Testing power transformers high voltage transformers are some of the most important and expensive pieces of equipment required for operating a power system. 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. We just apply three phase 415 v supply to hv winding, with keeping lv winding open. Testing potential transformers relay testing training. Making a wellinformed choice in equipment for transformer testing is an important step towards ultimately improving transformer life management decisions. Contract specific procedure for testing of electrical equipment and 2kv ohl. The test and assessment of transformers is a complicated task. Full load current is applied on the primary side of thetransformer. The testing facilities at xihari also include an extension environmental laboratory. In addition to detecting problems associated with high resistance contacts and connectors, the megger winding tester will also detect open circuits dropout test. Electrical routine testing of high voltage bushings. Medium and high voltage eis transformer testing with ieee.
The dielectric voltagewithstand test is commonly known as the hipot test. The primary and secondary voltages are measured to determine the ratio v2v1. Alok pandey assistant professor assistant professor department of electrical department of electrical engineering engineering a seminar on high voltage testing of electrical transformer presented by hari shankar singh. Highvoltage transformers are some of the most important and expensive pieces of. Definitions, general requirement, generation and measurement, test procedure, methods of evaluation, uncertainty in tests and measurement. To test the insulation integrity you will need a megohmmeter or hipot rated to produce the specified maximum test voltage. Testing of hv cables supplementary information page 1 of 24 reference sp0407r02 ver 2 ergon energy corporation limited abn 50 087 646 062 1. We repeat the test for all tap position separately. As 12431982 voltage transformers for measurement and. The purchase, preparation, assembly, operation and maintenance of transformers represent a large expense to the power system. This 12 min video will help you to understand the applicable standard, standard procedure, purpose of. A variable ac source is applied on the primary side. Some utilities have started doing onsite high voltage testing using mobile test systems, and have reported positive results 1.
Eltek labs conducts low, medium and high voltage eis transformer testing. As the pt secondary is normally grounded through an internal jumper, an external switch is often used to isolate the pt from ground during testing. It is typical the use of high voltage testing on transformers to confirm performance. Threeormorewinding transformers will have winding designation h, x, y and z, where h is the highvoltage winding or, the highest kvarated winding in case windings have the same. The capacitors are connected between the system voltage and the polarity of a pt. Before conducting a transformer winding resistance test, it is important to observe all safety warnings and take proper precautions. 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. When ac hipot tests are used for routine maintenance, the power transformer can be examined at rated voltage for 3 min instead of testing at 65% of factory test voltage. The secondary winding usually low voltage side of thetransformer is short circuited. The figure below shows the typical cascading connection of two transformers. During the test cables are subjected to a test voltage significantly higher than what they experience during normal operating conditions. Testing power transformers high voltage transformers are some of the most important and expensive pieces of equipment required for operating a power. Power transformer testing procedures and schemes photo credit. It must be pointed out that a single measurement on a transformer typically.
Testing circuit and procedures are important to follow as per manual to avoid any. Pdf transformer testing type test and routine test of. Watch our video about medium and high voltage eis transformer testing to arrange testing of transformers, request a quote online now or call 6369495835. Compare bolted connection resistances to values of similar connections. Optional perform an applied voltage test on all high and lowvoltage windingstoground. Check that all parts of the transformer are properly assembled and tight. Oil dielectric ac test sets provide replicable, accurate measurement of breakdown voltage of insulating oils used in electrical equipment. Introduction this reference is intended to give a basic overview of insulating materials that can be used during high voltage withstand testing, in particular cable testing. High voltage test is done by applying 80% of factorytested voltage. Designed to verify that the insulation of a product is adequate enough to withstand high voltage. It is carried out as a type test as well as routine test. We measure the induced voltages at hv and lv terminals of the transformer to find out actual voltage ratio of the transformer. The values associated with the testing methods shall be in accordance with the applicable table 100.
Check of phase displacement the polarity of singlephase transformers and connection symbol of threephase transformers shall be checked in each winding. This test procedure covers the general high voltage tests required for the high voltage, high power alternating current generator described as one of the selected power sources in u. Optional perform an applied voltage test on all high. Cvts are often used in high voltage 115kv and higher applications and use a series of capacitors as a voltage divider. Hence, it demands special consideration during routine maintenance. By means of cascading, the size of the transformer and the insulation bushing. Current that starts out high and drops after the insulation has been charged to full voltage much like water flow in a garden hose when you first turn on the spigot. Past 500 kv, it is no longer economical to use a single transformer the size is much too big. Power transformer testing procedures and schemes eep. Some tests and procedures may be performed by specialists during the. Use the following test procedure for pt insulation tests.
Hipot test is the most common type of electrical safety test. For doing r phase the other phases are shorted and earthed. High voltage testing 149 the high voltage is applied across the device under test by means of a transformer. Very low frequency vlf withstand testing is the application of an ac sinusoidal waveform, generally at 0. This test is conducted on the high voltage side hv sideof the transformer. Check nameplate ratings and hv, lv terminal markings. High voltage onsite power transformer testing ee publishers. Many of the details of a complete and effective testing procedure can be obtained from this source.
Insulation resistance tester, microohmmeter, high voltage test. If a very high voltage is required, the transformer is usually build up in stages by cascading. Performed by stressing the insulation of the product far beyond what it would encounter during normal use. The test methods of the evaluation of electrical insulation systems eis are developed mainly by two organizations. While doing the hv test the steps to be followed are as below. 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.
The ac hv test value should not surpass 75% of the factory test value. The amperage rating for your transformer fuse may be labeled on the transformer. Electrical substations can also be divided into public and. Absorption current also an initially high current which then drops for reasons discussed under the section timeresistance method. Instrument transformer theory and testing steve hudson, pe. As viewed from the highvoltage side, h 1 bushing terminal will be located on the right. The transformer must be deenergized before this procedure, unless it. A calibration service for voltage transformers and high. The core losses are very small because applied voltage isonly few percentages of nominal voltage and hence can. General inspection mechanical checks general visual inspection and compliance with the drawings and manuals. In these situations where more than 500 kv is required, two units are cascaded in series to produce the required voltage.
Ac hv test value should not surpass 75% of the factory test value. If the display passes, disconnect the hipot tester. If the reading is above the amperage rating for the transformer, the circuit is drawing too much power. The voltage ratio shall be measured on each tapping and verified aginst manufacturer approved power transformer testing procedure. Testing of high voltage cables manual horizon power. Test this by hooking up the secondary to its circuit and using your dmm to test the secondary lines. High voltage testing requires larger power sources and on site generation and transformer equipment to produce the power and voltages required. Lv transformer electrical substation consists, therefore, of the set of devices dedicated to the transformation of the voltage supplied by the distribution network at medium voltage e. The procedure of the transformer ratio test is simple. These lightweight, rugged units are designed for field and laboratory use the dts series provides repeatable and accurate measurements of the breakdown voltage of insulating oils used in electrical equipment. The main high voltage tests are included in type and routine tests made by the manufacturer in the factory to meet the required standards, quality and reliability. Air force technical document afapltr822057, volume 2, high voltage testing. H is the higher voltagerated winding and x is the lower voltage winding.
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