IEC09000023-1-en.vsd
~
~
Z
A
Z
B
Z
L
A
B
IED
I
fA
Fault
IEC09000023 V1 EN-US
Figure 262: 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-US
(Equation 467)
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 3-phase
output is then:
min
1.3
s
I
I
³
×
EQUATION79 V3 EN-US
(Equation 468)
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
IEC09000024-1-en.vsd
~
~
Z
A
Z
B
Z
L
A
B
IED
I
F
Fault
IEC09000024 V1 EN-US
Figure 263: Fault current: I
F
100
Is
IP
IBase
>>=
×
EQUATION1147 V3 EN-US
(Equation 469)
1MRK 505 343-UEN B
Section 8
Current protection
403
Application manual
Summary of Contents for Relion 670 series
Page 1: ...RELION 670 SERIES Line differential protection RED670 Version 2 1 IEC Application manual...
Page 2: ......
Page 40: ...34...
Page 64: ...58...
Page 150: ...144...
Page 406: ...400...
Page 472: ...466...
Page 494: ...488...
Page 512: ...506...
Page 524: ...518...
Page 604: ...598...
Page 686: ...680...
Page 718: ...712...
Page 722: ...716...
Page 758: ...752...
Page 759: ...753...