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. Current transformers play an important role in the monitoring and protection of electrical power systems. Ensure the ct is connected to system properly in all respect primary and secondary. Ct analyzer current transformer testing, calibration and. Testing facilities are required by some code of practice applications click here for more information. Current transformer testers vanguard instruments company.
Current transformer design guide an effective design of a ring type c. All of the ezct2kas test leads can be connected to the ct output terminals x1, x2, x3, x4 and x5, eliminating the need for lead switching during testing. The resistance in the secondary winding of the current. This test also performed as a routine test of transformer. May 10, 20 for confirming the specifications and performances of an electrical power transformer it has to go through a number of testing procedures.
It is a lightweight, rugged, userfriendly test set that performs basic and routine testing of cts and vts pts. Check for cracks in door current transformers, and that equipotential point of window type cts has been connected to the busbar. There are four typical types of current transformers. A system and method for testing an online current transformer is provided. Current transformer accuracy is specified by the standards ieee std c57. If a current transformer is not properly sized based upon secondary loop burden, it may result in a decrease in ct secondary current. Back to the basics current transformer testing ct 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. Portable ct pt analyzertransformer testgfuve electronics. Efficient current transformer testing with omicron ct analyzer.
Trax is a multifunction test system for transformer substation testing. Parameters of short circuit testthis is a big advantage of dpatt3bi that it can be usedfor transformer testing. Hence, it is essential to inspect and calibrate those instrument transformers at regular intervals. Transformer testing commissioning, routine, diagnostic. 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. The megger mrct is a light weight, robust, portable unit used to perform demagnetization, ratio, saturation, winding resistance, polarity, phase deviation, and insulation tests on current transformers. The procedure of the transformer ratio test is simple.
Instrument transformer theory and testing steve hudson, pe engineering manager 10737 lexington drive knoxville, tn 37932. This test is considered as one of the main test, its aimed to test. Ieee standard ratings for current and voltage transformers cts and vts. Metering accuracy cts are used where a high degree of accuracy is required from low. The ezct2ka can perform the current transformer ct excitation test, measure the ct winding resistance and ct current ratio automatically. Ct test and current transformer test procedure with testing. In this book we have laid down important aspects on transformer. Transformer on no load condition its phasor diagram.
Transformer testing type tests and routine tests of. Current transformer tester model ctt5 testing applications design features. Connect a primary injection kit or for cts up to 100a a secondary injection kit can be used. Transformers are an electrical component that transmit electrical energy between at least two circuits. The value of full load current for transformers of different ratings is shown in the following table. Making a wellinformed choice in equipment for transformer testing is an important step towards ultimately improving transformer life management decisions. Introducing the ctvt45 instrument transformer test set, a multifunction tester designed to test all types of current transformers and voltage transformers. A load impedance is measured of an internal instrumentation associated with the current transformer. The test and assessment of transformers is a complicated task. On pressing button 3 of the keypad of dpatt3bi, wpf page appears on the lcd display showing copper losses. The current transformer is solely assessed through its external behavior without considering what is happening inside. A read is counted each time someone views a publication summary such as the title, abstract, and list of authors, clicks on a figure, or views or downloads the fulltext.
Traditional current transformer testing follows a blackbox approach. Single connection permits all taps on the current transformer to be tested automatically, without operator intervention. They dictate that testing facilities should be available and close to the meter. The current transformer includes a primary winding and a secondary winding. The primary winding can consist merely of the primary current conductor passing once through an aperture in the current transformer core window or bartype, or it may consist of two or more turns wound on the core together with the secondary winding wound type. It evolved from the simple gonogo verdict into a sophisticated segment within transformer manufacturing. Current transformers used for protective relaying also have accuracy requirements at overload currents in excess of the normal rating to ensure accurate performance of relays during system faults. For outdoor current transformers, the following step is need as per above figure. A load is disconnected from the current transformer. Apprentice electrical technician test ett about the test there are 40 questions with a maximum time limit of three hours.
Check for level, colour of oil in the sight glass for outdoor current transformers. This amounts to a rigorous examination of the transformer intended to. Instrument transformers for metering purposes must have a high degree of accuracy up to class 0. This ms excel spreadsheet is actually detailed instruction for each procedure necessary for correct testing of power transformer. 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. Sverker 900 measuring instruments pdf manual download. Ct analyzer the number one in current transformer testing. Gf1061 portable ct pt analyzer is mainly used for field or lab testing, it can finish the measurements m and protection p class ct, pt and typ class ct. Gf106tportable ct pt analyzer639km related products. Test current is applied through both the a and bphase secondary leads. Transformer manufacturers perform two main types of transformer testing type test of transformer and routine. In reality, however, it is not possible to neglect the excitation. Heres a summary of the current transformer testing paper.
Instrument transformer theory and testing steve hudson, pe engineering manager 10737 lexington drive. The current or series transformer has a primary coil of one or more turns of thick wire connected in series with the line whose current is to be measured. Nov 26, 2010 traditional current transformer testing follows a blackbox approach. Presentation on current transformers submitted by roopal pancholi b. The secondary consists of a large number of turns of fine wire. 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. View and download megger sverker 900 application note online. The transformer testing can be done in different types. Short ct links then isolate the external wiring to confirm ct circuit will not be opened. The mrct automatically calculates ratio errors, saturation curves, and knee points. Testing of power transformers seems like a similar experience. Some tests are done at a transformer manufacturer premises before delivering the transformer. An operating current continues to flow through the primary winding during testing of the current transformer.
A primary part of commissioning a transformer involves testing it after its installation in the field. Selecting current transformers janitza electronics. So transformer ratio test is an essential type test of transformer. Portable precision current transformer testing ct pt analyzer. The test code covers measurement and calculation of ratio and phase angle, demagnetization, impedance and excitation measurements, polarity determination, resistance measurements, shorttime characteristics, temperature rise tests, dielectric tests, and measurement of opencircuit voltage of current transformers. A current is not circulated through the primary winding. Transformer on no load condition when the transformer is operating at no load, the secondary winding is opencircuited, which means there is no load on the secondary side of the transformer and, therefore, current in the secondary will be zero. Us6680616b2 inservice testing of current transformers. This information is required to insure the ct will perform under all circumstances. A method for testing electronic instrument transformers is described, including electronic voltage and current transformers evts, ects with both analog and digital outputs. Tech electrical, iii year, v semester k72 submitted to mr. Trax multifunction transformer and substation test system.
We always recommend current transformers with the same precision class for the umg measuring devices. I wrote an article for the neta world magazine in 2004 that covers several different manual techniques for current transformer testing that should help even the most experienced technicians. This ct tester is precisionmade, just like all of the raytech products you already know. Use small jumper to short the ct secondary from ct box, the measurement will be gone at panel. 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.
The ezct2ka can perform the current transformer ct excitation test, measure the ct winding resistance and ct currentratio automatically. The test system replaces numerous individual testing devices which makes testing with trax a time saving and cost effective alternative to conventional measurements using separate instruments. Current transformer testers vanguard instruments company, inc. The testing device consists of a precision voltage transformer pvt, precision current transformer pct, data acquisition boards daq1 and daq2, synchronous sampling pulse circuit spc and computer pc. When installing telecom or computer systems close to heavy current equipment or traction power supplies careful thought has tobe given to the possibility of overvoltages or interference voltages that could be caused by power lines or system frequency phenomena. Capable of performing saturation, ratio, polarity, winding resistance, and insulation tests on current transformers, the mvct can also be used for testing metering and protection class voltagepotential transformers. Electronic voltage and current transformers testing device. The instrument current transformers supply, and isolate, the secondary relays, meters and other instruments, providing the suitable and manageable secondary quantities which are proportional to those in the primary. In this test we confirm the ct secondary connection. Magnetisation current and coreloss current in transformers, 1072016. On theother hand, when j is large, then theuse of a detector of highimpedance may shift theload from transformer of higher. Apprentice electrical technician test ett preparation guide. Supplier of test equipment to the electric utility industry.
To confirm the physical condition and electrical characteristics of current transformer installed in the installation. Circle the statement below where the secondary ratio current. Current transformer tester model ctt5 testing applications design features technologies phenix r gis switchgear portable transformer. Power transformers application guide reference number iec 600768. Routine tests and type tests of transformers electrical4u. The megger mvct test set is a lightweight, robust, portable unit capable of testing both current and voltage transformers. At less than 20 lb 10kg the mvct is a highly portable unit that also offers accuracy in testing. The block diagrams of testing evts and ects are shown in figures 1 and and2, 2, respectively. So for ensuring proper performance of electrical power transformer, voltage and turn ratio test of transformer one of the important tests. The current transformer is solely assessed through its external behavior without.
Test blocks are used during the installation of current transformer andor voltage transformer operated meters. Transformer testing has developed considerably over the past years. Current transformers testing and commissioning guidelines. Abb field engineering services instrument transformer onsite testing.
Current transformers are defined by accuracy classes depending on the application. The need for a comprehensive current transformer testing regime is evident when the alternative is considered. A fault leading to an open secondary could cause the primary current to overwhelm the insulation, causing the winding to short circuit. Oct 08, 2016 current transformer they generally used to step down current in a very predictable fashion with respect to current and phase. Burden testing is important to verify that ct is supplying current to a circuit that does not exceed its burden rating. In order to reduce electrical failures, mechanical failures, winding deformation, thermal failures and insulation breakdowns of a transformer, the transformer testing should be done. For all ct loops, each loop must have only one earth point, otherwise secondary current will be divided. Nov 15, 2019 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 which is approximately zero. In order to promote public education and public safety, equal justice for all, a better informed citizenry, the rule of law, world trade and world peace, this legal document is hereby made available on a noncommercial basis, as it is the right of all humans to know and speak the laws that govern them.
891 600 750 786 108 33 646 1041 69 642 1279 1382 198 515 570 757 1195 671 85 36 1420 592 774 1210 206 897 678 18 753 290 253