Detection of broken rotor bars in induction motors using state and parameter estimation

The detection of broken rotor bars in induction motors is studied. 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, one with a broken bar, from identical 3 hp induction motors. The estimated rotor resistance is clearly greater for the rotor with the broken bar.>