Large scale voltage stability constrained optimal VAr planning and voltage stability applications using existing OPF/optimal VAr planning tools

Traditionally in optimal VAr planning, the feasible operation has been translated as observing voltage profile criteria ensuring that the system voltage profile is acceptable for system normal and post contingency conditions. This feasibility definition is not sufficient when considering the VAr planning practice of the utilities concerned with voltage stability problems. Presently, these utilities use two reinforcement criteria for VAr additions. While for VAr design in the regions the voltage profile criteria is considered, for bulk transmission system VAr resources are designed to guard against voltage instability. This paper reports on the findings of a recently completed EPRI project evaluating the existing optimal VAr planning/OPF tools for voltage stability constrained VAr planning and voltage stability applications. Two of the selected tools were adapted to address these applications on four large scale utility systems (up to 6000 buses). The results were also verified using EPRI's voltage stability program (VSTAB). The results obtained indicate that OPF/VAr planning tools can be used to address voltage stability constrained VAr planning and voltage stability applications in an accurate way. Additional advantages offered by these tools are easier procedures, less computation and avoidance of engineering judgment in identifying the amount of VAr requirement at the candidate sites.