Control of electric field and voltage distribution of a 765kV system polymeric insulator used in Indian transmission systems

Composite insulators are being subjected to higher electrical stresses with the increased transmission voltage levels being adopted universally. In addition to high electrical stresses at the energized end, the electric field distribution along the length of the insulator being non uniform may lead into problems associated with corona causing deterioration of material of no ceramic insulators. Therefore, the control of electric field strength in the vicinity of such insulators is an important aspect to be considered in the design. In this paper, the authors have attempted to determine the adequacy of the grading ring design proposed by the manufacturer M./S. G.K. Xianghe Electricals, Pvt. Ltd., India for use in 765kV system by computing the electric field distribution along the insulator length. In the next step, an attempt was made to suggest a suitable Corona / Grading ring design for minimizing the electric field at the energized high voltage end as well as at ground end in addition to reducing the non linearity in the electric field distribution along its length using Finite Element Software. The results of the optimization study are presented here.