Overvoltage Distribution Characteristics of Long Distance Gas Insulated Transmission Lines

Abstract

When gas insulated transmission line (GIL) is applied to long-distance transmission in urban underground pipe gallery, it will generate overvoltage due to capacity rise effect, which may threaten the insulation safety of equipment. However, at present, there is little research on voltage distribution along long-distance GIL. In this paper, the transmission line distributed parameter model is used to establish the voltage distribution calculation model along GIL, and the voltage distribution characteristics along GIL at different distances and voltage levels are calculated by taking typical transmission voltage levels as examples. The results show that the maximum value of GIL no-load line overvoltage occurs at 1 / 4 of the electromagnetic wavelength on the line from the head end of the line, and the line voltage increases with the distance when it is within 1/4 of the wavelength from the head end of GIL line. Through the analysis of overvoltage distribution of GIL lines with typical length, it is found that within 20 km, the increase rate of GIL end overvoltage is lower than 0.03% compared with that of the head end, and the influence of GIL line end overvoltage can be ignored. Considering 1.1 times of insulation withstand capacity, for 800 kV GIL line, the impact of Overvoltage on GIL equipment insulation can only be considered when its length reaches about 410 km. The results of this paper have reference significance for overvoltage protection and insulation test of long-distance GIL lines.