ABB Relion 670 Series Applications Manual page 162

Section 8
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 73.
3I
0
67N
ANSI05000151 V2 EN-US
Figure 73: Step 1, second calculation. Remote busbar with, one line taken out of service
The requirement is now according to Equation 43.
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 74.
3I
0
67N
One phase-to-ground fault
ANSI05000152 V2 EN-US
Figure 74: Step 1, third calculation
156
×
0
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One- or two-phase-ground-fault
en05000151_ansi.vsd
ANSI05000152_2_en.vsd
1MRK 511 401-UUS F
(Equation 43)
Bay control REC670
Application manual