ABB RER670 - Page 174

IEC09000023-1-en.vsd
~ ~
Z
A
Z
B
Z
L
A B
IED
I
fA
Fault
IEC09000023 V1 EN-US
Figure 53: 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:


Im ,
f
AfB
in MAX I I
EQUATION284 V2 EN-US (Equation 38)
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 39)
In case of parallel lines with zero sequence mutual coupling a fault on the parallel
line, as shown in Figure 54, 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 54: Two parallel lines. Influence from parallel line to the through fault
current: I
M
Section 8 1MRK 506 375-UEN A
Current protection
168 Railway application RER670 2.2 IEC
Application manual