Setting The Starting Voltage; Setting The Ramp Time - Siemens SIRIUS 3RW30 Manual

12.2.4

Setting the starting voltage

U potentiometer
The starting voltage value is set with the U potentiometer. This value determines the starting
torque of the motor. A lower starting voltage results in a lower starting torque (softer start) and
a lower starting current.
The starting voltage selected must be sufficiently high to ensure that motor starts up smoothly
as soon as the start command is received by the soft starter.
12.2.5

Setting the ramp time

t potentiometer
You define the length of the required ramp time with the t potentiometer. The ramp time
determines the time taken to increase the motor voltage from the parameterized starting
voltage to the mains voltage. This time merely influences the motor's acceleration torque,
which drives the load during the ramp-up process. The actual motor starting times are load-
dependent and can differ from the 3RW soft starter settings.
A longer ramp time results in a lower starting current and a reduced acceleration torque as
the motor starts up. The startup is slower and smoother as a result. The ramp time must be
long enough for the motor to reach its nominal speed. If the time selected is too short, in other
words if the ramp time ends before the motor has started up successfully, a very high starting
current that can even equal the direct starting current at the same speed occurs at this
instant.
The SIRIUS 3RW30 soft starter can be damaged in this application (set ramp time shorter
than the actual motor ramp-up time). A maximum ramp-up time of 20 s is possible for the
3RW30. An appropriately dimensioned SIRIUS 3RW40 or 3RW44 soft starter should be
chosen for startup processes with a motor ramp-up time > 20 s.
SIRIUS 3RW30 / 3RW40
Manual, 01/2010, 535 1995-02 DS01
Commissioning
12.2 Commissioning the 3RW30
95