3
Arc Protection Relay
REA 10_
Features
• Loop-type sensor fiber, radial sensor fiber
or lens-type sensor for arc detection
• Two high-speed semiconductor outputs for
tripping
• Tripping from light only or secured with
fast, adjustable three-phase or two-phase
and neutral overcurrent condition
• Total operate time <2.5 ms
• Wide area automatic or manual backlight
compensation
• Two RJ45 ports for chaining the extension
units
• Two opto-connectors for fast ON/OFF sig-
nal transfer between central units
• Circuit-breaker failure protection, i.e.
delayed output for higher-level circuit
breaker
• Self-supervision unit for monitoring the
sensor fiber, operating voltages and
cabling between central units and exten-
sion units
Application
Consequences of an arcing short circuit or
earth fault within a low or medium voltage
switchgear can be very serious. An arc can
destroy costly equipment, and cause pro-
longed and expensive downtime. Further-
more, an arc can cause serious injuries to
personnel.
Sources of arcing can be e.g. failure of insula-
tion, mal-operation of a device, improper bus
or cable joints, overvoltage, corrosion, pollu-
tion, moisture, ferro-resonance (instrument
transformers) and even ageing under electri-
cal stress. Most of these could be prevented
by sufficient maintenance. But in spite of all
precautions, human errors by personnel can
also lead to arc faults.
Time is critical when it comes to detecting
and minimising the effects of an arc. An arc
fault lasting 500 ms may cause severe dam-
age to the installation. If the arc lasts less than
100 ms the damage is often smaller, but if the
arc is eliminated in less than 35 ms the dam-
age is almost unnoticed.
Substantial damages and serious conse-
quences of an arc fault hazard can be miti-
gated with fast acting REA 101 Arc
Protection System. In addition to arcing short
circuits, even arcing earth faults with current
levels below normal load current can be
detected and interrupted already before they
escalate to two or three-phase short circuit.
Normally applied bus bar protection relaying
arrangements may be too slow to ensure safe
fault clearance times at arc faults. E.g. opera-
tion time of the overcurrent relay controlling
the incoming CB may have to be delayed
hundreds of milliseconds for selectivity rea-
sons. This delay can be avoided using
REA 10_ arc protection system: Total fault
clearance time can be reduced to max 2.5 ms
plus circuit breaker’s action time.
Furthermore, autoreclosure trials doomed to
fail at cable compartment faults can be elimi-
nated with arc protection.
The arc protection relay REA 101 and the
extension units REA 103, REA 105 and REA
107 are designed to be used for the protection
of medium and low-voltage air-insulated
switchgear. The central unit type REA 101
operates independently or together with the
extension units REA 103, REA 105 and
REA 107. These extension units allow the
number of sensor fibers and/or lens sensors to
be increased, thus extending the area to be
protected. In an arc situation, the fault place
is quickly localized by inspecting the area
covered by the sensor that detected the arc.
The design of the extension units REA 103
and REA 105 is nearly the same. The main
difference between the units is that the
REA 105 is provided with two fast trip out-
puts capable of opening, for example, the bus
coupler or both circuit breakers of a duplex
feeder. Thus selective tripping is achieved.
The REA 107 is also used for the extension of
the protection area. It has inputs for eight
lens-type sensors. The arc protection relay
REA 101 is provided with two output ports,
to each of which a maximum of five exten-
sion units can be chained.
1MRS750929-MBG
Issued: 1May 1999
Status: Updated
Version: D / 22.06.2005
Data subject to change without notice
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