ABB Relion 670 Series Applications Manual page 137

1MRK 511 401-UUS F
~
ANSI09000022 V1 EN-US
Figure 56: Through fault current from A to B: I
Then a fault in A has to be applied and the through fault current I
In order to get the maximum through fault current, the minimum value for Z
value for Z
~
ANSI09000023 V1 EN-US
Figure 57: Through fault current from B to A: I
The IED must not trip for any of the two through-fault currents. Hence the minimum theoretical
current setting (Imin) will be:
³
Imin MAX I
EQUATION78 V1 EN-US
A safety margin of 5% for the maximum protection static inaccuracy and a safety margin of 5% for
the maximum possible transient overreach have to be introduced. An additional 20% is suggested
due to the inaccuracy of the instrument transformers under transient conditions and inaccuracy in
the system data.
The minimum primary setting (Is) for the instantaneous phase overcurrent protection is then:
³
I 1.3
s
EQUATION79 V3 EN-US
Bay control REC670
Application manual
A
Z
A
IED
have to be considered.
A
A
Z
A
IED
Fault
,
( I )
fA fB
×
I
min
© Copyright 2017 ABB. All rights reserved
I
fB
B
Z
Z
L B
Fault
fB
I
fA
B
Z
L
fA
~
ANSI09000022-1-en.vsd
has to be calculated, Figure 57.
fA
and the maximum
B
Z
~
B
ANSI09000023-1-en.vsd
Section 8
Current protection
(Equation 24)
(Equation 25)
131