Analysis of rotor fault detection in inverter fed induction machines at no load by means of finite element method

This paper analyzes a new method for detecting defective rotor bars at zero load and standstill by means of modeling using the finite element method (FEM). The detection method uses voltage pulses generated by the switching of the inverter to excite the machine and measures the corresponding reaction of the machine phase currents, which can be used to identify a modulation of the transient leakage inductance caused by asymmetries within the machine. The presented 2D finite element model and the simulation procedure are oriented towards this approach and are developed by means of the FEM software ANSYS. The analysis shows how the transient flux linkage imposed by voltage pulses is influenced by a broken bar leading to very distinct rotor-fixed modulation, that can be clearly exploited for monitoring. Simulation results are presented to show the transient flux paths. These simulation results are supported by measurements on a specially manufactured induction machine.