Online Monitoring of Capacitance and Dissipation Factor of Motor Stator Winding Insulation during Accelerated Life Testing

Offline dissipation factor testing is one of the standard approaches to examine the condition of ac motor's stator winding insulation. An online technique to continuously monitor the condition of the groundwall and phase-to-phase insulation for ac machine stator windings insulation has been proposed. Dissipation factor and capacitance can be accurately monitored online based on the differential leakage current measurements for each phase. To further investigate the relationship between dissipation factor and the condition of stator winding insulation, an online high-voltage life testing is conducted on medium-voltage stator coils. The dissipation factor of the stator coils is continuously monitored online during such testing. The experimental results show that the dissipation factor can reliably reflect the health condition of stator winding coil insulation, and therefore can potentially be used for online monitoring the condition of stator winding insulation of ac machines. As an initial attempt to monitor dissipation factor during insulation life testing, the results presented in this paper are of great importance for future development work towards novel online monitoring technologies for rotating machines.