ABB Relion REC670 Applications Manual page 131

1MRK 511 358-UEN A
Step 1
This step has directional instantaneous function. The requirement is that overreaching of the
protected line is not allowed.
3I
0
IN
IEC05000150 V4 EN-US
Figure 55: Step 1, first calculation
The residual current out on the line is calculated at a fault on the remote busbar (one- or two-
phase-to-earth fault). To assure selectivity it is required that step 1 shall not give a trip at this
fault. The requirement can be formulated according to equation 39.
³
I 1.2 3I (remote busbar)
step1
EQUATION1199 V3 EN-US
As a consequence of the distribution of zero sequence current in the power system, the
current to the protection might be larger if one line out from the remote busbar is taken out of
service, see figure 56.
3I
0
IN
>
IEC05000151 V2 EN-US
Figure 56: Step 1, second calculation. Remote busbar with, one line taken out of service
The requirement is now according to equation 40.
³
I 1.2 3I (remote busbar with one line out)
step1
EQUATION1200 V3 EN-US
Application manual
×
0
One- or two-phase-earth-fault
×
0
One- or two-phase earth-fault
or unsymmetric short circuit
without earth connection
IEC05000150-3-en.vsd
IEC05000151-en-2.vsd
Section 7
Current protection
M15282-123 v5
(Equation 39)
(Equation 40)
125