Some aspects of system modelling for the estimation of lightning performance of high voltage substations

The computation of lightning overvoltages in a gas-insulated substation is carried out for different overhead line equivalent circuits. Models of the back-flashover characteristics of the line insulation in front of the substation are analysed, and an investigation is made into the influence of the number of overhead line spans represented in the equivalent circuit. The results show that the inclusion of three overhead line spans in the equivalent circuit is sufficient for the estimation of the substation lightning performance. The influence of the instantaneous value of the power frequency voltage at the moment of lightning strike is also analysed. Direct strikes to a phase conductor and to the tower top with back flashover are simulated. For relatively small values of lightning current, the phase voltage at the moment of strike has a significant influence