ABB ret650 - Elimination of Zero Sequence Currents

Section 1
Operate
conditionally
UnrestrainedLimit
Section 2
Section 3
Restrain
Operate
unconditionally
5
4
3
2
1
0
0 1 2 3 4 5
IdMin
EndSection1
EndSection2
restrain current
[ times IBase ]
operate current
[ times IBase ]
SlopeSection2
SlopeSection3
en05000187-2.vsd
IEC05000187 V2 EN-US
Figure 30: Representation of the restrained, and the unrestrained operate
characteristics
100%
Ioperate
slope
Irestrain
D
=
D
×
EQUATION1246 V1 EN-US
(Equation 11)
and where the restrained characteristic is defined by the settings:
1. IdMin
2. EndSection1
3. EndSection2
4. SlopeSection2
5. SlopeSection3
6.1.3.2 Elimination of zero sequence currents
M15266-286 v7
A differential protection may operate undesirably due to external earth-faults in
cases where the zero sequence current can flow on only one side of the power
transformer, but not on the other side. This is the case when zero sequence current
cannot be properly transformed to the other side of the power transformer. Power
1MRK 504 169-UEN A Section 6
Differential protection
Transformer protection RET650 2.2 IEC 79
Application manual