ABB Relion 670 Series Applications Manual page 158

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
IN
>
IEC05000151 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
IN
One phase-to-earth fault
IEC05000152 V2 EN-US
Figure 74: Step 1, third calculation
In this case the residual current out on the line can be larger than in the case of earth fault on
the remote busbar.
³
I 1.2 3I
step1
EQUATION1201 V3 EN-US
152
×
0
0
>
×
0
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One- or two-phase-earth-fault
1MRK 511 401-UEN Rev. K
IEC05000151-en-2.vsd
IEC05000152-en-2.vsd
Bay control REC670
Application manual
(Equation 43)
(Equation 44)