Attempt to Understand the Degradation Process of GFRP Insulator with Void Defect at Cryogenic Temperature

Abstract

Glass Fiber Reinforced Plastic (GFRP) is usually employed as the insulator material of superconducting cable terminal, owing to its excellent mechanical properties and insulation strength at cryogenic temperature. However, in the presence of a void defect, both the insulation life span and mechanical strength of GFRP decrease significantly at superconducting temperature conditions. In this paper, efforts have been made to investigate the degradation process of GFRP at cryogenic temperature and give insight into its degradation mechanism. By comparing PD activities at 278.7 K, 223 K and 153 K in initial phase of aging, it is found that PDs are inclined to be inhibited at lower temperature. Experiments indicate that the deposited charge accumulation and mechanical properties degradation, instead of chemical aging and PD energy, play a crucial part in dielectric degradation. At cryogenic temperatures, the local heat accumulation brought by PDs increases the material internal mechanical stress, and the accumulation of deposited charges causes instantaneous energy release. On the basis of the decrease of the mechanical properties of the material, the crack expands rapidly, which leads to the dielectric failure of the material. In conclusion, the degradation of GFRP at cryogenic temperature is the result of the combined effects of deposited charge accumulation and mechanical properties decline.