ABB REG670 Applications Manual page 177

1MRK 502 071-UEN -
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 69: Operate-restrain characteristic
D
Ioperate
= ×
slope 100%
D
Irestrain
EQUATION1246 V1 EN
IdMin: IdMin is the constant sensitivity of section 1. This setting can normally be
chosen to 0.10 times the generator rated current.
In section 1 the risk of false differential current is very low. This is the case, at least
up to 1.25 times the generator rated current. EndSection1 is proposed to be set to 1.25
times the generator rated current.
In section 2, a certain minor slope is introduced which is supposed to cope with false
differential currents proportional to higher than normal currents through the current
transformers. EndSection2 is proposed to be set to about 3 times the generator rated
current. The SlopeSection2, defined as the percentage value of DI
proposed to be set to 40%, if no deeper analysis is done.
In section 3, a more pronounced slope is introduced which is supposed to cope with
false differential currents related to current transformer saturation. The
SlopeSection3, defined as the percentage value of DI
80 %, if no deeper analysis is done.
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
/DI
diff Bias
/DI , is proposed to be set to
diff Bias
(Equation 32)
, is
171