State the methods used to measure insulation resistance and explain Dielectric Absorption method.

State the methods used to measure insulation resistance and explain Dielectric Absorption method.
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1 Answer

Answer :

There are three types of tests for measuring insulation resistance: 

1. Spot test reading or Short Time test 

2.Time-resistance test or Dielectric absorption test or Testing methods based on the PI & DAR 

3. Step voltage test 


Explanation to measure insulation resistance by Dielectric Absorption method:- 

The megger is connected across the insulation. Take successive readings at fixed time interval For this method, two readings are taken at 30 seconds and 60 seconds respectively to calculate DAR And also for 1 minute and 10 minutes, respectively to calculate PI. The PI and DAR are commonly used to quantify the time resistance test result. A curve is plotted from the readings. Good insulation shows a continuous increase in the resistance value over a period of time and if value of PI is greater than 2 or 4 and value of DAR is greater than between 1.25 to 1.6 If reading is stagnant and it does not increase as expected, the insulation may be weak and service may be needed and if value of PI is less than 2 and value of DAR is less than 1.25

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