ABB RELION Series, Technical Manual

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set to “Delta”) and residual voltage (Uo). Both alternatives are covered by setting the
configuration parameter
Phase voltage Meas to "Accurate".
When the Phase voltage Meas setting is set to "Ph-to-ph without Uo" and only phase-
to-phase voltages are available (but not Uo), only short-circuit measuring loops (fault
loops “AB Fault”, “BC Fault” or “CA Fault” or “ABC Fault”) can be measured
accurately. In this case, the earth-fault loops (fault loops either “AG Fault”, “BG
Fault” or “CG Fault”) cannot provide correct fault distance estimates and the
triggering of the function in case of earth fault is automatically disabled.
5.4.5 Application
The main objective of the feeder terminals is a fast, selective and reliable operation in
faults inside the protected feeder. In addition, information on the distance to the fault
point is very important for those involved in operation and maintenance. Reliable
information on the fault location greatly decreases the downtime of the protected
feeders and increases the total availability of a power system.
SCEFRFLO provides impedance-based fault location. It is designed for radially
operated distribution systems and is applicable for locating short circuits in all kinds
of distribution networks. Earth faults can be located in effectively earthed and low
resistance/low-reactance earthed networks. Under certain limitations, 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 Figure 257
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”.
Section 5
1MRS758755 A
Protection related functions
502 REC615 and RER615
Technical Manual