Distributed static series compensator (DSSC) is a member of the family of distributed flexible AC transmission system devices that can be attached directly to conductors of transmission lines. DSSCs are able to compensate for and adjust the line reactance; thus, they could be widely used in stability-limited transmission systems. Owing to economic matters, the optimal placement of DSSCs is of a great interest from practical viewpoints. This study presents an approach to find the optimal locations of DSSCs to enhance the system loadability and reliability using the DC load flow model. The optimisation problem is solved using the mixed-integer linear programming. A compromise between improving the system loadability and reliability is fulfilled and a wide range of non-dominated optimal solutions is calculated. The final solution is then selected using the fuzzy satisfying method. Numerical studies are conducted on the IEEE reliability test system (IEE-RTS). Nomenclature

The deployment of flexible ac transmission system (FACTS) devices, despite miscellaneous benefits and applications, has been restricted mainly due to their large investment costs. Accordingly, the notion of distributed FACTS (D-FACTS) was recently proposed. Distributed static series compensators (DSSCs), as a new member of D-FACTS, are directly clamped to conductors of transmission lines. The possibility of controlling the compensation rate of DSSCs from the control center affords the active control of network power flow. This paper presents a comprehensive reliability model for the DSSC. The model is then reduced and a state-space representation is extracted for a transmission line with a number of DSSCs. To illustrate the worth of DSSC utilization, the increment in the expected interruption cost is computed by using a composite reliability assessment. In the contingency analysis procedure, incorporating the active control of power flow provided by DSSCs makes the optimal load curtailment subproblem nonlinear. In order to linearize the subproblem, a novel set of inequalities is extracted. Numerical analysis on the IEEE Reliability Test System (RTS) is conducted to examine the effect of DSSC on composite reliability indices. The results reveal the effectiveness of proposed models and illustrate that DSSCs enhance the system reliability.Index Terms-Distributed static series compensator (DSSC), flexible ac transmission system (FACTS), linear programming, power system reliability.