On-line reactive power compensation schemes for unbalanced three phase four wire distribution feeders

A new reactive power compensation method is developed to reduce the negative and zero sequence components of load currents and to improve the load bus power factor of unbalanced three-phase four-wire distribution feeders. Negative and zero sequence currents may cause additional losses and damage to power systems. Load compensation at the load bus is an effective method to eliminate those undesired sequence currents. The compensation technique uses a Y-connected and a Δ-connected static reactive power compensators (SVCs) to give a different amount of reactive power compensation to each phase. The compensation formulas are very suitable for on-line control by measurement of phase voltages and currents in real time. The compensation effect can also be achieved even if one leg of the SVCs is out of service. In addition to balancing effect and power factor improvement at the load bus, the SVCs can also be used to support the load bus voltage and to maintain the substation feeder at unity power factor. Digital simulations are made with the load data measured from an 11.4 kV secondary substation feeder