ABB REL650 - Page 184

~ ~
Z
A
Z
B
Z
L1
A B
I
M
Fault
IED
Z
L2
M
C
Line 1
Line 2
ANSI10000278_2_en.vsd
ANSI10000278 V2 EN
Figure 85: Two parallel lines Influence form parallel line to the through fault current:
I
M
The minimum theoretical current (I
min
) for the overcurrent protection function will be:
Imin MAX I
fA
I
fB
I
M
, ,( )³
EQUATION82 V1 EN (Equation 103)
Where I
fA
and I
fB
have been described in the previous paragraph. Considering the safety
margins mentioned previously, the minimum setting Is as given in equation below:
Is
³1.3·Imin
EQUATION83 V2 EN (Equation 104)
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:
100
Is
Pickup
IBase
= ×
ANSIEQUATION1147 V1 EN (Equation 105)
Section 7 1MRK 506 334-UUS A
Current protection
178
Application manual