Stator fault diagnosis in induction motors using power decomposition

Abstract

A power decomposition technique (PDT) has been used to derive positive and negative sequence components of arbitrary three phase signals in the time domain, in order to detect deterioration in the stator of induction motors. Negative sequence currents arising from supply unbalance are calculated using the reactive component of motor negative sequence impedance, which is essentially independent of temperature. The effects of variation in load, supply voltage, and supply voltage unbalance, have been eliminated by using a recursive least squares method to characterize the associated variation in motor reactance and residual negative sequence current in the healthy motor. Compensation is also applied for nonsimultaneous current sampling of motor fault current. Negative sequence fault currents as low as 0.1 percent of full load current can be detected in the presence of normal variations in load, voltage, and unbalance.