Design Scheme and Experimental Research on the Main Insulation Structure of 126 kV OIP Bushing Based on a New-Type Aramid Insulation Paper

Aramid paper with higher heat resistance grade is considered to be an ideal material for the internal insulation in oil-impregnated-paper (OIP) bushing in order to improve its electrical, thermal and mechanical performance. However, due to the significant differences in dielectric and mechanical properties between aramid and cellulose paper, specified design for main insulation structure should be put forward. This paper took the aramid-based 126 kV OIP bushing as an example, and for the first time combined equal-capacitor and equal-margin method to propose a quantitative internal insulation structure design scheme. Compared with conventional bushings at the same voltage level, the capacitor core volume and screen number has been respectively reduced by 50% and 7 layers. Then, the internal electric field distribution of conventional and aramid-based bushing was compared using COMSOL simulation, with the highest value increased by 36.4%. Finally, a prototype 126 kV aramid-based OIP bushing was produced according to the design scheme proposed, and type tests were carried out. Results showed that partial discharge and dielectric loss were respectively 5.03 pC and 0.483%, meeting the requirements of national standard, which proves the feasibility and superiority of the aramid-based insulation system, providing a research foundation and data support for its further engineering application.