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Replacing Of Dol/star Delta With Soft Starter Saves Energy?


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#1 AB2005

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Posted 13 January 2013 - 03:22 AM

Hello;

 

Today, energy saving concepts are being applied at everywhere due energy crises.

Now someone claimed that if we replace the DOL or start delta starter with soft starter, it will save the energy as when we start the motor via DOL or SD, it draws 600-800% current and SS reduces that starting current. But i think replacing SS would not save much energy and pay back period would be very long. If starting current is increased by DOL or SD then power factor of motor also drops in that starting period. So the starting torque and real power is not much higher.

What are your comments?


"Don't assume any thing, always check/ask and clear yourself".

#2 marke

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Posted 13 January 2013 - 05:03 AM

Hello AB2005

 

Long time no see!!

 

The soft starter will not save energy, it will in fact use a little more due to the voltage drop across the SCR unless you also use a bypass contactor.

Some manufacturers claim incorrectly that you will reduce your maximum demand charges. This is also incorrect. The start time is so short relative to the metering integration period, that the lower current for a longer time will yeild the same integral.

 

There are some soft starters that include an energy saving function. This is based on technology developed originally by Frank Nola at NASA. I also held patents on this technology back in the 80s, but the reality is that you can only save a portion of the iron losses on small motors ar light load. No real practical application on most industrial loads.

 

Best regards,

Mark.



#3 Madala

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Posted 13 January 2013 - 03:15 PM

I agree with Mark the only way you will cut down on the inrush of current is using a power factor correction unit the capacitors will help to regulate the starting current so that you do not have such a load on starting up. Due to heavy loads imposed on line you have a voltage drop which in turn increases the amperage for starting. The power factor ciorrection unit compensates for this.



#4 marke

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Posted 14 January 2013 - 01:09 AM

Hello Madala

 

Power factor correction will not siginificantly improve the starting current of an induction motor.

This is a theory has has been put on a number of occasions, but the problem is that during start, the inductive (reactive) portion of the current varies significantly as the motor accelerates.

When the motor is at rest, the reactive current is in the order of 6 times the rated current of the motor, at half speed, the reactive current is more like 3 times the rated current of the motor.

 

To use capacitors to give a start current improvement, you need mulitple stages which are controlled by the instantaneous speed of the accelerating motor.

 

Best regards,

Mark.






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