Switching overvoltage analysis and air clearance design on the KEPCO 765 kV double circuit transmission system

This paper presents the results of the air clearance design on the KEPCO 76 5 kV double circuit transmission system. At first we performed the switchin g overvoltage study, The switching overvoltage was analyzed by EMTP (Electr o-Magnetic Transient Program) and TNA (Transient Network Analyzer). The ful l scale test for the air insulation strength of 765 kV double circuit trans mission tower was performed by 4 MV outdoor impulse generator, The simultan eous fault clearing case of single line-to-ground fault at each circuit was considered because the probability of simultaneous single line-to-ground f ault at each circuit is very high, However, the reclosing overvoltages with preinsertion resistor are lower than the simultaneous fault clearing overv oltages when the transmission line is short (about 170-180 km), The maximum phase to ground switching overvoltage in the simultaneous fault clearing c ase is 1.9 p.u. and the maximum switching overvoltage between phase to phas e is 3.3 p.u. The required air clearance in a tower at the altitude of belo w 1000 m is 4950 mm to endure the maximum switching overvoltage of 1.9 p.u, The standard deviation of 5% in switching surge flashover voltage was veri fied from the full scale test.