Thermal Ageing of Enameled Wires for Electrical Machines

Abstract Around 40% of failures in electrical machines are attributed to the degradation of enameled wire insulation in stator windings. Electrical failure modes are often associated with premature cracking or delamination of polymeric winding insulation, which is subjected to combined electrical, thermal, mechanical, and environmental stresses throughout the motor’s lifecycle. With the widespread use of such systems, understanding their ageing mechanisms is crucial. This research focuses specifically on the effects of thermal ageing to develop ageing models and innovative strategies for extending their operational lifetimes. This experimental study involves an accelerated thermal ageing campaign, where H-class enamel wires were exposed to high temperature (230 °C) for varying durations of up to 30 days, followed by comprehensive characterization. Analytical techniques employed include visual inspection, cross-sectional analysis, Attenuated Total Reflectance Infrared Spectroscopy (ATR-IR), Thermogravimetric Analysis (TGA), dielectric measurements, and partial discharge inception voltage (PDIV and RPDIV) assessments. These investigations aim to provide insights into the physico-chemical and electrical changes occurring in the insulation material over time.