Comparison of External Insulation Level between AC and DC Overhead Transmission Lines

Abstract

It is important to choose suitable insulator strings that matching the voltage level when trying to change an AC transmission line into a DC one. Historically based, most published works discuss the way of determining the number or the length of insulators for overhead transmission lines, which mainly consider about voltage levels, pollution classes, insulator types and their pollution performances. It calls for too much work for a line restructuring project. In order to simplify the work, a comparison of the choosing of insulator strings between AC and DC overhead transmission line is made in this paper. Two main results are obtained. One is that the ratio, which defined as α, of the number of insulator on DC transmission line and that on AC transmission line ranges from 1 to 2.5 with the decreasing of voltage level under the same pollution class, the other is that the value α remains substantially constant under the same voltage level, and it will decrease slightly as the pollution class increases. The results provide theoretical basis for the choosing of insulator strings in line restructuring projects.