Investigation of Voltage Imbalance Due to Distribution Network Unbalanced Line Configurations and Load Levels

In distribution power systems line transposition is not a common practice and phase loading levels are always changing. Therefore, perfect balance is never achieved at a distribution level. Non-transposed lines can cause unequal voltage drops between phases and this may be further exacerbated by uneven loads in each phase. Consequently, the voltage magnitude of a certain phase may suffer a severe decrease, breaching the lower voltage limit or unbalanced three-phase voltages at a remote bus may violate the percentage voltage imbalance accepted in the standards. This paper examines the mechanism of causing uneven voltage drops and investigates the impacts of unbalanced line configurations with different phase loading levels on network voltage imbalance. Methodologies are proposed to analyze voltage drops affected by line and load imbalance. Based on these methods, general guidelines are recommended to mitigate the voltage problems, which are useful for network analysis, planning and reconfiguration.