ABB REL650 Applications Manual page 207

1MRK 506 334-UUS A
Application manual
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 98, should be calculated.
A
Z
~
A
ANSI09000025 V2 EN
Figure 98: Two parallel lines. Influence from parallel line to the through fault current:
I
M
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
Where:
I and I have been described for the single line case.
fA fB
Considering the safety margins mentioned previously, the minimum setting (Is) is:
Line 1
C
Z
L1
M
Fault
Z
L2
I
M
IED
Line 2
Section 7
Current protection
B
Z
~
B
ANSI09000025_2_en.vsd
(Equation 116)
(Equation 117)
(Equation 118)
201