Transformer bushing cts should be tested using the current ratio test. Precautions should be taken when making this test on current transformers to. Current transformer with winding or secondary wiring. The international electrical testing association neta is an accredited standards developer for the american national standards institute ansi. The importance of instrument transformer tests is often underestimated. Operate the network enterprise process as 12431982 voltage transformers for measurement and protection. There are three basic styles used to transformer system voltages to control voltages. Excitation hysteresis curve corresponding to the internal magnetization processes of the magnetic core.
Perform insulationresistance tests of the current transformer and. Also you should make tests at about the same temperature, or correct them to the same temperature. A record of the relative humidity near the equipment at the time of the test is also helpful. In this book we have laid down important aspects on transformer testing in order to enhance the understanding of the testing procedures and its outcome. Abb field engineering services instrument transformer. The flux flows through the core and induces a current on the secondary winding.
If no evidence of distress or insulation failure is observed by the. Current transformers play an important role in the monitoring and protection of electrical power systems. Testing and protection of current transformer practical experiences. The name instrument transformer is a general classification applied to current and. Transformer testing has developed considerably over the past years. Potential transformers pts or voltage transformers vts pts or vts are the most common device used.
Neta developed specifications for the acceptance of new electrical apparatus prior to energization and for the maintenance of existing apparatus to determine its suitability to remain in service. Ac dielectric withstand test voltage shall not exceed 65 percent of factory test voltage for oneminute duration. Ensure the ct is connected to system properly in all respect primary and secondary. Ct ratio with burden testing secondary connection is made through the test switch same connection that is used for the rest of the site testing.
As a current passes through the primary winding it induces a magnetic flux in the steel core. Inductive current and voltage transformers ct and vt and capacitive voltage. For units with solidstate components that cannot tolerate the applied voltage, follow manufacturers recommendations. Cts are instrument transformers used for converting primary current into a reduced secondary current for use with meters, relays, control equipment and other instruments. Ratio testing with applied burden is the most accurate and complete approach for testing at ct in service. So transformer ratio test is an essential type test of transformer. Cts are instrument transformers used for converting primary current into a reduced secondary current for use with meters, relays, control equipment and other instruments the importance of instrument transformer tests is often underestimated. Equuipment for testing current transformers nvlpubsnistgov. Back to the basics current transformer ct testing valence. The complete guide to electrical insulation testing. Standard for acceptance testing specifications for. Instrument transformer theory and testing steve hudson, pe engineering manager 10737 lexington drive knoxville, tn 37932 phone. Instrument transformers can be simplified with basic magnetic circuits.
To confirm the physical condition and electrical characteristics of current transformer installed in the installation. Some transformer tests are carried out for confirming the basic design expectation of that transformer. Increase the voltage slowly to the test voltage and let stand for one minute. The purpose of this standard work practice swp is to standardise and prescribe the method for testing current.
So for ensuring proper performance of electrical power transformer, voltage and turn ratio test of transformer one of the important tests. Inspection and test procedures for instrument transformers. The importance of current transformer tests is often underestimated. Electrical testing methods on instrument transformers. Testing and commissioning instrumenttransformers free download as powerpoint presentation. Scribd is the worlds largest social reading and publishing site. Perform insulationresistance test of each current transformer and its secondary wiring with respect to ground at volts dc for one minute. In this book we have laid down important aspects on transformer. This test also performed as a routine test of transformer.
Neta is the leading source of specifications, procedures, testing, and requirements. Dc dielectric withstand test voltage shall not exceed 100 percent of the ac rms test voltage specified in ansi c57. Testing of power transformers seems like a similar experience. The equipment and test procedure developed at the bureau of standards for measuring the ratio and phase angle of current transformers up to currents of. Some tests and procedures may be performed by specialists during the assembly. Connect the megohmmeter to one terminal of the h side of the pt and the negative to one side of the x side and to ground. These devices use standard transformer theory with 23 windings one primary with one or two secondary windings with a magnetic connection via an iron core. These tests are done mainly in a prototype unit not in all manufactured units in a lot.
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