Experimental Research on Discharge Characteristics and Altitude Corrections for Typical Long Air Gaps at High Altitude Area

Due to unbalanced energy resources and allocation of productive force in China, our country has to develop and build ultra-high voltage grid. As most of western regions in China are located in high attitude area, the construction of power transmission and transformation project would inevitably go though these different altitude regions with average elevation of over 1000 meters. The atmospheric condition in different altitude regions has distinctive impact on the discharge voltage of outdoor insulators. The experimental results from low altitude regions cannot be used for engineering design of high altitude applications. The characteristic of air gap discharge is the basis of UHV transmission line external insulation design. Studying the discharge characteristics of side-phase discharge and its altitude correction can not only provide reference for choosing air gap distance in power projects at high altitude, but also be used for correcting air gap discharge voltage at high altitude. For the purpose of obtaining air gap discharge voltage and its correction in different altitudes, typical phase-to-phase air gap was selected, and comparative experiments were conducted under the same configuration condition at the different altitude areas such as Wuhan (35m), Chengdu (500m), Guiyang (1000m), Kunming (2100m). The experiments were carried out under extreme weather conditions which considered air pressure, temperature and humidity, including direct alternating current (AC) voltage discharge tests with gap length of 1.3m, lightning impulse (LI) voltage discharge tests with gap length of m, and switching impulse (SI) voltage discharge tests with gap length of 3.3m and 4.2m. According to the test results, the influence of atmospheric conditions and altitude correction factors of AC, LI, and SI discharge voltage were calculated and analyzed systemically in this paper. Finally, altitude correction parameters of typical air gap discharge voltage at high altitude of 2100m in voltages of AC, LI and SI were proposed, and the impact of proposed changes in the voltage range under the influence of factors such as temperature, humidity, and barometric pressure, etc., obtained modified formula to meet the needs of practical engineering.