Electrical energy need is increasing day by day along with the developing industry and growing population. New generation facilities are established near the primary energy sources to meet the demand. The generated energy is transported to the load location by transmission lines. Decrease of the power transfer capacity and great value of the power angle cause some problems, especially at the long-distanced places between the generation and the load location. In this context, series capacitors are used to increase transfer capacity on long transmission lines. It is also known that the series capacitors allow load sharing between the parallel lines and improve transient stability of the network. In addition to these positive contributions to the network, the series capacitor affects operation of the distance relay negatively. In this study, a sample test system is modeled by using Digsilent PowerFactory software in order to investigate the effect of series capacitor on loading of long transmission lines, transient stability of the network and operation of distance protection relays. Load flow and short circuit analysis were performed on the test system. The advantages and disadvantages of the series capacitors on the transmission system were investigated.