Investigation of the DC arc propagation of insulator string and its performance at low air pressure

Air pressure affects the electrical performance of polluted insulator. The dc pollution flashover process of 7-unit XP-160 insulator string under low air pressure was presented by laboratory tests in this paper. During the tests, the flashover voltage and the critical flashover current were measured. Also, based on the insight of insulator flashover process, the length of discharge path, the arc propagation velocity and arc radius under different air pressure were investigated and measured. The research results indicate that, the position of arcing point is stochastic and multipoint arcing phenomenon exists. Surface arc will levitate and develop into air-gap arc under low air pressure. The length of discharge path is related to air pressure and pollution degree, and it is always shorter than the total creepage of insulator string. The leakage current, the arc shape and arc propagation velocity, are also related to air pressure. In this study, it was measured that the arc radius (ra) varied from 1.5 to 3.5 mm, and the characteristic exponent describing the influence of air pressure on arc radius (m) varied from -0.35 to -0.65. The research results are of some significance for revealing the mechanism of flashover and discharge performance of arcs.