Power transformer testing measuring capacitance and power factor or dissipation factor. The high voltage winding of the transformer under test and the high. Transformer testing type tests and routine tests of. For most power transformer testing, this generator is 120 hz, 180 hz or 240 hz. Figure 6 shows the saturation curve of the voltage transformer model developed. Ac dielectric withstand test voltage shall not exceed 65 percent of factory test voltage for oneminute duration. Series resonances are occurring between leakage reactance of transformer and capacitance to ground. Fullwave lightning impulse withstand test at rated bil. Analysis on the influence factors of capacitor voltage. It is recommended to select the highest test voltage within the limitations of the.
By means of cascading, the size of the transformer and the insulation bushing. The applied voltage will be limited by the test sets power supply, but in no case should the test voltage exceed the linetoground voltage of the winding. Listoffigures 1 scheringbridge 2 2 basicmeasurementcircuitforthecalibrationofahighvoltagecapacitor 5 3 basicmeasurementcircuitforthecalibrationofavoltagetransformer. All class ii power transformers shall be induced voltage tested with the required test levels induced in the high voltage winding. Capacitor voltage transformer cvt, which is with simple structure, convenient maintenance, functional diversity and high impact pressure strength, is widely used. Expected for a 5 legged core or shell type transformer with a delta connected secondary winding. Power transformer testing procedures and schemes photo credit.
Capacitance 1611b test bridge section 1 introduction 1. The capacitive voltage transformer cvt is also called capacitive potential transformer. Capacitive voltage transformer is mainly used for measurement of voltage and for protection purpose. If a very high voltage is required, the transformer is usually build up in stages by cascading. These tests are done to assess the condition of transformer after installation and compare the test results of all the low voltage tests with the factory test.
The constant voltage transformer cvt has a wide application, particularly where reliability and inherent regulating ability against line voltage changes are of prime importance. One end of the secondary winding is connected to one end of the primary winding. Iwanusiw, consultant eltel industries, bangalore, india. Figure 2typical megger test instrument hookup to measure insulation resistance. The capacitive voltage transformer stepdown the high voltage input signals and provide the low voltage signals which can easily measure through the measuring instrument.
The burden with which the transformer is to be tested is connected across the secondary winding, and the normal primary voltage, at the normal frequency is applied to the primary winding. Understanding the value of electrical testing for power. Capacitive voltage transformers cvts have been widely used. Checking capacitor banks for failed capacitors introduction this technical note provides background information on capacitance testing of medium voltage double bushing capacitors commonly used in capacitor banks and harmonic filter banks with rated line voltages greater than 2. Factory tests not achieving as much winding stress as field conditions 2. The ferroresonance phenomenon in voltage transformers is analyzed in this section through several software simulation examples, using the software tool matlab. Pf shows a flat response as a function of test voltage power factor vs. Kolar, senior member, ieee abstractparasitic capacitances of conventional transformers can be used as resonant elements in resonant dcdc converters in order to reduce the overall system size. A potential transformer is a conventional transformer having primary and secondary windings. Voltage is applied to the high voltage windings, one at a time. High voltage winding to ground with low voltage winding.
Checking power capacitor banks for failed capacitors. Insulation power factor testing of power transformers oleh w. The goal of partial discharge measurement is to certify that no harmful partial discharge sources exist. Power factor and capacitance baseline established at 10 kv. In this article we are going to have details of the parameter which are mentioned on a nameplate of capacitive voltage transformer. The output of a constant voltage transformer is essentially a square wave, which is desirable for rectifier output applications while, also. Capacitance in a transformer winding cannot be avoided. A calibration service for voltage transformers and high.
Conversely, a stepdown transformer receives energy at a higher voltage and delivers it at a lower voltage for distribution to various loads. The voltage difference between turns, between winding layers and between windings to core create these parasitic elements. The input voltage, vi, is held constant while monitoring the voltage, v2, sweep through the frequency with the power oscillator. Ensure that the transformer tank and core are solidly grounded, also connect both the test. Basics, maintenance, and diagnostics xi contents continued page 9.
The following tests are routinely conducted in the field on the transformer. The capacitive potential divider, inductive element and the auxiliary. The test circuit, in figure 1711 functions as follows. Capacitor voltage transformer cpb 72 pdf english pdf drawing. If no evidence of distress or insulation failure is observed by the. Electrical routine testing of high voltage bushings. Capacitor voltage transformer cpb is designed for revenue metering and protection in high voltage networks. Ddn or dfn for capacitors followed by 2 or 3 numbers indicating the maximum voltage of the network for which they are designed. Ac voltage is preferable to dc voltage for transformer testing because ac voltage simulates the internal stress that the transformers face during operating conditions.
Capacitor voltage transformer cvt or ccvt construction. Generator stepup transformers, used in reclamation powerplants, receive electrical energy at generator voltage and increase it to a higher voltage for transmission lines. Excitation current test performed at different voltages on a single phase transformer voltage and current exhibits. The cable, winding, current transformer, potential transformer, transformer bushing, on which tan delta test or dissipation factor test to be conducted, is first isolated from the system. Technical guide type o plus c ii ehv condenser bushings. On rare occasions winding capacitance is increased to reduce ringing in switching transformers. The induced voltage test is the final dielectric test. When performing overall power factor and capacitance measurements, the following test preparations are recommended. Connecting cable where c m is the capacitance voltage transformer of the meter and the connecting cable and the leads and v 2 is the meter reading capacitance divider with a suitable matching or isolating potential transformer tuned for resonance condition is often used in power systems for voltage measurements. High voltage circuit breaker testing with omicrons cibano 500 and cb mc2. The complete guide to electrical insulation testing. A transformer is a specific form of a coupled circuit in which the coupling mechanism is the mutual. Testing current transformers burden test only if we cannot get to the primary side of the ct we can check that the output is constant as burden changes. Low high low lhl pattern will be obtained on a 3legged core type transformer if the traditional test protocals are not followed.
It is also used for power line communication between different substations. Smart test set for sweep frequency response analysis. Ultraprecise test set for dissipationpower factor and capacitance measurements on high voltage assets with an external source and reference capacitor lightweight test set for fast and reliable moisture content determination of oilpaper insulated power transformers. The capacitor voltage transformer cvt is used for line voltmeters, synchroscopes, protective relays, tariff meter, etc. Power factor testing nov2005 doble engineering company. Tan delta test loss angle test dissipation factor test.
Step voltage sv dielectric discharge index dd capacitance measurement microprocessor controlled high voltage insulation tester. A voltage transformer vt is a transformer used in power systems to step down extra high voltage signals and provide a low voltage signal, for measurement or to operate a protective relay. Instrument transformer theory and testing steve hudson, pe. C electrical power from one voltage to another voltage keeping the frequency same by electromagnetic induction discover the worlds research 16. The test as it is termed, measures the capacitance and dissipation factor or loss factor of the transformer insulation system. High voltage winding to low voltage winding and ground b. This test is normally performed with an insulation power factor test set. Neutral on high side wye configured transformer is inaccessible.
Power transformer testing measuring capacitance and. If no evidence of distress or insulation failure is observed by the end of the total time of voltage application during the dielectric withstand voltage test, the test specimen is. Voltage transformer testing swp page 3 of 19 standard work practice sp0508 ver 7 ergon energy corporation limited abn 50 087 646 062 if any risks cannot be managed or reduced to an acceptable level. High voltage testing 149 the high voltage is applied across the device under test by means of a transformer. In addition to power supplies, transformers find use in circuits as power line isolators, impedance matchers, pulse transformers, voltage amplifiers, and as speaker drivers in radio circuits. Voltage three phase two winding oil filled transformer. During the test the instrument transformers are submitted to forces of from 0,5 1g, according to ieee standard. Chapter 17 winding capacitance and leakage inductance. In such cases it is necessary to utilise all reserves of the existing impulse voltage test generator. Understanding insulation resistance testing pdf 0712 technical assistance 800 34391. Factory tests are on transformer without load and without cables 3. Then, calculate the capacitance using equation 177. In general, part of the designers task is to keep capacitance to a minimum.
The transformer testing performed before commissioning the transformer at the site is called the precommissioning test of transformer. Test voltage max 12,000v shortcircuit current max 5ma. Power transformer testing transformers may be tested using ac or dc voltage. The figure below shows the connections for testing a potential transformer using a resistance potential divider. Dc dielectric withstand test voltage shall not exceed 100 percent of the ac rms test voltage specified in ansi c57. And its capacitance and dielectric loss angle measurement is an important test on testing the insulation of the equipment. Scribd is the worlds largest social reading and publishing site. Kew 3128 is suitable for analyzing the insulation characteristics of cables, transformers, motors, generators, highpressure switches, etc. A very lowfrequency test voltage is applied across the equipment whose insulation to be tested. Using transformer parasitics for resonant converters a.
In its most basic form, the device consists of three parts. Capacitance voltage transformer phasor diagram of cvt. A capacitor voltage transformer cvt or ccvt, is a transformer used in power systems to step down extra high voltage signals and provide a low voltage signal, for metering or operating a protective relay. The capacitance and dissipation factor test is an ac low voltage maintenance test and is very similar to the power factor test. Power transformer testing procedures and schemes eep. We will discuss how capacitance occurs, references to formula for calculating, how capacitance is modeled, how cd is measured with three cautionary notes and guidelines to aid in evaluating measuring cd. Diagnostic testing and monitoring of power transformers. Power transformer capacitance and dissipation factor test.
1151 631 816 10 1555 1197 1139 423 1416 825 10 372 1297 1540 19 53 1585 1276 543 609 1619 957 723 1605 1319 333 539 804 770 738 430 770 486 254 899 671 168 794 743 1384 412 52