South Sumatera is located in tropical area with high ground flash density; therefore the occurrence of transmission line due to lightning strike is very high. Installation of lightning protection such as Transmission Line Arrester (TLA) is an alternative solution to improve transmission performance toward lightning strike threat. The selection of installation location must be well determined and calculated in order to obtain the effective and efficient performance of the TLA itself. This paper describe the methods to determine the optimum TLA installation location by calculating vulnerability index using cluster and weighted method on transmission line (SUTT) with voltage level 70 kV and 150 kV in South Sumatera. The required data for the evaluation are lightning density, insulator fault, ground resistance and the height of the tower. TLA location determination on transmission tower is performed by using simulation and then validated by comparison with insulator fault data.The optimum location has been studied for the TLA installation on several transmission towers in South Sumatera. The most effective installation is obtained when the TLA is installed on the upper most phase conductor.