Induction motor rotor fault diagnosis method based on double PQ transformation

Abstract

This paper presents a new rotor fault diagnosis method for induction motors which is based on the double PQ transformation. We construct the PQtransformation matrix with the positive sequence fundamental voltage components and their Hilbert transformation as elements. The active power P and the reactive power Q are obtained through the PQ transformation of the stator currents. As both P and Q are constant for a healthy motor, they are represented by a dot on the PQ plane. Whereas the P and Q for a rotor broken bar motor are represented by an ellipse because they comprise an additional frequency component 2sf_s (_s is the slip and f_s is the supply frequency). Thus, by distinguishing these two different patterns, the rotor broken bar fault is detected. We use the major radius of the ellipse as the fault indicator and the distance between the point of no-load condition and the center of the ellipse on the PQ plane as its normalization value. We thus arrive at the fault severity factor which is fairly independent of the load level and the inertia value of the induction motors. Experimental results have demonstrated that the proposed method is effective in identifying the rotor-broken-bars fault and at determining the severity of the fault.