A New Method for Monitoring Grounding Insulation Degradation of Induction Motors Based on Common-Mode Switching Transients

Nowadays, inverter-driven machine systems are operated under rapid and frequent switching actions, where high dv/dt and transient over voltages lead to high electrical stresses on the winding insulation, which is susceptible to deterioration. The system's dependability can be increased and maintenance costs can be decreased with online insulation status monitoring. In this paper, a new online monitoring method for grounding insulation degradation based on common-mode switching transients is proposed. First, we analyze the spectral variation rule of common-mode impedance after the degradation of grounded insulation. Then, we chose the common-mode switching state as the voltage excitation based on the common-mode equivalent impedance circuit. Finally, the grounding insulation degradation is monitored online by extracting the transient oscillating current after switching action. The online experiments verify that the method can effectively monitor the machine winding grounding insulation state.