Assessment of Real-Time Optimal Voltage Control

This paper reports the results of a detailed study of on-line voltage/var control performed on the Ontario Hydro system. The first part of the study is an assessment of active transmission loss savings obtained by optimizing generator voltages and transformer taps with an Optimal Power Flow program using data from a state estimator. In the second part of the study, the question is addressed of how frequently the generator voltages and transformer tape should be optimized in order to achieve a large percentage of the loss savings indentified in the first part. The study showed that the reduction in active losses is sufficient to justify further effort toward implementing voltage control. The results of the second part showed that for the load curve studied, most of the savings could be achieved with voltage control cycle times of about one hour. A new quadratic programming-based optimal power flow algorithm is also presented which exhibits execution times suitable for real-time applications. Sample execution times are given for various systems which confirm that exact optimal power flow solutions can be obtained in a fraction of the control cycle times suggested in the second part of the study.