Condition monitoring and diagnostics of motor and stator windings – A review

Condition-based maintenance (also called predictive maintenance) requires diagnostic tools to determine when significant insulation aging has occurred, and thus when maintenance is necessary to avoid an in-service failure. Over the years many off-line diagnostic tests and on-line monitoring systems have been proposed and implemented, especially on critical motors and generators. In the past decade, most of the research has concentrated on improving existing off-line diagnostic tests and on-line monitoring such as magnetic flux, partial discharge, temperature, endwinding vibration, etc. However, some newer tests such as polarization/depolarization current, dielectric spectroscopy and on-line leakage current monitoring have been introduced. These tests and monitoring systems are reviewed. Tests and monitoring systems for rotor winding insulation and stator winding insulation are addressed separately.