Elimination Of Zero Sequence Currents - ABB RET650 Applications Manual

1MRK 504 169-UEN A
6.1.3.2
Transformer protection RET650 2.2 IEC
Application manual
operate current
[ times IBase ]
5
4
3
2
1
IdMin
0
0
EndSection1
IEC05000187 V2 EN-US
Figure 30: Representation of the restrained, and the unrestrained operate
characteristics
D
Ioperate
= ×
slope
100%
D
Irestrain
EQUATION1246 V1 EN-US
and where the restrained characteristic is defined by the settings:
IdMin
1.
EndSection1
2.
EndSection2
3.
SlopeSection2
4.
SlopeSection3
5.

Elimination of zero sequence currents

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
Operate
unconditionally
UnrestrainedLimit
Operate
conditionally
Section 1
Section 2
SlopeSection2
1 2
EndSection2
Section 6
Differential protection
Section 3
SlopeSection3
Restrain
3 4 5
restrain current
[ times IBase ]
en05000187-2.vsd
(Equation 11)
M15266-286 v7
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