Detecting incipient stator winding conductor faults in inverter fed machines

In variable speed drive applications the inverter fed induction machine is one of the most reliable systems. However, increasing demands on efficiency leads to higher wear of all system components. Unexpected machine breakdowns cause economic losses and/or undesired scenarios in safety-critical areas. Thus condition monitoring of all components can reduce the risk of outages due to faults. High electrical and magnetic forces together with increased environmental stresses in rough application fields lead to a higher probability of stator winding faults. Beside inter-turn short-circuit faults open-circuit winding faults are under the most frequent types of faults. Open-circuit winding faults usually start with a crack or conductor deformation. Thus the resistance in the corresponding stator winding phase is increased. Detecting such faults already in an early stage provides the possibility to react timely before a more severe fault occurs. This work presents a method to detect open-circuit winding-faults in an early stage without additional hardware. The method is based on the identification of the phase resistance by combination of measured current reaction to different voltage steps. A specific signal processing chain supplies a fault indictor able to detect the fault by magnitude and position.