Approach to trace and locate long-term voltage instability risk in power system planning

With the integration of a quadratic optimisation method into one single Monte Carlo simulation, the system-wide and local risk index functions are developed to quantify the relations between the system-wide and local voltage stability risk and load levels. Each defined risk index function is a function of load level under various possible pre-contingency and contingency states and load uncertainty. Based on the proposed risk index functions, a method of tracing and locating long-term voltage instability risk in power system planning is presented. The methodology can trace the overall system-wide voltage instability risk in a planning timeframe and locate weak branches and buses. The effectiveness of the proposed method is demonstrated using the IEEE 14-bus system and an actual utility system with 171 buses.