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Performance of power transmission lines has a great impact on reliability of a particular power supply system of a country. Unreliable power transmission lines can even lead to total power failures resulting with great financial losses. The lightning back flashover effects are recognized as one of the major causes of transmission line outages, especially in tropical countries with frequent lightning. Several types of solutions are presently available to address the issue of lightning back flashovers. However, the modern concept of transmission line mounted surge arresters is of great popularity due to its excellent performance, ease of installation and the low cost compared to the other solutions. This paper describes a case study carried out on one of the critical hill-country 220kV power transmission lines of the Sri Lankan transmission network, having several past records of lightning back flashover related outages leading to total system failures. The study described in this paper mainly focuses on the way of analyzing the back flashover events by transient modeling and subsequent simulation of the selected transmission line in an electromagnetic transient computer program. The study uses the Power System CAD (PSCAD) software program as the software tool for the purpose of modeling and simulation. Simulations are carried out with and without Transmission Line Arrester (TLA) to evaluate TLA's impact on back flashover. The results of the simulations show that the installation of 02nos. of TLA at top phases of each selected towers improve the overall performance.