Dynamic expansion planning of sub-transmission substations and defining the associated service area

•Through the proposed methodology the MINLP problem is decreased to MIP problem.•The service area of substations and expansion planning is defined simultaneously.•Efficient operation of substations over the planning time horizon is determined.•The duration curve of load demands and nodal prices are considered.•Dynamic, multi stage and static expansion planning approaches are compared.

In this paper, a new methodology is presented for dynamic expansion planning of sub-transmission substations (DEPSS). The proposed method deals with the expansion schemes of the facilities which should be installed and/or reinforced in order to make the sub-transmission system capable of supplying the forecasted demand at the lowest cost while all technical constraints are satisfied. DEPSS is inherently a mixed integer nonlinear programming (MINLP) problem due to the prevalent electrical and expansion constraints, cost indices in objective function and decision variables. This nonlinear problem is simplified to a linear problem without any neglecting by the proposed method. The location, capacity and construction time of substations and MV feeders, as well as the optimal service area of substations are determined through a dynamic approach for the planning years. Meanwhile, the optimal operation capacities of substations are determined at each load level in every planning year. The effectiveness of the proposed optimization method is discussed in the first case study which is related to just placement and defining the associated service area. Also, the proposed dynamic method is tested on a realistic case study and compared with the static and multistage approaches.