Impulse Tests of Insulators
- Impulse Voltage Withstand Test
- Impulse Flashover Test
1. Impulse Voltage Withstand Test
- The test setup is shown in Figure.
- The impulse generator is adjusted to produce a standard 1.2/50 impulse wave of peak value equal to the specified value of the impulse withstand voltage corrected for atmosphere conditions in accordance with I.S. Five impulse voltage waves are applied to the insulator.
- If there is no flashover or puncture, the insulator is considered to have passed the test.
- If during the application of these five waves puncture occurs or if there is more than one flashover, the insulator is considered to have failed to comply with the standard. If flashover of only one insulator occurs, a new series of ten impulse waves are applied.
- The insulator is considered to have passed the test if during new series of tests there is no flashover or puncture.
2. Impulse Flashover Test
- The procedure is almost similar to that of impulse voltage withstand test. The desired voltage to be applied is 50% of flashover impulse voltage.
- This is somewhat difficult to achieve due to practical limitations.
So the two sets of readings are taken for following condition.
Condition 1 : Flashover impulse voltage in the range of 40 % to 80 % of rated value.
Condition 2 : Flashover impulse voltage in the range of 20 % to 80 % of rated value.
For both conditions, 4 to 5 readings are taken. There should not be major damage to the insulation surface due to this test. i.e. if major damage is not there, the insulator has passed the test. Minor scratches, surface spots may be produced which are permitted.