Online insulation condition monitoring of traction machines using inverter induced voltage injection

Stator insulation defects in the machine winding of traction drives can be analyzed by evaluating the current response resulting to inverter induced voltage injection. Due to effects occurring during the aging of the insulation, e.g. change of parasitic electrical components, deviations of the high frequency components of the current response can be monitored. The insulation degradation of a stator winding system is a long developing process and usually takes place over a long period. With the proposed method stator insulation degradation can be detected already at an incipient stage by comparing the high frequency transient current response of the drive system from the first initial startup with continuous measurements during operation. No additional current transducers are necessary than the transducers already applied for the control of the machine. Investigations are conducted with a 1.4 MW induction machine designed for a traction application having form-wound coils equipped with fiber-insulated winding taps and a silicon carbide voltage source inverter enabling high dv/dt rates of up to 25kV/μs. Additionally, in order to investigate insulation degradation of the stator winding system, results of measurements of a form wound coil specimen are presented.