SUMMARY
The optimal placement of Thyristor Controlled Series Compensators (TCSCs) in transmission systems is formulated as a multi‐objective optimization problem with the objectives of simultaneously maximizing transmission system loadability, minimizing transmission loss, minimizing the cost of TCSCs, and minimizing the voltage deviation at the load buses. The thermal limits of transmission lines and voltage limits of load buses are considered as security constraints. This problem is solved in two stages. In the first stage, multi‐objective particle swarm optimization, multi‐objective comprehensive learning particle swarm optimizer, and weighted sum method are applied to obtain the non‐dominated solutions. In the second stage, two different multi‐criterion decision‐making tools, namely Technique for Order Preference by Similarity to Ideal Solution and Fuzzy C‐Means clustering are employed to assist the decision maker in deciding the best trade‐off solution. The proposed approach is successfully tested on IEEE 14 bus system and IEEE 118 bus system. Copyright © 2011 John Wiley & Sons, Ltd.