ABB REC650 Applications Manual page 120

Section 6
Current protection
114
3I
0
67
67N
N
ANSI05000150 V2 EN
Figure 46: 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-ground 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 38.
³ ×
I 1.2 3I (remote busbar)
step1 0
EQUATION1199 V3 EN
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 47.
3I
0
67N
ANSI05000151 V2 EN
Figure 47: Step 1, second calculation. Remote busbar with, one line taken out of
service
1MRK 511 286-UUS A
One- or two-phase ground-fault
ANSI05000150_2_en.vsd
One- or two-phase-ground-fault
en05000151_ansi.vsd
(Equation 38)
Application manual