Optimal Future Sub-Transmission Volt-Var Planning Tool to Enable High PV Penetration

This paper proposes a reactive power planning tool for sub-transmission systems to mitigate voltage violations and fluctuations caused by high photovoltaic (PV) penetration and intermittency with a minimum investment cost. The tool considers all existing volt-ampere reactive (var) assets in both sub-transmission and distribution systems to reduce the need of new equipment. The planning tool coordinates with an operational volt-var optimization tool to determine all scenarios with voltage violations and verify the planning results. The planning result of each scenario is the solution of a proposed optimal power-flow framework with efficient techniques to handle a high number of discrete variables. The final planning decision is obtained from the planning results of all selected violated scenarios by using two different approaches - direct combination of all single-step solutions and final investment decision based only on the scenarios that are representative for the power-flow voltage violations at most time steps. The final planning decision is verified using a realistic large-scale sub-transmission system and 5-minute PV and load data. The results show a significant voltage violation reduction with a less investment cost for additional var equipment compared to conventional approaches.