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Energy Saving by Reducing Motor Voltage?


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#1 schow

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Posted 13 November 2004 - 06:47 AM

Dear all,

I found that there are some motor energy saver makers in the market applied the SCR technologies to control the input operating voltage of 3-phase AC induction motors.

They claimed that a motor would only need full voltage during start-up and after that the operating voltage could be reduced but this is only applicable to those over-sized motors.

Can anyone tell me if this really works? On the other hand, SCR controlled voltage would have harmonics problem, can we use a step down transformer to reduce the voltage?

A typical 3-phase AC motor would normally have input voltage between 380-440VAC. If I have a 3-phase supply of 415VAC, and I use a 3-phase transformer to step down 15% of the supplies, now I have about 350VAC. Can I gain 15% energy saving?

Can anyone advice? ;p;

#2 marke

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Posted 14 November 2004 - 06:35 PM

Hello schow

Have a look at my paper on these energy saving devices at http://www.LMPhotonics.com/energy.htm
There have been many discussions on this technology on this forum and others. The suppliers of this technology make a big play on "oversized" motors, but the efficiency of the motor only begins to fall significantly when the shaft load is well below 50%. A motor that is twice the size required will stil be operating at high efficiency, so little savings can be made.

You can only save a portion of the energy that is being wasted. Eith this technology, the energy that is saved, is part of the iron loss and the savings can only be achieved at very light load. Maximum saving under open shaft conditions.

Study the efficiency and loss curves for the induction motors that you are interested in.

Best regards,




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