Rockwell Automation 150 MNL/SMC DIALOG+/APP-PROD GUIDE - Manual (Page 159)

8-6 Reduced Voltage Starting
Solid-state The main function of solid-state controllers is their ability to provid
a soft start or stepless reduced voltage start of AC motors. The same
principles of current and torque apply to both electromechanical
reduced voltage starters and solid-state controllers. Many solid-state
controllers offer the choice of four starting modes: soft start, current
limit start, dual ramp start, or full voltage start in the same device.
Figure 8.7 Solid-state Controllers
In addition to selecting the starting modes, the solid-state controlle
allows adjustment of the time for the soft start ramp, or the current
limit maximum value, which enables selection of the starting
characteristic to meet the application. The most widely used version
is the soft start. This method provides a smooth start for most
applications.
The major advantages of solid-state controllers are the elimination of
the current transition point and the capability of adjusting the time to
reach full voltage. The result is no large current surge when the solid-
state controller is set up and correctly matched to the load, as
illustrated in Figure 8.8.
Figure 8.8 Soft Start
Percent
Voltage
10
Time (seconds)
Adjustable 0-30 seconds
Run