Test connection w 1 synchronous generator 2 test transformer 3 current trans. Sfra testing on transformers electrical test equipment. 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 rather high. Transformer nameplate ratio, tnr ratio between the specific labelled linetoline voltage of a higher voltage winding to a. The transformer shall conform in all respects to highest standards of engineering, design, workmanship, this specification and the latest revisions of relevant standards at the time of. In addition to the above transformer testing methods, the power transformer also goes through some other tests, performed on it, before the actual commissioning of the transformer at the site. Testing of three phase power transformer ijireeice. Megger provides thoughtfully equipped transformer test instruments for routine screening needs. The following sections of the ansineta standard for acceptance testing specifications for. Instrument transformers for metering purposes must have a high degree of accuracy up to class 0. 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. Power failure or sudden power outage as a result of blown on the high voltage distribution fuses or consequent loss of a transformer cannot be overemphasized. Scribd is the worlds largest social reading and publishing site.
Standard for acceptance testing specifications for electrical. Sweep frequency response analysis test sfra test electrical4u. The latest sfra test sets make these techniques more accessible, more convenient and. Magnetization and primary injection test of current transformer for protective relaying jacob tsado 8 current transformers. The power transformer of rating 10 kva, 1 v440 v, 3phase, 50 hz, dyn11 has been specially developed inhouse for carrying out sfra testing by. Insulation power factor testing of power transformers. Routine tests and type tests of transformers electrical4u. Hipot test is typically used for acceptance testing or after transformer repair testing. What is the correct procedure for dvdf and hv test on. How to calculate efficiency of the transformer at a given load and power factor. Ratings, voltage ratio, tapping range, impedance and other technical parameters may be selected as per cbip publication no.
It is also known as iovtinduced over voltage test, it is one of the routine test of transformers usually performed to check in turn insulations of the windings. The transformer has been built to standard damage has not been sustained during transit or installation. Feb 18, 2014 the value of the test voltage between phases and between phase and earth is measured at the lv side on an accurate voltage transformer. Testing of power transformers seems like a similar experience. The test methods used by the authors for presenting the results are described.
The purchase, preparation, assembly, operation and maintenance of transformers represent a large expense to the power system. Hence, it is essential to inspect and calibrate those instrument transformers at regular intervals. Transformers are the most critical part of electrical transmission and distribution network, also when it is come to quality and continuity requirements on delivery of electrical energy. The electrical field tests recommended for routinely testing a transformer include. The following definitions are used in megger ttr test instruments. On distribution transformer this type of switch may also be used to change nameplate voltage andor configuration. According to 3 sfra method determines the transformer responses in a time or frequency area. Iec6007618 sfra of power transformers, typical test. In addition to that some transformer tests are also carried out at the consumer site before commissioning and also periodically in regular and emergency basis through out its service life. This guide is based on the operation of the n4l sfra45 sweep frequency response analyzer and will provide a. Transformer sweep frequency response analysis sfra by g m kennedy, a j mcgrail and j a lapworth, doble engineering, sweep frequency response analysis sfra is one of the most powerful diagnostic tools for assessing mechanical damage to a transformer winding.
The different tests conducted in a distribution transformer as per the standards are discussed below. Connection on cpc100 will be same as the shown figure. A typical excitation current test data pattern for a threelegged core is two similar current readings and on lower current reading. Transformer nameplate voltage, tnv labelled linetoline voltage for a winding defined on transformer template. Transformer testing commissioning, routine, diagnostic. Measure the voltage at the both primary and secondary termination at all the phases. When ac hipot tests are used for routine maintenance, the power transformer can be examined at. Type test and routine test of transformer electrical mastar. The procedure of the transformer ratio test is simple. To connect the ground reference cable and test leads and run sfra. The standard test suites are designed for individual samples to deliver a routine set of oil analysis at low cost. The ac hv test value should not surpass 75% of the factory test value. Iec6007618 sfra of power transformers, typical test sequences this application note will discuss typical transformer configurations and measurement sequences as specified in the iec6007618 international standard. Testing power transformers highvoltage transformers are some of the most important and expensive pieces of equipment required for operating a power system.
The above standard testing is offered in specific diagnostic suites designed to provide the maximum condition information on the transformers. Apply 3 phase supply voltage 415 v ac across the primary termination of the transformer. Because a test confirms what you know, if you can apply in real life what you have learned in a classroom, under strict, rigorous and controlled conditions. Sfra testing on transformers dismantling a power transformer to determine its condition is hardly ever a practical possibility. Interpretation of sweep frequency response analysis sfra.
Sweep frequency response analysis sfra is a method to evaluate the mechanical integrity of core, windings and clamping structures within power transformers by measuring their electrical transfer functions over a wide frequency range. The objectives of this experiment are to find the approximate per phase equivalent circuit parameters of a 3. Ltc because in order to change taps, the transformer has to be taken out of service or at least disconnected from the load. Sweep frequency response analysis test or in short sfra test can detect efficiently, displacement of transformer core, deformation and displacement of winding, faulty core grounds, collapse of partial winding, broken or loosen clamp connections, short circuited turns, open winding conditions etc. Unlike the tests described previously, in the present case nominal voltage is applied. Measurement of winding resistance iec 6007611 clause. Etc provides this testing as a service to our customers to ensure compatibility between the ballastlamp or driver and our dimming system. For example, unless there is reason to be concerned about winding deformation, a leakage reactance test is probably not necessary. Nov 17, 2019 sweep frequency response analysis test or in short sfra test can detect efficiently, displacement of transformer core, deformation and displacement of winding, faulty core grounds, collapse of partial winding, broken or loosen clamp connections, short circuited turns, open winding conditions etc. So for ensuring proper performance of electrical power transformer, voltage and turn ratio test of transformer one of the important tests. Condition monitoring of power transformer by using sfra test. Oil diagnostic suites for transformer oil diagnostics.
Sep 26, 2017 mainly two types of transformer testing are done at manufacturer premisestype test of transformer and routine test of transformer. Repeat the test for the other phases and the other secondary cores. Performance test of faulty distribution transformers along. The latest sfra test sets make these techniques more accessible, more convenient and more dependable that ever. 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. May 10, 20 so transformer ratio test is an essential type test of transformer. From which side of a large transformer, would you like to carry out s. By using the latest proven sfra test techniques, it is possible to accurately assess transformer condition without dismantling it. This test is very reliable for condition monitoring of physical condition of transformer windings. Field testing of a power transformer before putting into service 50mva. Power outages cause loss of income for power consumers and. Magnetization and primary injection test of current. Dismantling a power transformer to determine its condition is hardly ever a practical possibility.
Basics, maintenance, and diagnostics vii contents continued page 4. The preference is that all large power transformers 1 mva be tested with ttr test set. Apply the formula or plot the values in the graph to get the vector group. May 15, 2016 sfra stands for sweep frequency response analysis. This test also performed as a routine test of transformer. This study focuses on the temperature of transformer winding, voltage ratio across hvlv, asymmetrical flux distribution in the core, insulation resistance of paper. The power loss is also a very convenient number when checking the accuracy of measurements.
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