Voltage and Reactive Power Control in Closed Loop Feeders with Distributed Generation

This paper investigates voltage and reactive power control in radial and closed loop distribution systems and how the presence of distributed generation (DG) affects the control. Comparative analysis between voltage and reactive power control in radial and closed loop feeders, based on coordination of OLTC, substation capacitors (the shunt capacitors installed at the substation secondary bus) and feeder capacitors (the shunt capacitors located somewhere along the feeder) is presented. The known benefit of closed loop operation is examined in a case study. It is shown that the feeder losses and the voltage fluctuation decrease with the change from radial to closed loop operation. The decrease of voltage fluctuation in the feeder is shown not to reduce the OLTC and capacitor operation. It is also shown that in a certain case closed loop operation can even decrease the maximum allowed DG capacity in the feeders. Further, while it is known that the closed loop operation can defer the distribution line upgrade due to load growth, if the contingency operation is taken into account, the closed loop operation will even earlier request the distribution line upgrade.