Analysis of Power Factor Over Correction in a Distribution Feeder

Capacitor banks are commonly connected to the power system to enhance its reliability by providing voltage support, improving power factor, and increasing the system capacity. They are usually switched in and out of the system according to the amount of connected load. This paper analyzes measurement data of a distribution utility with capacitor banks located downstream from the power quality monitor. It was observed that the amount of reactive power injected into the system was larger than the necessary, resulting in power factor over correction. The paper then provides an analysis method to determine the capacitor bank size to achieve a desired power factor correction. An algorithm is also proposed to override a switching control (usually time, voltage, or temperature), such that the switching is performed only if the power factor is below a preset minimum value. Moreover, it is advised to switch each phase individually, as the reactive power flow differs significantly between the three phases.