Adequacy of the superposition method for probabilistic assessment of unbalance in distribution networks

Voltage unbalance is a power quality phenomenon that causes overheating and accelerated thermal ageing of equipment, reduced efficiency of the load and overall network, and therefore additional financial cost to both distribution network operators (DNOs) and customers. Once a new source of unbalance appears in the network, the overall level of unbalance in the network will generally increase; hence the system losses will be raised. This paper develops a methodology for probabilistic estimation of unbalance in the network and for establishing the effects of multiple sources of unbalance. A real 24-bus network was used in simulations. Both daily variation of loads in accordance with daily loading curve and uncertainty in load parameters contributing to unbalance are considered in order to robustly establish the effects of individual loads on propagation of unbalance in the network. The proposed methodology enables DNOs to estimate the level of unbalance in the network even when the full monitoring data are not available.