Arc Protection Relay
REA 10_
1MRS750929-MBG
4
Design
Arc protection relay REA 101
Overcurrent detection unit
The selection switch is used to select between
three-phase current measurement or two-
phase and neutral current measurement.
Three-phase current measurement
The three-phase currents are measured via
transformers. When the current on one phase
exceeds the selected reference level, an over-
current signal is activated.
The selection switch is used to select the cur-
rent reference level for the current inputs L1,
L2 and L3. The available current level set-
tings are 0.5, 1.0, 1.5, 2.5, 3.0, 5.0 and 6.0
times the rated current (In = 1.0 A or 5.0 A).
Two-phase and neutral current measure-
ment
When the current in L1, L3 or L2 (neutral
current) exceeds the selected reference level,
an overcurrent signal is activated.
The available current level settings for L1 and
L3 are 0.5, 1.0, 1.5, 2.5, 3.0, 5.0 and 6.0 times
the rated current (In = 1.0 A or 5.0 A).
The available current level settings for L2 are
0.05, 0.1, 0.15, 0.25, 0.3, 0.5 and 0.6 times
the rated current (In = 1.0 A or 5.0 A).
Light detection unit
The light captured by the sensor is amplified
and compared to the pre-selected light refer-
ence level. Once the light exceeds the set ref-
erence level, a light signal is activated.
The selection switch is used to activate the
arc detection sensor.
The selection switch is used to select auto-
matic or manual light reference level.
If the automatic reference level is selected,
the unit forms the reference level based on
the backlight intensity measured by the sen-
sor.
When the manual reference level is selected,
the unit forms the reference level based on
the value that was selected with the light ref-
erence level adjustment potentiometer on the
front panel.
The sensor fiber condition is monitored by
sending a test pulse through the fiber. If a test
pulse is not received at regular intervals at the
other end of the fiber loop, the “Sensor Fault”
LED and the self-supervision LED “IRF” are
activated, and the IRF relay resets.
If the sensor-monitoring feature is not
needed, it can be deactivated by using the
selection switch.
Sensitivity of sensors
A050616
Fig. 1
Sensitivity of REA 10_ sensors at various
backlight compensation settings
The intensity of a high-current arc light in a
two- or three-phase short circuit can be tens
of thousands of luxes. The intensity of a nor-
mal office lighting is 200-300 luxes.
The exact determination of the detecting
reach of the light sensors is difficult, because
the detecting reach depends on several fac-
tors:
• Light source energy
• Fiber length
• Reflectances
• Backlight compensation settings
Sensitivity of fiber sensors
The incidence angle of the light is not rele-
vant with fiber sensors.
When an arc protection system is designed,
the length of the sensor fiber per one switch-
gear compartment must be selected according
to the possible short-circuit or earth-fault cur-
rent, and the distance between the sensor and
arc. When selecting sensor fiber length, refer
to the table 1.
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