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 68: Operate-restrain characteristic
100%
Ioperate
slope
Irestrain
D
=
D
×
EQUATION1246 V1 EN-US (Equation 29)
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
diff
/DI
Bias
, is 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,
1MRK 502 071-UUS A Section 7
Differential protection
Generator protection REG670 2.2 ANSI and Injection equipment REX060, REX061, REX062 181
Application manual
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