The planning, operation and control of power system are having great significance governed by security considerations. In an interconnected power system network obtaining maximum performance, maintaining system stability limits and facilitating efficient system operation are the challenging tasks. The estimation of effect of contingencies and planning suitable measures are desirable issues for maintaining security of complex power system. This paper describes the application of particle swarm optimisation (PSO) technique including thyristor controlled series capacitors (TCSCs) in order to eliminate or minimise line overloads under single contingency. A fuzzy logic composite criterion-based severity index is used as an objective to be minimised in order to improve the security of the power system. The proposed TCSC included PSO-OPF approach enhances the static security. A case study example on IEEE 30-bus test system demonstrates the applicability of the proposed approach. Copyright © 2014 Inderscience Enterprises Ltd.