Detection of Broken Bars in Induction Motor Through the Analysis of Supply Voltage Modulation

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