ABB RELION 670 Series Applications Manual page 410

Section 8
Current protection
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IEC09000023 V1 EN-US
Figure 249: Through fault current from B to A: I
The function shall not operate for any of the calculated currents to the protection. The
minimum theoretical current setting (Imin) will be:
³
Imin MAX I
EQUATION284 V1 EN-US
A safety margin of 5% for the maximum static inaccuracy and a safety margin of 5% for
maximum possible transient overreach have to be introduced. An additional 20% is suggested
due to inaccuracy of instrument transformers under transient conditions and inaccuracy in the
system data.
The minimum primary current setting (Is) is:
I = 1.3 × I
s
EQUATION285 V3 EN-US
In case of parallel lines with zero sequence mutual coupling a fault on the parallel line, as
shown in figure 250, should be calculated.
~
IEC09000025 V1 EN-US
Figure 250: Two parallel lines. Influence from parallel line to the through fault current: I
The minimum theoretical current setting (Imin) will in this case be:
404
I
fA
A
Z Z
A L
IED
Fault
,
I
( )
fA fA
min
A C
Z
L1
Z
A
Fault
Z
L2
I
M
IED
B
Z
B
IEC09000023-1-en.vsd
fA
Line 1
B
Z
B
M
Line 2
IEC09000025-1-en.vsd
1MRK 504 152-UEN B
~
(Equation 438)
(Equation 439)
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Application manual
M