Thermal Aging of Aerospace Electro-Hydrostatic Actuator (EHA) Motor Insulation Systems

Abstract

During the entire service cycle, the Electro-Hydrostatic Actuators (EHAs) are subjected to multi-physical stresses, including coupling effects, including high temperatures, severe temperature variation, and high-frequency pulses. These stresses not only act on the mechanical structures but also continuously degrade the dielectric properties and mechanical strength of the insulation materials, with long-term accumulation potentially leading to deterioration in insulation performance. Consequently, whether the insulation system can remain stable under such harsh conditions becomes a core factor constraining EHA reliability, and its insulation reliability directly determines the operational safety of aircraft actuation systems. Targeting the aerospace EHA motor insulation system, this paper aims to construct a systematic condition assessment method and a life degradation feature based on the dynamic evolution characteristics of multi-dimensional dielectric parameters. This study conducts accelerated thermal aging and thermal cycling tests on a 270 V Type I aerospace EHA motor insulation system, with multi-parameter tracking of equivalent capacitance (Ceq), partial discharge inception voltage (PDIV), and leakage current (I). The results indicate that Ceq exhibits high sensitivity to early-stage insulation damage. PDIV presents non-monotonic fluctuations during aging, and combined with Paschen’s law, the reduction in air-gap dimensions due to thermal expansion in the mid-stage is the physical origin of its phased recovery—verifying the rationale in using PDIV as the electrical safety boundary. In contrast, leakage current shows significant hysteresis, remaining robust at 0.35–0.55 mA until a sharp jump signals the formation of through-going conductive channels, which serve as the ultimate failure criterion. On this basis, a hierarchical assessment framework is constructed: Ceq captures degradation precursors, PDIV defines the safety boundary, and leakage current acts as the final failure indicator. This study refines the multi-stress evaluation method for aerospace motor insulation and provides experimental support for reliability assessment and life prediction of actuation systems in next-generation more-electric aircraft.