Detection of Stator Faults in Induction Machines using Residual Saturation Harmonics

Stator fault is one of the most commonly occurring fault in AC machines. Recent estimates suggests that 30-40% of all reported induction machine faults are stator fault related. Going by the number of occurrences, the position of stator faults is only second to bearing related faults. Third harmonic line currents, caused by the interaction of reverse rotating field and saturation related permeance variation, third harmonic component in the line voltage, and the speed ripple consequent to reverse rotating field, have been reported to increase under stator fault conditions. Since reverse rotating field produced by voltage unbalance cannot be distinguished from those produced from stator faults, the measurement of third harmonic in line current may not be a reliable estimator of stator faults, particularly at an incipient stage. The third and the other triplen related harmonics are however found to be a very decisive indicator of the fault, if measured in the machine terminal voltages just after switch-off. The fault detection technique is independent of machine parameters and supply unbalances. Simulation as well as experimental results with very few shorted turns show that not only the presence of stator fault but also the phase in which the fault has occurred can be detected reliably