Transmission Network Planning: A Method for Synthesis of Minimum-Cost Secure Networks

A new method is proposed for solving the problem of minimum-cost expansion of power transmission networks. The problem is formulated as a mixed-integer program that explicitly considers both the investment costs of new lines and the operating costs associated with the system. The d.c. load flow equations for the network are embedded in the constraints of the mathematical model to avoid sub-optimal solutions that can arise if the enforcement of such constraints is done in an indirect way. The solution of the model gives the best line additions, and also provides information regarding the optimum generation at each generation point. The security is attained by an iterative procedure using a concept similar to that of the Cutting Plane methods of integer programming. The "Security Cuts\´ successively exclude the insecure solutions from the solution space of the problem until the solution obtained by the cost minimizing algorithm is a secure one. The important feature of this procedure is that the added constraints never exclude any secure solutions, thus security is attained without losing optimality. It is shown that the model is applicable to both static and multi-stage planning cases, and an application of the method to a real-world example with 22 right-of-ways is given.