The study of sampled value differential protection

The sampled value differential protection is described in this paper. The selections of S, R of the protection are investigated with respect to different restraint modes. The basic selective rule is to ensure the restraint effectiveness of the sampled value differential protection equal or superior to the corresponding phasor differential protection during external faults. The particular fuzzy operating zone of the proposed protection is also discussed and its expressions are presented. The operating characteristic phasor analyzing method is proposed to analyze the operating characteristic of sampled value differential protection, which uses the phasor relationships of input currents of the protected system to represent the operating zone, fuzzy operating zone and restraint zone.