ABB ret650 - Page 111

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 42: 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 17)
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 18)
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 19)
1MRK 504 169-UEN A Section 7
Current protection
Transformer protection RET650 2.2 IEC 105
Application manual