What is a soft starter ? And it's operating principle.

Telegram: https://t.me/electricalengineeringpor...
Facebook page:   / electricalengineeringch  
Facebook group:   / electrical.engineering.ch  
Twitter:   / electri88225030  


What is a soft starter ?

Soft starter is a device usually used to start a motor at a slower pace over a set time,

instead of starting with the full starting torque.

Why starting with the full torque is not preferable in some applications?

starting the motor with the full torque, make it draws an excessive amount of inrush current, which can be the reason of unwanted consequences,

like burn out the motor.

Wear and tear in the equipment and it's mechanical parts, increasing the demand of repair.

Full torque starts or sudden stop could also cause an undesirable effect with the application

For example,

When a pump is stopped immediately that can lead to water hammering.

In this example the soft starter can be used to reduce the voltage to the pump to prevent water hammering during the stoppage.

A soft starter can control the motor to have a slower start by limiting the voltage to the motor,

so the generated torque will be reduced too.

That will create an increase in the slip causing the motor to slowly build up the full torque, over a set time.

And reducing the amount of inrush current as a result.

This also protect the equipment parts from wear.

because of slowing the motor torque thus the speed of the motor during starting.

sometimes soft starters are compared with variable frequency drives, in the way of controlling the motors.

But soft starter doesn't control the speed of the motor,

it's just reducing the voltage to the motor.

The drive can control the motor frequency and speed during startup, ,

operation,

and on stop.
for example:

If we have a conveyor,

the soft starter can reduce the starting torque,

which can give a soft and smooth start for the conveyor.

but reducing the voltage during the stoppage may not result in a controlled stop.

But with the variable speed drives,

we can control the motor frequency and the speed in the whole operation,

The drive can control the motor speed ramp up to achieve the optimum startup,

Also it can control back the ramp down so also the optimum stoppage can be obtained,

The drive control won't be affected by the belt mechanical parts status, or the load.

Normally in soft starter, you can set the initial starting voltage.

from 30% to 70% of the nominal voltage,

Also you will set the starting time,

this is the time required for the soft starter to reach the full output voltage.

Another feature in the soft starter, and it's for better motor protection.

In the some soft starters you have the ability to set two overload settings,

one to monitor the motor during the startup,

the second one is to monitor the motor during the operation.

that is because the different motor current characteristics in both stages.

Soft starter is preferred to be protected with a semiconductor fast acting fuse,

Many other features and setting you will find it in details in your soft starter.

If you have father questions about the soft starter or any other electrical subject, please comment on the video.
#troubleshooting #Maintenance #Electrical #electricity #engineering #motor