.

Pengaruh THD yang tinggi adalah terjadinya over voltage dan over current, yang bisa terjadi antara lain :

Bunyi mendengung yang keras pada trafo.
Putaran motor dapat berbalik arah yang menyebabkan putarannya terkunci, sehingga menimbulkan arus yang sangat besar.
Putaran kWH meter yang lebih cepat, padahal pemakaiannya tetap.
Ledakan pada capacitor.
dsb

Pemilihan Capacitor :

Classic solution:
THD (I) < 15% atau THD (U) < 2% maka gunakan ==> kapasitor standar 400VAC/50Hz
Comfort solution:
15% < THD (I) < 25% atau 2% < THD (U) < 3% maka gunakan ==> kapasitor yang dioverrated di 525VAC/50Hz

Harmony solution:
25% < THD (I) < 40% atau 3% < THD (U) < 4% maka gunakan ==> kapasitor yang dioverrated di 525VAC/50Hz + Detuned Reactor (DR) dengan tuning order 190Hz

Fungsi Capacitor Bank

2010-09-06T14:03:00.000+07:00

Secara umum beban yang sering digunakan, terutama pada industri, adalah beban induktif, seperti motor listrik, lampu TL, heater dsb. Dengan adanya beban induktif ini menyebabkan nilai cos phi yang rendah. Standar dari PLN adalah minimal 0.85.

PLN akan membebankan biaya kelebihan pemakaain kVARh pada pelanggan, jika faktor daya (cos phi) nya kurang dari 0.85

Untuk memperbaiki faktor daya ini, maka digunakan capacitor bank, yang berfungsi sebagai kompensator dari beban-beban induktif.

Load Characteristics

2010-07-07T23:29:00.000+07:00

Introduction

Motor loads are classified into two main groups depending on how their torque requirement varies with operating speed. The following paragraphs deal with the various load types found in industry.

Constant Torque LoadThe torque demanded by the load is constant throughout the speed range. Loads of these types are essentially friction loads. Figure 2.1 shows the constant torque and it’s effect on horsepower demanded by the load.

Since HP is a product of Torque times speed, and torque remains constant in this type of load, horsepower is a function of speed.

Examples of this type of load are conveyors and extruders. Constant torque is also used when shock loads, overloads or high inertia loads are encountered.

Variable Torque Load

With this type of load, the torque demand increases with speed, usually speed squared (Speed^2).

Torque Constant x (Speed)^2

Horsepower is typically proportional to speed cubed (Speed^3).

Figure 2.2 shows the variable torque and it’s effect on horsepower demanded by the load.

Examples of loads that exhibit variable load torque characteristics are centrifugal fans, pumps and blowers. This type of load requires much lower torque at low speeds than at high speeds.

Constant Horsepower Operation

This is a function of the motor being operated above base motor speed. The horsepower demanded by the load is constant within the speed range. The speed and torque are inversely proportional to each other. Figure 2.3 shows the constant horsepower and variable torque demanded by the load.

Examples of this type of load are center-driven winders and machine tool spindles.

Capacitor Bank

2010-06-27T22:55:00.000+07:00

Proses Kerja Kapasitor

Kapasitor yang akan digunakan untuk meperbesar pf dipasang paralel dengan rangkaian beban. Bila rangkaian itu diberi tegangan maka elektron akan mengalir masuk ke kapasitor. Pada saat kapasitor penuh dengan muatan elektron maka tegangan akan berubah. Kemudian elektron akan ke luar dari kapasitor dan mengalir ke dalam rangkaian yang memerlukannya dengan demikian pada saaat itu kapasitor membangkitkan daya reaktif. Bila tegangan yang berubah itu kembali normal (tetap) maka kapasitor akan menyimpan kembali elektron. Pada saat kapasitor mengeluarkan elektron (Ic) berarti sama juga kapasitor menyuplai daya treaktif ke beban. Keran beban bersifat induktif (+) sedangkan daya reaktif bersifat kapasitor (-) akibatnya daya reaktif yang berlaku menjadi kecil.

Pemasangan Kapasitor
Kapasitor yang akan digunakan untuk memperkecil atau memperbaiki pf penempatannya ada dua cara :
1. Terpusat kapasitor ditempatkan pada:
a. Sisi primer dan sekunder transformator
b. Pada bus pusat pengontrol
2. Cara terbatas kapasitor ditempatkan
a. Feeder kecil
b. Pada rangkaian cabang
c. Langsung pada beban

Perawatan KapasitorKapasitor yang digunakan untuk memperbaiki pf supaya tahan lama tentunya harus dirawat secara teratur. Dalam perawatan itu perhatian harus dilakukan pada tempat yang lembab yang tidak terlindungi dari debu dan kotoran. Sebelum melakukan pemeriksaan pastikan bahwa kapasitor tidak terhubung lagi dengan sumber. Kemudian karena kapasitor ini masih mengandung muatan berarti masih ada arus/tegangan listrik maka kapasitor itu harus dihubung singkatkan supaya muatannya hilang.
Adapun jenis pemeriksaan yang harus dilakukan meliputi :
· Pemeriksaan kebocoran
· Pemeriksaan kabel dan penyangga kapasitor
· Pemeriksaan isolator

Komponen Panel Capasitor komponen yang terdapat pada panel kapasitor antara lain :
1. Main switch / load Break switch
Main switch ini sebagai peralatan kontrol dan isolasi jika ada pemeliharaan panel . Sedangkan untuk pengaman kabel / instalasi sudah tersedia disisi atasnya (dari) MDP.Mains switch atau lebih dikenal load break switch adalah peralatan pemutus dan penyambung yang sifatnya on load yakni dapat diputus dan disambung dalam keadaan berbeban, berbeda dengan on-off switch model knife yang hanya dioperasikan pada saat tidak berbeban .Untuk menentukan kapasitas yang dipakai dengan perhitungan minimal 25 % lebih besar dari perhitungan KVar terpasang dari sebagai contoh :Jika daya kvar terpasang 400 Kvar dengan arus 600 Ampere , maka pilihan kita berdasarkan 600 A + 25 % = 757 Ampere yang dipakai size 800 Ampere.
2. Kapasitor Breaker.
Kapasitor Breaker digunkakan untuk mengamankan instalasi kabel dari breaker ke Kapasitor bank dan juga kapasitor itu sendiri. Kapasitas breaker yang digunakan sebesar 1,5 kali dari arus nominal dengan I m = 10 x Ir.Untuk menghitung besarnya arus dapat digunakan rumusI n = Qc / 3 . VLSebagai contoh : masing masing steps dari 10 steps besarnya 20 Kvar maka dengan menggunakan rumus diatas didapat besarnya arus sebesar 29 ampere , maka pemilihan kapasitas breaker sebesar 29 + 50 % = 43 A atau yang dipakai 40 Ampere.Selain breaker dapat pula digunakan Fuse , Pemakaian Fuse ini sebenarnya lebih baik karena respon dari kondisi over current dan Short circuit lebih baik namun tidak efisien dalam pengoperasian jika dalam kondisi putus harus selalu ada penggantian fuse. Jika memakai fuse perhitungannya juga sama dengan pemakaian breaker.
3. Magnetic Contactor
Magnetic contactor diperlukan sebagai Peralatan kontrol.Beban kapasitor mempunyai arus puncak yang tinggi , lebih tinggi dari beban motor. Untuk pemilihan magnetic contactor minimal 10 % lebih tinggi dari arus nominal ( pada AC 3 dengan beban induktif/kapasitif). Pemilihan magnetic dengan range ampere lebih tinggi akan lebih baik sehingga umur pemakaian magnetic contactor lebih lama.
4. Kapasitor Bank
Kapasitor bank adalah peralatan listrik yang mempunyai sifat kapasitif..yang akan berfungsi sebagai penyeimbang sifat induktif. Kapasitas kapasitor dari ukuran 5 KVar sampai 60 Kvar. Dari tegangan kerja 230 V sampai 525 Volt.
5. Reactive Power Regulator
Peralatan ini berfungsi untuk mengatur kerja kontaktor agar daya reaktif yang akan disupply ke jaringan/ system dapat bekerja sesuai kapasitas yang dibutuhkan. Dengan acuan pembacaan besaran arus dan tegangan pada sisi utama Breaker maka daya reaktif yang dibutuhkan dapat terbaca dan regulator inilah yang akan mengatur kapan dan berapa daya reaktif yang diperlukan. Peralatan ini mempunyai bermacam macam steps dari 6 steps , 12 steps sampai 18 steps.

Peralatan tambahan yang biasa digunakan pada panel kapasitor antara lain :
- Push button on dan push button off yang berfungsi mengoperasikan magnetic contactor secara manual.- Selektor auto – off – manual yang berfungsi memilih system operasional auto dari modul atau manual dari push button.
- Exhaust fan + thermostat yang berfungsi mengatur ambein temperature dalam ruang panel kapasitor. Karena kapasitor , kontaktor dan kabel penghantar mempunyai disipasi daya panas yang besar maka temperature ruang panel meningkat.setelah setting dari thermostat terlampaui maka exhust fan akan otomatic berhenti.

Setup C/K PFR
Capacitor BankAgar Power Factor Regulator (PFR) yang terpasang pada Panel Capacitor Bank dapat bekerja secara maksimal dalam melakukan otomatisasi mengendalikan kerja capacitor maka diperlukan setup C/K yang sesuai.Berikut ini cara menghitung C/K pada PFR:Sebuah Panel Capacitor Bank 6 Step x 60 KVAR, 3 Phase, 400 Volt, dengan CT sensor terpasang 1000/5A. Berapa nilai setup C/K ?Solusi:60 KVAR = 60.000 VAR60.000=86 A400 x 1.732C/K=I c1=86=0,43CT Ratio1000/5

Keuntungan yang diperoleh dengan dipasangnya Power Capacitor
-Menghilangkan denda PLN atas kelebihan pemakaian daya reaktif.
-Menurunkan pemakaian kVA total karena pemakaian kVA lebih mendekati kW yang terpakai, akibatnya pemakaian energi listrik lebih hemat.
-Optimasi Jaringan:
- Memberikan tambahan daya yang tersedia pada trafo sehingga trafo tidak kelebihan(overload).
- Mengurangi penurunan tegangan (voltage drop) pada line ends dan meningkatkan daya pakai alat-alat produksi.
- Terhindar dari kenaikan arus/suhu pada kabel sehingga mengurangi rugi-rugi.
Memperbaiki Faktor daya berdasarkan rekening listrik PLN.

Berdasarkan rekening listrik PLN suatu perusahaan pada tahun 1977 diperoleh data seperti dibawah ini.
1. Beban : 345 KVA
2. Pemakaian kWh
LWBP : 77.200 kWh
WBP : 34.000
kWhTotal : 111.200 kWh
3. Kelebihan kVARh : 10.656 kVARh
Cos phi = KW/KVA
Tan phi = KVAr/KW
sesuai dengan ketentuan PLN ,Yang Tidak terkena kelebihan KVAR kalau cos phi = 0.85
Cos phi = 0,85 ==> phi = 31,8maka tan 31,8 = 0.62
Jika KWH diketahui = 1111.200 ,
maka batas tidak terkena biaya kelebihan KVARH dapat dihitung sebesar :
KVARH ( batas ) = KWH x tan phi = 111.200 x 0,62 = 68.944
Dengan adanya kelebihan KVARH sebesar 10.656,besarnya KVARH ( Total ) menjadi :
KVARH ( total ) = KVARH ( batas ) + KVARH ( lebih )= 68.944+10.656 = 79.600
Tan phi = KVARH ( total ) / kWh = 79.600/111.200 = 0,716
phi = 35,6Cos phi = cos 35,6 = 0,813
Memperbaiki nilai Cos phi
Untuk menghindari biaya kelebihan KVARH,maka perlu dipasang " Capasitor ".
Misalnya direncanakan COs phi ditingkatkan menjadi = 0,92
Besarnya pemakaian listrik rata-rata dihitung sebagai berikut :
KW ( rata-rata) = Pemakaian listrik per bulan / ( 30 hari x 24 jam )= 111.200 / ( 30x24)= 154,4KW
Cos phi = 0.92 ---> phi=23,1
Tan phi = 23,1 = 0,426 = KVAR/KWKW = 154,4 ---> KVAR = 0,426X154,4 = 66KVARH ( total) = 79.600KVAR = 79.600/ ( 30X24) = 111
Jadi kapasitor yang perlu dipasang = 111 - 66 = 35
KVARKapasitor yang digunakan = 6 x 7,5 KVAR ,dengan Regulator 6 Step

LOADING SYSTEM PROGRAM APC2 DI BOARD YPP110A

2010-04-05T21:56:00.000+07:00

Jika menggunakan program “Loader32” tidak bisa, maka jalankan prosedur berikut :

On-kan YPP110A, connect power 24VDC
Jalankan MSDOS prompt
cd c:\apc2_lib_221\apcsys
ketik perintah : loader –apc apc221.img
….OK to load ? Yes
Overwrite QDP10 ? Yes
Jika saat loading ada error, misalnya : MS DOS can not load image file, stops at 1020 atau error yang lain, maka keluar dari DOS.
Lepas power supply APC
Pasang lagi power supply APC, display 7-segment akan menunjukkan PL
Jalankan program Loader32 dari Windows.
Setelah loading selesai, maka display 7-segment menjadi E1

Cara Penggantian Cooling Fan di ACV700 - ABB AC Drive

2010-04-05T21:45:00.001+07:00

Fan berjalan normal saat:

- Setelah main switch di-onkan, fan akan berjalan 1 menit

- Bila inverter start

- Bila temperature heat sink diatas 45 derajat celcius.

Fan akan berhenti saat:

- Modulation dihentikan dan temperature heat sink dibawah 40 derajat celcius.

Jika fan tidak berjalan seperti yang disebutkan diatas, cek :
1. Fan motor protection switch F11 untuk type inverter GTO.
2. Tegangan auxiliary 220VAC.
3. Tegangan auxiliary +24VDC.
4. Apakah relay K1 di Main Circuit Interface Card kondisi on setelah main power dionkan. Jika tidak, ganti Main Circuit Interface Card sesuai type ACVnya.
5. Insulation resistance dari fan dan connectionnya.
6. Bearing fan dengan memutar fan secara manual. Ganti fan jika diperlukan.
7. Sensor temperature heat sink NTC sensor (330Ohm) dan connectionnya.
8. Connection terminal X11 di SNAT600MCI (GTO Inverter) atau terminal X309 (IGBT Inverter) di SNAT726INT Main Circuit Interface Card.
9. Ganti SNAT603CNT Motor Control Card.

CARA MENGGANTI FAN UNTUK IGBT INVERTER UNIT (FRAME R4,R5)

Inverter unit harus dikeluarkan dari panel sebelumnya supaya bisa mengganti fan di frame R4 dam R5. Jika punya spare inverter module, ganti inverter unit yang rusak dengan spare untuk menghemat waktu. EEPROM D8 parameter memory circuit harus dilepas dari SNAT603CNT yang asli dan dipasang di spare module card SNAT603CNT.

Prosedur penggantian:
1. Lepas main power supply dengan membuka main switch ACV700. Tunggu 5 menit dan cek dulu tegangan AC dan DC sebelum memulai pekerjaan.
2. Lepas semua kabel disekitar inverter unit. Tandai kabel supaya mudah dalam pemasangan kembali.
3. Keluarkan inverter unit dari panel.
4. Lepas kabel motor fan dari terminal X10.
5. Buka tutup depan dari inverter unit dan lepas fan dengan membuka bautnya.
6. Pasang fan baru di inverter unit.
7. Pasang tutup depan dan connect kembali kabel fan motor.
8. Pasang inverter unit kembali dan connect kabel-kabelnya.

CARA MENGGANTI FAN UNTUK IGBT INVERTER UNIT (FRAME R7,R9)

Prosedur penggantian:
1. Lepas main power supply dengan membuka main switch ACV700. Tunggu 5 menit dan cek dulu tegangan AC dan DC sebelum memulai pekerjaan.
2. Lepas semua kabel dari SNAT603CNT dan SNAT609TAI.
3. Lepas tutup depan unit ACV700.
4. Lepas kabel fan motor.
5. Lepas 2 baut mounting untuk fan. Baut terletak di bagian depan dari unit.
6. Cek dulu tipe fan yang rusak dan sparenya.
7. Pasang spare fan di unit.
8. Pasang kembali semua dan kerasi baut-baut fan.
9. Connect kembali kabel motor fan.
10. Pasang tutup depan.
11. Pasang kabel-kabel di card,

My Projects

2010-03-21T14:28:00.001+07:00

Crescendo Teknik

2010-03-09T14:24:00.006+07:00

Crescendo Teknik sudah berpengalaman dalam pembuatan, instalasi, troubleshooting dan proses otomatisasi semua peralatan electrical.

Kami siap membantu anda dalam desain, instalasi/pemasangan dan commisioning, sampai peralatan/mesin anda berjalan sesuai yang anda inginkan.

- Troubleshooting mesin.

- Desain elektrikal, pemasangan dan commisioning untuk pemasangan peralatan baru.

- Desain mesin, pemasangan mesin, relokasi mesin.

- Pemrograman PLC, pemasangan dan commisioning (PLC: Allen Bradley, Mitsubishi, Toshiba, Omron, LG, Siemens, Beckhoff, Schneider dsb).

- Pembuatan panel dan pemasangan (MDP, SDP, capacitor bank, MCC dsb).

- Desain inverter, pemasangan dan commisioning.

- Solusi untuk saving energy.

- Desain dan pemasangan motor.

- Pengadaan spare part.

dsb

Hubungi: CTSurabaya@gmail.com atau Daniel 081-23-5353-00, 031-77 10 9199

AC Drives and Soft Starter (8) - Finish

2010-01-26T19:51:00.003+07:00

Sample Applications

Provided here are four sample applications. Two will be for pumps, and two will be for conveyors. These examples do not require variable speed or precise speed regulation, so a VFD or soft starter could be used.

Application 1) A pump is being started on full voltage. There is significant water hammer and the pipe bracing needs constant maintenance.
Answer: A soft starter will fit the application. It provides controlled torque during acceleration and has been shown to minimize and in many cases eliminate water hammer. There is no concern about current limitations as the application is now being started on full voltage.

Application 2) A new irrigation pump is being installed in a rural location. Because of this, the maximum current draw from the utility line without significant voltage drop has been calculated as 200 percent of the motor nameplate reading.
Answer: An inverter is preferred over a soft starter. In some instances soft starters can accelerate pumps with as little as 200 percent current. Application experience indicates that more often 250 – 300 percent current is required. The VFD can provide the torque required to accelerate the pump within the current limit restrictions of the distribution system.

Application 3) An overland conveyor requires 100 percent torque to accelerate when starting fully loaded. The maximum current draw from the utility is limited to 500 percent of the motor full load amperes. The conveyor will normally be started unloaded; however, on occasion it may need to be started when it is loaded. Rate of acceleration is critical to prevent the conveyor belt from being damaged

Answer: Initially a soft starter seems to be the correct choice. The soft starter can provide 101 percent torque with 450 percent current (table 1). However the rate of acceleration, which equates to starting time is critical. The load also varies from unloaded to fully loaded. In this case a VFD would be the correct solution.

Application 4) A 20 horsepower motor drives an overhead plastic chain conveyor through a gearbox. It starts and stops frequently. Full voltage starting could be used, but if the conveyor starts too quickly the product will swing and may be damaged or the chain may break.
Answer: A soft starter would fit the application. There is no time constraint and no limitation on current. Ramp start would typically be used to allow for minor load variations reflected back to the motor. If the gear reduction is high enough, a current limit start could provide a smoother start.

Conclusion
These examples were designed to show how slight application variations can change the type of motor starting that is required. Each application must be evaluated on its on merits. Neither soft starters nor VFD’s are the perfect solution for all situations.

AC Drives and Soft Starter (7)

2010-01-26T19:49:00.000+07:00

Application Differences

With the knowledge of VFD and soft starter principles of operation and motor performance with each, application differences can be reviewed. With the list of applications being very similar, the general application parameters will be covered along with several application examples.
Motor speed is a parameter where a VFD has an advantage over soft starters. First, and most obvious, is where the speed of the motor needs to be varied from 0 to line frequency and sometimes higher than line frequency. The soft starter applies line voltage and frequency; therefore, the operating speed is fixed.

The second speed-related advantage to which an inverter relates is processes that require a constant speed. If a fixed frequency is applied to a motor, the actual speed of that motor is not precisely regulated by the input frequency. The output speed is actually regulated by the load applied to the motor. So if a process requires very tight speed regulation, the frequency applied to the motor must be changed in relation to the load that is applied. With the use of feedback to the VFD this can be accomplished. Again the soft starter only applies line frequency so any speed regulation is not possible.
On applications where acceleration time needs to be consistent, an inverter should be used. This is due to the fact that acceleration time for a soft starter is more dependent on the load than the selected ramp time. If acceleration time is not an issue and controlling the torque or current is that is needed, then a soft starter is a good candidate for the application. (Note: some soft starters use feedback, such as tachometers. These units can provide timed acceleration with varying loads. It should be noted that current during feedback acceleration could reach the same level as starting at full voltage – 600 – 800 percent of full load).
With regard to stopping, a VFD will bring the motor to a rest in a specified time. This may be built into an inverter or may require a dynamic braking optional function for high inertia and overhauling type loads. The soft starter with a soft stop feature can only extend the stopping time, and just like acceleration, the stopping time is dependent on the load. If stopping time and stopping characteristics are not critical then a soft stop may fit the application.
Some specially designed soft starters can also provide braking. These are designed to reduce stopping time where coast to rest is very long. If the load is not a pure inertia and can vary, the stopping time will also vary.
Where limiting current is the prime reason for not starting at full voltage, the first method to be considered today is usually soft starters. This is due to the cost differential between a soft starter and a VFD at the ampere ratings that current limiting becomes a factor. In most instances the soft starter is an appropriate choice.
There are applications where the additional cost of an inverter is appropriate. These cases are where the motor cannot provide sufficient torque to start the load with the ampere limitations imposed by the distribution system.
Table 1 shows the motor torque provided at various levels of soft starter current limit. Unlike soft starters, drives can accelerate a motor to full speed at full load torque with line current that does not exceed the full load amperes of the motor. Keep in mind that the power into the VFD is equal to the power out plus the losses. Therefore, for those loads that require higher torque than the soft starter can provide with the limits imposed by the distribution system, an inverter may be the required solution.
If starting torque is a concern when selecting a drive or starter, keep in mind the drastic difference in the amount of torque that can be developed for a given amount of line current. The drive has a much higher torque per ampere ratio.

AC Drives and Soft Starter (6)

2010-01-26T19:46:00.001+07:00

Motor Characteristics Using Soft Starters

Unlike the ac drive, the line current and motor current for a soft starter is always the same. During starting the current varies directly with the magnitude of the applied voltage. The motor torque varies as the square of either the applied voltage or current.
The most critical factor when evaluating a soft starter is the motor torque. Standard motors produce approximately 180 percent of the full load torque at starting. Therefore, a 25 percent reduction in voltage or current will result in the locked rotor torque equal to the full load torque (180%*(.75)2 = 101%). If the motor draws 600 percent of the full load current on starting, then the current in this example will reduce the normal 600 percent starting current to 450 percent of the full load current.

Table 1 below gives more examples of the effects of reducing the voltage or current on a motor’s locked rotor torque. This data is valid for soft start and series impedance starting. They do not apply to other types of reduced voltage starting such as autotransformer and wye-delta starting.
When applying soft starters, the same constraint as electromechanical reduced starters applies. That constraint is “will the motor be able to produce enough torque to get the load started with the current the soft starter is allowing to flow to the motor?”
Soft starters do have an advantage over conventional reduced voltage starting. They are able to adjust voltage, current, and, therefore, torque over a wide range instead of single or a few fixed values. This can be seen in Figure 10. When voltage or current is held to a constant value, the speed-torque curve labeled “Current Limit” is produced. This curve would move up or down depending on the current limit setting. The upper boundary of this adjustment is the “Full Voltage” curve.
The soft starter can also ramp the voltage from an adjustable initial value up to full voltage over an adjustable time frame. This is represented by the “Soft Start” curve. A stepless transition, which is designed to eliminate current/torque transients, is produced by this ramp.
The operating speed of the motor cannot be varied because the soft starter only adjusts the voltage to the motor and not the frequency. The frequency applied to the motor is always the line frequency. Because of this, the acceleration time is more dependent on the load than the ramp time.

AC Drives and Soft Starter (5)

2010-01-26T19:43:00.002+07:00

Motor Characteristics Using VFD’s

During acceleration, the inverter applies different frequencies to the motor. It also changes the voltage but in direct proportion to the frequency. This is know as constant volts per hertz and provides constant torque while the motor accelerates.
A series of speed torque curves is shown in figure 9. These relate to speed torque curves at various frequencies. The “constant torque” line represents the full load or rated torque of the motor.

This “constant torque” line is actually the full load point on a locus of curves representing the speed torque curves of the motor from 0 to full speed. The inverter produces rated motor torque from 0 to rated speed. It will produce full load torque while drawing much less than full load current from the power line during starting. This is due to the fact that the motor is effectively always running at speed for the applied frequency.
When full voltage starting, the slip of the motor at 0 speed is 100 percent and the motor is highly inductive. This results is the very high inrush current, 600–800 percent, and relatively low starting torque, 150–180 percent of full load torque, compared to the current draw. Almost all of the motor current here is reactive. Reactive current, by nature, does not produce torque.
When a motor runs at speed the slip is typically in the area of one to three percent. Under this condition the reactive current is much less and the motor produces rated torque at rated current. With a VFD the motor runs virtually at speed during acceleration. Since the voltage is reduced at low speeds, the input current can be 10 percent or less with more than 150 percent torque.
Since the motor always runs at speed, or within rated slip, the acceleration time is dependent on the ramp time setting. This assumes that the drive has been properly selected for the load.

AC Drives and Soft Starter (4)

2010-01-26T19:40:00.003+07:00

Operation of Soft Starters

Timing of when to turn on the SCR’s is the key to controlling the voltage output of a soft starter. During the starting sequence the logic of the soft starter determines when to turn on the SCR’s. It does not turn on the SCR’s at the point that the voltage goes from negative to positive, but waits for some time after that. This is known as “phasing back” the SCR’s. The point that the SCR’s are turned on is set or programmed by what is called either initial torque, initial current or current limit setting.

The input voltage to the soft starter is the same as the VFD shown in figure 3. The result of phasing back the SCR’s is a nonsinusoidal reduced voltage at the terminals of the motor which is shown in figures 7. Since the motor is inductive and the current lags the voltage, the SCR stays turned on and conducts until the current goes to zero. This is after the voltage has gone negative. If compared to the full voltage waveform in figure 3, it can be seen that the peak voltage is the same as the full voltage wave. However the current does not increase to the same level as when full voltage is applied due to the inductive nature of motors.
When this voltage is applied to a motor, the output current looks like figure 8. As the frequency of the voltage is the same as the line frequency, the frequency of the current is also the same. As the SCR’s are phased on to full conduction, the gaps in current fill in until the wave form looks the same as applying the motor directly across the line.

AC Drives and Soft Starter (3)

2010-01-26T19:35:00.003+07:00

Variable Speed Drive Operation

The ac line voltage, figure 3, is rectified with a passive diode bridge. This means that the diode(s) conduct whenever the line voltage is greater than the voltage on the capacitor section. The resulting current waveform has two pulses during each half-cycle, one for each diode conduction
window.
The waveform, figure 4, shows some continuous current when the conduction transitions from one diode to the next. This is typical when a reactor is used in the dc link of the drive and some load is present. Inverters use pulse width modulation to create the output waveforms. A triangle waveform is generated at the carrier frequency where the inverter IGBT’s will switch.
This waveform is compared with a sinusoidal waveform at the fundamental frequency that is to be delivered to the motor. The result is the voltage waveform shown in figure 5.
Figure 6 shows the resulting current waveform at the motor with a PWM signal applied.
The inverter output can be any frequency below or above the line frequency up to the limits of the inverter and/or the mechanical limits of the motor. Note that the drive is always operating within the motor slip rating

AC Drives and Soft Starter (2)

2010-01-26T19:32:00.002+07:00

Soft Starters

The soft starter operates on a different premise. This principle is that by adjusting the voltage applied to the motor during starting, the current and torque characteristics can be limited and controlled.

For induction motors, the starting torque (LRT) is approximately proportional to the square of the starting current (LRA) drawn from the line. LRT ∞ I2. This starting current is proportional to the applied voltage (V). So the torque can also be considered to be approximately proportional
to the applied voltage. LRT ∞ V2.. By adjusting voltage during starting, the current drawn by the motor and the torque produced by the motor can be reduced and controlled.
By using six SCR’s in a back-to-back configuration as shown in figure 2, the soft starter is able to regulate the voltage applied to the motor during starting from 0 volts up to line voltage. Unlike the VFD, line frequency is always applied to the motor. Only the voltage changes.
Feedback from the motor to the logic circuit controlling the SCR firing is required to stabilize motor acceleration.

AC Drives and Soft Starter (1)

2010-01-22T00:00:00.003+07:00

Abstract:

There are usually several choices for starting motors. Two of these, ac variable frequency drives (VFD’s) and soft starters, seem to have similar characteristics. Terms and descriptions used in product literature are nearly the same. Even the list of possible applications is similar. However, the technology and performance are significantly different. When these differences are understood, it becomes clear when and where to properly apply each of them.

Introduction
The objective of this paper is to provide the basic technical information to understand the differences. First covered are the operating principles of the VFD and soft starter. How motor performance is affected is the other key to selection of the proper starting method. Finally, guidelines will then be presented.

Variable Speed Drives
The VFD works on the principle that the ac line voltage is converted to a dc voltage. This dc voltage is then inverted back to a pulsed dc whose rms value simulates an ac voltage.
The output frequency of this ac voltage normally varies for 0 up to the ac input line frequency. On certain applications the frequency may actually go above the line frequency.
Though high performance current regulated ac drives capable of operating in “torque mode” are available, the more prevalent volts per hertz drive is addressed here. The most common VFD’s manufactured today work using pulse width modulation to create the output sine wave. The conducting components used in drives are diodes, SCR’s, transistors and IGBT’s. These inverters have three distinct and different sections to their power circuits as shown in the typical inverter block diagram figure 1 below.
The first section uses a diode or SCR full-wave bridge to convert the ac line voltage to dc. Filtering of this dc is done in the second section with a capacitor to supply the inverter bridge with a stable dc power source. A dc link choke is normally present on 10 horsepower and larger drives. The final section uses a transistor or IGBT bridge to deliver a pulse width modulated (PWM) dc voltage to the motor. The effective rms voltage delivered to the motor is dependent on the fundamental output frequency that the inverter bridge is commanding. This is what leads to the term “volts per hertz drive.”
The control or logic section of the inverter and user programmed settings determine the frequency output of the inverter. During acceleration, the frequency will vary according to a predetermined algorithm such as linear ramp or s-curve, from minimum or 0 Hz up to commanded speed.
The drive can also be programmed to skip over certain frequencies that may cause a mechanical resonance.

How to choose the right soft starter?

2010-01-21T23:48:00.005+07:00

Electronic soft starters are today still more applied, and the scope is partly to reduce the start current and partly to reduce the mechanical stress occurring in transmissions and machines during start. However, it is important to choose the right soft starter for each application.

Construction of soft starters
Soft starters are constructed in several different ways, dependent on which applications they are to be applied for. They may be constructed for regulation of the motor in one, two or three phases with time-controlled start ramp or current-controlled start.

The 1-phased
types are primarily applied in applications for which a reduction of the mechanical influence at start of for example transmissions or other types of machines is wanted. This type of soft starters does not reduce the start current very much; it will typically be about 85% of the nominal start current.

The 2-phased
regulated soft starters can be applied for the majority of industrial applications. The start current is typically about 50-65% of the nominal start current In the non-regulated phase the current will during start be about 15% higher compared with the two other regulated phases.
In applications for start of motors with large moments of inertia and long start times, this soft starter will not be optimal, as the phase unbalance may imply that the thermal overload protection will cut out (differential release).

The 3-phased
regulated types fit for all types of applications. The start current will typically be about 35-50% of the nominal start current. This type is well suited for both general motor applications, but also where there is a need for start of motors with large moments of inertia and long start times, for example in connection with start of fans, flywheels etc. Please be aware of the thermal load degree, see underfig.1&2.

The soft starter and its applications
As mentioned, the soft starter is designed for the various applications in which it is an advantage to apply them. Fig. 1 describes various application fields and load classes: Light start 10A, standard start 10, heavy start 20 or very heavy start 30, and the advantages to be obtained by applying soft starters.
In the table the typical, maximally occurring start current that might occur during the start of the motor is stated.
As it appears from the table, most applications are categorized in trip class 10, that is the release characteristic that thermal overload relays and circuit breakers are normally delivered with. Please be aware that very few applications fall into the category “very light start”, trip class10A.

Thermal overload protection
Motor installations shall be overload protected. Most often this is done by use of contactors and/or fuses, or by using circuit breakers with short-circuit protection. It is important that the soft starter is protected by the thermal release characteristic, which is standard in class 10 (see fig. 2).
In fig. 2 the time for coherent overload grades can be seen. For example an overload of 8 times for 3 seconds at class 10 is allowable. It is important that the soft starter is thus dimensioned that it can resist the intermittent overloads that might occur during start, for example if the motor is blocked.

Short-circuit protection
All motor installations shall be short-circuit protected, as mentioned either by use of fuses or by using circuit breakers. The short-circuit protection can be executed according to the short-circuit coordination Type 1 or Type 2. Type 1 protects the installation, but not the connected components. Type 2 protects both the installation and components.
The size of the protection to be chosen can be seen in the technical data for the soft For example will 1800 A2s correspond to it that the soft starter can be protected by a 16 A D 0 fuse (gL/gG). (The short-circuit current shall be able to exceed 120A in order to protect in a proper way).
Under the same conditions it can be mentioned that a circuit breaker offers sufficient short-circuit protection acc. to Type 2, which is preferable.

Ambient temperature
The soft starter shall fulfil the specifications described in the product norm for soft starters EN60947-4-2. Here all technical specifications are to be mentioned at an ambient temperature of 40oC. Soft starters have a power dissipation corresponding to about 1W/A/regulated phase. This means that for a 3-phased regulated soft starter with a load of 10 A, a power dissipation of about 30 W will occur. In some cases it may be an advantage to mount anelectro mechanic contactor as by-pass of the soft starter. By this, the power dissipation is reduced substantially, and thus a fan for cooling of the panel should be superfluous.

Some soft starters are provided with a built-in by-pass contactor.
A feature of these soft starters is that most often they do not allow large intermittent loads and that the number of starts per hour is limited. Furthermore, it is most often difficult to get a short-circuit protection acc. to short-circuit coordination Type 2.

When you choose soft starters it is important to take the following into consideration:
• Load class
• Thermal overload protection
• Number of starts per hour
• Short-circuit protection
• Environment

Electro Motor Starter

2010-01-21T23:31:00.004+07:00

Untuk menggerakan elektro motor, diperlukan peralatan pendukung yaitu, motor starter atau biasa disebut starter. Saat ini dikenal ada beberapa macam jenis starter. Diantaranya seperti berikut ini.

Direct On Line (DOL) Starter
Starter model ini sangat banyak dipakai saat ini, terutama untuk motor motor kecil. Komposisi komponennya terdiri dari satu contactor dan satu proteksi arus dengan TOR atau elektronik. Kelemahan starter model ini adalah kemungkinan timbulnya arus start yang sangat tinggi. biasanya bisa mencapai 6 sampai 7 kali. Pada saat starter ini di start, torsi saat start ini juga sangat tinggi dan biasanya lebih tinggi dari kebutuhan. Ini dapat terlihat adanya lonjakan/ gerakan yang keras saat motor di start. Tingginya torsi start ini juga akan memberikan tekanan lebih pada coupling dan beban.Komponen penyusun starter ini harus mempunyai ampacity yang cukup besar. Perlu diperhitungkan juga arus saat start motor, demikian juga ukuran range overloadnya.

Star Delta Starter
Starter ini mengurangi lonjakan arus dan torsi pada saat start. Tersusun atas 3 buah contactor yaitu Main Contactor, Star Contactor dan Delta Contactor, Timer untuk pengalihan dari Star ke Delta serta sebuah overload relay. Pada saat start, starter terhubung secara Star. Gulungan stator hanya menerima tegangan sekitar 0,578 (seper akar tiga) dari tegangan line. Jadi arus dan torsi yang dihasilkan akan lebih kecil dari pada DOL Starter. Setelah mendekati speed normal starter akan berpindah menjadi terkoneksi secara Delta. Starter ini akan bekerja dengan baik jika saat start motor tidak terbebani dengan berat.

Autotransformer Starter
Starter ini pada prinsipnya hampir sama dengan Star Delta Stater yaitu dengan mengurangi arus dan torsi saat start. Pada Autotranformer terdapat beberapa tap yang dapat menurunkan tegangan line. Starter akan mengatur masuknya tegangan yang mengalir ke motor dimulai dengan tegangan yang paling rendah bertahap sampai ke tegangan normal. Jika Star Delta starter hanya dua step, dengan autotransformer bisa beberapa step. Ini berguna untuk mengurangi lonjakan arus dan torsi saat start.

Soft Starter
Softstarter sangat berbeda dengan starter lain. Alat ini mempergunakan thyristor sebagai komponen utamanya. Tegangan yang masuk ke motor akan diatur dimulai dengan sangat rendah sehingga arus dan torsi saat start juga rendah. Pada saat start ini tegangan yang masuk hanya cukup untuk menggerakkan beban dan akan menghilangkan kejutan pada beban. Secara perlahan tegangan dan torsi akan dinaikan sehingga motor akan mengalami percepatan kehingga tercapai kecepatan normal. Salah satu keuntungan mempergunakan alat ini adalah kemungkinan dilakukannya pengaturan torsi pada saat yang diperlukan, tidak terpengaruh ada atau tidaknya beban.

Frequency Drive
Frequency Drive sering disebut juga dengan VSD (Variable Speed Drive), VFD (Variable frequency Drive) atau Inverter. VSD terdiri dari 2 bagian utama yaitu penyearah tegangan AC (50 atau 60 HZ) ke DC dan bagian kedua adalah membalikan dari DC ke tegangan AC dengan frequency yang diinginkan. VSD memanfaatkan sifat motor sesuai dengan rumus sbb :

RPM = (120.f)/p

dimana

RPM : Kecepatan putar/ speed motor (RPM)

F : Frequency (Hz)

P : pole

Jadi dengan mengatur frequency tegangan yang masuk, maka kecepatan motor akan dapat diatur pula. Demikian pula pada saat start, dimulai dengan frequency rendah sampai rated frequency nya hasilnya kecepatan motor akan mengalami percepatan yang lebih halus.

Why Soft Starts?

2010-01-20T14:48:00.005+07:00

The 3-phase induction motor is over 100 years old and obviously many design changes and variations have appeared over the years. However certain fundamental characteristics remain the same and it is the problems that these inherent features cause that electronic soft start aims to solve.

1. Direct-On-Line

Reduced Voltage Starting:
2. Star/Delta
3. Auto Transformer
4. Soft Starts

1. Direct-On-Line
The main method of starting the AC motor is direct-on-line starting. This simply means an electro-mechanical switch is opened and closed to stop and start the motor.

Disadvantages
Electrical
-High inrush current (typically 6 x full load which can cause several problems)
-Necessities over sizing of installation (particularly important on generator and UPS fed supplies)
-Limits Expansion
-Reduces service life of electrical components
Mechanical
-Excessive applied starting torque (typically 2.5 x full load)
-Increases wear on drive chain components
-Reduces service life of mechanical components

2. Star/Delta
This method requires both connections for each phase (six in all) to be taken to the starter. Three contactors are used to first connect the motor in star and then to delta after a given time. Connecting the motor in star reduces the voltage applied to each winding to about 60% of the line voltage. This reduces the starting torque and current (typically 3.5 x FLC). After a given time the motor is switched to delta connection and then runs as if direct-on-line. Its main advantages are that it is relatively simple and low cost. The major problem with this method is that the reduced voltage level is in a single stage and is fixed. sometimes this voltage is not ideal, the torque it produces (65% of full load torque) may be too small and the motor stalls or does not give complete acceleration, or if it is too great the motor still starts with a pronounced snatch. The star/delta transition will produce a second current and torque peak which is almost the equivalent of having two direct-on-line starts. On some loads the motor sometimes almost stalls during this transition time. This method of starting does however have the advantage of being a low cost and simple solution if its limitations can be tolerated.

Advantages
-Low cost and simple

Disadvantages
-Torque too high – causes snatch
-Torque too low – motor stalls
-Transition peak up to 20 x In
-Motor can stall in transition

3. Auto Transformer
This method uses transformer action to reduce the voltage applied to the motor and current seen by the supply. An improved torque/amp ratio is achieved and starting current is typically 3 x FLC, depending on the voltage rapping selected. Normally the voltage is applied to the motor in voltage steps through the transformer with the taps being selected through contactors. Typical tappings are 50%, 70%, followed by full voltage being applied to the motor. The major disadvantages are size and cost, and of course the mechanical snatch at switch on is not controllable and can still cause problems. Also once the tappings have been selected, it may be necessary to change them according to changes in load parameters.
Advantages
-Simple operation

Disadvantages
-Poor controllability
-Bulky
-Very Expensive

4. Soft Starts
The soft start is designed to apply an adjustable voltage to the motor and increase this voltage gradually over a user-selectable acceleration period. The acceleration time being dependent on the application and desired characteristics. The added advantage of this method of reduced voltage control is that the motor can also be stopped gradually by slowly reducing the output voltage to the .‘Soft Stop’ feature offers a smooth stop in many process industries such as pumps, where fast stops can result in ‘water hammer’ and mechanical damage.

Advantages
-Reduced starting current
-Reduced starting torque
-Less mechanical stress
-Improved control of acceleration and deceleration

Electrical Systems: Power Factor Correction (2)

2009-11-29T20:32:00.003+07:00

Power Factor Charges
Many utilities charge for low power. To measure power factor, the most common type of utility meter measures the total kVAr-hours and kVA-hours over the billing period and calculates the average power factor as:

PF = Cos [ ArcSin (kVArh / kVAh) ]

The most common methods of charging for low power factor are:

1. Adding a demand penalty when the power factor dips below a set amount (usually 90%)

2. Basing the demand charge on the supplied power Ps (kVA), rather than the actual power used Pa (kW).

3. Basing part of the overall charge on the reactive power kVAr, which increases as power factor decreases.

Electrical Systems: Power Factor Correction (1)

2009-11-29T20:26:00.004+07:00

Resistive devices, like electric resistance heaters and incandescent lights transform all the power supplied to the device into heat or useful energy. Inductive devices, like motors, use some of the power supplied to the device to energize the inductive windings and create a magnetic field. This power, called reactive power, is alternately stored and given up by the windings, but is not used to do actual work. When this happens, the line supplying power to the device now carries the actual power used by the device and the reactive power created by the device.

Actual power used by the device is measured in kW, reactive power created by induction devices is measured in kVAr, and the apparent power in the supply lines is measured in kVA. The mathematical relationships between these types of power are described by the “power triangle” shown below. For example,

The ratio of the actual power consumed by equipment (Pa) to the power supplied to equipment (Ps) is called the power factor.

PF = Pa / Ps = kW / kVA = cos Phi

Devices which generate/require large amounts of reactive power in relation to actual power consumed have low power factors. Such devices include:

• Motors
• HID and fluorescent lights with low PF ballasts
• Devices which convert AC power to DC power such as:
• DC drives
• Welding machines
• VFDs
• Induction furnaces

Fully loaded motors generally have a power factor of about 80%. However, if the motor is under loaded, the fraction of reactive power (for the coil) to actual power (for mechanical work) increases and the power factor decreases.

Two potential problems are associated with low power factor. First many utilities have explicit or implicit charges for low power factor. Second, low power factor increases the current, and hence losses, in transformers and the electrical distribution system. These losses cost money and generate excess heat in the electrical distribution system, which may shorten equipment lifetime or cause production shut downs. These potential problems are discussed in the sections that follow.

Gate Driver Optocouplers in Induction Cooker (4) - Finish

2009-06-22T19:53:00.001+07:00

Summary
In this article, the half-bridge series resonant and quasi resonant induction cooker topologies along with three gate driver methods were discussed. In order to reduce the design size and audible switching noise while improving power efficiency, these resonant converters are chosen.

The discrete transistor gate driver circuit is cost effective but increases design complexity while providing no safety isolation. The gate drive transformer consumes board space due its size and requires additional work and cost to achieve higher switching duty cycle above 50%. Finally, gate drive optocoupler integrated ICs saves board space through high level feature integration while providing high voltage safe isolation and noise immunity all in one package.

Gate Driver Optocouplers in Induction Cooker (3)

2009-06-22T19:50:00.003+07:00

Gate Driver Circuits for IGBT Power Switches
Three types driver circuits, the discrete transistor circuit (Figure 5), gate driver optocoupler (Figure 6) and gate driver transformer (Figure 7) can be used to drive the power switches in induction cooker application. There are several issues associated with high-frequency gate drivers; the parasitic inductances, power dissipation in the gate-drive circuit and the losses in the power switching devices in the gate driver.

Typically, the switching frequency of an induction cooker is between 25kHz to 40kHz. In order to rapidly charge turn on and off the power switch, the gate current inductance loop between the driver and power switch should be as low as possible. Hence it is advisable to design the layout of the circuit to reduce the parasitic inductances. Since the driver rapidly charge and discharge the gate capacitor of the IGBT, a higher peak gate current may be needed for proper operation. Due to this, the power dissipation within the gate drive circuit is important to manage the increase switching speed. The higher peak current is also desirable to increase the charging and discharging during turn on and off as it will help reduce the switching losses of the IGBT.
The discrete gate drivers are constructed using the bipolar transistors. NPN and PNP emitter followers can achieve reasonable drive capability. However, using several discrete components to build the driver and other functions or protection operation like Under Voltage Lockout (UVLO) is not as space efficient as using integrated ICs. Moreover discrete transistor drivers do not provide sufficient safety isolation or noise immunity.
Two types of isolation method are discussed in this article; pulse transformer and gate driver optocoupler. The pulse transformer is a traditional and simple solution which suffers from saturation limitation for a given transformer size that can reduce efficiency. Normally, a transformer can only transmit AC information and have a limited duty cycle of up to 50% due to the transformer volt-second relationship. Additional capacitor and zener diode on the secondary size can be added to allow a higher duty cycle. However, this increase the design board size and parasitic inductances which in turn increases power losses in the driver circuit.
Gate driver optocoupler ic is an integration of LED for safety isolation, transistors to provide drive current and protection functions like UVLO or Desaturation Detector. Gate driver ICs are easy to design and will save PCB board space in the application. Due to the integrated design, the drive circuitry can be located very close to the power switch which not only saves PCB space but also improves the overall noise immunity of the system. However, like any integrated ICs, power dissipation is main concern observed by designers.
For the single switch resonant converter, designer has the option of the discrete gate driver topology, gate transformer or gate driver optocoupler. As discussed in the previous section, the quasi-converter resonant voltage can be higher compared to the DC link voltage and this voltage stresses the power semiconductor switch. In most commercial low cost single switch induction cooker design, the discrete gate driver circuit is used as there is no upper power switch and both controller and the power semiconductor are able to share the same power ground. However, in cases where safety isolation and reduction of driver losses becomes an issue, the gate drive optocoupler or transformer are excellent alternatives.
For the half-bridge converter, a floating or high-side power switch needs to be driven. A high side discrete solution would increase the component count while not providing any isolation. As shown, the pulse transformer galvanic isolation solution increases in complexity for duty cycle switching above 50%. Also, the solution size is larger because of the additional discrete components on top of the transformer size. The gate driver optocoupler IC provides a good level of protection, isolation, and common-mode noise rejection. This resolves much of the problems that are associated with transformer driver or transistor discrete solution as mentioned earlier.

Gate Driver Optocouplers in Induction Cooker (2)

2009-06-22T19:48:00.001+07:00

By applying the transformer equivalent circuit, designers are able to map the load pot (secondary of transformer) to the primary side of circuit where the resonant inductor, Lr and capacitor Cr are located. From this, we can obtain the equivalent circuit for half-bridge and quasi resonant circuit, shown in Figure 3 and Figure 4. From these equivalent circuits, the operation of the induction cooker, the sizing of the resonant inductor, capacitor and control algorithm can be conceived.

In order to reduce component size, minimize switching losses and reduce audible noise during operation (above 20kHz resonant frequency), induction cooker circuit typically utilizes resonant or soft switching techniques. This circuitsoft switching technique can be subcategorized into two methods: Zero-voltage switching and Zero-current switching.
Zero-voltage switching occurs when the transistor turn-on at zero voltage. Zero-current switching refers to elimination of turn-off switching loss at zero current flow. The voltage or current administered to the switching circuit can be made zero by using the resonance created by an L-C resonant circuit. This topology is named a “resonant converter.” This allows the application to utilize resonant frequency and obtain the benefits mentioned compared to conventional hard switching techniques.
The advantages of half-bridge series resonant are stable switching, and lower cost due to streamlined design. The voltage within the circuit is limited to the level of the input voltage which reduces the voltage stress across IGBT power switch. This in-turn allows the designer to lower the cost by choosing a lower rating IGBT. The disadvantage is that the overall half-bridge control is more complicated, the size of heatsink and PCB area is bigger and insulated gate driver circuits, especially on the upper IGBT (S1 in Figure 1).
The advantage of quasi-resonant converter is that it needs only 1 IGBT power switch which reduces design size PCB and heat sink. The disadvantages are that the quasi resonant switching the high resonant voltage which can be higher than the DC input voltage stressed on to IGBT power switches. This requires a higher cost and blocking voltage power components.

Gate Driver Optocouplers in Induction Cooker (1)

2009-06-22T19:44:00.002+07:00

What is Induction Cooking?
We start by first comparing the difference between conventional gas cooking and induction cooking. In induction cooking methods, energy is transferred directly to the pot or pan while conventional cooking first generate a fire and heat energy which is then transferred to the cooking pot. Hence due to this two step energy transfer of conventional cooking, the efficiency of the induction cooking is much better.

Figure 1 & 2 shows two circuit topologies for induction cooker, the half-bridge series resonant converter Figure 1 and quasi-resonant converter Figure 2 [2]. In both topologies, there exist the resonant elements Lr and Cr. For circuit simplification, the load pot, R is assumed to be of pure resistive element. In both topologies, an ac input supply of 220V 50Hz is converted into an uncontrolled dc voltage by a full-bridge rectifier. This DC voltage is then converted into a high frequency AC voltage by the inverter IGBT (insulated gate bipolar transistors) switches, S1 and S2 in the case of the half-bridge circuit, which can be controlled using a micro-controller. Due to the high frequency switching AC, the element coil will then produce a high frequency electromagnetic field which will penetrate the ferrous material cooking pot. From Faraday’s Law and skin effect, this generates eddy current within the cooking pot which then generates heat to cook the food inside the pot.

IGBT Gate Drivers in High-Frequency Induction Cookers (3)

2009-06-21T11:52:00.003+07:00

Gate driver circuits for IGBT power switches
Three types of driver circuits, using discrete transistors (Fig. 5), gate driver optocouplers (Fig. 6) or gate driver transformers (Fig. 7) can be used to drive the power switches in the induction cooker. There are several issues associated with high-frequency gate drivers: parasitic inductances, power dissipation in the gate-drive circuit and the losses in the power switching devices in the gate driver, all of which are involved when selecting an appropriate driver circuit.

Typically, the switching frequency of an induction cooker is between 25 kHz and 40 kHz. In order to rapidly turn on and off the power switch, the gate current inductance loop between the driver and power switch should be as low as possible. Hence it is advisable to design the layout of the circuit to reduce the parasitic inductances. Since the driver rapidly charges and discharges the gate capacitor of the IGBT, a relatively high peak gate current may be needed for proper operation. A higher peak current is also desirable to increase the charging and discharging rates during turn-on and turn-off, to help reduce the switching losses of the IGBT. Due to this, managing the power dissipation within the gate drive circuit becomes increasingly important as the switching speeds are increased.
Discrete gate drivers are constructed using bipolar transistors, and NPN and PNP emitter followers can achieve reasonable drive capability. However, using several discrete components to build the driver, while simultaneously incorporating necessary operational and protective functions such as under voltage lockout (UVLO), is not as space efficient as using integrated circuits. Moreover most discrete transistor driver designs do not provide sufficient safety isolation or noise immunity.
Two methods of providing electrical isolation are pulse transformers and gate driver optocouplers. The pulse transformer is a traditional and simple solution, which, however, suffers from the potential for core saturation in a reasonably-sized transformer, resulting in reduced efficiency. A pulse transformer can only transmit AC signals, and most designs have a limited duty cycle ranging up to 50 percent due to the transformer volt-second relationship.
An additional capacitor and zener diode on the transformer secondary can be added to permit a higher duty cycle. However, this increases the circuit board size and parasitic inductances, which, in turn, increases power losses in the driver circuit.
The gate driver optocoupler IC integrates an LED light source and optical receiver for safety isolation, with transistors to provide sufficient drive current, and protection functions such as UVLO or desaturation detection.
Gate driver ICs are easy to design with, and will save PCB board space. Due to the integrated design, the drive circuitry can be located very close to the power switch, which not only saves PCB space but also improves the overall noise immunity of the system. However, as with any ICs, power dissipation is a major concern.
For the single-switch resonant converter, the designer has the option of the discrete gate driver, gate transformer or gate driver optocoupler topologies. As discussed previously, the quasiconverter resonant voltage can be higher than the DC link voltage and this voltage stresses the power semiconductor switch. In most commercial low cost single switch induction cooker designs, the discrete gate driver circuit is used as there is no upper power switch, and both the controller and power semiconductor are able to share the same power ground. However, in cases where safety isolation and reduction of driver losses becomes an issue, the gate drive optocoupler or transformer are excellent alternatives.
For the half-bridge converter, a floating or high-side power switch needs to be driven. A high-side discrete solution would increase the component count, and not provide any isolation. As shown, the pulse transformer galvanic isolation solution becomes increasingly complicated for duty cycle switching above 50 percent. Also, the solution size is larger because of the additional discrete components on top of the transformer size. The gate driver optocoupler IC provides a good level of protection, isolation, and common-mode noise rejection. This resolves many of the problems that are associated with transformer or discrete transistor drivers.

Summary
In this article, the halfbridge series resonant and quasi resonant induction cooker topologies along with three gate driver methods were discussed. In order to reduce the design size and audible switching noise while improving power efficiency, these resonant converters are chosen. The discrete transistor gate driver circuit is cost effective but increases design complexity while providing no safety isolation. The required size of the gate drive transformer consumes board space, and requires additional work, cost and board space to achieve switching duty cycles above 50 percent. Finally, the use of gate drive optocoupler ICs saves board space through high level feature integration while providing high voltage safety isolation and noise immunity all in one package.

IGBT Gate Drivers in High-Frequency Induction Cookers (2)

2009-06-21T11:45:00.003+07:00

How does an induction cooker work?
Figures 1 and 2 show two circuit topologies for induction cookers: the half-bridge series resonant converter, Fig. 1, and the quasi-resonant converter, Fig. 2. In both topologies, there exist the resonant elements Lr and Cr. For circuit simplification, the load pot, R, is assumed to be a purely resistive element.

In both topologies, an AC input supply of 220V 50 Hz is converted into an unregulated DC voltage by a full-bridge rectifier. This DC voltage is then converted into a high frequency AC voltage by the inverter IGBT (insulated gate bipolar transistor) switches—S1 and S2 in the case
of the half-bridge circuit—which can be controlled using a microcontroller. Due to the high frequency switching AC, the element coil will produce a high frequency electromagnetic field which will penetrate the ferrous material of the cooking pot. From Faraday’s Law and skin effect, this generates eddy current within the cooking pot which then generates heat to cook the food inside the pot.
By applying the transformer equivalent circuit, designers are able to map the load pot (secondary of transformer) to the primary side of the circuit where the resonant inductor, Lr, and capacitor, Cr, are located. From this, we can obtain the equivalent circuit for the half-bridge and quasi resonant circuits, shown in Figs. 3 and 4. From these equivalent circuits, the operation of the induction cooker, and the values of the resonant inductor, capacitor and control algorithm
can be derived.
In order to reduce component size, minimize switching losses and reduce audible noise during operation, induction cooker circuits typically utilize resonant or soft switching techniques. Soft switching can be subcategorized into two methods: zero-voltage switching and zero-current switching. Zero-voltage switching occurs when the transistor turns-on at zero voltage. Zero-current switching refers to the elimination of turn-off switching loss at zero current flow. The voltage or current provided to the switching circuit can be made zero by using the resonance created by an L-C circuit. This topology is named a “resonant converter.”
The advantages of a half-bridge series resonant circuit are stable switching and lower cost due to simplified design. The voltage within the circuit is limited to the level of the input voltage, which reduces the voltage stress across IGBT power switch. This, in turn, allows the designer to lower the cost by choosing an IGBT with a lower voltage rating. The disadvantage of this approach is that the control of the half-bridge circuit is relatively complicated and the required size of the heatsink and PCB area is greater, because of the high side gate driver circuit required for the upper IGBT, S1 in Fig. 1)
The advantage of a quasi-resonant converter is that it needs only one IGBT power switch, which reduces the size of the PCB and heat sink. The disadvantages are that the quasi-resonant switching develops a resonant voltage which can be higher than the DC input voltage, increasing stresses on the IGBT power switches. This requires highercost components with higher blocking
voltage capabilities.

IGBT Gate Drivers in High-Frequency Induction Cookers (1)

2009-06-21T11:41:00.001+07:00

Efficiency of induction cookers is 84 percent
Today, with the constant demand for energy saving devices, high-frequency induction cookers, already a trend in Europe, are gaining popularity in the rest of the world. These kitchen devices offer high efficiency that reduces energy usage, reduces cooking time and, simultaneously, improves user safety, particularly around children, since all heat is localized to the pan itself.

According to the U.S. Department of Energy, the typical efficiency of induction cookers is 84% compared to the 40 percent of gas cookers. In this article, two typical induction cooker designs, the halfbridge series-resonant and the quasiresonant topology, are discussed. The merits and disadvantages of these two high-frequency inverter topologies along with three gate driver circuits, discrete transistors, optocouplers integrated circuit and transformers for high frequency
operation are also discussed.

What is induction cooking?
In an induction cooktop, a magnetic field transfers electric energy directly to the object to be heated. By inducing in electric current into the ferrous cooking utensil, heat is generated in the object, and the cooking surface only gets hot from the heat reflected from the object being heated: no heat is directly produced by the induction element. Because of this direct transfer of energy, there are fewer losses, which translates to a higher level of efficiency.
This compares with conventional cooking in which a heat source, for example an electrical resistance element or a flame, transfers heat energy to the cooking pot. The two-step energy transfer is inherently less efficient than direct inductive heating.

Veritron Error Message List

2009-06-06T10:46:00.002+07:00

Error Message List (Source : Paeset2 Software)

Motor Insulation Systems (7) - Finish

2009-05-25T20:43:00.002+07:00

Significance Of Winding Configuration and Method
Figure 6 is a representation of one (1) coil of a motor winding consisting of several turns.

The coil voltage is distributed among the turns so that the turn to turn voltage is less than the full coil voltage.

If the coil is wound concentrically, each turn of the coil is wound next to the previous turn and the coil is built up in successive layers. This ensures that each turn of the coil is in contact only with immediately preceding and successive turns, and the first turns in the coil are separated from the last turns. This means that the voltage between two (2) conductors that are next to each other is always less than the full voltage that is applied to the coil. If the coils are wound randomly, the positions of the individual turns are not controlled. With random winding, it is possible that the first turn of the coil may be in contact with the last turn. If the first turn of the coil is in contact with the last turn, two (2) layers of magnet wire insulation must withstand full coil voltage. Figure 7 shows the comparison between concentric and random winding. Most motors rated for operation at 600V or less have random windings.

Motor Insulation Systems (6)

2009-05-25T20:41:00.001+07:00

Carrier Frequency
As the inverter’s carrier frequency is increased, the output current waveform supplied to the motor becomes more sinusoidal. This improved output current waveform decreases motor heating thus improving motor insulation life.
At this higher carrier frequency, however, more individual voltage pulses are output and for a given cable length, rise time and motor surge impedance, the potential for voltage overshoot increases. The power generated during this overshoot will be dissipated in the motor’s windings, and insulation life will be decreased.

Figure 5, below, shows insulation life of a generic motor, when both cable length and inverter carrier frequency (fc) are varied. Note that with a 150 ft. cable length, insulation life drops from 100,000 hours to 25,000 hours, when carrier frequency is increased from 3 to 12 Khz. The longest life occurs with short cable lengths and low carrier frequencies.

Motor Insulation Systems (5)

2009-05-25T20:39:00.000+07:00

Vibration
One mechanical stress phenomenon that is more likely to appear on inverter applications than line-started ones is resonance (when a mechanical system oscillates at it’s natural frequency). A common example of resonance is the vibrations noted on the side view mirror on an old car. As the car accelerates from standstill to freeway speeds, engine and frame vibrations are transmitted to the mirror’s mounting base. At some point during acceleration, these vibration frequencies change and the mirror stabilizes again. Motor, pump and machinery designers all take resonance into account when designing their product.

They will add mass, change support struts, or increase mounting base lengths to ensure that the item’s natural frequency is well above 60Hz. When the machine is assembled onto a base, coupled to a motor, and bolted to a concrete pad, the natural frequency decreases, but, by design, remains higher than the running speed when excited to 60Hz. However, as the machine speed is changed with an inverter, the likelihood of stumbling onto the system’s resonant frequency increases dramatically. Once resonance is reached, severe vibrations can occur in the motor, stressing stator coils, brinelling bearings, and even fatiguing bolts and castings to the breaking point. As the coils continue to move, they’ll ultimately chafe through all layers of insulation, and a failure will result. Since this new resonant point is determined not by the parts of the machine, but instead by the assembly of parts, it must be corrected at the system level. This is best done during start-up. Although additional supports can be welded onto bases and belt ratios altered, the most cost effective method to avoid these resonance frequencies is to program an offset to the critical frequency. During acceleration and deceleration the inverter will pass through the critical resonance frequency but the critical frequency offset will prevent the inverter from operating at the programmed frequency band, thus avoiding the mechanical resonance.

Voltage or Dielectric
The Dielectric properties of a material are the characteristics of the material that make the material an electrical insulator rather than a conductor. When there is a voltage difference across the thickness of an insulating material, the voltage causes a Dielectric Stress that opposes the material’s ability to prevent current from flowing through the material. The Dielectric Strength of a material is a measure of the material’s capability to withstand dielectric stress. An insulation
system’s rated operating voltage is determined by the dielectric strength of the insulating materials. If the insulation is subjected to excess voltage, it can fail suddenly and catastrophically. Gradual deterioration can be caused by voltage levels that exceed the insulation rating but do not cause catastrophic failure. The other forms of stress - thermal, environmental, mechanical and vibration - lead to a reduction in the insulation’s ability to withstand dielectric stress. The insulation ultimately fails when it can no longer withstand the applied voltage and the flow of short circuit current causes catastrophic failure.

Motor Insulation Systems (4)

2009-05-25T20:36:00.002+07:00

4. Insulation Stresses

Several different physical phenomena can cause electrical insulation to deteriorate or fail. These include thermal, contamination, mechanical, vibration, voltage, carrier frequency and the method of winding the turns of insulation.

Thermal
The service life of an insulation system is generally determined by thermal stress. All insulation systems deteriorate over a period of time due to the effects of thermal stress. If the insulation always remains at its rated temperature, it should not fail during its rated service lifetime. If the insulation continually exceeds rated temperature, its lifetime will be shortened in proportion to the level and duration of the excess temperature. The insulation may last longer than the rated lifetime if its temperature remains below the rated level for significant periods of time.
Figure 4 shows the relationship of insulation life versus temperature normalized at 25°C (100% life). Increasing the temperature to 130°C decreases insulation life to 83% from nominal. Increasing the temperature further to 155°C (Class F insulation limit) or 180°C (Class H insulation limit) will further reduce insulation life.

Environmental
Contamination of the motor windings reduces dielectric strength dramatically, especially when fast rise time, high frequency voltages from IGBT inverters, are involved. A drip-proof motor that has successfully operated in a moist, sloppy pump pit may fail in short order when transferred from line power to inverter power. This is because contaminants such as oil, salt, acid, alkalies, grease, dirt, detergents, disinfectants, carbon black, chlorines or metal dust create conductive paths along the surface of the varnished windings, especially when combined with moisture from the surrounding environment. This facilitates high frequency surface tracking, which can effectively produce short circuits between otherwise insulated portions of the windings.

Mechanical
When a motor is line-started at full voltage, the powerful magnetic fields produced push and pull the stator coils back and forth, and large inrush currents generate rapid heating of the stator conductors, causing them to expand. The surrounding iron stator core heats up less, has a lower thermal expansion rate, and doesn’t move at the same rate as the copper coils it supports. As a result, the copper coils strain against the varnish that adheres them to the core, causing fractures where the coils exit the core. Each successive across-the-line motor start repeats the cycle of flexing and expanding, worsens these breaks, and increases the chance that a conductor will abrade it’s remaining insulation and short to ground.
Once the insulation has cracks, moisture and contaminants will find their way in, further reducing insulation integrity. Similar expansion rate differences are present in the motor’s rotor circuit, where the iron core expands slower than the copper conductors (used in large motors) it holds, and faster than aluminum conductors (used in smaller motors). Generally, however, the stator windings fail before the rotor does.
During inverter starts, however, motor voltage and frequency are slowly increased rather than applied at full value. Motor coils are not subjected to the excessive heating and flexing that occurs during line starts, thus extending motor life. Only when the inverter is bypassed, does the motor experience the starting stresses described above.

Motor Insulation Systems (3)

2009-05-25T20:35:00.001+07:00

3. Design Variations

The types and amounts of insulating materials used can vary considerably from one (1) manufacturer to another. Some manufacturers may omit some or all of the paper insulating components and depend upon the varnish coated wire to serve in their places. This is, however, more typical of fractional horsepower (HP) motors, due to the cost of the added insulation in relation to the overall cost of the motor. Manufacturers often offer various motor product lines that provide a variety of application benefits at various price levels. One such example is the “inverter duty rated motor”. Some of these product lines include differences in the designs of their insulation systems. From time to time, new insulating materials are introduced with improved electrical, mechanical, thermal or chemical properties. An example of new magnet wire insulation technology is Phelps-Dodge’s Inverter Spike Resistant (ISR)® wire. This wire was originally purported to provide adequate protection against voltage overshoot caused by the fast rise times of IGBTs without the need for additional motor phase papers or sheets.
Field reports, however, have shown that this wire alone provides only a minimal extension to motor longevity.

Motor Insulation Systems (2)

2009-05-25T20:32:00.001+07:00

2. A Typical Motor Insulation System

Motor insulation systems vary considerably among the various motor manufacturers, but the following paragraphs provide a general description of the various components that comprise a typical insulation system.

Magnet wire is insulated with a thin coating of a varnish that is specifically designed as an electrical insulation material. The magnet wire insulating varnish provides the turn-to-turn insulation and a portion of the other elements of the motor insulation. In most motors, a large part of the winding-to-ground insulation is provided by a paper insulation lining in the stator slots. Paper insulation is also used to separate the windings of different phases. These components of the insulation system are called Slot Papers and Phase Papers. A rigid piece of insulation called a Top Stick Slot Wedge may be inserted in the opening of the slot to hold the windings securely in position. A diagram of a stator slot, showing the slot paper, a phase paper and the top stick are shown in Figure 2, below.

Figure 2 Stator Slot Insulation -- Slot Paper, Phase Paper and Top Stick

At each end of the stack of laminations, portions of the coils of wire, called the end-turns, pass from one slot to another. The end-turns are often separated from one another by paper insulation. Once the coils are wound into the stator laminations, the stator is dipped into a tank of insulating material, and baked, to coat the windings with another layer of insulation. This additional coating compensates for nicks and irregularities in the original coating, created during the manufacturing process and adds insulation to the magnet wire. After the additional coating cures, the stator may be dipped a second time for added protection from contaminants and moisture. This second, and subsequent dips and bakes, are typically an option offered by motor manufacturers.

Motor Insulation Systems (1)

2009-05-25T20:29:00.002+07:00

1. Motor Stator Construction

The stator of an AC motor consists of a stack of steel laminations that have coils of magnet wire set into slots.

Figure 1 is a representation of a stack of stator laminations showing the slots that receive the coils of wire. A number of coils are distributed among the slots to provide a group of coils that define each pole of the motor. For each pole, there are coils designated for connection to each phase of power.
Figure 1 Motor Stator Lamination Stack

The various electrical conductors that form the motor stator windings must be electrically insulated from each other and from the metal parts of the motor structure. Insulation is required wherever there is a difference of electrical potential between two (2) conductors. Turn-to-turn insulation prevents one (1) turn of a coil from short circuiting to an adjacent turn. Coil-to-coil insulation prevents various series or parallel connected coils from shorting to one another. Phase-to phase insulation separates the coils of one (1) phase from those of an adjacent phase. Winding-to-ground insulation prevents any part of the stator windings from shorting to the stator laminations.

Copper Wire

2009-05-03T23:31:00.003+07:00

We are able to supply copper wire with dia. 0.5mm; 0.1mm; 1mm and 2mm as per sample (it means-with out insulation = 100% copper) continuously.

Please note that:

- Offered net. prices: contact us at kecapi27@gmail.com

- Term of Payment: Cash against shipping documents.

- Loading capacity: 12MT per 20 FCL standard-container (max. 15MT)

- Quantities availability: 48 MT / month .

Commutator Surface Conditions

2009-05-02T20:34:00.002+07:00

Grade

2009-05-02T20:22:00.005+07:00

The grade of the brush is usually found stamped on the face of the carbon. The grade indicates the material composition of the brush. It represents one of the more technical challenges in carbon brush applications. Brush grades are usually classified according to the manufacturing processes and the types of materials used. The different grades in use today are derived through a variation of raw materials, molding pressures, temperature and duration of the baking process and after- treatments. These elements produce varied resistivity, hardness, and strength that in turn affect contact drop, friction and commutator filming. All grades fall within the four major categories of carbon graphite, electrographitic, graphite and metal graphite. The major characteristics of each category and a summary are listed on the opposite page.

There are only a few major carbon block makers in the world. Each of these manufacturers can make as many as 100 different grades. Each grade is designed to perform under certain operating conditions. Careful consideration is given to the actual running loads, the duty cycle, the voltage, the speed and the environment. Repco, Inc. supplies product from these major carbon manufacturers.
In addition, there are also carbon brush fabricators. A fabricator purchases carbon block, cuts it to size, adds hardware and stamps its own grade designation on the face of the brush.
Over the years, this practice has greatly added to the number of grades in the marketplace today. Our computer cross-reference system allows us to identify OEM and aftermarket brushes. Therefore, Repco, Inc. can supply carbon brushes for any motor including these major motor manufacturers:
• Baldor
• Century
• Lincoln
• Louis Allis
• Electric Machinery
• General Electric
• Gettys
• Imperial
• Indiana General
• Leeson
• Marathon
• Northwestern
• Pacific-Scientific
• Reliance
• U.S. Emerson
• Westinghouse

CARBON-GRAPHITE BRUSHES made their entrance early in the brush industry. Their properties of high hardness, material strength and pronounced cleaning action usually give long brush life under severe operating conditions, although they may not commutate as well as those with softer grades. These grades are limited to lower current densities and are used on slower machines, particularly those with flush mica commutators. The high friction generated with this type of material also makes it unattractive for some modern day applications.

ELECTROGRAPHITIC BRUSHES are baked at temperatures in excess of 2400 C. This process physically gives the material more of a graphitic structure. They generally have good commutating characteristics, but may not always be used because of high currents, or severe mechanical or atmospheric conditions. This material is fairly porous which permits treatment with organic resins. The treatments increase strength and lubricating ability which in turn helps increase brush life. These brushes are generally free from abrasive ash.

METAL GRAPHITE BRUSHES are generally made from natural graphite and finely divided metal powders. Copper is the most common metallic constituent, but tin, silver and lead are also used. This material is ideal for a variety of applications because of its low resistivity. Metal graphites are used on commutators of plating generators and wound rotor induction motors where low voltage and high brush current densities are encountered. They are also used for grounding brushes because of their low contact drop. These brushes exhibit a definite polishing action.

GRAPHITE BRUSHES are composed of natural or artificial graphite bonded with resin or pitch to form a soft brush material. Natural graphite usually contains ash, which gives the brush an abrasive, cleaning action. The fast filming properties of these brushes is beneficial in protecting the commutator or slip ring during operation in contaminated atmospheres. Their low porosity is also valuable in reducing commutator threading. They are not capable, however, of sustained operation at higher currents, like electrographic materials.

CARBON-GRAPHITE
• Used on older machines
• High strength and hardness
• Low resistance & poor commutation
• For machines that require some polishing action
• Generally, slower speed machines

GRAPHITE
• Good film characteristics
• Smooth ride
• Reduces threading
• Thermally limited
• Generally used on slip rings & FHP motors

METAL GRAPHITE
• Good for current densities
• Low contact drop
• Polishing action
• Metal content application
50% - material handling, battery charging & welding generators
60% - plating generators & rings
75% & up - rings & grounding brushes

ELECTROGRAPHITIC
• Good commutating ability
• Adequate strength with low abrasiveness
• Good friction characteristics
• Versatile
• Resistance, strength, hardness and density can be controlled through raw material
combinations
• Very widely used today in all types of motors & generators for:
steel and paper mills, excavation,
cement, transportation & aerospace

Basic Operation of AC Induction Motors (6) - FINISH

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Voltage and Current Waveforms

Today’s AC variable speed drive systems (up to 600 Volts and about 1500 HP) are dominated by PWM configurations. The current waveforms seen today (Figure 14) are much closer to the ideal sinusoid, thanks mostly to higher switching rates of transistors. The availability of low switching loss devices has allowed this to occur.

One of the negative aspects of the newer devices is that the low switching loss is typically accompanied by a very short transition time. This short transition between on and off states implies a high dV/dt output of the inverter. The high dV/dt results in capacitively coupled current flow according to Equation 4.

In addition to the capacitively coupled current, the high dV/dt also results in a higher peak voltage (ringup) due to cable-to-load mismatch. Finally, the high dV/dt also results in an instantaneous high voltage across the first windings within the ac motor. A companion paper, “AC Induction Motor Insulation Issues in High dV/dt Environments,” addresses this in greater detail.

Conclusions
AC induction motors are likely to continue to be increasing sources of variable speed rotating power. Their successful use in variable speed applications is a function of the collective understanding of the various parties involved in the specification, design, application, and integration of the system.

Basic Operation of AC Induction Motors (5)

2009-05-02T20:08:00.003+07:00

Constant Power Operation

The prior discussions regarding voltage boost and field oriented control as a means to maintain motor flux have been presented in regard to "constant torque" operation. This can also he thought of as operation "below base speed" (Figure 10).

Above the speed at which the output voltage of the controller is maximum, the controller can no longer maintain constant flux as speed is increased further (since the voltage cannot be increased to keep pace with the frequency). This is equivalent to where a DC motor begins to be "field weakened" to achieve higher speeds. Both for AC as well as DC machines, voltage (armature voltage for DC) remains constant, so for constant load current, constant output power
is available.
As the frequency supplied to an AC induction motor is increased (with voltage held constant), the resultant "field weakening" causes a reduction in the motor peak torque capability as seen in Figure 11.
This family of curves can alternatively be drawn as speed - power, rather than speed - torque curves (Figure 12). The fact that the peak power decreases as speed is increased by field weakening is the most "inherent" limitation to the "constant power speed range" of an AC induction motor drive.

A technique which is commonly employed to achieve wider speed ranges above base speed (constant power) is to utilize some of the “constant flux” speed range to augment the inherent constant power capability. By selecting a motor winding which does not require full voltage until some speed already into the desired constant power speed range, the constant power speed range can be extended as seen in Figure 13. The plots of Figure 13 show an example where the application demands a constant 100 HP from 650 RPM to 3200 RPM. By utilizing this technique, the motor size does not have to be increased in order to satisfy the wide constant power speed range.

This same technique is also used to extend the constant power speed range of DC systems as well. In the case of DC, it is to avoid commutation limits to the top speed at which constant power can be provided. For both AC and DC systems, the “price” which is paid to use this technique is an oversized source of power (higher kVA inverter or DC supply). Wind and unwind applications, along with machine tool spindles employ this technique quite commonly.

Basic Operation of AC Induction Motors (4)

2009-05-02T20:06:00.000+07:00

"Field Oriented" Control

In order to obtain even better yet control of AC motor torque, adjustable frequency controls often can make use of a regulation scheme known as "field-oriented" or "vector" control. This technique is intended to control the motor flux, and thereby be able to decompose the AC motor current into "flux producing" and "torque producing" components. These current components can be treated separately (in the control), then recombined to create the actual motor phase currents. This results in a solution to the boost adjustment problem, plus provides much better control of the motor torque - which allows much higher dynamic performance.

One way of looking at field oriented control is that the inverter would like to be able to have the same sort of simple, direct control of both flux and torque that is enjoyed with separately-excited dc motors. With dc motors, the flux level is controlled by simply regulating the field current, while the torque is controlled by regulating the armature current. By using field oriented control, the inverter can treat the ac induction motor as if it had the same sort of independently regulated flux and torque characteristic. When the actual induction motor phase currents are decomposed into flux and torque producing components (in the control, not in the motor), this gives the opportunity to “decouple” these two and achieve better system performance as a result.
In order to accomplish field-oriented control, the controller needs to have an accurate “model” of the motor. Over the last several years a large number of different schemes have been proposed to accomplish the “flux and torque control” desired. Many provide this control without the use of a speed feedback (tachometer) signal. These are typically referred to by the generic term of “sensorless” vector control. Many of today’s techniques also involve some sort of self-tuning at startup in order to obtain information which helps to more accurately model the motor – and thereby produce more optimal control. In addition, there are also techniques by which the models can adaptively adjust to changing conditions, such as the motor temperature going from cold to warm (which impacts the slip).

Basic Operation of AC Induction Motors (3)

2009-05-02T19:55:00.005+07:00

Adjustable Frequency, Variable Speed Operation

For steady-state (as opposed to starting) operation, AC induction motors offer a reasonably linear torque per amp and high power factor characteristic. This is seen in Figure 5 as the part of the speed torque curve between "breakdown RPM" and "synchronous (no load) RPM." It is this portion of the AC induction motor range of operation within which adjustable frequency drives function.

By varying both the frequency and voltage supplied to an AC motor, the controller can cause the motor to operate on a continuum of speed torque curves which allows operation in the "linear" region between breakdown and synchronous speeds (Figure 6).

This then allows the motor to operate near its optimal torque per amp or maximum efficiency point for a given load and speed.
As long as the motor flux is maintained constant while the frequency and voltage are varied, the basic "shape" of the speed torque curve will remain unchanged. The motor flux is proportional to the internal "counter-emf" divided by the frequency of that generated voltage. This can be described as:
where F is the motor flux,

Eg is the internally generated voltage due to motor rotation, f is the stator frequency, and k is a motor constant related to the winding turns, etc.
The flux paths for a four pole configuration are as seen in Figure 7 (for an instant in time). This pattern rotates at an effective speed given by Equation 1.

The motor counter-emf (Eg) can also be thought of as the voltage across the magnetizing reactance (Xm) in the equivalent circuit of Figure 3.
Maintaining constant flux while the speed (frequency) is varied can then be seen as requiring constant ratio of Eg / f (or constant Im).
Since Eg is a motor internal voltage, this needs to be related to the terminal voltage of the motor. From the AC motor equivalent circuit, it can been seen that the voltage drops across the stator resistance and leakage reactance represent the difference between Eg and the terminal voltage Vt.
If a controller were to maintain a constant ratio of TERMINAL voltage to frequency (Vt / f), rather than Eg / f, this would result in a noticeably decreasing flux level at lower speeds (frequencies).
The curves of Figure 8 demonstrate the effect of this failure to maintain the motor flux. It can be seen that the peak value of torque falls off at the reduced flux levels. In fact, the peak torque is approximately proportional to the square of the flux level, so the drop-off can be significant. The torque per amp is also (directly) proportional to the motor flux, so increased current draw for a given load (torque) will also result from reduced flux.

As a means to improve the system characteristics (beyond the curves of Figure 8), controllers often compensate for the difference between Vt and Eg in order to select the correct voltage for a given frequency. This compensation is often referred to as "voltage boost." Since the major detrimental effect of constant Vt / f is at low voltages, low frequencies (low speeds), the voltage drop across the stator leakage reactance is usually ignored (as the impedance of an inductor is proportional to frequency). This leaves the drop across the stator resistance as the major source of a discrepancy between Vt and Eg at these low speeds.
Many controllers use a value of voltage boost which compensates for the IR drop of the stator at a current equal to the motor full load amps.

Vb is the per phase (line-to-neutral) voltage boost,
Rl is the per phase stator resistance,
IFL is the motor full load current.

This would result in a voltage versus frequency characteristic as shown in Figure 9. A weakness in this technique of boosting voltage is that the value of Vb is only "correct" for a single value of load current. If the full load current is used to set the voltage boost, then the motor will be overfluxed for lighter loads, and underfluxed for overload conditions. Depending on the low speed performance required by a given application, this may or may not be a problem.
It is now common to provide a “more intelligent” voltage boost function in many controllers. This can provide a closer to optimal operating condition at low speeds, resulting in better low speed torque delivery from the system.

Basic Operation of AC Induction Motors (2)

2009-05-02T19:50:00.003+07:00

Speed / Torque Curves

As an AC induction motor is started, the values of resistance and reactance offered by the motor (or seen by the power source) will vary. At the instant of applying power to a stopped motor, the magnetic field is rotating much faster than the (stationary) rotor. This implies 100% slip, so R2/s is minimized. As a result, the current drawn at starting (locked rotor) conditions is quite high. Also, it is common to design rotor slots which have dramatically different impedance at high slip (say 60 Hz for starting) versus at normal running where slip is typically in the range of 0.2 - 2 Hz. This changes the values of both X2 and R2 from starting to running conditions.

As a motor accelerates to speed from a standstill, the changing impedances result in a unique characteristic developed torque and current drawn during the time of acceleration. Depending on the design of the motor, a torque / current characteristic such as one of those shown in Figure 4 would typically result. The NEMA Design B motor is considered the most "general purpose" of these characteristic shapes, with Design C and D typically used for more "difficult to start" loads. Table 2 gives some ranges of characteristics for integral HP, 1200
and 1800 RPM motors.

As can be seen from all of these speed / torque / current curves, the current drawn by an AC motor in accelerating a load up to speed can be dramatically higher than the nominal running current. At the same time, the developed torque (during acceleration) may in some cases be less than the rated full load torque. Various methods exist to control the starting current drawn by an AC motor but the torque per amp seen during (fixed frequency) starting is always much lower than at running conditions.
The nature of an AC induction motor’s acceleration to running speed is such that it can impose high stresses on both the stator and the rotor. The high current draw also stresses the upstream power system, including cabling, transformers, switchgear, etc. For this reason, there is often significant effort made to "control" AC motor starting and acceleration - both in terms of motor design as well as application.

Basic Operation of AC Induction Motors (1)

2009-05-02T19:44:00.004+07:00

Terminology and Equivalent Circuits

Before trying to understand the operation of AC induction motors on adjustable-frequency power (variable-speed), it will be useful to briefly review the basic fixed-frequency (constant speed) operation of AC induction motors. The fundamental electromagnetic components are the stator and rotor.
Examples of typical laminations which comprise the basic magnetic path in the stator and rotor are shown in Figure 1. In the most common configuration, the stator has three interconnected phase windings, and the rotor winding is a set of short circuited bars known as a "squirrel cage." A wound stator and an aluminum die cast (squirrel cage) rotor are seen in Figure 2.

With balanced three phase voltages applied to the windings of the stator, balanced currents flow in the three interconnected phase windings. These currents produce a magnetic field which can be thought of as "rotating" within the stator at a speed given by Equation 1.

N1 = 120 x f /P (1)
N1 = rotational speed of stator magnetic field in RPM (synchronous speed)
f = frequency of the stator current in Hz
P = number of motor magnetic poles

For various numbers of motors poles, Table 1 shows the synchronous speeds based on 60 Hz and 50 Hz frequencies.
The natural tendency is for the rotor to "follow" the rotating magnetic field, and at no-load the rotor will turn at a speed virtually equal to Nl. Any difference in the rotational speed of the magnetic field and that of the rotor will result in a voltage being induced in the rotor squirrel cage winding. The resultant rotor current interacts with the magnetic field to produce torque. The difference in rotor mechanical speed versus magnetic field rotational speed is what is known as "slip."
The equivalent circuit for an AC induction motor can help visualize some of the motor characteristics.

Figure 3 shows a typical equivalent circuit for AC induction motors. The variable resistor “R2/s”
represents the way slip causes increased current and corresponding increased torque. The greater the slip, the lower this value of resistance, and the more current is going to flow in this branch of the circuit. When the slip is virtually zero at a “no-load” condition, this resistor is seen to be a very high value. As a result, the current can be thought of as all going through the “XM” or magnetizing branch of the circuit.

Troubleshooting Drives

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Inverter Duty Failures

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It has been documented that some electric motors fail in inverter applications. This has often been attributed to inverter voltage “spikes.” While this is relatively correct, it misses some important aspects to the mode of failure.
The number of pulses that a PWM drive fires in order to control the current waveform to the drive is known as the carrier frequency. The carrier frequency tends to run from 2 to 18 kHz in most modern PWM drive. In addition, each voltage pulse is not a square waveform. They have a tendency to overshoot on startup, causing a “ringing” effect at the peak voltage of the pulse. Insulation systems are designed, not only for temperature, but also for “rise time,” how fast the voltage increases over time.

Initially, it was thought that inverter duty failures occurred only on the first few turns of the electric motor winding. It was later found that this was not correct for all cases. Instead, it was discovered, a phenomenon normally seen in electric motors rated at 6,000 VAC, and above, known as Partial Discharge, was now occurring in motors rated as low as 460VAC. This phenomenon is similar to a lightning storm within the windings themselves. Within voids in the winding insulation, charges build up, then discharge (much like a capacitor). The end result is ozone, which begins to break down the insulation on the wires, eventually causing a current path, or short.
The mode of failure for motors in this environment is as follows:
· The motor and drive are placed a distance apart and the carrier frequency is set high (ie: above 8kHz) in order to keep the motor quiet. The lower the carrier frequency the louder the motor noise. No filtering is put in place.
· The pulses from the drive travel out to the motor. Based upon the impedance of the cable and motor, a reflection of the pulse travels back to the drive. This cycles through the “free-wheeling” diodes of the inverter and travel back out with the normal pulses. This adds on to the peak voltage, causing a greater peak (as much as 2 to 4 times, usually 2) with an extremely fast rise time. (ie: less than .1 u-sec per 500 V versus the 1 u-sec per 500 V recommended by NEMA).
· In some cases, the voltage spikes will cause the weakest part of the winding insulation to fail and the motor shorts.
· In other cases, small voids in the insulation begin to have partial discharge problems, the ozone eats away at the insulation, until, finally, the insulation becomes weak enough for the spikes to break through.

It should be pointed out that this tends to be a rare problem. Following are measures to avoid the chance of this problem occurring to you:
· Check with the motor manufacturer to ensure that the motor can operate in an inverter environment.
· Use filters in the inverter system (ie: from line reactors to spike arrestors, designed for inverter use).
· Read the VFD operators manual. It will often state the minimum distances and frequency settings.
· Use proper wire sizes.

Power Quality

2009-05-02T19:31:00.003+07:00

Harmonics and electrical noise are potential problems when power electronics are utilized. As more AFD's are put into use, utilities may force users to install harmonic filtering from entering their systems. IEEE Recommended Practices and Requirements for Harmonic Control in Electrical Power Systems; IEEE Std. 519 - 1992; is written to attend to this issue. The standard has been written to limit the harmonic content introduced into the system by either the utilities or the customer.

(Note: The limits are, generally, 5% voltage distortion and 3% current distortion at the Point of Common Connection (PCC) or the point at which the utility power enters the customer plant.)
Harmonic content has attracted quite a bit of attention when discussing power quality and power electronics. Harmonics, created by the load, generally come from feedback into the line from electronic power supplies. Voltage and current harmonics tend to create alternate fields within motors and rotors, cause transformers to overheat, and interfere with other electronic systems. Odd harmonics of the fundamental frequency are generally found in power electronic systems.
In motor systems the following fundamentals of 60 Hz can be recognized:
Harm: 1st 3rd 5th 7th etc.
Rot: pos. zero neg. pos. etc.

Voltage and Current Harmonics

Positive harmonics rotate in the direction of the rotor. Other than the fundamental frequency, this type of harmonic causes heating within the stator. Negative rotating harmonics rotate against the rotor causing overheating of the rotor and reducing torque.
Zero rotating harmonics generally cause system neutrals to overheat. In the case of electronic drives, in general, the predominant harmonics are the 5th and 7th.

Variable Speed Concerns

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Whenever load speeds are varied, there are many considerations which must be taken into account. These concerns are both electrical and mechanical in nature.

The electrical problems associated with electronic drives generally concern the insulation. Because of the type of output generated by the inverter, there is great stress placed upon the insulation and the temperature rise of the windings may increase. In other cases, the motor may be run below its minimum self-cooling speed. The main trouble is that for every 10 degrees C, the insulation life of the windings are reduced by half. If the temperature rise is allowed to climb too high, the motor will overload and burn-up in a very short time. An additional problem, which is rare, is inverter resonance.
These difficulties can be avoided through the following means:
· Rewind or replace the motor - Rewind the motor to a higher insulation class, or replace it with a new motor. the new motor may be of the energy efficient or inverter duty type.
· Provide external cooling - This is especially important in cases where the self-cooling ability of the motor is compromised.
· Re-set the parameters - inverter resonance is found in cases where the drive parameters are not properly set. If this is not the case, the drive should be programmed to by-pass those frequencies where the problems are found.

Mechanical considerations include mechanical resonance and driven load incompatibility. Mechanical resonance can be defined as the speed of the driven load that matches its natural frequency. If this speed is found and maintained, the equipment will develop extremely high levels of vibration and may shake itself apart. Load incompatibility can be defined as loads which may not be operated at speeds lower than their design speed. For instance, many gearboxes have a minimum speed at which the lubricating oil may not be properly moved over the contacting parts.
Mechanical resonance can be avoided by programming the drive to avoid the appropriate frequency(s). The resonance levels may be determined by using a vibration analyzer and operating the machine through the entire speed range. Another way is by performing a "ring-test" using vibration analysis equipment. Load incompatibility can only be avoided by not allowing the drive to operate below a minimum speed.

Variable Frequency Drives (4) - FINISH

2009-05-02T19:23:00.003+07:00

4. Basic Operation of a PWM Inverter (VFD)

In this section we will discuss how the five basic drive system components work together. After this discussion we shall include a detailed, component level, discussion of operation.

The rectifier circuit of a pulse width modulated drive normally consists of a three phase diode bridge rectifier and capacitor filter. The rectifier converts the three phase AC voltage into DC voltage with a slight ripple. This ripple is removed by using a capacitor filter. (Note: The average
DC voltage is higher than the RMS value of incoming voltage by: AC (RMS) x 1.35 = VDC)
The control section of the AFD accepts external inputs which are used to determine the inverter output. The inputs are used in conjunction with the installed software package and a microprocessor. The control board sends signals to the driver circuit which is used to fire the inverter.
The driver circuit sends low-level signals to the base of the transistors to tell them when to turn on. The output signal is a series of pulses, in both the positive and negative direction, that vary in duration. However, the amplitude of the pulses are the same. The sign wave is created as the average voltage of each pulse, the duration of each set of pulses dictates the frequency.
By adjusting the frequency and voltage of the power entering the motor, the speed and torque may be controlled. The actual speed of the motor, as previously indicated, is determined as:

Ns = ((120 x f) / P) x (1 - S)

where: N = Motor speed; f = Frequency (Hz); P = Number of Poles; and S = Slip.

Variable Frequency Drives (3)

2009-05-02T19:20:00.001+07:00

3. Basic Drive System

The AFD consists of several basic components:

Line Voltage - In this case 3-phase AC voltage.
Input Section - Consists of a rectifier and filter. Transforms the AC voltage into DC voltage.
Control Section - The control board accepts real world inputs and performs the required operations. The tasks are performed by a microprocessor.
Output Section - This section includes the base drive circuits and the inverter. The base drive signals are low level signals that tell the inverter to turn on.
Motor - Already described.

Variable Frequency Drives (2)

2009-05-02T19:19:00.001+07:00

2. Constant Torque Loads

Direct Current electric motors, eddy-current clutches, transmissions, etc. used to be the best way of controlling process speed. With present AC drive technology, greater speed control and fewer losses can be realized. Additionally, there are fewer moving parts that would have to be maintained.

Vector drives can deliver full rated torque from full speed to zero RPM. Torque can be controlled, with precision, allowing even large motors to position loads much like servo motors. This allows for greater flexibility of control over the other methods of speed control.

Variable Frequency Drives (1)

2009-05-02T19:14:00.004+07:00

1. Variable Torque Loads

Variable loads offer a tremendous opportunity for energy savings with AFD's. The areas of greatest opportunity are fans and pumps with variable loads.

Fan and pump applications are the best opportunities for direct energy savings with AFD's. Few applications require 100% of pump and fan flow continuously. For the most part, these systems are designed for worst case loads. Therefore, by using AFD's, fluid affinity laws can be used to reduce the energy requirements of the system (Fig. 1).

Fig.1 Pump and Fan Affinity Laws

Eq. 1: N1 / N2 = Flow1 / Flow2
Eq. 2: (N1 / N2)^2 = Head1 / Head2
Eq. 3: (N1 / N2)^2 = T1 / T2
Eq. 4: (N1 / N2)^3 = HP1 / HP2

By using the affinity laws, you can determine the approximate energy savings:

Ex. 1: 250hp Fan Operating 160 hrs / Week

hp1 / hp2 : (N1 / N2)^3
100% spd = 40 hrs = 100% ld = 250hp
75% spd = 80 hrs = 42% ld = 105hp
50% spd = 40 hrs = 13% ld = 31hp
kWh / wk = (hp) x (0.746) x (hrs / eff)
250 x 0.746 x (160 / 0.95) = 31,411kWh/wk

Assuming no loss of efficiency at reduced speeds:
(250 x 0.746 x (40/0.95)) + (105 x 0.746 x (80/0.95)) + (31 x 0.746 x (40/0.95)) = 15,422 kWh

By using an AFD the approximate kWh savings per year would look like:
(31,411 - 15,422) x 50 = 800,000 kWh/yr

AC Induction Motor Design (8) - FINISH

2009-05-02T18:56:00.001+07:00

10. Inverter Duty Motors

Inverter duty motors are specially designed to withstand the new challenges presented by the use of inverters. There are a number of ways to designate motors "inverter duty," however, several things must exist as a minimum:

Class F insulation - to withstand the higher heat generated by non-sinusoidal current from the drive.
Phase insulation - Insulation between phases is a must to avoid "flashover" between phases from current surges.
Layered Conductors - To reduce turn to turn potential between conductors.
Solid varnish system - to reduce partial discharge and corona damage.
Tight machine tolerances and good air gap concentricity - to reduce shaft currents and resulting bearing damage.

A proper inverter duty motor will have special rotor bar construction designed o withstand variations in airgap flux densities and rotor harmonics. Additionally, the first few turns of wire may be insulated to better withstand standing waves which occur due to the faster rise times in modern inverter technology.
Caution: Some manufacturers may only de-rate motors. This is done by reducing the motor by (about) 25%. Therefore, a 10 hp motor may be rated as a 7.5 hp motor.
It should be noted, also, that an inverter application does not always require an inverter duty motor. The old motor or an energy efficient motor may be sufficient for the application.

AC Induction Motor Design (7)

2009-05-02T18:53:00.001+07:00

9. Energy Efficient Electric Motors

The Energy Policy Act of 1992 (EPACT) directs manufacturers to manufacture only energy efficient motors beyond October 24, 1997 for the following: (All motors which)

- General Purpose
- Design B
- Foot Mounted
- Horizontal Mounted
- T-Frame
- 1 to 200 hp
- 3600, 1800, and 1200 RPM
- Special and definite purpose motor exemption

To meet NEMA MG1-1993 table 12.10 efficiency values. The method for testing for these efficiency values must be traceable back to IEEE Std. 112 Test type B.
Energy efficient motors are really just better motors, when all things are considered. In general, they use about 30% more lamination steel, 20% more copper, and 10% more aluminum. The new lamination steel has about a third of the losses than the steel that is commonly used in standard efficient motors.
As a result of fewer losses in the energy efficient motors, there is less heat generated. On average, the temperature rise is reduced by 10 degrees centigrade, which has the added benefit of increasing insulation life. However, there are several ways in which the higher efficiency is obtained which has some adverse effects:
- Longer rotor and core stacks - narrows the rotor - Reduces air friction, but also decreases power factor of the motor (more core steel to energize - kVAR).
- Smaller fans - reduces air friction - the temperature rise returns to standard efficient values.
- Larger wire - Reduces I2R , stator losses - Increases starting surge (half - cycle spike) from 10 to 14 times, for standard efficient, to 16 to 20 times, for energy efficient. This may cause nuisance tripping.

In general, energy efficient motors can cost as much as 15% more than standard efficient motors. The benefit, however, is that the energy efficient motor can pay for itself when compared to a standard efficient motor.

$ = 0.746 * hp * L * C * T (100/Es -100/Ee)
where hp = motor hp, L = load, C = $/kWh, T= number of hours per year, Es = Standard efficient value, and Ee = Energy efficient value --- Eq. 5

AC Induction Motor Design (6)

2009-05-02T18:49:00.002+07:00

8. Electric Motor Insulation

With all this discussion about motor operation, losses, torque curves, and inrush, it is only fitting to review the thermal properties of electrical insulation. In general, when an electric motor operates, it develops heat as a by-product. It is necessary for the insulation that prevents current from going to ground, or conductors to short, to withstand these operating temperatures, as well as mechanical stresses, for a reasonable motor life. Insulation life can be determined as the length of time at temperature. On average, the
thermal life of motor insulation is halved for every increase of operating temperature by
10 degrees centigrade (or doubled, with temperature reduction).

There are certain temperature limitations for each insulation class (Table 3) which can be used to determine thermal life of electric motors. Additionally, the number of starts a motor sees will also affect the motor insulation life. These can be found as mechanical stresses and as a result of starting surges.
When a motor starts, there is a high current surge (as previously described). In the case of Design B motors, this averages between 500 to 800% of the nameplate current. There is also a tremendous amount of heat developed within the rotor as the rotor current and frequency is, initially, very high. This heat also develops within the stator windings.
In addition to the heat developed due to startup, there is one major mechanical stress during startup. As the surge occurs in the windings, they flex inwards towards the rotor. This causes stress to the insulation at the points on the windings that flex (usually at the point where the windings leave the slots). Both of these mean there are a limited number of starts per hour (Figure 4). These limits are general, the motor manufacturer must be contacted ( or it will be in their literature)for actual number of allowable starts per hour. this table also assumes a Design B motor driving a low inertia drive at rated voltage and frequency. Stress on the motor can be reduced, increasing the number of starts per hour, when using some type of "soft start" mechanism (autotransformer, part-winding, electronic soft-start, etc.).

AC Induction Motor Design (5)

2009-05-02T18:47:00.001+07:00

7. Design E Motor Discussion

The design E motor was specified to meet and international standard promulgated by the International Electrotechnical Commission (IEC). IEC has a standard which is slightly less restrictive on torque and starting current than the Design B motor. The standard allows designs to be optimized for higher efficiency. It was decided to create a new Design E motor which meets both the IEC standard and also an efficiency criterion greater than the standard Design B energy efficient motors.

For most moderate to high utilization application normally calling for a Design A or B motor, the Design E motor should be a better choice. One should be aware of slight performance differences.
Although the NEMA standard allows the same slip (up to 5%) for Designs A, B, and E motors, the range of actual slip of Design E motors is likely to be lower for Designs A and B.
There are a number of considerations which must be observed with Design E motors:

Good efficiency - as much as 2 points above Design B energy efficient.
Less Slip - Design E motors operate closer to synchronous speed.
Lower Starting Torque - May not start "stiff" loads.
High Inrush - As much as 10 times nameplate full load amps.
Availability - Presently low as the standard has just passed.
Starter Availability - Control manufacturers do not have an approved starter developed at this time.
National Electric Code - Has no allowance for higher starting amps. Design E motors will require changes to NEC allowances for wire size and feed transformers.
Limited Applications - Low starting torque limits applications to pumps, blowers, and loads not requiring torque to accelerate load up to speed.
Heavier Power Source Required - High amperage and low accelerating torque mean longer starting time and related voltage drops. May cause nuisance tripping of starter of collapse of SCR field with soft starters.

AC Induction Motor Design (4)

2009-05-02T18:44:00.002+07:00

6. NEMA Motor Design Classifications

NEMA defines, in NEMA MG 1-1993, four motor designs dependant upon motor torque during various operating stages:

Design A: Has a high starting current (not restricted), variable locked-rotor torque, high break down torque, and less than 5% slip.
Design B: Known as "general purpose" motors, have medium starting currents (500 - 800% of full load nameplate), a medium locked rotor torque, a medium breakdown torque, and less than 5% slip.
Design C: Has a medium starting current, high locked rotor torque (200 - 250% of full load), low breakdown torque (190 - 200% of full load), and less than 5% slip.
Design D: Has a medium starting current, the highest locked rotor torque (275% of full load), no defined breakdown torque, and greater than 5% slip.

Design A and B motors are characterized by relatively low rotor winding resistance. They are typically used in compressors, pumps, fans, grinders, machine tools, etc.
Design C motors are characterized with dual sets of rotor windings. A high resistive rotor winding, on the outer, to introduce a high starting torque, and a low resistive winding, on the inner to allow for a medium breakdown torque. They are typically used on loaded conveyers, pulverizers, piston pumps, etc.
Design D motors are characterized by high resistance rotor windings. They are typically used on cranes, punch presses, etc.

to be continued....

AC Induction Motor Design (3)

2009-05-02T18:40:00.003+07:00

5. Torque

By varying the resistance within the rotor bars of a squirrel cage rotor, you can vary the amount of torque developed. By increasing rotor resistance, torque and slip are increased. Decreasing rotor resistance decreases torque and slip.

Motor horsepower is a relation of motor output speed and torque (expressed in lb-ft):

HP = (RPM * Torque) / 5250 --- eq. 5

The operating torques of an electric motor are defined as (Ref. NEMA MG 1-1993, Part 1, p.12):

Full Load Torque: The full load torque of a motor is the torque necessary to produce its rated horsepower at full-load speed. In pounds at a foot radius, it is equal to the hp times 5250 divided by the full-load speed.
Locked Rotor Torque: The locked-rotor torque of a motor is the minimum torque which will develop at rest for all angular positions of the rotor, with rated voltage applied at rated frequency.
Pull-Up Torque: The pull-up torque of an alternating current motor is the minimum torque developed by the motor during the period of acceleration from rest to the speed at which breakdown torque occurs. For motors which do not have a definite breakdown torque, the pull-up torque is the minimum torque developed up to rated speed.
Breakdown Torque: The breakdown torque of a motor is the maximum torque which it will develop with rated voltage applied at rated frequency, without an abrupt drop in speed.

AC Induction Motor Design (2)

2009-05-02T18:31:00.003+07:00

3. Induction Motor Construction

An induction motor consists of three basic components:

Stator: Houses the stator core and windings. The stator core consists of many layers of laminated steel, which is used as a medium for developing magnetic fields. The windings consist of three sets of coils separated by 120 degrees electrical.
Rotor: Also constructed of many layers of laminated steel. The rotor windings consist of bars of copper or aluminum alloy shorted, at either end, with shorting rings.
Endshields: Support the bearings which center the rotor within the stator.

4. Operating Principles

The basic principle of operation is for a rotating magnetic field to act upon a rotor winding in order to develop mechanical torque. The stator windings of an induction motor are evenly distributed by 120 degrees electrical. As the three phase current enters the windings, it creates a rotating magnetic field within the air gap (the space between the rotor and stator laminations). The speed that the fields travel around the stator is known as synchronous speed (Ns). As the magnetic field revolves, it cuts the conductors of the rotor winding and generates a current within that winding. This creates a field which interacts with the air gap field producing a torque. Consequently, the motor starts rotating at a speed N <> Ns in the direction of the rotating field.

The speed of the rotating magnetic field can be determined as:

Ns = (120 * f) / p --- eq. 1

Where Ns is the synchronous speed, f is the line frequency, and p is the number of poles found as:

p = (# of groups of coils) / 3 --- eq. 2

The number of poles is normally expressed as an even number.
The actual output speed of the rotor is related to the synchronous speed via the slip, or percent slip:

s = (Ns - N) / Ns --- eq. 3

%s = s * 100 --- eq. 4

to be continued..........