You can find informations in my paper (by Christodoulou C.A., Avgerinos M.V., Ekonomou L., Gonos I.F., Stathopulos I.A.) entitled "Measurement of the resistive leakage current in surge arresters under artificial rain test and impulse voltage subjection", IET Science, Measurement & Technology, Vol.3, Issue 3, pp.256-262, May 2009.

Hi.

The following papers might give u an idea for measuring the leakage current of ZnO varistor.

http://www.energy.siemens.com/us/pool/hq/power-transmission/high-voltage-products/surge-arresters-and-limiters/publications/monitoring-1400180.pdf

http://elocos.railnet.gov.in/MSG_ESC/Lightning_Arrestor.pdf

http://www.arresterworks.com/arresterfacts/pdf_files/ArresterFacts_036_Arrester_Condition_Monitoring.pdf

http://cdn.intechopen.com/pdfs-wm/17630.pdf

http://file.scirp.org/pdf/JPEE_2014042317015419.pdf

These are the basic papers which can be referred.

Earlier they were using compensation techniques for removal of capacitive components from the total leakage current for the measurement of resistive leakage current.

Now software developed by using FFT method can be used for leakage current measurement.

Mahesh, what do you mean? Do you want to calculate the leakage current theoretically and compare with your measurements or do you want to split the total leakage current into its resistive and capacitive components?

If you want to calculate it theoretically the IEEE proposes some models, depending the type of surge you want to describe (fast, medium or low front impulse).

On the other hand, it you want to use your measurements (total current and applied voltage) to obtain the resistive and capacitive current, the easiest way is to do it using a resistive/capacitive bridge in the lab. If you do not have the bridge, you will have to  choose a method for decomposing the current.

Do you need to do it many times or just few? I might be able to help you!

Hi Mahesh. As you know, leakage current is unwanted since it increases the watt loss during steady state operation. Leakage current is the current value at a certain voltage below the breakdown voltage. If you wish to use the Standard to measure leakage current, you need to know the Voltage RMS Rating of your varistor sample; the Standard will tell you at what voltage you should measure the leakage current.

However, if you chose Not to use the Standard, you need to find the Voltage at 1mA, and find the leakage current at a voltage 20% below the Voltage at 1mA.

Again if you chose Not to use the Standard, you can also determine the Exact Breakdown Voltage at the Onset of Nonlinear Region, and determine the leakage current 20% below the breakdown voltage.

Hope this helps