Rockwell Automation 150 MNL/SMC DIALOG+/APP-PROD GUIDE - Manual (Page 160)

Reduced Voltage Starting 8-7
Current limit starting can be used in situations where power line
limitations or restrictions require a specific current load. The next
illustration shows a 450% current limit curve. Other values may be
selected, such as 200%, 300%, or 400%, depending on the particular
application. Current limit starting is also used in applications wher
higher starting torque is required compared to a soft start, which
typically starts at less than 300% current. Current limit starting is
typically used on high inertia loads, such as ball mills.
Figure 8.9 Current Limit Start
Solid-state controllers control the voltage applied to the motor, even
when the motor is up to speed, because of the semiconductors used in
the power circuit. This allows solid-state reduced voltage to provide
an energy saving function for motors that run unloaded or lightly
loaded for long periods of time. Intelligence within the solid-state
controller determines when the motor is lightly loaded. The voltage
to the motor can then be reduced by properly controlling th
semiconductors until the motor is operating at an optimum point.
This same intelligence detects when a load is reapplied and increases
the voltage to prevent stalling.
Other features available with solid-state controllers include additional
protection to the motor and controller, and diagnostics to aid in set-up
and troubleshooting. Protection typically provided includes shorted
SCR, phase loss, open load lead, SCR overtemperature, and stalled
motor. Appropriate fault messages are displayed to aid in
troubleshooting when one of these faults trip out the solid-state
reduced voltage controller.
600
450
100
%
Full
Load
Current
0 % Speed 100