Siemens SIRIUS 3RW40, Manual

Page: 102 / 212

Commissioning
12.4 Commissioning the 3RW40
SIRIUS 3RW30 / 3RW40
102
Manual, 01/2010, 535 1995-02 DS01
12.4.4 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.
12.4.5 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 3RW40 soft starter additionally limits the current to the value set with the current
limiting potentiometer. As soon as the current limiting value is reached, the voltage ramp or
the ramp time is interrupted and the motor is started with the current limiting value until it has
started up successfully. In this case, the motor ramp-up times may be longer than the
maximum parameterizable 20 seconds ramp time or the ramp time that is actually set on the
soft starter (for further information about the maximum ramp-up times and switching
frequencies, refer to the Technical data chapter > 3RW30 13, 14, 16, 17, 18-.BB.. power
electronics [Page 124]) ff. and 3RW40 24, 26, 27, 28 power electronics [Page 149] ff.).