Timing, Siting, and Sizing of Sub-transmission Substations and Distributed Generation Units Along Planning Horizon

Abstract

Development of distributed generation has provided new opportunities in power system planning. In this article, distributed generation units are considered as an alternative for supplying the load of a sub-transmission system, and a new mathematical framework is presented for expansion planning of an optimal sub-transmission substation and allocation of distributed generation units as well as defining the associated service area. The proposed method focuses on dynamic expansion planning and operation of distributed generation units and substations in a way with lowest cost. Dynamic expansion planning of a sub-transmission system is inherently a mixed-integer non-linear programming problem due to the prevalent electrical and expansion constraints, cost indices in the objective function, and decision variables. This non-linear problem is simplified to a linear problem by the proposed method. The cost function of the developed method consists of investment, construction, and installation costs of sub-transmission substations as well as connection costs of substations to the upper network, new medium-voltage feeders, and distributed generation units. The costs of purchased energy from the upper network and distributed generation units forecasted as nodal prices are added to the objective function. Moreover, prevalent constraints are considered. The proposed approach is applied to a realistic case study.