ABB RET650 Technical Manual page 101

1MRK 504 135-UEN A
Technical manual
operate current
[ times IBase ]
5
4
3
2
1
IdMin
0
0
EndSection1
IEC05000187 V2 EN
Figure 33: 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 typical reason for existence of the false differential currents in this
section. The slope in section 1 is always zero percent.
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
95