HIGH VOLTAGE TESTS OF ELECTRICAL APPARATUS 1Type Test To Check The Design FeaturesRoutine Test To Check The Quality Of The Individual Test Piece.High Voltage Tests Include(i) Power frequency tests(ii) Impulse tests
TESTS OF INSULATORS2POWER FREQUENCY TESTS(a)Dry and wet flashover tests:AC voltage of power frequency is applied across the insulator and increased at a uniform rate of 2% per second of 75%of their estimated test voltage.If the test is conducted under normal conditions without any rain –dry flashover test.If the test is conducted under normal conditions of rain –wet flashover test(b) Dry and wet withstand tests(one minute)The test piece should withstand the specified voltage which is applied under dry or wet conditions.
3Impulse withstand voltage test:If the test object has withstood the subsequent applications of standard impulse voltage then it is passed the testImpulse flashover test:The average value between 40% and 60% failure is taken, then the insulator surface should not be damaged.Pollution Testing:Pollution causes corrosion ,deterioration of the material, partial discharges and radio interference. Salt fog test is done.IMPULSE TESTS ON INSULATORS
TESTING OF BUSHINGS4Power frequency tests(a ) Power Factor-Voltage Test:Set up as in service or immersed in oil.Conductor to HV and tank to earth.Voltage is applied up to the line value in increasing steps and then reduced.The capacitance and power factor are recorded in each step.(b) Internal or Partial discharge Test:To find the deterioration or failure due to internal dischargesConducted using partial discharge arrangementsPerformance is observed from voltage Vs discharge magnitude.It is a routine test.(c ) Momentary Withstand Test at Power frequencyBased on IS:2009The bushing has to withstand the applied test voltage without flashover or puncture for 30 sec.
5(d) One Minute withstand Test at Power FrequencyMost common & routine testTest is carried in dry &wet for one minute.In wet test, rain arrangement is mounted as in service. Properly designed bushing should withstand without flashover for one minute.(e) Visible Discharge Test at Power FrequencyConducted based on IS:2009Conducted to determine radio interference during serviceConducted in dark roomShould not be any visible discharges other than arcing horns/ guard rings.TESTING OF BUSHINGS
6TESTING OF BUSHINGSImpulse voltage tests:Full wave Withstand TestThe bushing is tested for either polarity voltagesFive consecutive full wave is appliedIf two of them flashed over, then 10 additional applications are done.If the test object has withstood the subsequent applications of standard impulse voltage then it is passed the test.