Dispatch of Main Transformer ULTC and Capacitors in a Distribution System

This paper presents a dynamic programming method for solving reactive power / voltage control problems in a distribution system. The objective of this paper is to properly dispatch main transformers under load tap changers, substation capacitors, and feeder capacitors based on hourly forecast 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 the main transformer can be restrained. The constraints that must be considered include the maximum allowable number of switching operations in a day for under load tap changer and each capacitor, and the voltage limit on the feeder and secondary bus voltage is limited. To demonstrate the usefulness of the proposed approach, reactive power /voltage control in a distribution system within the service area of the 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.