ABB REC670 Applications Manual page 151

1MRK 511 401-UEN A
Bay control REC670 2.2 IEC
Application manual
A
Z
~
A
IEC09000025 V1 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 IP>> is given in percentage of the primary base current
value, IBase. The value for IP>> is given from this formula:
Is
>>= ×
IP 100
IBase
EQUATION1147 V3 EN-US
Line 1
C
Z
L1
M
Fault
Z
L2
I
M
Line 2
IED
M
Section 8
Current protection
B
Z
~
B
IEC09000025-1-en.vsd
(Equation 24)
(Equation 25)
(Equation 26)
145