Thermal Degradation Phenomena of Polymer Film on Magnet Wire for Electromagnetic Coils

Polymer film insulation degradation is a major problem for electric machines which leads to short circuits, overheating, and eventually the occurrence of catastrophic failure. Electrical insulation materials provide the vital function of turn-to-turn, phase-to-phase, and phase-to-ground electrical isolation for the electromagnetic coils and windings. This article investigates the characterization of early-onset degradation of thin-film magnet wire insulation at elevated temperatures from 200 to 275  $^{\circ }$ C. Sample specimens were analyzed after ageing for 100 h in terms of their physical properties (surface roughness, mass), chemical properties [Fourier transform infrared (FTIR) spectroscopy], dielectric properties (capacitance and dissipation factor), and electrical properties (voltage breakdown strength and resistance). The results show that the specimen roughness and mass increase and decrease uniformly, respectively, with increased ageing temperature. Similar degradation results trends with respect to ageing temperature for the dielectric properties and electrical insulation strength is documented. The article also reports an extended ageing study which investigates early breakdown voltage on sample specimens over a much longer time duration, that of up to 1600 h.