Ultra-Sensitive Monitoring of Line-End Coil Insulation Degradation in Inverter-Fed Machine Using PT Symmetry

The line-end coil insulation, a vulnerable point in winding insulation, is subjected to higher transient voltage stress and a greater risk of breakdown, making it both attractive and challenging to monitor at an early stage. To improve the sensitivity of early line-end coil insulation monitoring, this article proposes a novel approach based on parity-time (PT) symmetry, utilizing an external resonator magnetically coupled with the system's high-frequency common-mode (HFCM) switching oscillation. The effect of damping rate splitting near the exceptional point (EP) is used to detect early degradation of line-end coil insulation with enhanced sensitivity. Initially, the HFCM switching oscillation in the inverter-fed machine system is considered an internal resonator, and its modal features are analyzed. Subsequently, an external resonator is designed to operate at the EP of PT symmetry, and the extracted damping rate feature of the HFCM switching current is explored for online monitoring. Experimental results demonstrate that insulation capacitance degradation can be effectively identified with a sensitivity of approximately 0.8%, which is at least six times greater than that achieved by the conventional method utilizing resonant frequency characteristics. This method is characterized by its noncontact safety, ultra-sensitivity, and robustness.