ABB RELION 670 SERIES REG670 - Page 352

~ ~
Z
A
Z
B
Z
L1
A B
I
M
Fault
IED
Z
L2
M
C
Line 1
Line 2
ANSI09000025_2_en.vsd
ANSI09000025 V2 EN-US
Figure 171: 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 171)
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:
Is ³1.3·Imin
EQUATION83 V2 EN-US (Equation 172)
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-US (Equation 173)
Section 9 1MRK 502 071-UUS A
Current protection
346 Generator protection REG670 2.2 ANSI and Injection equipment REX060, REX061, REX062
Application manual