ABB REL650 Applications Manual page 184

Section 7
Current protection
178
A
Z
~
A
ANSI10000278 V2 EN
Figure 85: Two parallel lines Influence form parallel line to the through fault current:
I
M
The minimum theoretical current (I
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 as given in equation below:
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
) for the overcurrent protection function will be:
min
1MRK 506 334-UUS A
B
Z
~
B
ANSI10000278_2_en.vsd
Application manual
(Equation 103)
(Equation 104)
(Equation 105)