Identification of thermal failure profiles in stator winding insulation by impedance spectroscopy

This paper presents a novel application of impedance spectroscopy as a means of inspection for stator winding insulation. It proposes, for the first time, a means for health monitoring and failure identification during thermal degradation effects in the insulation systems of stator coils from a concentrated stator winding. By periodical ex-situ inspection of these coils, the thermal ageing data of the insulation are profiled up to the point of failure. The study maps this evolution of thermal degradation patterns via novel interpretation of the impedance frequency responses, using well known techniques such as the Bode and Nyquist plots. This grants further insight into the characteristics shown in the ageing profiles over time and frequency. These new profiles enable the identification of critical points that can act as pre-emptive indicators of coil health and failure inception. This is a key finding as it renders the capability to provide an adequate lifing tool for electrical machine windings and coil assemblies within industrial settings. The insulation system examined in this study is taken from the coils of a concentrated stator winding in a 2MW permanent magnet generator used in an aerospace application.