Assessment of valve actuator motor rotor degradation by Fourier analysis of current waveform

The authors present a test report of a motor diagnostic system which uses Fourier analysis of the motor current waveform to detect broken rotor bars in the motor or defects in the driven equipment. The test was conducted on a valve actuator motor driving a valve actuator which was in turn driving a dynamometer to measure the actuator torque output. The motor was gradually degraded by open circuiting rotor bars. The test confirmed the efficacy of the waveform analysis method for assessing motor rotor degradation, and also provided data regarding the change in the waveform characteristics as motor rotors were gradually degraded to failure