ABB REC670 Applications Manual page 179

1MRK 511 401-UEN A
Bay control REC670 2.2 IEC
Application manual
3I
0
IN
>
IEC05000155 V3 EN-US
Figure 75: Step 2, selectivity calculation
A second criterion for step 2 is according to equation 43.
3I
0
³ × ×
I 1 .2 I
step2 step1
3I
0 1
EQUATION1203 V4 EN-US
where:
I is the current setting for step 1 on the faulted line.
step1
Step 3
This step has directional function and a time delay slightly larger than step 2, often
0.8 s. Step 3 shall enable selective trip of earth faults having higher fault resistance
to earth, compared to step 2. The requirement on step 3 is selectivity to other earth-
fault protections in the network. One criterion for setting is shown in Figure 76.
3I
0
IN >
IEC05000156 V3 EN-US
Figure 76: Step 3, Selectivity calculation
3I
0
³ × ×
I 1 .2 I
step3 step2
3I
02
EQUATION1204 V4 EN-US
where:
I is the chosen current setting for step 2 on the faulted line.
step2
Section 8
Current protection
3I
01
IN
>
One phase-to-earth
fault
IEC05000155-en-2.vsd
(Equation 43)
3I
02
IN
>
One phase-to-
earth fault
IEC05000156-3-en.vsd
(Equation 44)
M15282-164 v6
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