ABB REL670 2.2 IEC - Page 465

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-US
Figure 252: 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 446)
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 447)
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-US
(Equation 448)
1MRK 506 369-UEN B Section 9
Current protection
Line distance protection REL670 2.2 IEC 459
Application manual