ABB Relion REQ650, Руководство по применению

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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 41: 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 6)
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
³
1.3·Imin
EQUATION83 V2 EN
(Equation 7)
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 8)
1MRK 505 291-UEN A
Section 6
Current protection
89
Application manual