Testing of Insulator

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Testing of Insulator :


Electrical insulators are tested to avoid unwanted insulator failure, the electrical insulator must undergo the following tests: 
1) Flashover tests of insulator
2) Performance tests
3) Routine tests

 Flashover test are mainly of three types :-

(i) Power frequency dry Flashover Test of insulator :  Here insulator to be tested is mounted in a practical manner as it is used on poles  and Variable power frequeny voltage source are connected to the insulator. Applied voltage is gradually raised upto minimum flashover voltage. This voltage is maintained for one minute and observe that there should not be any flashover or puncture occurred. It should be capable to sustain at minimum specified voltage for one  minute.

(ii) Power frequency Wet Flashover Test / Rain Test of Insulator : Here Again the practical condition of insulator is  developed with applied variable power frequency voltage source. After that we create artificial raining condition by spraying water on it. Now applied voltage is gradually increased up to the specified minimum power frequency voltage value and observe for one minute. It should not puncture and sustain without any flashover.

(iii) Power Frequency Flashover voltage test of Insulator : Insulator to be tested is mounted in a practical manner as it is used on poles  and applied voltage is gradually increased but voltage is raised till surrounding air breaks down.

Performance Test of Insulator :-  Some tests performed on insulator are as follows : 

(A) Temperature Cycle of Insulator : 
1) The insulator is first heated in water at 70 degree for one hour.
2) And then this insulator is immediately cooled in water at 7 degree for another one hour.
3) Same process  is done for three times and dried well to inspected the glazing of the insulator.
4) After completing the processs the Glazing of insulator should not be damaged.     

(B) Puncture Voltage Test of Insulator :
Insulator is suspended in an insulating oil and voltage of 1.3 times of flash over voltage is applied to the insulator. Under such condition it should not be puncture.


(C) Porosity test of Insulator :
The insulator are immersed in a alcohol solution of fuchsine dye under pressure for 24 hours and then sample is removed to clean and examined.

(D) Mechanical Strength Test of Insulator :
Insulator is applied by 2.5 times the maximum working strength.  The insulator must be capable to sustain for about one minute under such condition without damage. 


Routine Test of Insulator :- Each of the insulator must undergo the following routine test 

(A) Load Test of Insulator :
Insulator is applied under load with 20% excess of specified maximum working load for about one minute and examined. 

(B) Corrosion Test of Insulator :
Insulator with its galvanized or steel fittings is suspensded into a copper sulfate solution for one minute and again same process is repeated for 4 times and examined that there should not be any deposition of metal.  

(C) High voltage test :
Here the pin insulators are inverted and put into water up to neck and water is put into the spindle hole. Then high voltage is applied for 5 minutes. After completing this test there should be no damage in insulator.

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