VLT
®
Soft Starter Pocket Guide 43
Two-Speed Motors: Are soft starters suitable for use
with two-speed motors?
Soft starters are suitable for use with Dahlander and dual winding
motors, provided that separate motor protection is used for both low
and high speed operation.
Dual-winding motors have one shaft with two separate pole
confi gurations (e.g. 4 pole and 8 pole), providing two diff erent speeds.
The speed is selected using external contactors (AC3 rated).
Dahlander motors are often used for two-speed compressor or fan
applications. The motor windings are externally confi gured using
contactors for high speed (dual star) and low speed (delta) operation.
MCD 201 soft starters are designed for use with external
motor protection devices and are ideal for two-speed motor
applications. MCD 202 soft starters have motor protection
built in and are less suitable for two-speed applications.
MCD3000 soft starters off er dual motor settings, which
allows separate start profi les to be confi gured for each
speed.
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