Leakage error compensation in induction motor current measurements for rotor fault diagnosis

Frequency-domain current signature analysis for fault detection on induction machines typically requires a very fine frequency resolution to distinguish between spectral components that differ from each other by multiples of the (usually very low) slip frequency. It is well known that if such a high resolution is not achieved, significant leakage errors may arise and misleading diagnostic information can be obtained from the measured current spectrum. This paper presents a leakage error compensation technique that allows accurate results even when the resolution is limited by the requirement of short observation time. This technique is based on the independent knowledge of the frequencies of the relevant components in the spectrum, which only depend on the power supply frequency and on the motor rotation speed, whose measurements are often available. The proposed method is here applied to the detection of rotor bar breakages and it is tested on simulated motor current waveforms.