The following tests are routinely conducted in the field on the transformer. Prior to testing, short the primary winding of the ct under test by connecting h1 and h2, then short the secondary winding of the ct under test by connecting x1 and x2x5. During normal operation, a current transformer ct transforms higher current into a more. 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. It is typically used for test specimen that have small capacitance and as a result the power factor tan delta of the test circuit is. This ms excel spreadsheet is actually detailed instruction for each procedure necessary for correct testing of power transformer. In this book we have laid down important aspects on transformer testing in order to enhance the understanding of the testing procedures. So transformer ratio test is an essential type test of transformer. It evolved from the simple gonogo verdict into a sophisticated segment within transformer manufacturing. If available, take down the ratings of the transformer.
This connection has all of the interfaces required to connect current and voltage inputs from a three phase transformer into the mto300 unit. Back to the basics current testing valence electrical. Testing potential transformers relay testing training. 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. The first neta maintenance testing specifications for electrical power equipment and systems was published in 1975. Power transformer testing fat test inspection for industry. Procedure of polarity test of transformer connect the circuit as shown above with a voltmeter v a across primary winding and another voltmeter v b across the secondary winding. There are four typical types of current transformers. The primary winding can consist merely of the primary current conductor passing once through an aperture in the current transformer. Efficient current transformer testing with omicron ct analyzer. Introduction the procedures stated in this document cover the activities in preliminary tests and inspections, functional performance tests. Measurement shall be carried out with direct current dc by the voltage drop method or the bridge method as specified in the manufacturer approved power transformer testing procedure. The testing times have been greatly reduced using modern microprocessor based test.
Electrical testing methods on instrument transformers. 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. The following sections of the ansineta standard for acceptance testing specifications for. Transformers regulate the voltage in circuits, but in.
The importance of current transformer tests is often underestimated. Procedure for current transformer factory and site acceptance tests note. This guide provides a general overview of the regulatory framework and approval process and explores the specific manufacturing responsibilities and test procedures associated with electrical safety testing. Our test systems provide highprecision, automatic testing and assessment of current transformers to iec 600441, iec 600446, iec 618692, ieee c57. Primary interface connection from the transformer to the unit. 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. Since 1989, revised editions of the maintenance testing specifications have been. Abb field engineering services instrument transformer. Standard for acceptance testing specifications for. 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. The basics of current transformers nk technologies. A fault leading to an open secondary could cause the primary current.
A test set operator connects the leads, pushes the buttons, and records the. Knee point voltage and magnetization curve have to be tested by using current transformer test kit mct. The complete guide to electrical insulation testing. This test also performed as a routine test of transformer. 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. You can repeat the procedure above for each tap of a.
Optional measure the resistance of each winding at the designated tap position. Excitation hysteresis curve corresponding to the internal magnetization processes of the magnetic core. Magnetization and primary injection test of current. Testing and commissioning procedure for electrical installation 1. Measure core insulation resistance at 500 volts dc if the core is insulated and if the core ground strap is removable. Thepoten tialcircuitofthewattmetermaynowbeusedasavoltmeterto. Testing and commissioning requirements for switchgear. The following sections of the ansineta standard for acceptance testing. 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 performed by means of direct voltage dc, reduce the test.
Equuipment for testing current transformers nvlpubsnistgov. Before proceding with transformer measurements the test engineer will become familiar with the safety rules of section 2. Raise the conductor to the specified maximum test voltage and hold for 15 minutes. Perform insulationresistance tests of the current transformer and. The current transformer is solely assessed through its external behavior without considering what is happening. Magnetization and primary injection test of current transformer for protective relaying jacob tsado 8 current transformers. The voltage ratio shall be measured on each tapping and verified aginst manufacturer approved power transformer testing procedure.
Figure 5 shows the result of the curve fitting for core 1, considering the y axis to be the current. 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. Testing and protection of current transformer practical experiences. Ct analyzer the number one in current transformer testing. A distinction has to be made between a metering class and a protection class current transformer. After the current transformers have been subjected to the dielectric type tests 3, 4 and 5 they shall be subjected to all the routine tests.
Meggers range of current transformer test equipment allows you to construct an in depth test and maintenance programme to prevent problems before they occur. C electrical power from one voltage to another voltage keeping the frequency same by electromagnetic induction discover the worlds research 17. Brooks testingpotentialtransformers 421 needstobemeasuredwithonlymoderateaccuracy. Procedure for current transformer factory and site. D r a f t doble engineering company 85 walnut street watertown, massachusetts 024724037 usa pn 5000397 72a2244 rev. A routine series of diagnostics and testing for your current transformer should include ct saturation testing. The purpose of this standard work practice swp is to standardise and prescribe the method for testing current. Inductive current and voltage transformers ct and vt and capacitive voltage.
Standard for testing specifications electrical power. 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. Transformer testing has developed considerably over the past years. The current transformer is solely assessed through its external behavior. Power transformer testing transformers may be tested using ac or dc voltage. Traditional current transformer testing follows a blackbox approach. Back to the basics current transformer ct testing valence. Following is an approximate sequence for transformer testing. On theother hand, when j is large, then theuse of a detector of highimpedance may shift theload from transformer of higher. So for ensuring proper performance of electrical power transformer, voltage and turn ratio test of transformer one of the important tests. Instruction manual for transformer ohmmeter dc winding. The need for a comprehensive current transformer testing regime is evident when the alternative is considered.
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