Effects of AC Corona Discharge on GFRP Core Rods Used in Composite Insulators

Composite insulators are extensively employed in transmission lines worldwide. However, power insulators in China confront challenges from complex and harsh
conditions, experiencing environmental, electrical, and mechanical stresses simultaneously. Accidents involving what has become known as decay-like fracture of composite insulators have been reported many times. This study investigates the impact of AC corona discharge on the properties of glass fiber-reinforced plastic (GFRP) core rods using a multi-needle corona system. With increasing corona intensities and durations, the following conclusions have been drawn: the permittivity and loss tangent of the core rod increase, exacerbating subsequent discharges. The main chain (C C bonds) in the epoxy resin breaks, and the content of methyl and benzene ring decreases. Hydrolysis of ester groups leads to the failure of curing agents and coupling agents, and the interface between the epoxy resin matrix and glass fiber gradually fails. The macro and micro morphology show deterioration, such as erosion of epoxy resin matrix,
disordered distribution of glass fibers, and separation of the fiber-resin interfaces. After removing surface epoxy resin, stresses act directly on fibers or defects accelerating the degradation process. The experimental results show that when it is undamaged, the epoxy resin protects the core rod from external corona radiation and the degradation of epoxy resin matrix is a prerequisite for the fracture of glass fibers. These results establish an experimental foundation for
understanding the impact of corona on core rods and the mechanism of decay-like aging.