What is soft starter?

Friday, November 25, 2016

In motor control, Soft Starter is used to start/ stop motor gradually increase/ decrease torque, current. So that it can help extend life time of Motor, also mechanism of machine.
There are 3 kind of motor control:
(1) Direct-on-Line Starter: mean using power apply directly to Motor
(2) Soft Starter: using SCR to control voltage of Motor
(3) Variable Frequency Diver: generally using SCR or IGBT working with Control board to vary Frequency, current to control motor  



Let's see Soft Starter:



Purpose? As it name, make motor start/ stop gently -> help motor/ mechnicalnism increasing life time
How it works? Use SCR to control voltage -> control Current and Torque

The motor torque is approximately proportional to the square of the applied voltage: Torqe ~ [Volt]^2
   Example: reduce 60% volt -> apply 40% volt -> apply 16% torqe -> reduce 84% torque
The current during the start is directly related to the voltage applied to the motor
Above table is summarize of start motor by Direct voltage, Alpha-Delta, Soft Starter


Note: above explain mainly take from content of Allen-Bradley publication
Link:
(1) Allen-Bradley publication
(2) ABB publication



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