ABB REC650 - Page 110

ANSI09000023-1-en.vsd
~ ~
Z
A
Z
B
Z
L
A B
IED
I
fA
Fault
ANSI09000023 V1 EN
Figure 41: Through fault current from B to A: I
fA
The function shall not operate for any of the calculated currents to the protection. The
minimum theoretical current setting (Imin) will be:
Imin MAX I
fA
I
fA
,( )³
EQUATION284 V1 EN (Equation 34)
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:
m
1.3.Is inI ³
EQUATION285 V2 EN (Equation 35)
In case of parallel lines with zero sequence mutual coupling a fault on the parallel line, as
shown in figure 42, should be calculated.
Section 6 1MRK 511 286-UUS A
Current protection
104
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