AbstractLightning stroke causes a current injection into transmission lines at the point of contact. The lightning performance can be difficult to understand without using simulation programs. PSCAD a powerful software was selected to develop the appropriate data required to investigate this phenomena.In this paper, two points along transmission line are selected for studying voltage–time (V–t) characteristics when any of those points is subjected to lightning strokes separately. The first assumed point is taken when lightning current is injected to the shielding wire at the top of the transmission tower, while, the other assumed point is taken when surge current is injected to the shielding wire at maximum sag location in the mid-span between two towers. The sag of transmission line has been newly developed and simulated using PSCAD.Both transmission line containing sag as well as lightning injection current are modeled. Fast transient of flashover as well as back flashover occurrence is investigated. The results revealed that the sag of transmission line has considerable influence on flashover and induced voltages across line insulators and phase lines as well. The influence of connecting surge arrester in substations is investigated. A proper transmission line arrester (TLA) is designed in order to minimize the occurrences of overvoltages due to flashover and consequently back flashover across insulators.