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Induction Motor Starting Current


kana

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Hi,

 

Is there any relation between the induction motor starting current and the reactive power drawn by the motor? I’m a bit confused here. I’m aware that by installing a reduced voltage starter the starting current of the induction motor can be reduced but there is a current spike while the changeover occurs in some electromechanical starters (ie star-delta or auto-transformer). Can this spike be eliminated by adding a capacitor in parallel? In some modern soft starter the term “energy saving” is used. What does this term refers to?

 

Kana

 

 

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Hello kana

 

Welcome to the forum.

 

The "spike" when you switch from star to delta is not due to reactive currents, rather it is due to the open transition nature of the switching.

Have a look at the information on star delta starting at http://www.lmphotonics.com/star_delta.htm

It is theoretically possible to reduce the start current by adding power factor correction, but in practice it is difficult to do as the amount of capacitance required is rotor speed related. You would need fast switching and multiple capacitors to make it work.

 

Best regards,

Mark.

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Hello Kana

 

how does a soft starter can save energy?

It doesn't, however with a soft starter you can sometimes shut down and restart a machine on demand, that would normally be left running.

 

Best regards,

Mark.

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Hello mark,

 

Thank you for the reply. I got your point. I was attracted and curious to know how soft starters can save energy after I came across a company which advertised their soft starters as energy saving devices.

 

 

 

Regards,

Kana

 

 

 

 

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Hello Kana

 

Some soft starters include the Nola type algorithm which is severely oversold, but in some (limited) circustances can save some (limited) energy.

There are plenty of discussions on this forum about these devices plus there is a paper at http://www.lmphotonics.com/energy.htm that may answer some questions.

 

There are also some that claim that the reduced starting current reduces energy and maximum demand penalties etc. This is also not true in most cases.

 

Best regards,

Mark.

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  • 9 months later...
Hello Kana

 

Some soft starters include the Nola type algorithm which is severely oversold, but in some (limited) circustances can save some (limited) energy.

There are plenty of discussions on this forum about these devices plus there is a paper at http://www.lmphotonics.com/energy.htm that may answer some questions.

 

There are also some that claim that the reduced starting current reduces energy and maximum demand penalties etc. This is also not true in most cases.

 

Best regards,

Mark.

hello mark,

 

i am curious about the nola type algorithm since it's something new for me..

 

could you please expalin more about it and the relations to the motor starting?

 

thanks before..

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