ABB Relion REC670 - Page 122

IEC09000023-1-en.vsd
~ ~
Z
A
Z
B
Z
L
A B
IED
I
fA
Fault
IEC09000023 V1 EN-US
Figure 49: 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-US (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:
I
s
= 1.3 × I
min
EQUATION285 V3 EN-US (Equation 35)
In case of parallel lines with zero sequence mutual coupling a fault on the parallel line, as
shown in figure 50, should be calculated.
IEC09000025-1-en.vsd
~ ~
Z
A
Z
B
Z
L1
A B
I
M
Fault
IED
Z
L2
M
C
Line 1
Line 2
IEC09000025 V1 EN-US
Figure 50: 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:
Section 7 1MRK 511 358-UEN A
Current protection
116
Application manual