Study on the operating characteristic of sampled value differential protection

The sampled value differential protection is described in this paper. The selections of S, R are investigated and the basic selective rule is to ensure that the restraint effectiveness of the sampled value differential protection be 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. In addition, the phasor analyzing method, in which the phasor relationships of input currents of the protected system are used to represent the operating zone, fuzzy operating zone and restraint zone, is proposed to analyze the operating characteristic. The engineering applications and test results are also introduced.