Toshiba GR200 Series Instruction Manual page 48

Figure 2.1-12 Operation accuracy depending on CT primary and DIF setting
Figure 2.1-12 also shows that the DIF operating value should be larger than the CT
primary 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
Table 2.1-4 shows the choice of 'α' value depending the number of CHs.
Table 2.1-4 Coefficient of operation accuracy
Step 3: Operating range affected by maximum fault current (I Fmax )
The DIF computation cannot be achieved if the DIF relay operates out of the dynamic
rage. That is, in the DIF relay, the determination is not carried out correctly when the fault
current is so large, and the CT primary is small, and the
65.653. Make sure that the maximum fault current (I Fmax ) and the 'Minimum CT primary
value' are satisfied in Equation (2.1-9):
Setting [DIF**-I]
CT primary value
→ Setting [ DIF**-I ] ≥ Maximum CT primary value ×
≥ α
α
Number of CHs
4
8
12
16
20
24
- 34 -
α
0.160
0.226
0.227
0.320
0.358
0.392
I
Fmax
⁄
CT primary value
Centralized GRB200
(Soft: 030, 031, 032, 033, 034)
6F2S1931 (0.20)
(2.1-8)
is larger than