Detection and localization of insulation deterioration in traction drives based on specific high frequency current response evaluation

In modern electric traction drives, on-line monitoring offers the advantage to decrease maintenance cost and increase the reliability. Especially, the electrical insulation is one of the most vulnerable components of an ac machine. Fast switching of the inverter results in high output voltage slew rates increasing the stress on the insulation as well as the rate of deterioration. The described stator insulation monitoring technique detects imminent deviations from a healthy stator insulation state by evaluation of the current response induced by inverter switching. Effects occurring during the aging of the insulation, e.g. changes of electrical parasitic components, lead to deviations in the transient current oscillation. Since the degradation of the insulation is usually a slowly developing process, the observation of the insulation condition is possible during operation and when the drive is put into service and continuing over the whole lifetime. The target of the approach is to detect the insulation degradation in an incipient stage. In order to operate the monitoring system economically, conventional current transducers typically used in industrial applications are used. Experimental results of a 1.4 MW induction machine for railway applications, fed by inverters with different semiconductor technologies (IGBT, SiC-MOSFET) are presented.