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Diffrence b/w VSD & Soft starter ?


sethar

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Hello Sethar

 

A soft starter comprises one or more SCR pairs connected in series with the supply to the motor. These SCRs are used to reduce the voltage applied to the motor during start. The reduced voltage results in a reduced starting current and torque.

A variable speed drive is an inverter that rectifies the incoming supply, generating a high voltage DC. This DC is then chopped up converting the DC back into AC of variable voltage and frequency. The speed of the motor is altered by altering the frequency applied to it.

 

Best regards,

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  • 2 weeks later...
Just to correct a slight mistake in the first response, a Soft Starter cannot change the output frequency, only the voltage. For that reason, a Soft Start cannot be used to change motor speed. It simply ramps the motor up (or down) but only operates continuously at full speed.
"He's not dead, he's just pinin' for the fjords!"
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  • 3 weeks later...

Hello Sethar,

 

In very simplistic terms, the function of each is as follows;

 

A soft starter is used to accelerate a motor/load from zero speed to rated speed over a user adjustable period of time. The process is achieved by controlling the voltage applied to the motor terminals during starting.

 

A variable frequency drive enables the user to control the speed of the motor/load. The process is achieved by varying both the voltage and frequency (Hz) of the supply to the motor.

 

Regards,

GGOSS

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