A Novel Nonintrusive Measurement Method of Bearing Currents in Inverter-Fed Motors

Electrical erosion caused by bearing currents is one of the main reasons for bearing failure in inverter-fed motors. The research of non-intrusive measurement of bearing currents contributes to risk assessment and early warning of bearing electrical erosion in electric motors, thereby enhancing the reliability of motor drive systems. This paper proposes a novel non-intrusive measurement method of bearing currents by measuring external electrical signals (bearing voltage and common-mode currents). Firstly, the relationship between bearing currents, bearing voltage, and common-mode (CM) currents is analyzed based on the CM model of the motor. Subsequently, the bearing voltage and CM currents are measured to detect and extract the characteristic signals induced by the discharge of the bearing oil film. The bearing voltage characteristic signals are detected using the instantaneous rate of change, while the CM current characteristic signals are extracted through a time-frequency features clustering method. The time-domain waveform of bearing currents is estimated by using the relationship between bearing currents and measured signals. Finally, the accuracy and effectiveness of the proposed method are verified by comparison with the intrusive measurement method. The proposed method demonstrates higher accuracy and reliability than traditional non-intrusive measurement methods.