Torque Control - Siemens Sirius 3RW44 System Manual

6.2.2 Torque control

Start torque
Limiting torque
Starting time
Maximum starting
time
Internal run-up
recognition
SIRIUS 3RW44 manual
GWA 4NEB 535 2195-02 DS 01
The motor speed and torque is calculated using the voltage and current r.m.s.
values as well as of the associated phase information between the line voltage
and the motor current (= cos ϕ = sensorless control) and the motor voltage is
controlled accordingly.
Torque control means that the torque generated in the motor is linearly
increased from a parameterizable start torque up to a parameterizable end
torque within an adjustable starting time.
The advantage over the voltage ramp is improved mechanical run-up behavior of
the machine.
The soft starter controls the torque generated at the motor continuously and
linearly according to the set parameters until the motor has completely run up.
For optimum torque control during the starting process, the motor data of the
motor connected to the soft starter should be entered in the selected
parameter. This can be specified using the Setting menu item.
The height of the start torque determines the switch-on torque of the motor. A
smaller start torque results in a smaller run-up torque and smaller starting
current. The start torque should be selected high enough so that the motor
starts immediately and softly when the start command is sent to the soft starter.
The height of the limiting torque determines which maximum torque should be
generated in the motor during running up. Thus this value can also act as an
adjustable torque limitation.
In order to obtain a successful run-up, the parameter value should be set to
about 150 % but at least high enough so that the motor does not become stuck
during startup. This ensures that enough acceleration torque is always created
during the whole motor run-up.
The starting time length determines in what time the start torque is increased to
the end torque.
A longer starting time results in a smaller acceleration torque over the motor
run-up. This results in a longer and softer motor run-up. The length of the
starting time should be selected such that the motor accelerates softly until it
reaches its nominal speed.
If the starting time ends before the motor has completely run up, the torque is
limited to the set limiting torque until the soft starter recognizes the run-up
process and closes the internal bypass contacts.
The maximum starting time parameter is used to determine after what
maximum time the drive should have fully run up. If the drive is not in nominal
operation upon completion of the set time, the starting procedure is aborted and
an error message is generated.
The soft starter features an internal run-up recognition. If a completed motor
run-up is recognized within the defined starting time, the ramp will be aborted
and the motor voltage will immediately be increased to 100 % of the line
voltage. The internal bypass contacts will close and the thyristors are bridged.
Device functions
6-5