A transmission line current differential protection based on virtual restraint current

Current differential protection widely used in transmission line based on comparing sum and difference of two side current phasors. Its sensitivity was impact by load current. A current differential protection based on virtual restraint current was proposed. The virtual current contains phase information of the bigger current and amplitude information of the smaller current. The sensitivity of criterion proposed was superior to present criterion for internal faults and its reliability was the same to present criterion for external faults and normal condition. The criterion performance was proven using RTDS simulations in a 500 kV power system considering critical fault cases.