Correlation Between Insulation Resistance, Polarity Index and Tan Delta?

Insulation resistance is measurement of leakage current it consist of capacitive charging current,di-electrical absorption current both will decay exponentially.then you will get true leak current surface leak and dielectric leak current which when calibrated in resistance it is dielectric resistance which carried out to find healthiness of current path

polarization index is ration of 10 min IR value and 1 min IR value it should be more then 2.It show accumulation of dirt and moisture on winding

Ten Delta done with special test kit to determine rate of deterioration of insulation and to avoid failure

thank joshid.

just for sharing....we have done tan delta measurement. Before tan delta measurement was done, we did insulation resistance (IR) test with the result IR< standard of insulation resistance and then followed by lower Index Polarity (about 1.3). with the result above, we did tan delta measurement, and the result is oK, (< IEC and VDE standard ). after 3 month, we tried to megger the motor and you know the result is lower. (< from standard). how do you think about it? could our tan delta measurement destruct the motor?

thank for your respond.

regards

Tan delta measurement cannot destruct the motor except the test voltage is higher than the rated insulation voltage.