Influence of current transducer transfer properties on stator insulation condition monitoring of inverter-fed drives

Insulation condition monitoring is important in case of inverter-fed machines due to the high strains on the machine and especially on its winding insulation system. In particular in traction applications the usage of new emerging semiconductor technologies, which enable higher inverter switching frequencies and rapid voltage rises, transient overvoltages at the machine occur. The insulation system suffers due to these overvoltages and a reduced lifetime and increased risk of unexpected outage of the drive are the consequences. A strategy to monitor the insulation health state during the operation of the drive based on transient current signal evaluation to detect incipient insulation degradation enables the possibility to define further maintenance tasks. Using only the measuring equipment available in the inverter, space and costs of the monitoring system are optimized. Experimental results of this concept, tested at a 1.4MW induction machine for railway application are presented. Additionally, the variance in the transfer function of different current transducer's of the same type and its influence on the proposed method is analyzed.