Challenges of Common Mode Current and Voltage Acquisition for Stator Winding Insulation Health Monitoring

Tracking of changes in common mode impedance has been employed for monitoring of insulation state of health in electrical machines. The insulation to ground equivalent capacitance and resistance may be derived from common mode impedance and phase angle, which, in turn, can be measured online, in an inverter-driven machine from common mode currents (CMC) and voltages (CMV). However, challenges regarding the behavior, location and acquisition method of CMC and CMV, have not been studied with sufficient detail up to date. In this paper, these conditions are analyzed in details, focusing in particular, on location of measurement, choice of sensor, limitations to bandwidth or variations due to operating conditions. Previous research has demonstrated good performance with slow switching Si-based converters. This paper, presents comprehensive experimental results employing a machine fed by a SiC inverter without output filter. It is demonstrated that the fast dv/dt transients and high switching frequency of SiC converters results in more demanding requirements for data acquisition.