Slow Speed Function - Siemens Sirius 3RW44 System Manual

Device functions
6.4

Slow speed function

Slow speed factor
Slow torque
Typical applications for slow speed function
6-16
This function allows an asynchronous motor to be temporarily operated in both
directions at a rotational speed that is lower than the rated rotational speed.
The rated rotational speed n
frequency (f) and its number of pole pairs (p).
A resulting slow speed frequency for the motor is defined by a specific thyristor
control. However, this function requires that only a reduced torque can be
generated in the motor. Due to possible overheating of the motor, this function
is not suitable for continuous operation.
The slow speed factor and the slow torque can be entered individually for both
directions of rotation.
By adjusting the slow speed factor, it is possible to control the motor with a
rotational speed (n
slow speed
in the same or opposite direction of rotation to that of the line.
The torque generated in the motor can be influenced using the slow torque. The
maximum torque which can be created depends on the slow torque that is
specified. 100 % slow torque can correspond to approx. 30 % of the motor
rated torque.
Line frequency
Fig. 6-10: Slow speed function
This function is suitable for applications with a low counter torque, e.g. when
machine tools are positioned.
Notice
To control the motor with the specified slow speed parameters, "slow speed"
must be assigned to one control input, and "motor right PS1/2/3" or "motor left
PS1/2/3" must be assigned to the other. Also refer to circuit proposal in Chapter
8.1.7.
Directions of rotation:
Right: rotation in line phase direction
Left: rotation against line phase direction
of the motor is determined by its line
motor
60
×
n f
----- -
=
Motor
p
) that is lower than the rated rotational speed either
n
Nom
n
= --------------------------------------------
Slowspeed
Slowspeedfactor
Resulting "slow speed frequency"
SIRIUS 3RW44 manual
GWA 4NEB 535 2195-02 DS 01