Diversified Assessment of Ground-Wall Insulation in Inverter-Fed Motors by Using Transient Characteristics of Leakage Current

Real-time assessment of ground-wall (GW) insulation condition is critical for the reliable operation of inverter-fed motors (IFMs) and many online monitoring methods have been proposed. However, the existing methods can only detect the overall insulation degradation condition, the refined assessment of degradation position is rarely reported. In this article, a diversified assessment method is proposed that can identify the severity, position, and phase of GW insulation degradation by using the transient characteristics of leakage current. A stator winding insulation model is established to analyze the relationship between leakage current and GW insulation in IFMs. After the theoretical analysis, the common-mode harmonic and differential-mode harmonic of leakage current are utilized to identify the severity and position of GW insulation degradation, respectively. Moreover, the initial oscillation amplitude of the leakage current is used to assess the degradation phase of GW insulation. The proposed method is validated on a 3-kW permanent magnet synchronous motor driven by a two-level inverter, and the experimental results are consistent with theoretical analysis.