ABB REC650 Applications Manual page 110

Section 6
Current protection
104
A
Z
~
A
IED
Fault
ANSI09000023 V1 EN
Figure 41: 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 ( I )
fA fA
EQUATION284 V1 EN
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 ³
1.3.I
s m in
EQUATION285 V2 EN
In case of parallel lines with zero sequence mutual coupling a fault on the parallel line, as
shown in figure 42, should be calculated.
I
fA
B
Z
Z
L B
fA
1MRK 511 286-UUS A
~
ANSI09000023-1-en.vsd
(Equation 34)
(Equation 35)
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