Analysis of Ultra-fast Inverter Switching Transition (dv/dt) Impact based on SiC Semi-conductors to Pre-active Insulation Monitoring of High Power Traction Motors

Abstract:
Today’s drives/motors in traction propulsion application are operating very close to borderline of maximum tolerable condition. In addition fast switching of the inverter (high dv/dt rates) in modern propulsion system causes increased stress for the motor windings and leads to insulation degradation. Thus, insulation condition monitoring is getting more and more important to ensure reliability and prevent breakdown of the traction motors in trains & locomotives, trams etc. The paper proposes an online insulation monitoring approach that is able to detect incipient insulation defects, by evaluation of the motor transient current’s response on voltage pulses injected by standard inverter switching. The applicability and performance of the method is verified by experimental results, based on voltage excitation with different very high dv/dt voltage rates (performed via VSI-inverter equipped by SiC semi-conductors). Different dv/dt-rates (up to 20 kV/mus) and their impact to the proposed insulation monitoring method are analyzed.