A novel online stator ground-wall insulation monitoring scheme for inverter-fed AC motors

Insulation failures are one of the most common failure modes of ac motors, especially high-voltage motors. Online monitoring of insulation health of ac motors is important for preventing unexpected outages and minimizing the associated financial losses particularly in critical applications. Previously, an online ground-wall insulation monitoring technique has already been proposed for 6-lead ac motors. In this paper, a novel online ground-wall insulation monitoring scheme is proposed for inverter-fed ac motors. This approach is based on measurement of common-mode insulation leakage current for online C/DF (capacitance and dissipation factor) monitoring. The proposed technique can be applied to both 3-lead and 6-lead ac motors and can also be extended to monitor the insulation health of the cable connecting the inverter and the motor. The proposed technique is demonstrated in the lab environment, and correlated with standard offline C/DF measurements.