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Siemens IC 10 · 2017
Overload Relays
SIRIUS 3RB2 Electronic Overload Relays
3RB24 for IO-Link for high-feature applications
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Overview
SIRIUS 3RB24 evaluation module
The modular, IO-Link powered 3RB24 electronic overload relays
(with monostable auxiliary contacts) up to 630 A (up to 820 A
possible with a series transformer) have been designed for
current-dependent protection of loads with normal and heavy
starting against excessive temperature rises due to overload,
phase asymmetry or phase failure. It comprises an evaluation
unit, a current measuring module and a connecting cable.
The evaluation module 3RB24 also offers an engine starter
function: The contactors, which are connected via the auxiliary
contacts, can also be actuated for operation via IO-Link. In this
way, direct-on-line, reversing and wye-delta starters up to 630 A
(or 830 A) can be connected to the controller wirelessly via the
IO-Link controller.
An overload, phase asymmetry or phase failure result in an
increase of the motor current beyond the set rated motor current.
This current rise is detected by means of the current measuring
module
(see page 7/132)
and electronically evaluated by the
evaluation module which is connected to it. The evaluation
electronics sends a signal to the auxiliary contacts. The auxiliary
contacts then switch off the load by means of a contactor.
The break time depends on the ratio between the tripping
current and current setting
I
e
and is stored in the form of a
long-term stable tripping characteristic curve
(see Manual)
. The
"tripped" status is signaled by means of a continuously illumi-
nated red "
OVERLOAD
" LED and also reported as a group fault via
IO-Link.
The LED indicates imminent tripping of the relay due to overload,
phase asymmetry or phase failure by flickering when the limit
current has been violated. This warning can also be reported to
the higher-level PLC via IO-Link at the 3RB24 overload relay.
In addition to the described inverse-time delayed protection of
loads against excessive temperature rises, the 3RB24 electronic
overload relays also allow direct temperature monitoring of the
motor windings (full motor protection) by connection with
broken-wire interlock of a PTC sensor circuit. With this tempera-
ture-dependent protection, the loads can be protected against
overheating caused, for example, indirectly by reduced coolant
flow and which cannot be detected by means of the current
alone. In the event of overheating, the devices switch off the
contactor, and thus the load, by means of the auxiliary contacts.
The "tripped" status is signaled by means of a continuously illu-
minated "
THERMISTOR
" LED and also reported as a group fault
via IO-Link.
To protect the loads against incomplete ground faults due to
damage to the insulation, humidity, condensation, etc., the
3RB24 electronic overload relays offer the possibility of internal
ground-fault detection (for details,
see Manual
, not possible in
conjunction with contactor assemblies for star-delta (wye-delta)
starting). In the event of a ground fault, the 3RB24 relays trip
instantaneously.
The "tripped" status is signaled by means of a flashing red LED
"Ground Fault" and reported at the overload relay 3RB24 as a
group fault via IO-Link.
The reset after overload, phase asymmetry, phase failure,
thermistor or ground-fault tripping is performed manually by key
on site, via IO-Link or by electrical remote RESET or automati-
cally after the cooling time (motor model) or for thermistor
protection after sufficient cooling. Trips in devices initiated by
function monitoring systems (broken wire or short-circuit on the
thermistor) can only be reset locally.
A motor current measured by the microprocessor can be output
in the form of an analog signal DC 4 mA to 20 mA for operating
rotary coil instruments or for feeding into analog inputs of
programmable logic controllers.
More information
Home page,
Industry Mall,
see www.siemens.com/product?3RB2
Application Manual "SIRIUS Controls with IE3/IE4 Motors",
see
Manual "SIRIUS 3RB24 Electronic Overload Relay for IO-Link",
see
Certificates,
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X
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Plug-in point for operator panel:
enables connection of the 3RA6935-0A operator panel.
Motor current and trip class setting:
Setting the device to the motor current and to the required trip
class dependent on the start-up conditions is easy with the two
rotary switches.
Connecting terminals (removable terminal block):
The generously sized terminals permit connection of two
conductors with different cross-sections for the auxiliary, control
and sensor circuits. Connection is possible with screw connection
and alternatively with spring-type connection.
Test/RESET button:
Enables testing of all important device components and functions,
plus resetting of the device after a trip when manual RESET is
selected.
Selector switch for manual/automatic RESET:
With this switch you can choose between manual and automatic
RESET.
Red LED "OVERLOAD":
A continuous red light signals an active overload trip; a flickering
led light signals an imminent trip (overload warning).
Red LED "THERMISTOR":
A continuous red light signals an active thermistor trip.
Red LED "GND FAULT":
A continuous red light signals an active ground-fault trip.
Green LED "DEVICE/IO-Link:
A continuous green light signals that the device is working
correctly, a green flickering light signals the communication
through IO-Link.
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© Siemens AG 201
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