Condition monitoring of stator faults in induction motors: Part II- A more sensitive indicator of inter-turn shortcircuits fault in stator windings under unbalanced supply voltage

Unbalanced supply voltage is the major problem in using negative sequence current and third harmonic component as interturn short-circuit fault indicators. The purpose of this paper is to present an original analytical formula of all harmonic components related to unbalanced supply voltage induction motors. This formula is derived by the use of the KU transformation theory and the development is given in the first part of these two parts of papers. This analytical study predicts the way in which these harmonics grow and it is an advanced step to discriminate between the effects of an inter-turn short- circuits and those due to unbalanced supply voltages. From this analysis, a more significant and sensitive indicator for the interturn short-circuits faults under unbalanced supply voltage conditions is proposed. Simulation results and experimental tests have validated the analytical formulas.