Estimation of switching surge flashover rate of 1200-kV UHVAC transmission line considering switching overvoltage waveshape

The insulation of the power transmission system experiences stresses due to power-frequency voltage under normal operating conditions, temporary overvoltages at or near power-frequency and transient overvoltages arising either from switching operations and faults or from lightning discharges. However, in the insulation design of extra-high-voltage and ultra-high-voltage systems, transient overvoltages arising from switching operations and faults become the controlling factor. Insulation failure probability under switching overvoltages is the main impressive concern in the estimation of switching surge flashover rate. In this paper, a practical method is used to estimate the switching surge flashover rate of insulation under switching overvoltages generated during energization, re-energization, fault initiation and fault clearing of an unloaded transmission line, which considers the variable characteristics of the insulation strength of the transmission line according to the switching overvoltage waveshape. The results focus on the comparison between traditional and practical methods which considers the effect of the front time on the first 1200-kV UHVAC transmission line in India.