Stop Modes - Siemens SIRIUS 3RW30 Manual

Functions

5.2 Stop modes

As soon as the selected current limiting value is reached, the motor voltage is reduced or
controlled by the soft starter to prevent the current from exceeding the limit. The set current
limiting value must be high enough to ensure that the torque generated in the motor is
sufficient to accelerate the motor to nominal speed. Three to four times the value of the
motor's rated operational current (Ie) can be assumed as typical here.
The current limiting function is always active because it is required by the intrinsic device
protection. If the current limiting potentiometer is set to the clockwise stop (maximum), the
starting current is limited to five times the set rated motor current.
Ramp-up detection (3RW40 only)
The SIRIUS 3RW40 soft starter is equipped with an integrated ramp-up detection function. If it
detects a motor startup, the motor voltage is immediately increased to 100 % of the mains
voltage. The internal bypass contacts close and the thyristors are bridged.
Figure 5-4
Typical applications for current limiting
Current limiting is used for applications with large centrifugal masses (mass inertias) and
therefore longer ramp-up times, e.g. fans, circular saws etc.
5.2 Stop modes
You can choose between different stop modes reflecting the wide range of applications for
SIRIUS soft starters. The motor stop can be optimally adapted to each particular application.
If a start command is issued during the stop process, the process is interrupted and the motor
is started again with the set start mode.
Note
If you select "soft stop" (3RW40 only) as the stop mode, the feeder (soft starter, cables,
feeder protective devices, and motor) may need to be dimensioned for higher values
because the current exceeds the rated motor current during the stop process.
30
Current limiting with soft starter
SIRIUS 3RW30 / 3RW40
Manual, 01/2010, 535 1995-02 DS01