1. A method of fault analysis for an electric power transmission or distribution system having a plurality of multi-phase buses, wherein a control system is in communication with the electric power transmission or distribution system, the control system including a processing circuit having a processor, the processing circuit being configured to monitor and control an operation of the electric power transmission or distribution system, the processing circuit configured to perform the following steps of the method: computing equivalent circuits for the multi-phase buses of interest, each equivalent circuit including an N×N impedance matrix where N corresponds to the number of phases of the multi-phase bus for which that equivalent circuit is computed; determining elements of the impedance matrices based on voltages resulting from a plurality of experimental current injection vectors and a factorized pre-fault admittance matrix, the pre-fault admittance matrix representing nodal admittance of the multi-phase buses without faults; determining a fault current injection vector for each multi-phase bus and fault type of interest based on the equivalent circuit determined for that multi-phase bus; determining a fault voltage vector for each multi-phase bus and fault type of interest based on the factorized pre-fault admittance matrix and the fault current injection vector determined for that multi-phase bus and fault type; and outputting a signal based on the determined fault voltage vector, the signal controlling transmission of the electric power transmission or distribution system.