The constant voltage transformer cvt has a wide application, particularly where reliability and inherent regulating ability against line voltage changes are of prime importance. Chapter 17 winding capacitance and leakage inductance. In its most basic form, the device consists of three parts. It is also used for power line communication between different substations. The capacitive voltage transformer stepdown the high voltage input signals and provide the low voltage signals which can easily measure through the measuring instrument. Electrical routine testing of high voltage bushings. Basics, maintenance, and diagnostics xi contents continued page 9. Checking power capacitor banks for failed capacitors. Test voltage max 12,000v shortcircuit current max 5ma.
Capacitor voltage transformer cpb 72 pdf english pdf drawing. Neutral on high side wye configured transformer is inaccessible. Tan delta test loss angle test dissipation factor test. Power transformer testing measuring capacitance and. 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 high voltage winding of the transformer under test and the high. In this article we are going to have details of the parameter which are mentioned on a nameplate of capacitive voltage transformer. Series resonances are occurring between leakage reactance of transformer and capacitance to ground. When performing overall power factor and capacitance measurements, the following test preparations are recommended.
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. Ensure that the transformer tank and core are solidly grounded, also connect both the test. Ac dielectric withstand test voltage shall not exceed 65 percent of factory test voltage for oneminute duration. On rare occasions winding capacitance is increased to reduce ringing in switching transformers. Capacitor voltage transformer cvt, which is with simple structure, convenient maintenance, functional diversity and high impact pressure strength, is widely used. The capacitive voltage transformer cvt is also called capacitive potential transformer. If a very high voltage is required, the transformer is usually build up in stages by cascading.
Power transformer testing procedures and schemes photo credit. Dc dielectric withstand test voltage shall not exceed 100 percent of the ac rms test voltage specified in ansi c57. The output of a constant voltage transformer is essentially a square wave, which is desirable for rectifier output applications while, also. High voltage winding to low voltage winding and ground b. The goal of partial discharge measurement is to certify that no harmful partial discharge sources exist. One end of the secondary winding is connected to one end of the primary winding. Figure 2typical megger test instrument hookup to measure insulation resistance. The following tests are routinely conducted in the field on the transformer. Pf shows a flat response as a function of test voltage power factor vs. This test is normally performed with an insulation power factor test set. 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. Capacitance 1611b test bridge section 1 introduction 1. Nameplate details of capacitive voltage transformer cvt. Voltage three phase two winding oil filled transformer. Iwanusiw, consultant eltel industries, bangalore, india. Fullwave lightning impulse withstand test at rated bil. Factory tests not achieving as much winding stress as field conditions 2. In general, part of the designers task is to keep capacitance to a minimum. Generator stepup transformers, used in reclamation powerplants, receive electrical energy at generator voltage and increase it to a higher voltage for transmission lines. The capacitive potential divider, inductive element and the auxiliary.
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. 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. Excitation current test performed at different voltages on a single phase transformer voltage and current exhibits. The ferroresonance phenomenon in voltage transformers is analyzed in this section through several software simulation examples, using the software tool matlab. Capacitive voltage transformer is mainly used for measurement of voltage and for protection purpose. The voltage difference between turns, between winding layers and between windings to core create these parasitic elements. Power transformer testing procedures and schemes eep.
Smart test set for sweep frequency response analysis. Capacitance in a transformer winding cannot be avoided. 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. 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. Transformer testing type tests and routine tests of. 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.
The test as it is termed, measures the capacitance and dissipation factor or loss factor of the transformer insulation system. High voltage circuit breaker testing with omicrons cibano 500 and cb mc2. 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. It is recommended to select the highest test voltage within the limitations of the. Figure 6 shows the saturation curve of the voltage transformer model developed. The complete guide to electrical insulation testing. All class ii power transformers shall be induced voltage tested with the required test levels induced in the high voltage winding. Capacitor voltage transformer cpb is designed for revenue metering and protection in high voltage networks. 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. Power transformer testing transformers may be tested using ac or dc voltage. 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. Factory tests are on transformer without load and without cables 3. A potential transformer is a conventional transformer having primary and secondary windings.
Power factor and capacitance baseline established at 10 kv. Power factor testing nov2005 doble engineering company. Analysis on the influence factors of capacitor voltage. The induced voltage test is the final dielectric test. Capacitive voltage transformers cvts have been widely used. Ac voltage is preferable to dc voltage for transformer testing because ac voltage simulates the internal stress that the transformers face during operating conditions. The test circuit, in figure 1711 functions as follows. 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. Capacitance voltage transformer phasor diagram of cvt. Diagnostic testing and monitoring of power transformers. 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. A transformer is a specific form of a coupled circuit in which the coupling mechanism is the mutual.
By means of cascading, the size of the transformer and the insulation bushing. Power transformer testing measuring capacitance and power factor or dissipation factor. Understanding the value of electrical testing for power. Voltage is applied to the high voltage windings, one at a time. Kew 3128 is suitable for analyzing the insulation characteristics of cables, transformers, motors, generators, highpressure switches, etc. Ddn or dfn for capacitors followed by 2 or 3 numbers indicating the maximum voltage of the network for which they are designed. For most power transformer testing, this generator is 120 hz, 180 hz or 240 hz. Capacitor voltage transformer cvt or ccvt construction. The transformer testing performed before commissioning the transformer at the site is called the precommissioning test of transformer. A software model has been developed based on test data obtained on a real voltage transformer. A very lowfrequency test voltage is applied across the equipment whose insulation to be tested.
Technical guide type o plus c ii ehv condenser bushings. If no evidence of distress or insulation failure is observed by the. 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. Instrument transformer theory and testing steve hudson, pe. Understanding insulation resistance testing pdf 0712 technical assistance 800 34391. Then, calculate the capacitance using equation 177. Listoffigures 1 scheringbridge 2 2 basicmeasurementcircuitforthecalibrationofahighvoltagecapacitor 5 3 basicmeasurementcircuitforthecalibrationofavoltagetransformer. Low high low lhl pattern will be obtained on a 3legged core type transformer if the traditional test protocals are not followed. Expected for a 5 legged core or shell type transformer with a delta connected secondary winding.
Step voltage sv dielectric discharge index dd capacitance measurement microprocessor controlled high voltage insulation tester. 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. During the test the instrument transformers are submitted to forces of from 0,5 1g, according to ieee standard. Using transformer parasitics for resonant converters a. 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. The input voltage, vi, is held constant while monitoring the voltage, v2, sweep through the frequency with the power oscillator.
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