Tower Air‐gaps discharge characteristics and insulation coordination for UHV AC double‐circuit line

In order to give out inverse V‐type insulator tower air‐gaps configuration of double‐circuit UHV AC power transmission line, different distance air‐gaps from high‐voltage electrode to tower frame discharge tests of inverse V‐string are carried out. Discharge characteristics curves of power frequency voltage, 1000 μs long wave‐front switching impulse voltage, and lightning impulse of UHV AC double‐circuit tower are obtained. Results show that the 50% discharge voltage gradient of bottom phase air‐gaps is higher than middle phase. 1000 μs wave‐front switching impulse 50% discharge voltage gradient of bottom phase air‐gaps is 4.6% higher than the middle phase. Based on the test results and the characters of operating voltage and overvoltage of UHV AC power transmission system, the UHV AC double‐circuit tower inverse V‐type insulator air‐gaps configuration is proposed. The air‐gap configurations of power frequency voltage and switching overvoltage are 2.9 and 6.5 m, and the lightning protection air‐gaps are 6.7 and 7.2 m, in mountains and plains.