A stator core quality assessment technique for inverter-fed induction machines

Localized heating caused by damage in the laminations or inter-laminar insulation of the stator core increases the core losses and can lead to machine failure. Therefore, it is important to monitor the quality of the stator core for reliable and efficient operation of the machine. The methods currently available for core quality assessment are inconvenient since they require an outage and the machine to be disassembled or operated under no load conditions. In this paper, a new method for monitoring the quality of the stator core for inverter-fed machines without motor disassembly or operation is proposed. The main concept is to use the inverter to apply a set of test signals to assess the quality of the core whenever the motor is at standstill. A set of high frequency pulsating magnetic fields are produced using the inverter, and the power loss is observed as a function of field circumferential position to detect core problems. An experimental study on 10hp induction motor verifies that local inter-laminar core faults can be detected with high sensitivity. The proposed technique is expected to provide a simple solution for frequent stator core quality assessment without motor disassembly, motor operation, or additional hardware for reliable and efficient operation of inverter-fed induction machines.