premium efficiency motors

[jcraft]

My question relates to premium and high efficiency motors. First, if you compare say a 10 hp standard motor to a 10hp high efficiency motor how is electrical savings accomplished. Under ideal conditions should the 10 hp standard draw the same line current as the high efficiency one? please enlighten me a little on the difference between standard and high efficiency. Thanks

 

[Marke]

Hello jcraft

The efficiency is improved by reducing the losses in the motor.
You will find that the high efficiency motors operate at reduced slip at full load, this reduces the slip losses, plus the iron and copper losses are reduced where possible.
The slip is reduced by reducing the effective rotor resistance under run conditions.

The line current on premium efficiency motors at rated load will typically be lower than standard motors.

Best regards

Mark Empson

http://www.lmphotonics.com

 

[Skogsgurra]

Yes. So it is.

There may be a slight reduction in starting torque with high efficiency motors. That's a direct consequence of the reduced rotor resistance.

Gunnar Englund

http://www.gke.org

 

[jraef]

As well as a higher inrush (magnetization) current for that instant when power is first applied. Premium efficiency motors can be as high as 20x FLA on inrush, often requiring different breakers or breaker settings to avoid nuisance tripping.

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[ozmosis]

jcraft
To really maximise on the effects that premium efficiency motors contribute to the overall saving criteria it is worth looking at what the motors will be doing. If they are running constantly for many hours/day then it makes sense to fit prem. eff motors as the cost difference between them is little looking at the ROI. The application is also important too. As already mentioned, you will lose starting torque so if your application is, say, a crusher motor in a quarry, it might not crush.
There are many articles about this and any motor manufacturer worth their salt will have enough information on this to keep you busy for years. For independant advise, I assume you are in the US as you are talking HP, try the US Dept of Energy section:

http://www.eere.energy.gov/femp/technologies/eep_emotors.cfm

 

[Farkel]

In the U.S.A. NEMA MG-1 defines the Efficiencys that motors need to meet EPACT. Any efficiencys above EPACT are considered Premium Efficiencys, due to better green steel laminations in the stator core, and rotor cage, smaller air gap between the two, use of AFBMA bearings, copper windings, and reduced eddy currents in the overall scheme of things.

 

[HCBFlash]

Something you don't often hear mention of in discussions of high efficiency motors is power factor issues. In one application I dealt with the load varied considerably and the P.F. changed more than the motor that had been replaced (causing the proj. eng'r to freak out).

Back to the original Q though, yes, slight reduction in measured line current.

Please let us all know how this works out for you!

 

[Mendit]

Take one of each apart and take a look inside, on premium motors there is almost 20% more iron core and winding. The rotor o/d is larger to deliver the torque.