Excitation transformer as an important component is connerted to the enclosure type isolated-phase bus in the main circuit and branch circuit of generator,in order to reduce the ground fault,phases fault and eliminate steel structure fever.However,the reversed phase-sequence of an excitation transformer and the isolated-phase bus was found in the construction of a power plant,this paper analyses the influences of excitation change current phase,excitation transformer differential protection,excitation regulator,generator rotor earth protection caused by this situation,and proposes two solutions.Considering the convenient of excitation system and relay setting calculation,the second scheme become the first choice.The simulation results meet the requirements of the excitation transformer differential protection,rotor earth protection and the excitation regulator,avoiding re-purchase and install the isolated-phase bus or replace the excitation transformer.