Rockwell Automation Low-Voltage Switchgear and Controlgear - Manual (Page 103)

Fig. 3.9-8
The Rockwell Automation pump control function for soft starters continuously controls the flow of the
medium during start-up and stopping and prevents hydraulic impacts with their adverse consequences.
3.9.7 Motor braking
For applications in which the natural coasting to a halt of the motor takes too long – for example
with drives with large inertial masses – the braking function of soft starters can be useful. By
appropriate control of thyristors, a braking torque is generated in the motor that results in
accelerated braking. The coming to rest of the motor is detected by measurements of the back
e.m.f. so that no additional devices such as standstill-sensors, contactors etc. are required. This
method is not suitable for EMERGENCY STOP shutdowns.
100%
Motor
Speed
Start Run Brake
Time (seconds)
Smart Motor Braking
Coast-to-rest
Automatic Zero Speed
Shut-off
Fig. 3.9-9
The shutdown time of a drive can be reduced with the braking function
3.9.8 Positioning speed and controlled braking
Precise positioning is frequently required in engineering applications, for which the motor speed
is temporarily reduced. Soft starters provide various options for accurate positioning, in one or
two senses of rotation and in combination with controlled braking. See
Fig. 3.9-10 to
Fig. 3.9-12 .
100%
Motor
Speed
Forward
15% - High
20% - High
7% - Low
10% - Low
Time (seconds)
Reverse
Start Run
Fig. 3.9-10
Soft starters with crawl speed in both directions for positioning purposes
LVSAM-WP001A-EN-P - April 2009 3-27