Study on the Aging Mechanism of Epoxy Impregnated Glass Fiber Composite Materials Under Multi-Factor Aging

Epoxy resin glass fiber (EP/GF) composite materials are an important component of the encapsulation insulation of dry-type air-core reactors. However, during the operation of high-voltage power systems in cold regions, composite materials are subjected to long-term coupling effects of thermal, electrical, and vibrational factors, which can lead to fatigue damage and cracking, thereby limiting their engineering applications. To investigate the failure mechanism of the encapsulation insulation of high-voltage dry-type aircore reactors in operation in cold regions of our country under alternating conditions of high and low temperatures with a large temperature difference, electrical performance tests of dielectric characteristics, direct current conductivity, and partial discharge were conducted on the samples. The experimental results indicate that the expansion coefficients of epoxy resin and glass fiber differ, and the composite material will endure stress when the external temperature changes. Additionally, during the thermo-electro-mechanical aging process, a debonding phenomenon occurs between the fibers and the matrix. Consequently, cracks will appear in the matrix resin, leading to a decline in insulation performance, as the molecular chains of the epoxy resin gradually break, forming numerous small molecular aggregates that promote the conductive properties of the insulation. The accumulation of broken molecular chains in the epoxy resin undergoes carbonization under aging, resulting in significant partial discharge signals even at lower test voltages. The study on the evolution of the failure of electrical characteristics of EP/GF insulation under thermal cycling aging and combined aging provides a basis for assessing the aging state of the external insulation of dry-type air-core reactors.