On Line Detection of Inverter Fed AC Machine Insulation Health State using High Frequency Voltage Excitation

Condition monitoring is gaining more and more importance in the past few years. As inverter fed operation puts additional stress on the machine's insulation system a breakdown of a drive system associated with costly outage of industrial processes or production plants is getting more likely. To enable a monitoring of the insulation system health state before an actual short circuit and breakdown occurs extensive test procedures are usually necessary that need both, additional equipment as well as disconnected drive. In order to enable a continuous monitoring a method is presented that enables the detection of changes in the machines insulation system during operation of the inverter. The method is based on a voltage excitation of the machine with a specific frequency range and measuring the corresponding current reaction. By observing changes at a specific frequency range, an insulation health indicator can be calculated that is able to detect deteriorations before an actual short circuit establishes. No additional sensors or measurement equipment is needed and the method can be implemented in modern inverter fed drives with minimum changes of configuration.