Analysis of simultaneous unbalanced short circuit and open conductor faults in power systems with untransposed lines and six-phase sections

The paper introduces a generalized method for analysis of multiple, simultaneous short circuit, open circuit, and open circuit falling conductor faults in mixed three-phase and six-phase power systems with untransposed lines. The method is systematic and suitable for all types of faults, any number of simultaneous faults, and any number of phases. Calculation of all network unbalanced voltages and currents during faults is done in one straightforward step. Coupling among sequence networks in untransposed transmission lines is accounted for. Coupling between the three-sequence networks of the three-phase part and the six-sequence networks of six-phase part is also derived. The method is applied also for transient stability study of mixed three-phase and six-phase power systems during any type of faults. Detailed derivation of the governing equations in each part is presented. Simulation results on the IEEE 300-bus system and the IEEE 30-bus system are given to validate the proposed method.