Probabilistic Estimation of Voltage Unbalance in MV Distribution Networks With Unbalanced Load

Voltage unbalance negatively affects distribution network operators and customers by introducing overheating, reduced efficiency, and reduced lifetime of power system equipment and customer devices. The overall unbalance in the distribution network that leads to additional system losses is contributed to by every individual source of unbalance. This paper first analyzes the propagation of unbalance originating from the main cause of voltage unbalance-asymmetrical loading and then develops a methodology for probabilistic estimation of unbalance in the network. By considering daily loading curves, normally distributed load and employing three-phase full Newton-Raphson load flow, the Monte Carlo simulations give the possible ranges of levels of voltage unbalance for specified buses. The analysis enables distribution network operators to derive the level of unbalance in the network from either historical monitoring data or probabilistic estimation when full monitoring data are not available. Finally, the methodology is validated on a section of the real U.K. distribution network and the results of assessment compared with actual monitoring data.