ABB REL650 Applications Manual page 179

1MRK 506 334-UUS A
Application manual
A fault in C has to be applied, and then the maximum current seen from the IED (I
the healthy line (this applies for single-phase-to-ground and two-phase-to-ground faults)
is calculated.
A
Z
~
A
ANSI09000025 V2 EN
Figure 81: 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:
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 safety
fA fB
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
Section 7
Current protection
B
Z
~
B
ANSI09000025_2_en.vsd
) on
M
(Equation 97)
(Equation 98)
(Equation 99)
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