A Stator Faults Diagnostic Approach Immune to Unbalanced Supply Voltage, Based on the Analysis of the Midpoint Electrical Potential of the Stator Star

The inter-turn short circuit fault (ITSCF) diagnostics in induction motors under unbalanced supply voltage conditions has been a challenging over the last few years. The asymmetries caused by both conditions are similar, and the detection of an ITSCF becomes compromised. An ITSCF diagnostic approach based on the analysis of the electrical potential of the midpoint of the stator star, in a symmetrical six-phase induction machine (S6PIM) supplied by unbalanced voltages, is addressed in this paper. Firstly, the measurement of the midpoint electrical potential and the six supply voltages are performed. Then, the obtained midpoint electrical potential of the stator star value is subtracted from the one that results from the sum of the measured six supply voltages, divided by six. This operation allows the isolation of the contribution of the unbalanced supply voltage presented in the midpoint of the stator star, which means that a zero value is obtained whenever the motor is operating healthfully, supplied by balanced or unbalanced voltages. However, in the event of the occurrence of a short-circuit, a fault-related component will result from the mentioned subtraction, and its amplitude increases as the fault severity increases. Secondly, to classify the fault severity, a fast Fourier transform analysis is applied to the obtained fault-related component at a frequency of the supply voltage, and its amplitude value is analyzed. Finally, simulation and experimental results, covering different load torques, unbalanced supply voltage levels and fault severities, are presented in order to prove the effectiveness of the proposed technique.