Starting Modes; Voltage Ramp - Siemens SIRIUS 3RW44 System Manual

6.2

Starting Modes

6.2.1 Voltage Ramp

Start voltage
Starting time
Maximum starting
time
Internal run-up
recognition
SIRIUS 3RW44 System Manual
GWA 4NEB 535 2195-02 DS 04
Different starting functions can be selected thanks to the large number of
applications for which the SIRIUS 3RW44 soft starter can be used. The motor
start can be set optimally according to application and deployment.
The simplest type of soft start with the SIRIUS 3RW44 is achieved using a
voltage ramp. The terminal voltage of the motor is increased from a
parameterizable start voltage to line voltage within an adjustable starting time.
This starting mode is preset in the quick start menu.
The level of the start voltage determines the switch-on torque of the motor. A
smaller start voltage results in a smaller start torque and smaller starting current.
The start voltage should be high enough so that the motor starts immediately
and softly when the start command is sent to the soft starter.
The length of the starting time determines the time in which the motor voltage is
increased from the set start voltage to the line voltage. This influences the
acceleration torque of the motor, which drives the load during the run-up
procedure. 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 reaches its nominal
speed within this time. If this time is too short, i.e. if the starting time ends before
the motor has run up, an extremely high starting current will occur at that
moment, reaching the value of the direct starting current at this speed. The soft
starter can, in this case, switch itself off via the internal overload protection
function and go into fault mode.
The "Maximum starting time" parameter is used to determine the time after which
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 by the device, the internal bypass contacts will close and the
thyristors are bridged. If this run-up recognition is performed before the set run-
up time is completed, the ramp is aborted and the motor voltage is immediately
increased to 100 % of the line voltage before the internal bypass contacts are
closed.
Device Functions
6-3