DETECTION OF BROKEN ROTOR BARS IN INDUCTION-MOTORS USING STATE AND PARAMETER-ESTIMATION

This paper studies the detection of broken rotor bars in induction motors. The hypothesis on which detection is based is that the apparent rotor resistance of an induction motor will increase when a rotor bar breaks. Here, the apparent rotor resistance is that in the balanced steady-state single-phase electrical model of an induction motor. To detect broken rotor bars, measurements of stator voltage, stator current, stator excitation frequency, and rotor velocity are taken over a small range of velocity. These measurements are processed by a near-least-square-error estimator to produce estimated motor states and parameters. In particular, rotor resistance is estimated and compared with its nominal value to detect broken rotor bars. As part of this estimation process, it is necessary to compensate for the thermal variation in rotor resistance. The broken-rotor-bar detector is evaluated experimentally using one stator and three rotors from identical 3-hp induction motors. In one rotor, a bar is broken by milling into the rotor. The apparent rotor resistance, as estimated, is clearly greater for the rotor with the broken bar.