Optimal Reactive Power Control against Voltage Collapse

(PSERC) is a multi-university Center conducting research on challenges facing the electric power industry and educating the next generation of power engineers. More information about PSERC can be found at the Center's website: Notice Concerning Copyright Material PSERC members are given permission to copy without fee all or part of this publication for internal use if appropriate attribution is given to this document as the source material. This report is available for downloading from the PSERC website. The authors wish to recognize their postdoctoral researchers and graduate students that contributed to the research and creation of the reports: The authors thank all PSERC members for their technical advice on the project, especially the industry advisors for the project: • Chetty Mamandur – CAISO ii Executive Summary In recent years, new attention has been given to system disturbances that have cascaded due to voltage instabilities and to unwanted relay operations. Unwanted relay operations due to voltage instabilities and transients have not been well understood. In this project, voltage instability phenomena were studied to develop a comprehensive approach for mitigating the effects of voltage transients and instabilities on designed operation of a protection system. The comprehensive framework covers monitoring, predicting, and assessing system performance for secure power system operation. The developed framework and methodology provide advanced tools use optimal control strategies that can be used to avoid voltage collapse with respect to system-wide voltage instability and undesired protection system operations. The project's specific objectives were: • to develop realistic models that accurately model voltage dynamics and their effects on protective schemes • to develop fast and flexible schemes for assessment of voltage stability and relay status • to develop optimal strategies to prevent voltage instability and maintain adequate relay margins. The project objectives were accomplished in two integrated steps. In this step of the project, we identified schemes for fast and flexible assessment of voltage stability and relay status. Then we developed optimal strategies for maintaining adequate voltage stability and relay margins. Voltage stability margin (VSM) assessment for online monitoring is a challenging problem computationally. We developed a predictor and corrector based framework to estimate VSM at local buses. The framework applies a Thevein Equivalent method as a predictor to approximate the maximum power that can be transferred. Since Thevein Equivalent is a linear approximation, it cannot consider system operational constraints which cause the VSM estimate by the predictor to be too …