In order to get the bird streamer flashover characteristics in high altitude area

the discharge of DC V-string insulators was studied in theYang Bajing high-altitude test base at an altitude of 4 300 m. The study results show that medium viscosity bird streamer is easy to form continuous channel and cause flashover. The flashover probability on the positive polarity transmission lines is slightly higher than that on the negative ones. The conductivity of bird excrement has a negligible effect on the flashover probability in the range of 1.9～20.9 mS/cm. Increasing the vertical air gap distance can reduce bird streamer flashover probability. Based on the experiment results

the recommended vertical air gap distance values of ±400 kV Chaila DC transmission line were proposed. After the influence of wind and bird streamer falling angle were taken into consideration

the protection radius was recommanded to set 3.5 m at 3 500～5 000 m altitude area. Bird streamer flashover is a mixed discharge of air gap breakdown and the surface discharge along the bird streamer channel

at the altitude of 4 300 m area

the minimum breakdown potential gradient is about 2.1 kV/cm

and the discharge between bird streamer and corona ring can be approximately equivalent to rod-rod gap discharge.