Quantitative Analysis Ageing Status of Insulation of High Voltage Motors by Polarization – Depolarization Current Measurements

Polarization and depolarization current (PDC) technique is an effective tool to assess the condition of insulation system in high voltage motors So far the PDC behaviors of insulation have been widely investigated. This Paper presents the assessment of insulation systems for high voltage induction motor through measurement of polarization depolarization current or charging and discharging current. However, with the increasing number of Motors choosing insulation , it is important to investigate the PDC characteristics of insulation to see whether the PDC technique can also be used to assess the condition of new insulation system using PDC accurately It is considered that the insulation systems are having different types and conditions of insulation aging. It demonstrates that the insulation resistance (IR) and polarization index (PI) can’t be used individually to judge insulation dryness and the combination of insulation resistance and PI. PDC analysis is 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 practically and theoretical background and some results of PDC measurements on High voltage motor duration from 0–600 days.