ABB REC670 Applications Manual page 173

1MRK 511 401-UUS A
Bay control REC670 2.2 ANSI
Application manual
The function shall not operate for any of the calculated currents to the protection. The
minimum theoretical current setting (Imin) will be:
 

Im in MAX I , I
f A fB
EQUATION284 V2 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 min
EQUATION285 V3 EN-US
In case of parallel lines with zero sequence mutual coupling a fault on the parallel line,
as shown in Figure 66, should be calculated.
A
Z
~
A
ANSI09000025 V2 EN-US
Figure 66: Two parallel lines. Influence from parallel line to the through fault
current: I
The minimum theoretical current setting (Imin) will in this case be:
³ , ,
I m in M A X I I I
( )
fA fB M
EQUATION287 V1 EN-US
Where:
I and I have been described for the single line case.
fA fB
Line 1
C
Z
L1
M
Fault
Z
L2
I
M
IED
Line 2
M
Section 8
Current protection
B
Z
~
B
ANSI09000025_2_en.vsd
(Equation 33)
(Equation 34)
(Equation 35)
167