Testing of Insulator


Testing of Insulator.

Insulator is generally used in electrical power transmission system to isolate  power conductor from the pole.It is prevent linkage current from conductor to ground.Before using the insulator some criteria are need to consider. 1.Mechanical strength, 2.high electrical resistance, 3. high dielectric strength.

There are various type of insulator,
1. Pin type
2. Suspension type
3. Sheckal type
4. String type

For the testing of insulator various electrical test to be performed are below,

  1. Impulse withstand test.
  2. 50% dry impulse flash over test.
  3. Wet flash over (one minute rain test).
  4. Dry flash over (one minute dry test).
  • Dry flash over (one minute dry test) :-

    For this test power frequency voltage is given to insulator by using cascade transformer. We can say for carry out this test. The test object is subjected to power frequency voltage and under the dry condition of sample. The power voltage is increased up to the specific voltage rating of insulator plate. This rating of voltage is maintain for one minute. After that one minute again the voltage is increase until the flash over occur. This process is repeat three to five times. Average flash over voltage is calculated of that five flash over. The avg voltage is must not be less then specific power frequency voltage.

  • Wet flash over test(one minute rain test) : –

    For the carry out this test artificial rain is need to created and its falls on the insulator. The test voltage is applied to insulator for one minute and rain is allow to falls on the insulator. Voltage is increase until flash over occur. After the few second again voltage is applied. Do same for 3 to 5 times and calculate the average flash over voltage. The avg voltage is must not be less then specific wet flash over voltage. water used to rain having some properties ate following,

testing of insulator

1. Conductivity of water is 100 micro semen
2. Direction of falling water is 45° vertical
3. Temperature of water is 15°c
4. Precipitation rate is 3 ± 10 % mm/min.

  • Impulse flash over test :-

    For performing this test insulator must be need to clean and dry. Impulse voltage generator is used to given impulse voltage to insulator. Impulse voltage which is characterized by 1/50 micro-sec, is applied. the amplitude of impulse wave is cause 50% of flash over. The test insulator must not be damage. Impulse voltage magnitude is not less then the 50% flash over. Which is given to the specified rating plate.

testing of insulator

  • Impulse Withstand Test :-

    It is main consideration is insulator is withstand against particular rating of impulse voltage. to performed this test standard impulse of 1/50 micro-sec is given to object. Whose value is equal to specific magnitude of rating plate. four to five times repeat this process. If during this process insulator may not damage or punctuated then it test is ok. Is there are two flash over occur from five times then insulator test is failed.

If any query or suggestion about Testing of Insulator please comment below or Email on sohal@electricalidea.com.



  1. You have used words like ‘impulse’ & ‘flash over’. Please explain these words as I’m unable to figure out what these are . Rest it was very informative and good. Can you please make this type of notes on 3phase Induction Motor.

    • impulse means huge. in this case Impulse testing systems are designed to generate impulse voltages that simulate lightning strokes and switching surges. flash over means when huge amount of voltage and current given to the insulator one saturation limit is there. when voltage and current cross that saturation limit the insulator burst and flash over occurs. that saturation limit is called withstand capacity.


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