ABB REG670 - Page 329

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
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
(Equation 178)
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 (Equation 179)
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:
100
Is
IP
IBase
>>= ×
EQUATION1147 V3 EN
(Equation 180)
1MRK 502 071-UEN - Section 9
Current protection
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062 323
Application manual