Approximate nominal PI section models are used for short transmission lines (of the order of 15 km), where the travel time is less than the solution time-step and the travelling wave model is utilised, when travelling time is greater than time step. There are two options for using travelling wave model (i) Bergeron’s model, when physical geometry of line regarding conductor radius & positions is not available (ii) Frequency dependent transmission line model, when physical geometry of transmission line regarding conductor radius & positions is available. The several line elements are represented by following models for simulation of transient: [8]