Polariziation Index - PI Test
A measure of safety, the polarization index test provide indication of buildup of dirt and moisture, the deterioration of insulation and the suitability for operation of the motor or generator. INTERSEL use it to determine the fitness of a motor, alternator or generator for use. This index is sought from calculating measurement of the winding (electrical) insulation resistance.
The fact that impurities in winding act as charge carriers and cause current leakage works as the basis for the Polarization Index test. Therefore, the index provides indication of the amount of impurities in the winding and its cleanliness.
Before testing all connection to the machine are removed and windings are discharged to the grounded machine frame. An electrical current of either 500 or 1000 volts DV is applied between the winding and ground. The amount is based on the machine rating. A reading is recorded at a point in time and another is recorded after a steady 10 minutes of voltage feed. The polarization index is the ratio between the 10 minute and one-minute measurement.