송전계통 접지봉의 임펄스 임피던스 저감에 관한 연구 = A Study on the Reduction of Impulse Impedance for Ground Electrodes at Transmission System

다국어 초록 (Multilingual Abstract)

Power system grounding is very important for stable operation of power facilities, electronic communication devices and human safety as well as for anti-lightning design of the system.
It is difficult however to estimate ground resistance exactly due to many uncertain parameters in nature such as soil resistivity, perceptivity, current density in soil, seasonal variation of those values and etc. It becomes more complicate under large impulse current like lightning surge currents due to their corona discharge in-soil, which has highly nonlinear cransient characteristics. Since the impulse currents caused by lightning stroke would give rise to insulation failures of power system facilities, it is necessary to distribute the currents into soil as soon as possible.
Unlike the ground resistance as in low frequency, impulse impedance doesn’t be reduced proportionally according to the increase of grounding area. Rather high soil resistivities in Korea makes it more difficult to reduce impulse impedance of grounding electrode.
This paper describes the measurement, design of grounding electrode and reduction method of ground resistance. In particular, grounding electrodes with needles were used to investigate the impulse impedance behaviour under fast-rising surge current. And we compared its performance with currently used common grounding electrodes by impulse test using outdoor impulse voltage generator.
The experimental result showed that the impulse impedance could be reduced considerably by grounding electrode with needles which causing corona discharge in soil more easily.