Research of Grading Ring for High Altitude 500 kV Compact Transmission Line

Corona performance is an key issue in the design and operation of high voltage transmission lines. Corona discharge phenomenon is relatively obvious for grading ring of 500 kV compact transmission suspension string in some northwest part of China, and need to be optimized as to meet the operation requirement of high altitude areas. In this paper, finite element analysis software is used to model actual compact transmission line and calculate surface electric field distribution of grading ring both before and after optimization. Corona discharge characteristic of grading ring is also performed according to the simulation result and discharge photon number of ultraviolet rays is recorded by ultraviolet image apparatus. It indicated that the maximum electric field intensity is decreased by nearly 35.9 % to 24. S kV/cm from 38.7 kV/cm by optimization of type, pipe diameter and installation method. The relationship between photon number of ultraviolet rays and applied voltage is approximate the power function, and the inception and extinction corona voltage after optimization is respectively 34.3 %, 43.3 % higher than before. The electric field distribution of grading ring is effectively improved by the optimization studied in this paper and grading ring can operate normally at high altitude about 3500 m, as to meet the altitude correction requirement of IEC 60071-2.