Fault analysis is necessary to design a protection system and circuit breakers for a power system network. The multiphase system is a new technology so very little work is found for the fault analysis of a multiphase system contrary, unlike a three‐phase system. The faults in a seven‐phase system may be either symmetrical or non‐symmetrical. A non‐symmetrical fault requires studying the sequence components of a seven‐phase system using Fortescue transformation. In the paper, non‐symmetrical fault analysis of the seven‐phase system has been analysed. For this, a new definition of sequence components of an unbalanced seven‐phase system has been proposed in this paper. Then the proposed sequence components are applied to different faults studies at the input and output sides of a seven‐phase transformer. Further, the effect of the construction of a seven‐phase transformer, that is, core type and shell type on its output is studied. Moreover, the effect of open‐phase input is analysed using simulation and hardware results. From the analysis, it is found that in certain configurations of a seven‐phase transformer, the seven‐phase output is produced even though open‐phase fault is present at the input while in other configurations, seven‐phase is not produced in the case of open‐phase fault.