An Accurate Calculation Method For Double-Circuit Faults

With the development of power grids interconnection and the increase of voltage level, double-circuit transmission lines are applied in power transmission more and more extensively. Taking the structural features of double-circuit lines into consideration, the fault of double-circuit lines is various, complex and of threat to stability of the power system. A systemic error, which results in inaccurate results, would be caused by the traditional computing method, so that the relay protection setting accuracy would be effected. Therefore, the research of accurate calculating method of double-circuit lines is of great practical and economic value.A modified virtual ports method for complex faults accurate calculating of unbalanced power system in sequence domain is presented. Considering to the effects of distributed capacitance, Bergeron model is used to establish transmission line model. The structural features of Bergeron model are applied to build double virtual ports of unbalanced parameters lines instead of single. By structuring the virtual fault ports and virtual fault networks, an unified calculation model of double-circuit transmission line fault calculation with unbalanced parameter lines is built. According to this calculation model, based on superposition theorem, the node voltage matrix of the all system could be computed to finish the fault calculation. The presented method is of simple structure, of logic unification, easy to implement with efficient and precision.An unsymmetrical power system with complex faults is analyzed as an example. The result proves that the method presented by this paper is of practicability availability and accuracy.