ABB Relion 670 Series Applications Manual page 141

1MRK 511 358-UUS A
~
ANSI09000022 V1 EN-US
Figure 60: Through fault current from A to B: I
~
ANSI09000023 V1 EN-US
Figure 61: Through fault current from B to A: I
The function shall not operate for any of the calculated currents to the protection. The minimum
theoretical current setting (Imin) will be:
³
Imin MAX I
EQUATION284 V1 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
EQUATION285 V3 EN-US
In case of parallel lines with zero sequence mutual coupling a fault on the parallel line, as shown in
figure 62, should be calculated.
Application manual
I
A
Z Z
A
IED
I
A
Z Z
A
IED
Fault
,
( I )
fA fA
min
fB
B
Z
L B
Fault
fB
fA
B
Z
L B
ANSI09000023-1-en.vsd
fA
Current protection
~
ANSI09000022-1-en.vsd
~
Section 7
(Equation 34)
(Equation 35)
135