On-line stator winding faults detection in inverter fed induction motors by stator current reconstruction

One frequent fault in electrical machines is the stator winding breakdown. The voltage stress due to the fast switching devices in voltage source inverters often leads to a failure of the interturn isolation and as a consequence to winding short circuits. This paper describes a simulation model to investigate the influence of stator faults due to inter-turn short-circuits as well as open windings on the operation of an inverter fed induction machine. Based on the simulation results a new method of stator fault detection is presented and analysed reference to its range of operation. This method utilises the behaviour of a current control loop which ensures symmetric stator currents even in the case of a stator fault. By evaluating the stator and the rotor equation of the induction motor the stator current space phasor can be reconstructed and compared with its actually measured value. Thus a signal can be obtained to detect machine faults. All the signals necessary to apply the proposed method to fault detection are already available in today's controlled induction motor drives. So the inverter and control electronics can be used to integrate the fault detection method into the inverter. Practical measurements are presented to verify the simulation results.