A comparative analysis of energy storage and N-1 network security in transmission expansion planning

In a restructured power system, one of the key objectives of transmission network expansion is to provide nondiscriminatory access to cheaper generation for all consumers. However, the robustness of the transmission network against all uncertainties such as credible contingencies should equally be maintained. Thus the development of effective methodologies and strategies to satisfy this objective is a major challenge faced by the transmission expansion planners in the new environment. In this paper a static transmission expansion model with energy storage is proposed. The energy storage is coordinated with transmission expansion planning in a system with base load generators and expensive peaking power plants. The energy storage is modelled to store the cheaper generation from the base load power plants at off peak periods and discharges to meet the demand at peak periods. Four distinct transmission expansion models with and without energy storage system (ESS) and N-1 network security constraint are developed for the comparative analysis. The whole problem is formulated as a mixed integer linear programming (MILP) problem with the objective of minimizing the operational cost of the generators as well as the transmission line and storage investment costs over several demand levels. The proposed methodology is demonstrated on the IEEE 24 bus reliability test system (RTS). The overall results from the model showed that energy storage benefits the system by deferring investment in transmission lines. The model also confirmed that the marginal benefit of storage diminishes as the investment in ESS increases. In addition, the economic viability of corrective planning over preventive planning of transmission network is also justified.