Polarization index

Polarization Index is an indicator which gives an idea of the cleanliness of the windings. It is a ratio of the Insulation Resistance Measured for 10 minutes to the insulation resistance value measured after 1 minute. Since it is a ratio; it does not have any units.

Polarization Ratio = Insulation Resistance after 10 minutes/ Insulation Resistance after 1 minute

The Polarization Index should be above 2.0 to be permissible. Machines having PI below 2.0 cannot be operated. The Polarization Index does not have any significant relation with temperature upto 50 deg. C. However, the Polarization Index test should not be conducted at a temperature beyond 50 deg. C

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