Abstract: Due to the possible stator winding inter-turn short circuit in large phase modifiers, there will be seriously potential risk for the safe operation of the phase modifier without inter-turn short circuit protection. Internal fault analysis and main protection configuration scheme optimization design of a 300 Mvar phase modifier manufactured by Shanghai Electric are carried out with the multi-loop method. The analysis showed that different main protection configuration schemes should be chosen for different outgoing modes of the phase modifier neutral point. Compared with the neutral point outgoing mode and main protection scheme based on the traditional electromagnetic current transformer, the split-phase transverse differential protection based on FOCT will completely change the current status of large turbo-generator without stator winding inter-turn short circuit protection and has little influence on generator design and manufacture, thus providing the high quality guarantee for the safe operation of the generator.