Characterization of short circuit faults and incipient insulation degradation between stator winding turns of induction motor

The aim of this work is to present a method to discriminate between dead short circuit and incipient or partial short circuit in induction motor stator winding when the dead short circuit conditions are introducing unbalance in three phase stator currents similar to the latter case and that too under different loading conditions. Unbalance in motor current may also be introduced by unbalance in supply voltage. Any unbalance in the motor currents caused either by fault or supply voltage unbalance or even inherent asymmetry in motor circuit makes negative sequence current to crop up. This paper presents a scheme to estimate the magnitude of negative sequence current introduced by motor faults only. Negative sequence current analysis employing Power Decomposition Technique (PDT) has been used to derive positive and negative sequence components from three phase current and voltage signals. Three-phase instantaneous current signals and voltages are both sampled simultaneously in time series. Entire analysis presented in this paper is based on experimentally obtained motor current signatures. The obtained results provide a satisfactory level of accuracy in terms of segregating two different types of stator fault cases.