ABB REL650 Applications Manual page 217

1MRK 506 334-UUS A
Application manual
The requirement is now according to equation 121.
³ ×
I 1.2 3I (remote busbar with one line out)
step1 0
EQUATION1200 V3 EN
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 104.
3I
0
67N
One phase-to-ground fault
ANSI05000152 V2 EN
Figure 104: Step 1, third calculation
In this case the residual current out on the line can be larger than in the case of ground fault
on the remote busbar.
³ ×
I 1.2 3I
step1 0
EQUATION1201 V3 EN
The current setting for step 1 is chosen as the largest of the above calculated residual
currents, measured by the protection.
Step 2
This step has directional function and a short time delay, often about 0.4 s. Step 2 shall
securely detect all ground faults on the line, not detected by step 1.
Section 7
Current protection
(Equation 121)
ANSI05000152_2_en.vsd
(Equation 122)
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