Its ratio between insulation resistance (IR) i.e. megger value for 10min to insulation resistance for 1 min. It ranges from 5-7 for new motors & normally for the motor to be in good condition it should be Greater than 2.5. Polarization Index Test (PI) – The PI test measures the ability of the insulation to absorb voltage over a period of time. This gives an indication of the overall insulation quality of the individual pieces of insulation in the transformer. This test is usually performed in conjunction with the Megger Test. It is measured as the ratio of insulation resistance (IR) for 10 minutes to insulation resistance for 1 minute.
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