Insulation condition monitoring of traction drives based on transient current signal resulting from differential and common mode excitation

In this work a method to detect stator insulation degradation of traction drives based on analyses of the transient current reaction caused by inverter switching is proposed. Two simple excitation methods are proposed to analyze the state of the inter-turn insulation as well as the groundwall insulation. With the standard hall-effect based closed loop current transducers used for the control of the machine as well, the transient signal ringing resulting from a switching transition of the inverter is analyzed. Based on a comparative monitoring method the transient part of the current response is analyzed to extract an insulation state indicator of the winding system. The approach is tested with a SiC-MOSFET inverter prototype as a source of excitation. Due to fast switching of the voltage source inverter and high output voltage dv/dt rates, the motor windings suffer under increased stress that leads to insulation degradation. With the ability to change the effective gate resistance small dv/dt variations and their influence on the proposed method is analyzed. The method is tested with 1.4MW and 5.5kW induction machines.