Arc flash protection
The arc flash protection is available on the optional hardware
module. The module supports connection of up to four sensors.
The sensors can be of lens or loop types, or a free mixture. Both
sensor types are supervised against sensor failure. Fast tripping
increases staff safety and limits material damage, therefore it is
recommended to use static power outputs (SPO) instead of
normal power outputs (PO). This typically decreases the total
operating time with 4..6 ms compared to the normal power
outputs.
Power transformer differential protection
The relay offers low-impedance differential protection for two
winding (two restraints) and three-winding (three restraints)
power transformers. The power transformer protection
application package includes the protection for a two-winding
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.
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.
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