In this book we have laid down important aspects on transformer. Ac voltage is preferable to dc voltage for transformer testing because ac voltage simulates the internal stress that the transformers face during operating conditions. Mainly two types of transformer are done by manufacturer before dispatching the transformer mainly 1 type test of transformer and 2 routine test. On theother hand, when j is large, then theuse of a detector of highimpedance may shift theload from transformer of higher. It is also done at site to ensure healthiness of a transformer that is to check loose connections, broken strands of conductor, high contact resistance in tap changers, high. It is carried out as a type test as well as routine test. A current transformer is similar to a electrical power transformer to some extent, but there are some difference in construction and operation principle. Transformers experience power loss due to load resistance, which you can test with an ohmmeter by touching the meters red and black pins to opposite ends of the transformers wiring. After the current transformers have been subjected to the dielectric type tests 3, 4 and 5 they shall be subjected to all the routine. The testing times have been greatly reduced using modern microprocessor based test equipment. Perform a polarity test of each current transformer page 12 4. Current transformer burdens are typically expressed in va.
Instrument transformer basic technical information and. For example, the potential transformer mentioned above having a rating of 480. Portable ct pt analyzertransformer testgfuve electronics. Circuits used in direct test of a current transformer by the. In this test we confirm the ct secondary connection. How to use an ohmmeter to test an ac transformer sciencing. Cts are required because standard current measuring devices are not configured to measure high current levels. Procedure for current transformer factory and site. The typical excitation current test data pattern for a threelegged core transformer is two similar current readings and one lower current reading. Back to the basics current transformer ct testing as test equipment becomes more sophisticated with better features and accuracy, we risk turning our field personnel into test set operators instead of skilled field service technicians.
Testing and protection of current transformer practical experiences. This information is required to insure the ct will perform under all circumstances. Portable precision current transformer testing ct pt analyzer. Back to the basics current transformer ct testing valence. Figure 5 shows the result of the curve fitting for core 1, considering the y axis to be the current and x axis to be the voltage, the following expression give the standard. Ct analyzer the number one in current transformer testing. Transformer winding resistance measurement is carried out to calculate the i 2 r losses and to calculate winding temperature at the end of a temperature rise test. Ieee standard requirements for instrument transformers ieee c57. C electrical power from one voltage to another voltage keeping the frequency same by. Ct analyzer current transformer testing, calibration and. The following sections of the ansineta standard for acceptance testing specifications for. Power transformer testing transformers may be tested using ac or dc voltage. The purpose of this standard work practice swp is to standardise and prescribe the method for testing current.
Pdf transformer is a static device which transforms a. Meggers range of current transformer test equipment allows you to construct an in depth test and maintenance programme to prevent problems before they occur. In this paper we will discuss how the cpc 100 of omicron is. Neta defines the standards by which electrical equipment is deemed safe and reliable. Pts step down high voltages to the voltage needed by the meter usually 120v occasionally 67v. It evolved from the simple gonogo verdict into a sophisticated segment within transformer manufacturing. Current transformers how to specify them schneider electric protection, control and monitoring electrical power management requires implementation of data processing units able to monitor networks or equipment and, as applicable, to initiate the appropriate actions. A current transformer is an instrument transformer, used along with measuring or protective devices, in which the secondary current is proportional to the primary current under normal conditions of operation and differs from it by an angle that is approximately zero. Efficient current transformer testing with omicron ct analyzer. Its secondary winding then provides a much reduced current which can be used for detecting overcurrent, undercurrent, peak current, or average current conditions. 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. Instrument transformers scale the large values of voltage or current to small.
Current transformers, or cts, are transformers used to step down the current level of highpower transmission systems to measure or monitor the current levels. Testing current transformers ratio vs applied burden cts installations can be fully verified in the field we can verify that the ratio is correct and constant as burden changes. Insulation resistance, ratio and polarity, excitation curve and winding resistance. This specification covers the design, manufacture, assembly, testing at the manufacturers. To confirm the physical condition and electrical characteristics of current transformer installed in the installation. Ieee standard requirements for instrument transformers. Test this by hooking up the secondary to its circuit and using your dmm to test the secondary lines. Before conducting a transformer winding resistance test, it is important to observe all safety warnings and take proper precautions. If the reading is above the amperage rating for the transformer, the circuit is drawing too much power. Specialized testing for ct continuous current capability.
Procedure for current transformer factory and site acceptance tests note. 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. A current transformer ct is an instrument transformer in which the secondary current is substantially proportional to primary current and differs in phase from it by ideally zero degree ct accuracy class or current transformer class. A current transformer ct is a type of transformer that is used to reduce or multiply an alternating current ac. The ctt5 burden test injects a current into the secondary loop to verify the integrity of the current circuit and to determine its impedance and va. As test equipment becomes more sophisticated with better features and accuracy, we risk turning our. Back to the basics current testing valence electrical. Ensure the ct is connected to system properly in all respect primary and secondary. Transformer bushing cts should be tested using the current ratio test method before the transformer has been completely assembled.
Current transformers current transformers cts provide a simple, inexpensive and yet accurate means of sensing current flow in power conductors. Common electrical tests on power transformers omicron. A distinction has to be made between a metering class and a protection class current transformer. Magnetization and primary injection test of current. 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. Cts should be tested before they are mounted on the transformer. Once you have completed the testing, you can also demagnetize the transformer. Transformer testing has developed considerably over the past years. If the cts are already mounted in the transformer, large highcapacity currenttesting leads can be. In some cases, cts may have to be tested by connecting test leads to both ends of an installed bushing. Standard for acceptance testing specifications for. Ensure that all equipment to be tested is properly grounded and treat all highvoltage power equipment as energized until proven otherwise by using the proper lockouttagout procedures. Basics, maintenance, and diagnostics xi contents continued page 9.
We also offer solutions for testing bushingtype current transformers for measurement deviations or phase faults. In addition some other tests are also carried out by the consumer at site before commissioning and also periodically. Ring core cts are available for measuring currents from 50 to 5000 amps, with windows power conductor opening size from 1 to 8 diameter. The basics of current transformers nk technologies. The ratio of an instrument transformer is the relationship of its primary rating to its secondary rating.
Equuipment for testing current transformers nvlpubsnistgov. Page 2 of 9 standard work practice sp0507 ver 5 ergon energy corporation limited abn 50 087 646 062. Current transformers iec 600446 requirements for protective current transformers for transient performance iec 618692. The amperage rating for your transformer fuse may be labeled on the transformer, but will also be. Use small jumper to short the ct secondary from ct box, the measurement will be gone at panel. The resistance of an alternating current ac transformer is held within the wires wound around its core. Current transformer basics and the current transformer. There are various test required on transformer to conform performance of transformer. Abb field engineering services instrument transformer. It produces a current in its secondary which is proportional to the current in its primary. Current transformer testing on site presentation calmet. The following tests are routinely conducted in the field on the transformer. Instrument transformers convert signal levels from dangerous high voltage or inconvenient high current, or current at high voltage to levels appropriate for metering.
Then to summarise, the current transformer, ct is a type of instrument transformer used to convert a primary current into a secondary current through a magnetic medium. With our testing system, you can use a single device to determine all of these parameters in an easy way. When the regulation began, the current was essentially constant in spite of the inductance of the windings and fluctuation of the battery voltage or lead resistance. Current transformers perform the following functions.
Current transformer testing swp check this is the latest process zone version before use. Alternative testing techniques for current transformers. The international electrical testing association neta is an accredited standards developer for the american national standards institute ansi. Section 7 of the ansineta standard for acceptance testing specifications for electrical power equipment and systems may be reproduced and used on a cut and paste basis for the particular type of equipment to be tested. Current transformers, along with voltage or potential transformers, are instrument transformers. Current transformer tester model ctt5 testing applications design features. Magnetization and primary injection test of current transformer for protective relaying jacob tsado 8 current transformers. Turnsratio test results should not deviate more than onehalf percent from either the adjacent coils or the calculated ratio. Saturation testing for a current transformer identifies the rated knee point against ieee or iec standards, the point at which the transformer is no longer able to output current in proportion to its specified ratio. The burden test is performed to verify that the ct is capable of supplying a known. Testing of power transformers seems like a similar experience. A test set operator connects the leads, pushes the buttons, and records the.
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