Dispatch of main transformer ULTC and capacitors in a distribution system

This paper presents a dynamic programming method for solving reactive power/voltage control problem in a distribution system. The objective of this paper is to properly dispatch main transformer under load tap changer, substation capacitor and feeder capacitors based forecast hourly loads of each feeder section and primary bus voltage such that the total feeder loss can be minimized, voltage profile can be improved, and the reactive power flow into main transformer can be restrained. The constraints that must be considered include maximum allowable number of switching operations in a day for under load tap changer and each capacitor, the voltage limit on the feeder, and limited secondary bus voltage. To demonstrate the usefulness of the proposed approach, reactive power/voltage control in a distribution system within the service area of Yunlin District Office of Taiwan Power Company is performed. It is found that a proper dispatching schedule for each capacitor and under load tap changer can be reached by the presented method.