Device functions
7.4 Slow speed function
3RW44 soft starters
134
Manual, 03/2017, NEB535219502000/RS-AB/008
7.4
Slow speed function
This function enables an induction motor to be operated temporarily in both directions at a
lower speed than the rated speed.
The motor's rated speed n
Motor
is determined by means of the line frequency (f) and the
number of pole pairs (p) of the motor.
A resulting slow speed frequency is stipulated for the motor by a specific thyristor control.
However, it is necessary for this function that only a reduced torque can be generated in the
motor. Due to possible heat rise of the motor, this function is not suitable for continuous
operation.
The slow speed factor and the slow speed torque can be entered individually for both
directions of rotation.
Slow speed factor
When the slow speed factor is set, the motor can be controlled with a lower speed (n
slow speed
)
than the rated speed either in or against the line phase direction.
Slow speed torque
The torque generated in the motor can be influenced with the slow speed torque. The
maximum torque that can be generated depends on the selected slow speed. 100% slow
speed torque can be equivalent to approximately 30% of the rated motor torque.
Figure 7-10 Slow speed function
