ABB Relion 670 series - Page 496

Imin MAX I
fA
I
fB
,( )³
EQUATION78 V1 EN (Equation 443)
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:
min
1.3
s
I I³ ×
EQUATION79 V3 EN (Equation 444)
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
F
in Figure
253.
ANSI09000024-1-en.vsd
~ ~
Z
A
Z
B
Z
L
A B
I
F
Fault
IED
ANSI09000024 V1 EN
Figure 253: Fault current: I
F
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:
100
Is
Pickup
IBase
= ×
ANSIEQUATION1147 V1 EN (Equation 445)
Section 9 1MRK 506 369-UUS -
Current protection
490 Line distance protection REL670 2.2 ANSI
Application manual