Non-invasive detection of rotor cage faults in inverter fed induction machines at no load and low speed

Rotor cage fault detection in inverter fed induction machines is still challenging nowadays as dynamics introduced by the control or the load influence the fault indicator signals usually applied. In addition, the detection is usually only possible when the machine is operated above a specific load level to generate a significant rotor current magnitude. This paper proposes a new method to detect rotor bar defects at zero load and around standstill. The method only uses the standard current sensors already available in modern industrial inverters and is thus non-invasive. It is thus well suited as start-up test for drives. By applying a transient voltage pulse sequence using the switching of the inverter and measuring the resulting current slope a new fault indicator is obtained. As a result, it is possible to clearly identify the fault-induced asymmetry in the machine transient reactances. Though the transient flux linkage cannot penetrate the rotor because of the cage, the faulty bar locally influences the zigzag flux leading to a significant change. Measurement results show the applicability and sensitivity of the proposed method.