An Improved Method for Inverter-Fed Motor Insulation Online Condition Monitoring by High-Frequency Leakage Current Analysis

Insulation degradation is an important cause of inverter-fed motor failures. In order to improve the safety of electric motor systems and to avoid sudden failures, timely monitoring of motor insulation degradation is necessary. The high-frequency common-mode leakage current flowing through the groundwall insulation reflects the degradation of the groundwall insulation, especially that of the first few turns. In this paper, an insulation condition monitoring method based on leakage current is proposed. An improved common-mode model of the winding suitable for leakage current analysis is proposed, based on the characteristics of the common-mode impedance curve of the motor. By analyzing the mathematical relationship between high-frequency leakage current and insulation degradation in the first few turns, the insulation condition indicators are proposed, and it is validated by the experimental results. Based on this method, a suite of hardware for pre-processing leakage current waveforms is designed, thus providing a cost-effective insulation monitoring method that minimises both hardware and software requirements.