Measurements; Power Quality; Fault Locator; Disturbance Recorder - ABB REX640 Product Manual

REX640
Product version: 1
power transformer. If support for three-winding power
transformer is needed, the corresponding protection add-on
package can be selected. Both low-impedance differential
functions feature three-phase multi-slope stabilized stages and
an instantaneous stage to provide fast and selective protection
against short circuits, winding interturn faults and bushing
flash-overs. A second harmonic restraint with advanced
waveform-based blocking ensures stability at transformer
energization. The fifth harmonic based blocking and unblocking
limits stabilize the protection performance in moderate
overexcitation situations. In case of three-winding differential
protection, the connection group phase shift matching can be
done with 0.1 degree resolution supporting cycloconverter
applications. If the tap-changer position information is
available, it is possible to further increase the protection
sensitivity by compensating the tap-changer position error
within the measured differential current.
The power transformer protection application package also
includes high-impedance differential functions for a phase-
segregated protection scheme. If this scheme is applied, the
related current transformers have to be correctly selected and
the necessary secondary circuit components, external to the
relay, defined.

10. Measurements

The base functionality of the REX640 relay contains a number of
basic measurement functions for current, voltage, frequency,
symmetrical components of currents and voltages, power,
power factor and energy. These measurement functions can be
freely connected to the measured secondary quantities
available in the relay. The relay can also measure various analog
signals via RTD and mA inputs. All these measurements can be
used within the relay configuration for additional logics. The
measurements are available locally on the HMI and can be
accessed remotely via communication. The information is also
accessible via Web HMI.
The relay is also provided with a load profile recorder. The load
profile feature stores the selected load measurement data
captured periodically (demand interval). The records can be
viewed on the LHMI and are available in COMTRADE format.

11. Power quality

In the EN standards, power quality is defined through the
characteristics of the supply voltage. Transients, short-duration
and long-duration voltage variations and unbalance and
waveform distortions are the key characteristics describing
power quality. The distortion monitoring functions are used for
monitoring the current total demand distortion and the voltage
total harmonic distortion.
Power quality monitoring is an essential service that utilities can
provide for their industrial and key customers. A monitoring
system can provide information about system disturbances and
their possible causes. It can also detect problem conditions
ABB
throughout the system before they cause customer complaints,
equipment malfunctions and even equipment damage or
failure. Power quality problems are not limited to the utility side
of the system. In fact, the majority of power quality problems
are localized within customer facilities. Thus, power quality
monitoring is not only an effective customer service strategy but
also a way to protect a utility's reputation for quality power and
service.
The protection relay has the following power quality monitoring
functions.
• Voltage variation
• Voltage unbalance
• Current harmonics
• Voltage harmonics
The voltage unbalance and voltage variation functions are used
for measuring short-duration voltage variations and monitoring
voltage unbalance conditions in power transmission and
distribution networks.
The voltage and current harmonics functions provide a method
for monitoring the power quality by means of the current
waveform distortion and voltage waveform distortion. The
functions provide selectable short-term 3- or 60- or 300 –
second sliding average and a long-term demand for total
demand distortion (TDD) and total harmonic distortion (THD).
The phase-specific harmonic content is measured for voltages
and currents, as well as DC component and fundamental
content. The dedicated harmonics measurement page in the
LHMI presents the measurements in a user-friendly manner.

12. Fault locator

The relay features an optional impedance-measuring fault
location function suitable for locating short circuits in radial
distribution systems. Earth faults can be located in effectively
and low-resistance earthed networks, as well as in
compensated networks. When the fault current magnitude is at
least of the same order of magnitude or higher than the load
current, earth faults can also be located in isolated neutral
distribution networks. The fault location function identifies the
type of the fault and then calculates the distance to the fault
point. The calculations provide information on the fault
resistance value and accuracy of the estimated distance to the
fault point.

13. Disturbance recorder

The relay is provided with a disturbance recorder featuring up to
24 analog and 64 binary signal channels. The analog channels
can be set to record either the waveform or the trend of the
currents and voltages measured.
The analog channels can be set to trigger the recording function
when the measured value falls below or exceeds the set values.
The binary signal channels can be set to start a recording either
on the rising or the falling edge of the binary signal or on both.
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