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The 3RW51 soft starter starts the motor as soon as the switch-on command is issued (t
the ramp-up time (t
elements) which starts up the motor smoothly.
The 3RW51 soft starter features internal ramp-up detection. The following operation occurs
when the motor reaches its rated operating speed before the ramp-up time has elapsed:
• The motor voltage is immediately increased to 100 % of the line voltage (t
• The external bypass contactor close
• The power semiconductors are bypassed and the soft starter is in bypass operation.
Cancelling the switch-on command activates the stopping mode and the motor is shut down.
The power semiconductors also ensure that the motor coasts down smoothly to a stop. As long
as the stopping time is active (t
for the motor to actually coast down to standstill (t
①
②
t
1
t
2
t
3
t
4
Functions
Note the information in chapter Firmware update (Page 153).
• Soft starting with parameterizable starting voltage and ramp up time for a smooth starting
of the drive
• Soft stopping with parameterizable stopping time for a smooth run-down of the drive
• Parameterizable current limit for avoiding current peaks
• Soft torque for smooth ramp-up and run-down (avoiding torque peaks by means of torque
limitation)
SIRIUS 3RW51 Soft Starter
Equipment Manual, 09/2020, A5E37108631002A/RS-AC/003
to t
), the current is conducted via power semiconductors (switching
1
3
Speed
Voltage
Motor start-up with set starting voltage U
Rated speed n
achieved
e
End of the set ramp-up time (t
Switch-on command is cancelled, motor is
switched off
to t
), the power is still supplied to the motor. It may take longer
4
5
).
6
t
End of the set stopping time (t
5
t
Motor at standstill
6
U
Set starting voltage
S
S
U
Rated operational voltage
e
-t
)
n
Rated operating speed of the motor
3
1
e
Description
3.3 Operating principle
). During
1
)
2
-t
)
5
4
19
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