Polarisation Index Test (Insulation Resistance Test) of HV Motors

The insulation resistance and polarization index tests of an electric motor or generator has been regarded as a useful tool in evaluating its windings for build up of dirt or moisture, deterioration of the insulation, fitness for high potential tests and suitability for further operation. IEEE Standard No. 43-2000 covers how the producer should test, determining Insulation Resistance and Polarization Index in detail. Lower value of IR indicates that the insulation has deteriorated. PI is a variation of the IR test. It is the ratio of IR measured after voltage has been applied for 10 minutes (R10) to the IR measured after one minute (R1), i.e.