Can anyone explain in simple terms how a soft starter works?

Thanks,
milliamp

Induction motors have largely become common place in industry today because of their simplicity and ruggedness. Although many applications may run at constant speed, many require variable speed such as conveyors.
There are several possible ways in which the speed of an induction motor may be varied which include changing the number of poles, altering the frequency, altering the rotor resistance and changing the line voltage to name a few.
Modern Soft starters utilize the latter in it's control of induction motors by adjusting the voltage as seen by the induction motors stator terminals using SCR's.
The basic principle behind a soft starter is that torque developed by an induction motor is propotional to the square of the voltage applied to it's stator terminals or quite simply, by using an ac controller the voltage applied to the motor can be controlled from nill to that of the value of the supply and the resulting torque is the square of the applied voltage.
I hope this answers your question millivanilli, sorry milliamp

Hey there Little Buddy,

Thanks for the detailed response, but I would like some more information if possible.

What are SCRs?

How do they control the voltage to the stator?

Thanks,
milliamp
PS: What's with the millivanili comment? :P

An SCR is a Silcon Controlled Rectifier, or a Thyristor. This is a power electronic switch that can be turned on by an "gating" signal. SCRs are used to reduce the voltage applied to the motor by being turned on for only a portion of each cycle in the same manner as a domestic light dimmer does. Turned on for only part of the time reduces the average voltage applied.
Best regards,