High resistance grounding faults occur more often than not in the distribution network. For the low resistance grounding system

the zero-sequence current protection with unchanged setting

which is widely used in the field

will refuse to operate. Based on an analysis of electric characteristic during a single-phase grounding fault

it is revealed that

no matter whether the fault is internal or external

the magnitude of zero-sequence current is always proportional to the magnitude of zero-sequence voltage at the protection installed point on the line. And both magnitudes will be reduced with an increase in grounding resistance. According to this feature

a new principle of grounding fault protection based on zero-sequence voltage ratio restraint is proposed

whose core is that a self-adaptive setting is constituted by producing a proportional current quantity according to the zero-sequence voltage magnitude. Both the protection sensitivity for low resistance grounding faults or metallic grounding faults and the protection reliability for high resistance faults can receive adequate attention. The system is resistant to high resistance capacity which is improved to 1 000 Ω. Finally

simulation is performed to prove the validity of the algorithm. This work is supported by National Natural Science Foundation of China(No. 51477184)and China Southern Power Grid Company Limited(No. GZHKJ00000020).