ABB RET670 Applications Manual page 406

Section 3
IED application
400
A
Z
~
A
ANSI09000025 V2 EN
Figure 182: 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
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
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
Line 1
C
Z
L1
M
Fault
Z
L2
I
M
IED
Line 2
M
1MRK504116-UUS C
B
Z
~
B
ANSI09000025_2_en.vsd
(Equation 337)
(Equation 338)
(Equation 339)
Application manual