Application - ABB RELION REX640 Technical Manual

1MRS759142 C
5.7.7
REX640
Technical Manual
set to "Delta") and residual voltage (Uo). Both alternatives are covered by setting the
configuration parameter Phase voltage Meas to "Accurate".
The function can operate correctly with only two phase-to-earth voltages if the
residual voltage is also measured and connected to the source UTVTR which provides
the phase-to-earth voltages to the function. In this case, the missing phase-to-earth
voltage is correctly calculated internally in the relay. If the measured residual voltage
is connected to SCEFRFLO input URES, Phase voltage Meas can be set 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", "CA Fault" or "ABC Fault") can be measured
accurately. In this case, the earth-fault loops (fault loops "AG Fault", "BG Fault" or
"CG Fault") cannot provide correct fault distance estimates and the triggering of the
function in case of an earth fault is automatically disabled. The situation is similar if
only two phase-to-earth voltages are measured and the measured residual voltage is
not connected to SCEFRFLO.

Application

The main objective of the feeder terminals is a fast, selective and reliable operation in
case of 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. With certain limitations, SCEFRFLO can
also be used for locating an earth fault 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 the 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.
Protection related functions
Section 5
Figure 604
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