ABB Relion 670 Series Applications Manual page 152

Section 7
Current protection
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 68.
3I
0
67N
ANSI05000151 V2 EN-US
Figure 68: 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
A higher value of step 1 might be necessary if a big power transformer (Y0/D) at remote bus bar is
disconnected.
A special case occurs at double circuit lines, with mutual zero-sequence impedance between the
parallel lines, see figure 69.
3I
0
67N
One phase-to-ground fault
ANSI05000152 V2 EN-US
Figure 69: Step 1, third calculation
146
×
0
One- or two-phase-ground-fault
en05000151_ansi.vsd
ANSI05000152_2_en.vsd
1MRK 511 358-UUS A
(Equation 40)
Application manual