Effects of simulation models of overhead transmission line basic components on backflashover surges impinging on GIS substations

Overvoltages arising in 150 kV and 400 kV GIS substations due to backflashover of the incoming overhead transmission lines were computed with the aid of ATP-EMTP simulations, by considering the effects of several simulation models of the basic transmission line components. The protection offered against impinging surges by surge arresters operating at the substation entrance is evaluated with respect to the basic insulation level of the GIS system. The computed overvoltages vary considerably among tower grounding system models and among insulator string flashover models whereas rather insignificantly among tower simulation models. There is no systematic variation in computed overvoltages among insulator string flashover models. Single vertical lossless line models and a constant rather than a current dependent resistance are considered, in terms of simulation simplicity and safe design, as satisfactory for simulating transmission line tower and its grounding resistance, respectively, in insulation coordination studies of substations.