A Study on Insulation Level Decrease of 22 kV Overhead Distribution Line in Isolated Neutral System

Abstract

For insulation design of 22 kV overhead distribution lines, major guidelines have been specified: (1) Have enough insulation ability against the line’s internal abnormal voltage, while arresters are used against external abnormal voltage such a lightning surge. (2) Decrease the line insulation level by using specific arresters capable of regulating the switching surge, resulting in an overall BIL decrease. The first specification is commonly adopted because the arrester’s absorption energy against the switching surge is not yet identified. The revised JEC testing voltage standard specified further lowered the insulation level (LIWV 100 kV), but its target was only for the 22 kV overhead distribution lines in a resistance grounded neutral system. Recently, focus is placed on studying for protecting the lines from direct lightning strikes, thus a variety of lightning protection equipment is widely applied on the lines. Consequently, guideline (2) above is also taken into account. In short, 22 kV overhead distribution lines will achieve both decreasing insulation level and improving lightning protection ability by installing many arresters for LIWV 100 kV in an isolated neutral system. Given these circumstances, to make this idea feasible, the authors studied the absorption energy of the proposed arresters against the internal abnormal voltage of the 22 kV overhead distribution lines in an isolated neutral system. The results revealed that the arresters are well applicable to the 22 kV overhead distribution lines.