Altitude Correction and Selection of Air Gap Discharge Voltage in Converter Stations in High Altitude Areas

A converter station is an important part of an HVDC transmission project. The shielding fittings at the end of converter station equipment are generally large in size, and the air gap between them and the surrounding grounding body is much more approximate to a slightly uneven electric field. Its discharge characteristics are quite different from rod-plane, rod-rod and transmission tower gaps. With relatively few UHVDC converter stations located at an altitude of 2,000m and above, and few discharge test curves of air gaps available in the world, in order to ensure a reliable design of converter stations and valve halls in high altitude areas, typical gaps of valve halls and DC fields in converter stations are analyzed, and a variety of typical gaps are obtained, including sphere-ground, sphere-wall/ground, valve tower-ground, and the most typical gap is sphere-plane gap. Discharge tests of 1.5m sphere-plane gap in converter stations are conducted at 55m and 4,300m above sea level. The altitude correction methods of gap discharge voltage specified by IEC60071-2, IEC60060-1 are analyzed, and the difference of discharge voltage and variation law of gap factor in high-altitude areas obtained by different altitude correction methods are compared and analyzed. According to the SI discharge test results of 1.5m sphere-ground gap and rod-plane gap at different altitudes, the minimum air gap distance required for valve hall at converter stations above 4,000m and below is calculated and analyzed using different altitude correction methods and gap factors. Research results can be used in the design of valve hall and DC field of converter stations in high altitude areas. On the other hand, it provides basic data for altitude correction of long air gap in high altitude areas.