ABB Relion 670 Series Applications Manual page 163

1MRK 511 401-UUS F
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
EQUATION1201 V3 EN-US
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.
3I
0
50/51N
67N
ANSI05000154 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 ground-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.
3I
0
50/51N
67N
ANSI05000155 V2 EN-US
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 ground-fault
ANSI05000154_2_en.vsd
3I
0x
One phase-ground-fault
50/51N
67N
ANSI05000155_2_en.vsd
Section 8
Current protection
(Equation 44)
M15282-144 v7
(Equation 45)
157