Operating Principle - Siemens SIRIUS 3RW50 Manual

1.3

Operating principle

Soft starters are used to start three-phase induction motors with reduced torque and reduced
starting current.
The 3RW50 soft starter starts the motor as soon as the switch-on command is issued (t
During the ramp up time (t
(switching elements) which start the motor up smoothly.
The 3RW50 soft starter features internal run-up recognition. If a successful motor run-up is
detected before the ramp up time elapses, the motor voltage is immediately increased to
100 % of the line voltage (t
semiconductors are bypassed. The 3RW50 soft starter is in bypass operation.
Coast-down to zero speed is activated when the switch-on command is cancelled (t
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
the motor. It may take longer for the motor to actually coast down to a standstill (t
①
②
t
1
t
2
t
3
t
4
SIRIUS 3RW50 soft starter
Manual, 09/2019, A5E35628455002A/RS-AA/001
1
). The internal bypass contacts close and the power
2
Speed
Voltage
Motor start-up with set starting voltage U
Rated operating speed n
e
End of the set ramp up time
(t -t )
3 1
Switch-on command is cancelled, motor is
switched off
to t ), the current is conducted via power semiconductors
3
t
5
t
6
U
S S
reached U
e
n
e
1.3 Operating principle
to t ), energy is still supplied to
4 5
End of the set stopping time
(t -t )
5 4
Motor at standstill
Set starting voltage
Rated operational voltage
Rated operating speed of the motor
Description
).
1
) and
4
).
6
11