Effects of rotor faults in squirrel-cage induction motors on the torque-speed curve

This study presents analysis and effects of rotor faults in squirrel cage induction motor on the torque-speed curve. In the study, the used experimental data were obtained from 10 HP, 25 HP, 30 HP and 50HP submersible induction motors. The experiments were made during the motors start up under no-load condition. Torque and speed of the motors were sampled and saved for every starting. The motor speed was computed from these data by using Fast Fourier Transform (FFT) and Short Time Fourier Transform (STFT). The motor torque values were computed by using average of the torque data window which represents every STFT window. So, the speed- torque curve was occurred. In the experiments; (i) a rotor with one broken rotor bar, (ii) a rotor with two adjacent broken rotor bars, (iii) a rotor with three adjacent broken rotor bars, (iv) a rotor with a highly resistance rotor bar, (v) a rotor with a broken end-ring faults and (vi) healthy motor were used. Then the results were analyzed. The effects of rotor faults on the speed- torque curve were ranked according to size of the rotor faults. The study differentiates in two points from the literature. The first point is the method of obtaining of the torque-speed curve and the second point is rank of the faults effects according to size of the faults. Test results revealed that the size of the rotor fault is directly proportional to its effects on the curve. And broken end-ring fault was found to procedure similar effects to broken bar faults.