Breakdown Behavior of Magnet Wire Under Aerospace-Relevant Low-Pressure Conditions

The reliability of magnet wire insulation is critical for the safe and efficient operation of aerospace electric machines exposed to extreme electrical and environmental conditions. Polyimide-based insulations are widely used due to their excellent thermal and dielectric properties; however, they face challenges such as space charge accumulation, partial discharge activity, and accelerated aging under combined stressors. This study investigates the dielectric breakdown behavior of MW35-C class magnet wire subjected to both AC and DC electrical stress under sub-atmospheric pressures representative of aerospace environments. Experimental measurements were performed on 13 AWG, 15 AWG, and 20 AWG wires, all sourced from the same manufacturer but differing in core conductor radius and total insulation thickness. The results were statistically analyzed using the Weibull distribution. To complement the experimental analysis, 3D finite element simulations were conducted to evaluate electric field distributions at the contact interface between wires. The results demonstrate that breakdown strength is significantly affected by ambient pressure, wire geometry (core radius and insulation thickness), and the volume effect. Among the tested wires, 20 AWG exhibited the highest breakdown strength, attributed to its favorable conductor-to-insulation ratio and reduced insulation volume, which lowers the probability of critical defects. These findings provide valuable insights for the design and qualification of robust insulation systems in all-electric and more-electric aircraft operating in low-pressure environments.