The Comparison of Critical Radiu sof Rod-plane Gap at Different Altitudes and Research on Altitude Correction

Rod-plane gap is a typical electrode structure. Rod-plane gap under positive switching impulse has been widely researched, but no standard rod structure is approved. Rod-plane gap discharge voltage is related to the shape and radius of rod, this relationship is interested in engineering. The influence of rod tip shape to the discharge voltage is researched with different rod structure, such as hemispherical, conical, and unsealed terminal shape. Also critical radius of sphere-plane gap is calculated through experiments of the sphere radius of 19 mm～475 mm, the gap distance is varying from 2m～5m. To obtain the critical radius at different altitudes, same experiment was carried out in Beijing (altitude of 50 m), Xining (altitude of 2254 m) and Yangbajing in Tibet(altitude of 4300 m), and effects of altitude on the critical radius is analyzed.The common altitude correction method for air gap discharge voltage currently is applied mainly to an altitude of 2000 m and below. The altitude of upcoming high altitude transmission line will be more than 4000 m above sea level. Existing correction method would not be applicable. Rod-plane gap discharge characteristics is the basic of study in various gap structures. Researching rod-plane gap discharge phenomena at different altitudes, can help to analyze the high altitude air gap discharge characteristics more accurately. In this paper, rod-plane gap discharge experiments are carried out in Beijing, Guiyang (altitude of 1016 m), Xining and Tibet Yangbajing area. The discharge voltage at different altitudes is obtained, and the gap distance is ranged between 2 m～5 m. Finally, through experimental and computational analysis of the test results, the conclusion of the existing correction methods do not apply to an altitude of 4300 m above sea level is obtained. An altitude correction method major in considering the changes in air pressure is suggested.