Estimation of Switching Surge Flashover Rate of a 1200 kV UHVAC Transmission Line due to Switching Overvoltages

The rapid increase in transmission voltages to fulfil higher demand of the transmitted power yields to put the switching surges as the governing factor in the insulation design process for EHV and UHV systems. Contemporary methods of insulation coordination utilise probabilistic approach and statistical methods particularly in the case of ultra-high voltage systems. This paper determines the statistical distributions of energization, re-energization, fault initiation and fault clearing overvoltages of the 1200 kV system modelled in PSCAD. Decisive figures like mean value, standard deviation and 2% statistical overvoltage values of switching overvoltage are estimated using randomness of the instants of closing with 526 operations for line energization and re-energization, and randomness of faulted phase, fault location and fault times with 3 faulted phases, 8 fault locations and 21 fault timings, 504 simulations for fault initiation and fault clearing. Ascertaining the investigations from the above simulations the stress on the towers is estimated. From the stress and insulation strength of the tower a systematic approach to calculate the switching surge flashover rate (SSFOR) is presented.