Efficiency of Induction Motor

Motor is designed for certain load with voltage and frequency as a constant parameter.

You can use the motor for the rated load ( full load ) , which is 100% efficiency.

You can use motor at lesser efficiency also. This is applicable where load is a variable one.- like grinding mill

You can use motor at 90-100% where load is constant. - like water pumps

But for long life of motor , better use 75-85% efficiency range.

but in energy efficiency context we can vary terminal voltage to reduce input current..

is there any range for this reduction

thankz for kind comments...

actually i am a student doing research on evaluation of energy efficiency of squirrel cage induction motor based on application process for final year project. i have no idea on how we can improve energy efficiency (not motor efficiency, is about saving energy) can evaluate. based on studies i have done for far, speed control is a best way to improve energy efficiency and for squirrel cage type it can be done by reducing terminal voltage or reducing frequency. reducing frequency not lead to significant energy savings. so only through terminal voltage reduction we can achieve speed reduction. but i a bit confuse this method...

please recommend and give suggestion for my project....i really needed...

Voltage, frequency, and phase relationship between voltage and current.

JR

I had a customer that had a process that took boards and cut them in to specified length. These boards were the floor boards in vans that truckers drag around the country. The saw made one cut every minute so it was doing nothing for 59 seconds. I have a device that was basically an SCR that could be adjusted so that the SCR provided full power during the cut and reduced the on time while the motor had no load. It reduced the running KVA from 5 kva to 1.5 kva during the 59 seconds the motor was idle. it worked very well. For some reason this company stopped making it.

Wareagle,

They are still made, that is the concept I was referring to. But because they were grossly over sold and 99% of the buyers discovered they had been scammed, many of the first wave of mfrs in the 70s and 80s went under. The rise of the internet and the ability to scam people on a massive scale with little or no sales cost has made them appear again, there are now literally dozens and dozens of mfrs out there with these things.

If that is truly the application, then it would save a little bit of energy. But remember, kVA is not energy! The kVA decrease that you see is not the whole picture, you have to actually measure the kW (which includes the power factor). Still, it sounds as though yours is one that would have benefitted. Cyclical load, necessary to remain running, unloaded between work cycles. That's the magic formula that makes them viable.

I also found that they worked on bowling pin resetters, I worked for a company that sold them all over the country to bowling alleys for that same reason in the 1980s. Saturated the market in about 3 years though...

There are some cases, especially with fans and pumps, where partial flow is adequate. For instance, if only half of the full flow of a fan is needed, the motor can be run at half speed and 1/8 of full power. This is done primarily by reducing the frequency, but the voltage should also be controlled proportional to frequency. This is what VFDs typically do.