Investigation on Polarization – Depolarization Current Measurements in Insulation Systems for High Voltage Motor

This paper presents the assessment of insulation systems for high-voltage induction motor through measurement of insulation resistance(IR), polarization index(PI) and polarization–depolarization current or charging and discharging current. It is considered that the insulation systems are having different types and conditions of insulation aging. It demonstrates that the IR and PI cannot be used individually to judge insulation dryness, and the combination of IR and polarization and depolarization current (PDC) analysis is a better technique of insulation quality assessment than the insulation resistance alone. The PDC analysis is non-destructive dielectric testing method for determining the conductivity and moisture content of insulation materials in high-voltage motors. On the basis of this analysis, it is possible to take further actions like overhauling, drying process and replacement of the winding of the motor. This paper also presents a description of PDC analysis technique with the practical and theoretical background and some results of IR, PI and PDC measurements on High-voltage motor.