ABB Relion Technical Manual page 106

Section 6
Differential protection
100
operate current
[ times IBase ]
5
4
3
2
1
IdMin
0
0
EndSection1
IEC05000187 V2 EN
Figure 32: Description of the restrained, and the unrestrained operate
characteristics
where:
D
Ioperate
= ×
slope 100%
D
Irestrain
EQUATION1246 V1 EN
The operate - restrain characteristic is tailor-made and can be designed freely by the user
after his needs. The default characteristic is recommended to be used. It gives good results
in a majority of applications. The reset ratio is in all parts of the characteristic equal to
0.95.
Section 1: This is the most sensitive part on the characteristic. In section 1, normal
currents flow through the protected object and its current transformers, and risk for higher
false differential currents is relatively low. An un-compensated on-load tap-changer is a
Operate
unconditionally
UnrestrainedLimit
Operate
conditionally
Section 1 Section 2
SlopeSection2
1 2
EndSection2
1MRK 502 048-UUS A
Section 3
SlopeSection3
Restrain
3 4 5
restrain current
[ times IBase ]
en05000187-2.vsd
Technical manual