Detection of Broken Bars in Induction Motor through the Analysis of Voltage Modulation

The paper presents an application of a novel method for diagnostics of electric and magnetic asymmetry of rotor cage in induction motor due to broken rotor bars. Increasing anomaly in magnetic field distribution results in a degradation of steady-state and dynamic performance of induction motor. It can be determined through the analysis of the average duty cycle of the modulated voltage. Broken rotor bars would cause torque and speed ripple which is compensated by speed control algorithm. Consequently oscillation in duty cycle of the modulated stator voltage appears. This effect can be simply detected without additional hardware. Correct evaluation of faulty motor performance is very significant part of condition monitoring and diagnostic procedure in modern supervision systems of electrical drives