Determining the Impact of Line Asymmetries on Network Voltage Unbalance based on Balanced Load Flow Studies

Determining the impact of the individual contributors to network voltage unbalance (VU) is a complex task due to the interaction between the sources of voltage unbalance in power systems. This becomes further complicated as the network itself contributes to network voltage unbalance when it is not symmetrical which is mostly the case in real networks. To account for the network asymmetry, the Technical Report IEC/TR 61000-3-13 which is used for the assessment of voltage unbalance emission limits applies a scaling factor Kue when apportioning the global allowance to end user consumers. Studies on the impact of the untransposed overhead lines on each and every individual busbar and on the overall network voltage unbalance are essential in: emission allocation studies, identification of power flow constraints, and in decision making related to future investments on VU mitigation. This paper proposes an effective methodology to determine the influence of different untransposed lines based on the results of balanced load flow studies. The methodology can be easily extended to obtain the influence of the other contributors as well.