Functions
7.4 Motor protection
3RW51 Soft Starter
Manual, 06/2019, A5E37108631002A/RS-AB/002
89
7.4
Motor protection
7.4.1
Electronic motor overload protection
The 3RW51 soft starter has an integrated motor protection, which is available even when the
soft starter is bypassed with the external contactor.
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 3RW51 soft starter shuts the motor down. The setting for
RESET MODE determines how the motor is restarted.
Parameters
NOTICE
Property damage due to overload.
If the trip class is set to CLASS OFF, the motor will not have any protection at all.
Parameter
Description
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.
