Research on the Calculation of Initial streamer Length in High-Altitude Sphere-Plate Gap Based on the streamer Injection Development Model

Ultra-high voltage direct current (UHVDC) transmission technology is a key energy transmission technology developed in China. The shielding fittings in the converter station valve hall, a crucial hub, play an important role in electrical load transmission, mechanical load bearing, and electromagnetic protection. However, as transmission projects extend to high-altitude areas in the western regions, reduced air pressure and lower air density lead to decreased insulation strength of the long air gaps between the sphere and the plate in the valve hall. There is an urgent need to study the discharge characteristics in high-altitude environments. In this paper, large-diameter sphere-plate long air gap tests under positive polarity operating impulse voltage were conducted at the Qinghai UHV test base at an altitude of 2,200 meters. By measuring characteristic parameters such as optical power, electric field strength, and current, and analyzing the development characteristics of the 0.6-meter diameter sphere-plate gap based on the experimental dataset and the streamer and discharge development model, the research provides theoretical support for the insulation design and optimization of DC transmission projects.