ABB Relion 670 series - Page 512

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 (Equation 455)
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 (Equation 456)
In case of parallel lines with zero sequence mutual coupling a fault on the parallel line, as
shown in Figure 262, should be calculated.
~ ~
Z
A
Z
B
Z
L1
A B
I
M
Fault
IED
Z
L2
M
C
Line 1
Line 2
ANSI09000025_2_en.vsd
ANSI09000025 V2 EN
Figure 262: 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:
I m in M A X I
fA
I
fB
I
M
, ,( )³
EQUATION287 V1 EN (Equation 457)
Where:
I
fA
and I
fB
have been described for the single line case.
Section 9 1MRK 506 369-UUS -
Current protection
506 Line distance protection REL670 2.2 ANSI
Application manual