Elimination Of Zero Sequence Currents - ABB REG670 Applications Manual

1MRK 502 071-UEN -
7.1.3.2
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
Application manual
operate current
[ times IBase ]
5
4
3
2
1
IdMin
0
0
EndSection1
IEC05000187 V2 EN
Figure 53: Representation of the restrained, and the unrestrained operate
characteristics
D
Ioperate
= ×
slope
100%
D
Irestrain
EQUATION1246 V1 EN
and where the restrained characteristic is defined by the settings:
1. IdMin
EndSection1
2.
3. EndSection2
SlopeSection2
4.
5. SlopeSection3

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 transformer
Operate
unconditionally
UnrestrainedLimit
Operate
conditionally
Section 1
Section 2
SlopeSection2
1 2
EndSection2
Section 7
Differential protection
Section 3
SlopeSection3
Restrain
3 4 5
restrain current
[ times IBase ]
en05000187-2.vsd
(Equation 16)
131