Analyzation of current characteristics on untransposed double-circuit lines

The parameters of transmission lines are usually not completely symmetrical in actual power grid. As to paralleled double-circuit line, this kind of asymmetry can bring current unbalance even under normal condition, and therefore may have a negative impact on the line temperature, losses and even traditional relay protection equipments. In this paper, we first discuss some factors that may affect the parameters of transmission lines. Then we provide a method which can be used to calculate the circulating currents between the paralleled two lines under normal condition. At last, we give a detailed analysis of one double-circuit transmission line in Northwest Power Grid using this method. By analyzing the proportion of current unbalance in different phasing arrangements, we can make some useful conclusions and a few suggestions to limit the current unbalance.