Fixed/switched type shunt capacitor planning of distribution systems by considering customer load patterns and simplified feeder model

A shunt capacitor planning strategy to reduce system resistive losses and improve voltage profile for distribution feeders has been proposed. The objective function consists of peak load loss, energy loss and shunt capacitor cost, while operational constraints such as bus voltage profile and real shunt capacitor size are considered throughout the overall solution procedure. A three-phase load flow program, which accounts for the mutual coupling effect between conductors, unbalanced loading among phases, and feeders with multiple lateral branches, is applied to enhance the computer simulation. The simplified feeder model has been developed to derive the equivalent circuit of minor lateral branches so that the data processing work for the feeder configuration can be reduced efficiently. Besides, the customer load patterns as well as the feeder load curve for various seasons are derived so that the section load behaviour can be estimated more realistically. According to the reactive load duration curve of the feeders studied, the capacitor operation strategy by considering both fixed and switched shunt capacitors is developed to determine the proper size, location and switching time of capacitors to enhance the system operation efficiency. Two practical feeders in the Taipower (Taiwan Power) distribution system are selected for demonstration to show the effectiveness of the proposed method. Capacitors with optimal size are installed according to the schemes derived by computer analysis. Field tests are then performed and the energy loss reduction as well as the improvement of power quality of the test feeders can be justified.