A Novel Method of Monitoring and Locating Stator Winding Insulation Ageing for Inverter-fed Machine based on Switching Harmonics

The online stator winding insulation monitoring is becoming an important topic in recent years and many online monitoring methods have been proposed. In these methods, the online common-mode impedance spectrum method can monitor the condition of the ground-to-wall insulation accurately based on switching harmonics and no additional signal injection equipment is needed. In this paper, the effect of the insulation ageing position on the CM impedance spectrum is studied and this effect can be used to locate the ageing position along the winding. Compared with the existing methods, the proposed method monitors the parallel capacitance in the frequency range both below and above the resonance frequency point. Using multi-frequency information, the proposed method can distinguish the ageing position and detect the local insulation degradation sensitively, which improves the performance of this monitoring method. The offline and online experimental results both validate the proposed method.