Toshiba GR200 Series Instruction Manual

Also see for GRB200: Instruction manual

6F2S1931 (0.20)Centralized GRB200(Soft: 030, 031, 032, 033, 034)- 34 -Setting [DIF**-I]CT primary valueOperation accuracy (%)Figure 2.1-12 Operation accuracy depending on CT primary and DIF settingFigure 2.1-12 also shows that the DIF operating value should be larger than the CTprimary value multiplied by α so that the operation accuracy is able to be within 5%. Equation(2.1-8) shows this relationship:Setting [DIF**-I]Maximum CT primary value ≥ α → Setting [DIF**-I] ≥ Maximum CT primary value ×α(2.1-8)Table 2.1-4 shows the choice of ‘α’ value depending the number of CHs.Table 2.1-4 Coefficient of operation accuracyNumber of CHs α4 0.1608 0.22612 0.22716 0.32020 0.35824 0.392Step 3: Operating range affected by maximum fault current (IFmax)The DIF computation cannot be achieved if the DIF relay operates out of the dynamicrage. That is, in the DIF relay, the determination is not carried out correctly when the faultcurrent is so large, and the CT primary is small, and the IFmaxCT primary value⁄ is larger than65.653. Make sure that the maximum fault current (IFmax) and the ‘Minimum CT primaryvalue’ are satisfied in Equation (2.1-9):