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67N
One- or two-phase ground-fault
50/51N
0
3I
ANSI05000154_2_en.vsd
ANSI05000154 V2 EN
Figure 49:
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
step2
0
I
0.7 3I (at remote busbar)
³
×
EQUATION1202 V4 EN
(Equation 41)
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
.
One phase-ground-fault
67N
50/51N
50/51N
67N
0
3I
0x
3I
ANSI05000155_2_en.vsd
ANSI05000155 V2 EN
Figure 50:
Step 2, selectivity calculation
A second criterion for step 2 is according to equation
.
1
1
0
step2
step1
0
3I
I
.2
I
3I
³
×
×
EQUATION1203 V4 EN
(Equation 42)
where:
Istep1 is the current setting for step 1 on the faulted line.
Section 6
1MRK 511 286-UUS A
Current protection
116
Application manual
Содержание REC650 ANSI
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