Transformer Testing Procedure Pdf
Thetransformerhumshould be observed for any abnormality. Magnetic balance test of transformer is conducted only on three-phase transformers to check the imbalance in the magnetic circuit. Ensure that test specimen is isolated from other equipments. The one of the winding is short circuited and voltage is applied to other winding. ThisvoltagedropUmaybecausedeitherinthetestobject internalpartialdischargeinthebushingorinthe transformerinsulatingsystem orinthetestcircuit externalpartialdischarge.
Knowledgeoftheinsulationresistanceisofvalue whenevaluatingtheconditionofthetransformerinsulation. For confirming the specifications and performances of an electrical power transformer it has to go through a number of testing procedures. In case tertiary is also connected, ensure the isolation of thesamepriortocommencementoftesting The measurement is performed in single phase mode. Materials Testing Equipment for Civil Engineering. The characteristic behavior of the insulating system of the transformerundertestmustbedefinedbyaspecialcalibratingprocedure.
The general pattern is two similar high readings on the outer phases and one lower reading on the center phase, pdf programm in case of three phase transformers. ConventionalScheringBridge Figureshowsthemeasuringcircuitfortheinsulationpowerfactormeasurementofatwowinding transformerusingaconventionalScheringbridge.
Dielectric test of a transformer is one kind of insulation test. Anymeasurementcomparisonsshouldalwaysbecarried outatthesamevoltage. This test also performed as a routine test of transformer.
Type Test of Transformer
The measuring impedance Zm can either be connected in series with coupling capacitor Ck or with the test objectcapacitanceCt. Zerovoltageorverynegligiblevoltagewithhigherexcitationcurrentinducedintheothertwowindingsshould beinvestigated. The graphshowspermissiblevoltageontheshieldwithoutgivingrisetocorona. Magnetising current readings may be effected by residual magnetism in the core. So transformer ratio test is an essential type test of transformer.
Magnetizing current test of transformer is performed to locate defects in the magnetic core structure, shifting of windings, failure in between turn insulation or problem in tap changers. ProvidingabasisforanindirectmethodtoestablishwindingtemperatureandTemperaturerise withinawinding. Measuringcircuitforthemeasurementofpowerfactorandwinding Capacitances. Thevoltageinducedindifferentphasesoftransformerinrespecttoneutralterminalsgivenin thetablebelow.
All the transformers with the same vector ground have same phase sequence and phase divergence between primary and secondary. The voltage induced in different phases of a transformer in respect to neutral terminals given in the table below. The voltage induced in different phases depends upon the respective position of the limb in the core.
So we have to choose a transformer suitable for parallel operation whose phase sequence and phase divergence are same. This test is performed to locate defect in magnetic core structure, shifting of windings, failures in turn insulationorproblemintapchangers.
TRANSFORMER testing manual final.pdf
The two wave types have different propagation velocities. Oil would be a perfect medium for the propagation of acoustic waves, with no attenuation or dispersion occurring. It is unnecessary to perform insulation resistance test of transformer per phase wise in three-phase transformer. Insulation resistance test of transformer is essential type test.
Routine tests of transformer is mainly for confirming the operational performance of the individual unit in a production lot. So for ensuring proper performance of electrical power transformer, voltage and turn ratio test of transformer one of the important tests.
For singlephase transformers the polarity can be either additive or subtractive. Direct current or alternating currentcanbeusedforthischeck. Therefore, transformerundertestmaybedemagnetisedbeforecommencementofmagnetizingcurrenttest.
POWE ER TRA ANSFOR RMER TESTIN NG
The magnitude of measurable apparent charge qm in pC must be defined by the calibrating procedure for eachtestcircuit. Theinitialmagnetising current at the time of switching will be very high, depending upon the particular moment in the cycle. Normalizedcoordinates Therearethreedifferentconditionsforthecalculatedapparentvelocityvapp. This method is theoretically only applicable for direct waves i. Another possibility is hidden damage totheinsulationcausedbyprecedingtests.
The acceptance criteria for the results of exciting current measurement should be based on the comparison with the previous site test results or factory test results. Temperature rise test of transformer is included in type test of transformer. Typicalnoisesources seetextforexplanation.
Keepthetestresultsasa baselinerecordtocomparewithfuturetests. Magnetic Balance and Magnetising Excitation Current test - a effective diagnostic tool. These tests are done mainly in a prototype unit not in all manufactured units in a lot. The identical results confirm no damage due to transportation. All such exposure time should be recorded in a log sheet to decide the oil processing drying and oil filling of transformer.
After that it may be checked for gas collection. Only if equally large impulses occur on the positive and the negative half cycles a conversion can be made.
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