According to historical data, most overhead transmission line faults are caused by lightning strikes. Lightning strikes account for majority of the line outages in many countries. Moreover, the increasing prevalence of hybrid cable – overhead line transmission systems means that lightning strikes on the overhead line can affect the underground cable and create over voltages in the system. To minimize the risk of over voltage in the system, it is important to study the behaviour of lightning transients and the methods to mitigate the impact of the same on the system. One method to do this is to choose an appropriate grounding method for the overhead line and underground cable. The grounding configuration will have a big impact on the lightning performance of the transmission system. The objective of this thesis is to analyse various grounding scenarios for the overhead line shield wire and the underground cable sheath and based on the results draw a conclusion and select the most suitable grounding strategy to improve the lightning performance of the transmission system.