Effect of Equalizing ring on flashover characteristics of cat-head composite insulator

Abstract

The installation of grading rings for composite insulators on high voltage transmission lines was an effective measure to improve the distribution of electric field and prevent brittle fracture of the core bar. In this paper, the flashover characteristics of insulators with and without the installation of the grading ring on the 110 kV voltage grade cat head tower were tested and simulated. Firstly, The U 50 , volt-time characteristics and discharge images of the insulators are studied by experiments. The experimental results show that the unit length U 50 of the insulator with the grading ring will increase compared to the insulators without the grading, and the volt-time characteristic position is basically unchanged while the starting point of the discharge channel is transferred from the fitting of insulators to the grading ring and the number of leading channel branches increase. Secondly, the electric field distribution around the insulator before and after the installation of the grading ring is studied by simulation. The simulation results show that the maximum field strength around the insulator decreases when the grading ring is installed, while the unevenness coefficient decreases and the average electric field strength increases. The simulation results agrees well with the test data. The research results can be used as a reference for the optimization design of the voltage equalization loop and the lightning protection of high altitude transmission lines.