Functions
7.4 Motor protection
SIRIUS 3RW52 Soft Starter
Manual, 01/2019, A5E35630451002A/RS-AD/004
99
7.4 Motor protection
The 3RW52 soft starter has 2 functions for protecting the motor:
● Electronic motor overload protection
● Thermistor motor protection with temperature sensor (optional)
Use a combination of both of these functions to implement full motor protection.
7.4.1 Electronic motor overload protection
Operating principle
The approximate temperature of the motor is calculated using the measured motor currents
and the parameter settings "Rated operational current I
e
" and "CLASS (trip class)". This
indicates whether the motor is overloaded or is functioning in the normal operating range.
When overload is detected, the 3RW52 soft starter shuts the motor down. The setting for
RESET MODE determines how the motor is restarted.
Parameters
Property damage due to overload.
If the motor is not monitored by a temperature sensor and if the trip class is set to CLASS
OFF, the motor will not have any protection at all.
Trip class The trip class specifies the maximum time within which a protective
device must trip from a cold state at 7.2 x the rated operational current
I
e
(motor protection to IEC 60947).
• CLASS OFF: Deactivates the electronic motor overload protection
• CLASS 10A / 10E / 20E: Tripping times according to the trip class
Rated operational current
I
e
The rated operational current I
e
is the current that can be continuously
conducted by the feeder (switchgear and motor). This is normally the
rated operational current I
e
of the motor and depends on whether the
motor is connected in an inline or an inside-delta circuit.
Recovery time following motor overload protection tripping
When the motor overload protection is tripped and Auto RESET MODE is set, the fault will
be reset automatically after a recovery time of 5 minutes. With selection of manual RESET or
remote RESET, a RESET is only possible following completion of the recovery time of 5
minutes.
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