ABB REC670 Applications Manual page 158

Section 8
Current protection
152
A
Z
~
A
ANSI09000025 V2 EN-US
Figure 58: Two parallel lines. Influence from parallel line to the through fault
current: I
The minimum theoretical current setting for the overcurrent protection function (Imin)
will be:
³ , ,
Imin MAX I I I
( )
fA fB M
EQUATION82 V1 EN-US
Where I and I have been described in the previous paragraph. Considering the
fA fB
safety margins mentioned previously, the minimum setting (Is) for the instantaneous
phase overcurrent protection 3-phase output is then:
Is ³1.3·Imin
EQUATION83 V2 EN-US
The protection function can be used for the specific application only if this setting
value is equal or less than the maximum phase fault current that the IED has to clear.
The IED setting value Pickup is given in percentage of the primary base current value,
IBase. The value for Pickup is given from this formula:
Is
= ×
Pickup 100
IBase
ANSIEQUATION1147 V1 EN-US
Line 1
C
Z
L1
M
Fault
Z
L2
I
M
IED
Line 2
M
1MRK 511 401-UUS A
B
Z
~
B
ANSI09000025_2_en.vsd
Bay control REC670 2.2 ANSI
Application manual
(Equation 24)
(Equation 25)
(Equation 26)