The aim of this paper is to introduce a practical way to find an optimal plan for electric power system reinforcement through line addition. Adding a line to the existing networkTis needed to improve system reliability and/or to raise its loadability. On the other hand line addition results in worsening voltage sag immunity of the system. In order to reach the most appropriate schedule, both system reliability and voltage sag must be considered. This paper assesses the effect of the line addition by comparing the cost gained from raising the overall system reliability with that lost due to worsening the voltage sag immunity. A novel approach to calculate the global reliability of the power system is proposed. This approach is capable of calculating the reliability of all power system nodes following one straightforward procedure which avoids repetition of calculations and drastically reduces the number of steps and execution time. Voltage sag immunity is evaluated by identifying the area of vulnerability caused by short-circuit (S.C.) on the system. The paper suggests using a knowledge-based expert system (E.S.) to help in selecting the appropriate reinforcing line. Representative case study is discussed to demonstrate the effectiveness of the proposed approach.
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