The unit-transverse differential protection is usually the first choice for generator protection. As there exists the unbalanced current with the generator running， its performance will be greatly affected. Following an analysis on the characteristics of the unbalanced current， some countermeasures are presented， including a new unit-transverse differential protection based on the fault contributed zero sequence current. As the fault current with the large generator is great and will make the current transformer saturated， which usually lowers the protection sensitivity， corresponding technological measures are also proposed.