DC Flashover Performance of Insulator String with Fan-shaped Non-uniform Pollution

Under continuous wind of single direction, the leeward area of insulator string may be polluted more seriously than windward area, making the pollution layer distributes like a fan-shape. In this paper, dc pollution flashover tests of 7-unit XP-70 insulator string with fan-shaped non-uniform pollution were carried out. Then the influence of fan-shaped non-uniform pollution on flashover voltage, flashover process, leeward side surface layer conductivity and surface pollution layer resistance were discussed. Research results indicate that, the ratio W/L of windward to leeward side salt deposit density (SDD) affects the dc flashover performance of insulator string. A reduction in W/L from 1/1 to 1/15 would give a decrease of 28% in flashover strength. Flashover voltage may also decrease when the occupation ratio (T) of leeward side increases from 10% to 30%. Under fan-shaped non-uniform pollution, U-50 can still be expressed by a negative exponential function of SDD, and the effect of fan-shaped non-uniform pollution on U-50-SDD relationship may mainly lie in changing the proportionality coefficient a rather than the exponent n; discharge path was restricted along the leeward side, which may make the air-gap arc easily formed and benefit the flashover process.