How to Optimize the Grading Ring for 330kV Transmission Line

Abstract: The simulation and calculation model is set up by the finite element method; the surface field strength of grading rings of 330kV transmission line with 4 kinds of different pipe diameters and 2 kinds of different curvature radius are calculated and analyzed. The visible corona tests are conducted at the UHV outdoor test field and AC test base climate lab to obtain the surface field distribution of grading rings with different structure types, comparison results and curves of corona inception voltage at different altitudes. The research results indicate that optimization of pipe diameter and curvature radius can effectively reduce the surface field strength of grading rings and enhance the corona inception and extinguishing voltages. 

Key words: high altitude, grading ring, corona discharge, finite element method, electric field distribution, altitude correction        

Introduction

Harms caused by corona discharge such as corona noise, wireless interference or electrostatic effect attract increasing attention from people. Results of relevant studies indicate that the corona discharge of 330kV AC transmission line grading rings in northwest high-altitude area is serious and grading rings have become one of main parts causing electromagnetic pollution. Given characteristics of corona discharge, it is difficult to meet the requirements of high-altitude operation. The factors affecting corona discharge of grading rings are complicated. Parts where the field strength is high are mainly located at the curves of uneven field strength distribution. The radius of electrode curvature at the curve is small so it is likely to have partial corona discharge; meanwhile, the discharge of grading rings are easily affected by operating conditions, including pressure, temperature and humidity etc.