ABB Relion 670 Series Applications Manual page 159

1MRK 511 401-UEN Rev. K
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 earth faults on the line, not detected by step 1.
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IEC05000154 V2 EN-US
Figure 75: Step 2, check of reach calculation
The residual current, out on the line, is calculated at an operational case with minimal earth-
fault current. The requirement that the whole line shall be covered by step 2 can be formulated
according to equation 45.
³
I 0.7 3I (at remote busbar)
step2
EQUATION1202 V4 EN-US
To assure selectivity the current setting must be chosen so that step 2 does not operate at
step 2 for faults on the next line from the remote substation. Consider a fault as shown in
Figure 76.
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Figure 76: Step 2, selectivity calculation
A second criterion for step 2 is according to equation 46.
Bay control REC670
Application manual
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One- or two-phase earth-fault
IEC05000154-en-2.vsd
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One phase-to-earth
fault
IEC05000155-en-2.vsd
Section 8
Current protection
M15282-144 v7
(Equation 45)
153