SCEFRFLO can also be applied for earth-fault location in unearthed distribution
networks.
Configuration example
A typical configuration example for SCEFRFLO triggering is illustrated in
where external triggering is applied, that is,
Calculation Trg mode is set to
“External”. The
OPERATE
signal from non-directional overcurrent function PHLPTOC
is used to provide an indication of a short circuit fault. The
OPERATE
signal from
the directional earth-fault function DEFLPDEF is used to provide an indication of an
earth fault at the protected feeder.
SCEFRFLO with the autoreclosing function
When SCEFRFLO is used with the autoreclosing sequence, the distance estimate
from the first trip is typically the most accurate one. The fault distance estimates
from successive trips are possible but accuracy can be decreased due to inaccurate
load compensation. During the dead time of an autoreclosing sequence, the load
condition of the feeder is uncertain.
The triggering of SCEFRFLO can also be inhibited during the autoreclosing
sequence. This is achieved by connecting the inverted
READY
signal from the
autoreclosing function DARREC, which indicates that the autoreclosing sequence is
in progress, to the
BLOCK
input of SCEFRFLO. Blocking of the SCEFRFLO triggering
is suggested during the autoreclosing sequence when the load compensation or
steady-state asymmetry elimination is based on the delta quantities. This applies
to the short circuit faults when
Load Com PP loops is set to “Enabled” or, for earth
faults, when
EF algorithm Sel is set to “Load compensation” or “Load modelling”.
5.7.6
Signals
Table 817: SCEFRFLO Input signals
Name
Type
Default
Description
I_A
SIGNAL
0
Phase A current
I_B
SIGNAL
0
Phase B current
I_C
SIGNAL
0
Phase C current
Io
SIGNAL
0
Residual current
I
1
SIGNAL
0
Positive sequence
current
I
2
SIGNAL
0
Negative sequence
current
U_A_AB
SIGNAL
0
Phase to earth volt-
age A or phase to
phase voltage AB
U_B_BC
SIGNAL
0
Phase to earth volt-
age B or phase to
phase voltage BC
Table continues on the next page
1MRS757644 H
Protection related functions
620 series
Technical Manual
855
