ABB REC670 Applications Manual page 177

1MRK 511 401-UEN A
Bay control REC670 2.2 IEC
Application manual
3I
0
IN
>
IEC05000151 V2 EN-US
Figure 72: 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 0
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 73.
3I
0
IN
>
One phase-to-earth fault
IEC05000152 V2 EN-US
Figure 73: 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.
One- or two-phase-earth-fault
Section 8
Current protection
IEC05000151-en-2.vsd
(Equation 40)
IEC05000152-en-2.vsd
171