Combined Fault Diagnosis of Stator and Rotor Windings in a PWM Inverter-Fed Induction Motor Using Frequency Spectrum of Estimated Air-Gap Torque

This paper presents a fault detection method for squirrel cage induction motors using the spectrum of air-gap torque calculated from the motor terminal voltage and current. The proposed air-gap torque estimation method has a novel technical feature that it can not only estimate the shaft torque with high accuracy, but also catch up with the characteristic harmonic torque signal that is useful for detecting the combined faults of stator winding inter-turn short circuit fault and broken rotor bars (including end-ring fault). The proposed method is implemented on a variable speed induction motor that can switch between a healthy state and the combined faults state. Estimating the shaft torque based on the air-gap torque calculation and detecting the combined faults at different loads and frequencies are carried out. Experimental results under both sinusoidal and non-sinusoidal voltage drives demonstrate the validity of the proposed method.