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A new method for studying the transient asymmetrical shunt and series faults in multi‐machine multi‐unified power flow controller (multi‐UPFC) power systems is proposed. Considering an arbitrary shunt or series fault in a power system, the method uses a combination of space phasors‐based sequence networks corresponding to the fault. Synchronous machines and UPFCs are modelled via injecting sequence current phasors. The quasi‐static Y‐matrix equations of the network are solved first, to obtain the sequence voltages of the terminal bus‐bars of synchronous machines. Then, these voltages are used to solve the non‐linear equations of the machines (in the rotors d‐q reference frames) in the subsequent step time (Δt). This procedure is repeated until a steady‐state condition is reached in the post‐fault condition. The proposed method for fault analysis has high processing speed and acceptable accuracy, which is very important for online protection and control computations. Based on the proposed method, a computer program has been developed that is applicable for the fault analysis of modern or conventional power systems with any size. The performance of the proposed method is studied by some simulation results and compared with other similar works. The simulation results very well support the accuracy and efficiency of the method. [ABSTRACT FROM AUTHOR]