Cross‐voltage short‐circuit calculation for mixed‐voltage quadruple‐circuit lines on the same tower

Abstract

Cross-voltage faults, i.e. multi-circuit faults that occur between different voltage level systems, in mixed-voltage quadruple-circuit transmission lines occur at times. The short-circuit calculations, which are the basis of the relay protection settings, for different faults are required. This study proposes a new method based on the theory of multiple fault analysis. First, the cross-voltage fault is regarded as a double multiple fault of the system. By retaining the fault nodes and the ground node, while eliminating all the intermediate nodes, the equivalent impedance of each sequence is obtained. Next, the fault reference phase is selected and the two-port network of each sequence that belongs to the reference phase is formed. Further, the port voltages of each sequence are transferred to a special phase using phase-shifting transformers. Then, a unified composite sequence network is formed according to the boundary conditions of the special phase. Finally, a set of equations are listed based on the composite sequence network in order to determine the fault currents and voltages. The simulation results in PSCAD agree well with the results calculated using the above algorithm, verifying the accuracy of this method.