Influence of fast inverter switching based on SiC semi-conductors on online insulation monitoring of high power traction machines

In modern drive applications fed by voltage source inverters, monitoring systems are of advantage to reduce the maintenance costs and prevent outages. The proposed insulation monitoring method detects stator insulation defects by evaluating the current´s transient response after step excitation by the inverter. Due to fast switching of the voltage source inverter at high output voltage dv/dt rates, increased stress appears on the insulation and leads to deterioration. Prior an actual breakdown occurs, the machine´s high-frequency behavior is altered and a change in the transient part in the current response following a step excitation can be used to indicate insulation degradation. The paper presents experimental results of a 1.4 MW induction machine, fed by SiC semiconductor inverter technology. Additionally, variations of the inverter output voltage switching rate were implemented and the effect on the monitoring method is analyzed.