ABB REL 356

ABB REL 356 Current Differential Protection
3-27
Settings and Application
Figure 1. Ratio of I
3
F
min
/I
F
Gmin
vs. C0 (C1 = 0.1, C2 = 0.7)
Case 3
When the minimum ground fault current is less than 12.5% of minimum three phase fault current C0 should be set to 2.5.
The recommended settings
C1 = 0.1
C2 = 0.7
C0 = 2.5
gives the following sensitivity for different faults:
Three phase faults
Phase-phase faults
min3min3minmin
60
min
33.0
2
3
38.038.0)21(
3
1
φφφφφφ
IIIIeCCIT
j
⋅=⋅⋅=⋅=⋅⋅+−=
±
ο
Single phase to ground faults
min3min3min
1.01
φφ
IICIT ⋅−=⋅−=
minminmin
0.1)021(
3
1
GG
IICCCIT
φφ
⋅=⋅++−=