Current transformer basics and the current transformer. Turnsratio test results should not deviate more than onehalf percent from either the adjacent coils or the calculated ratio. The name instrument transformer is a general classification applied to current and voltage. Measuring unit wm303iu the high voltage transformer hvt generates the test voltage for the accuracy test of the voltage instrument transformers. The standard converters consist of an inductive voltage. To confirm the physical condition and electrical characteristics of current transformer installed in the installation. Pdf and reduce the time it takes to complete your report generation. Power transformer testing transformers may be tested using ac or dc voltage. Replaces 7200pd9206, 031992 medium voltage transformer testing. The excitation current which is only 1 percent or less even at rated voltage becomes negligibly small during this test and hence is neglected.
Occasionally it is not possible to perform a current ratio test. Transformer testing transformers are tested at or above the rated voltage to be certain there are no excessive leakage paths to ground or between windings. The supply voltage required to circulate rated current through the transformer is usually very small and is of the order of a few percent of the nominal voltage. The current transformer will operate into either a short circuit or a resistive load until the voltage induced is enough to saturate the core or cause voltage breakdown. Please indicate the highest kva ratings you want to test, the corresponding voltages, the impedance, and the approximate percentage of your testing each represents. The magnetized iron core induces a voltage in the secondary coils. The typical excitation current test data pattern for a threelegged core transformer is two similar current readings and one lower current reading. Ht voltage 11kv lt voltage 415v pp kva rating 200 kva full load current 10. The following tests are routinely conducted in the field on the transformer. Unlike the voltage or power transformer, the current transformer consists of only one or very few turns as its primary winding. 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. Transformer core the composition of a transformer core depends on voltage, current, and frequency. Routine tests and type tests of transformers electrical4u. Products test equipment for instrument transformer.
Generally, aircore transformers are used when the voltage source has a high frequency above 20 khz. It is always best to minimize the voltage drop across the ct and burden resistor to in the millivolts range as opposed to the volts range. The tap voltage method cannot establish true orientation. Routine tests are carried out on every unit manufactured. Nov 26, 2010 traditional current transformer testing follows a blackbox approach. Transformer testing serves for the accuracy test including polarity check and demagnetisation for current and voltage transformers in low voltage, middle voltage and high voltage grids according to iec standard 600441, 600442, 600447, 600448 and 6185092 or ansi ieee c57. Ac voltage is preferable to dc voltage for transformer testing because ac voltage simulates the internal stress that the transformers face during operating conditions. If the secondary circuit is closed, a current will flow through the secondary circuit in proportion to the ct ratio.
Insulation resistance tester, microohmmeter, high voltage test. The current transformer is solely assessed through its external behavior without considering what is happening inside. To adjust the voltage of the transformer at off circuit not only at noload condition, the transformer has to be disconnected from the network. This primary winding can be of either a single flat turn, a coil of heavy duty wire wrapped around the core or just a conductor or bus bar placed through a central hole. Standardhigh voltage transformer svthvt mobile ct test system. Warning and caution notices are used throughout this manual where applicable and should be. May 10, 20 the transformer testing performed before commissioning the transformer at the site is called the precommissioning test of transformer. The resulting effect on instrument performance is usually negligible, although for precision metering a persistent change in the accuracy of the transformer may be. The resulting errors will be transfered as ratio and phase angle via interface.
This report describes the testing performed by bnl and documents the results. It is expressed in per unit or percent of the rated transformer winding. A current transformer operates with a set primary current and will try to output a constant current to the load, independent of the load. Ensure the ct is connected to system properly in all respect primary and secondary. Mct1605 current transformer saturation, ratio and polarity test set. Instrument transformer testing instrument transformers for metering purposes must have a high degree of accuracy up to class 0. The basics of current transformers nk technologies. The first procedure is to determine the primary and. Current transformer, standard for steadystate performance. Real time monitoring of transformer using iot ijert. Power transmission and distribution author page 242 200708.
This rise in output voltage can cause the current transformer core to trend toward saturation. A method for testing electronic instrument transformers is described. Back to the basics current testing valence electrical. Short circuit lt side and apply voltage at ht side of transformer until the full load current is achieved. These notices appear in the format shown below and are defined as follows. Page 2 of 9 standard work practice sp0507 ver 5 ergon energy corporation limited abn 50 087 646 062. Strategy and other partial discharge documents or consult. Current transformer testing swp check this is the latest process zone version before use. Voltage transformer testing swp page 2 of 19 standard work practice sp0508 ver 7 ergon energy corporation limited abn 50 087 646 062 sp0508r01. Portable ct pt analyzertransformer testgfuve electronics. Noload loss tests are measured at 100% of rated voltage.
A routine series of diagnostics and testing for your current transformer should include ct saturation testing to identify the knee point against ieee or iec standards, ct ratio tests to identify that the voltage ratio is within expected parameters and current transformer resistance testing for both the transformer windings and ct insulation. Current transformer if the secondary is opened with current in the primary, the primary magnetizing force builds up an extremely high voltage in the secondary, which is dangerous to personnel and can destroy the currenttransformer. Megger relay and current transformer test set advanced test. Electronic voltage and current transformers testing device mdpi. Two amran current transformers cts were tested to characterize the. B2 current and voltage transformers schneider electric. Chapter 16 current transformer design university of north. Capacitive voltage transformers and coupling capacitors 34. During that time, the effects of aging, regular operation, network faults.
Voltage transformer testing competency assessment sp0508c06. Highvoltage transformers are some of the most important and expensive. The transformation from primary to secondary current requires a small amount of energy to. Feb 08, 2015 a routine test of transformer is mainly for confirming operational performance of individual unit in a production lot. All transformers are subjected to the following routine tests. Transformer testing serves for the accuracy test including polarity check and demagnetisation for current and voltage transformers in low voltage, middle voltage and high voltage grids according to iec standard 600441, 600442. Hence, it is essential to inspect and calibrate those instrument transformers at regular intervals. Each of these materials is suitable for certain applications. Voltage transformers are used around the clock throughout the energy grid, and their life span can reach up to 40 years. Two amran current transformers cts were tested to characterize the propensity of an open. These are conducted with the transformer completely disconnected from the line and load. Onsite tests on high voltage power transformers is of increasing interest as part of.
Khandait, swapnil kadaskar, girish thakare published on 20170314 download full article with reference data and citations. Voltage transformer testing job safety analysis sp0508c03. 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 reports. Voltage and current injection with variable frequency.
Is quite similar to that of the potential transformer in that there nsiderations to assist in. For this reason, the secondary of a current transformer should always be shorted before removing a relay. Transformer bushing cts should be tested using the current ratio test. Instrument transformer basic technical information and. Ct tap ratios can be verified by applying a voltage across the full ct winding a tap voltage ratio test. Stationary and mobile transformer transformer testing. Tap changer is operated by means of a handle on the cover or a hand wheel on top or on sidewall of the transformer. Distribution transformer testing power partners usa. The mrct provides a microprocessorcontrolled variable voltage and current. Commonly used core materials are air, soft iron, and steel. Transformer installation records assembly log indicating datestimes and weather conditions, people during entire process records of all inspections and testing ratio including phase angle and current, megger, excitation current and voltage, insulation power factor and capacitance of windings and bushings. The iron core inside the transformer is magnetized. Current transformer white paper the basics of current transformers ratio the ct ratio is the ratio of primary current input to secondary current output at full load. Real time monitoring of transformer using iot written by mrs.
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