ABB RELION 670 SERIES Applications Manual page 496

Section 9
Current protection
490
³ ,
Imin MAX I ( I )
fA fB
EQUATION78 V1 EN
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 I
s min
EQUATION79 V3 EN
The protection function can be used for the specific application only if this setting value
is equal to or less than the maximum fault current that the IED has to clear, I
253.
I
F
A
Z
~ A
IED
ANSI09000024 V1 EN
Figure 253: Fault current: I
The IED setting value Pickup is given in percentage of the primary base current value,
IBase. The value for Pickup is given from this formula:
Is
=
Pickup
IBase
ANSIEQUATION1147 V1 EN
Z
L
Fault
F
×
100
1MRK 506 369-UUS -
B
Z
B ~
ANSI09000024-1-en.vsd
Line distance protection REL670 2.2 ANSI
Application manual
(Equation 443)
(Equation 444)
in Figure
F
(Equation 445)