IEC09000025-1-en.vsd
~ ~
Z
A
Z
B
Z
L1
A B
I
M
Fault
IED
Z
L2
M
C
Line 1
Line 2
IEC09000025 V1 EN-US
Figure 72: Two parallel lines. Influence from parallel line to the through fault
current: I
M
The minimum theoretical current setting for the overcurrent protection function
(Imin) will be:
Imin MAX I
fA
I
fB
I
M
, ,( )³
EQUATION82 V1 EN-US (Equation 98)
Where I
fA
and I
fB
have been described in the previous paragraph. Considering the
safety margins mentioned previously, the minimum setting (Is) for the
instantaneous phase overcurrent protection 3-phase output is then:
EQUATION83 V2 EN-US (Equation 99)
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:
EQUATION1147 V3 EN-US
(Equation 100)
1MRK 505 393-UEN B Section 8
Current protection
Line differential protection RED650 2.2 IEC 151
Application manual
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