ABB Relion REG670, Applications Manual

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impedance values for Z
B
in order to get the maximum through fault current from A to
B.
~ ~
Z
A
Z
B
Z
L
A B
IED
I
fB
Fault
IEC09000022-1-en.vsd
IEC09000022 V1 EN
Figure 168: Through fault current from A to B: I
fB
Then a fault in A has to be applied and the through fault current I
fA
has to be calculated,
Figure 169 . In order to get the maximum through fault current, the minimum value for
Z
B
and the maximum value for Z
A
have to be considered.
IEC09000023-1-en.vsd
~ ~
Z
A
Z
B
Z
L
A B
IED
I
fA
Fault
IEC09000023 V1 EN
Figure 169: Through fault current from B to A: I
fA
The IED must not trip for any of the two through-fault currents. Hence the minimum
theoretical current setting (Imin) will be:
Imin MAX I
fA
I
fB
,
( )
³
EQUATION78 V1 EN
(Equation 175)
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.
1MRK 502 071-UEN -
Section 9
Current protection
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062 321
Application manual