Energy Savers for Induction Motors 3

[Marke]

I was recently challenged

http://www.lmphotonics.com/forum/viewthread.php?tid=23&pid=170#pid170

over an article that I wrote in relation to Energy Savers for induction motors. (

http://www.lmphotonics.com/energy.htm

) The challenger contested that my article was unduly negative and some interesting dialog followed, some in public and some in private. To prove my bias, I was presented with a set of "certified" test results that showed considerable savings were made on a test motor. When I looked at the results, I discovered that the losses in the 15KW motor were 3.5KW at full load, 2.5KW at half load and a whopping 7.9KW at no load. I questioned the no load losses and it was suggested that "what is printed in Theory & what actually happens in practice experiments can be a whole lot different".
I have asked for suggestions as to why this sudden increase in losses occurs with induction motors and I have not had a reply. I have been unable to find any evidence of this myself, and in this case, I would expect that the true losses would be in the order of 2KW.

Does any one have any theory, evidence or experience to support this contention?

I believe that the losses at full load are primarily iron loss and copper loss and both are of the same order of magnitude. As the load is reduced, the iron loss stays essentially constant, while the copper loss reduces with the current squared. This certainly is supported by my experience in the field. Mark Empson

http://www.lmphotonics.com

 

[Marke]

Hello Electricpete
Smaller motors operate at a higher flux density than larger motors resulting in a higher magnetising current and iron loss. There are numerous reasons for this, but one is commercial. The higher the flux density, the higher the heat loss in the machine. For a given frame size, that would reult in an increasing frame temperature, however, the temperature rise of any given frame is a function of both the power dissipated and the thermal resistance of the frame. As frames get smaller, the ratio between volume and surface area changes yeilding a greater effective surface area per unit volume and thereby the ability to disspate more heat. If we take the approach of packing as much power into a frame as we can, then this becomes important.
From a commercial standpoint, the smaller the framesize for a given power rating, the lower cost and the greater the appeal to many customers. Wind the same power into a larger frame size and you get reduced losses and higher cost.
Large two pole motors typically have a magnetising curent in the order of 20 - 25%, while small motors can be as high as 70%! This is why the energy savers can yeild good results on small open shaft motors, but much less on large motors.
Best regards, Mark Empson

http://www.lmphotonics.com

 

[jbartos]

Suggestion: The voltage waveform has been addressed in one of the above postings. The harmonic content, very distorted voltage waveform, and higher motor terminal voltage at no load could cause the significant no-load loss. However, measuring techniques could also contribute to very inaccurate reading when the larger harmonic content is present.

 

[Marke]

Yes I agree, these are factors that can affect results, but this was presented to me as "the norm". You always get much higher energy savings than I have found or predict on the basis of known motor losses. The reason being that the off load losses are much much higher than the model suggests. It was also suggested that savings on larger machines were better than smaller machines. This also goes against my knowledge and experience.
From the discussions above, I haven't seen anything to make me change my mind on the savings potentials.
To me, iron loss is essetnially constant over all loading conditions, and copper loss reduces with the square of the current. I can not see a logical explanation for losses being higher at no load than full load appart from measurement problems.
Best regards, Mark Empson

http://www.lmphotonics.com

 

[jbartos]

Suggestion: Visit

http://www.oit.doe.gov/bestpractices/motors/factsheets/e-pact92.pdf

for the motor categorization under energy policy of 1992

 

[jbartos]

Small encore: The small motors tend to be treated differently and a motor category standing on its own. Visit

http://www.smma.org/

http://ts.nist.gov/ts/htdocs/210/214/scopes/eemot.htm

etc. for more info

 

[electricpete]

Mark - Thanks for your answer to my question. I can see that smaller frame sizes are more efficient at dissipating heat. But that would give an equal incentive for reducing copper as for reducing iron. To me it doesn't seem to steer the balance in either direction.

I have one alternate theory as to contributing factor: the air gap in a small motor is relatively larger compared to the air gap in a large motor. After all I've seen 8000hp 1200rpm motor with airgap of 0.12 inches If I try to scale that down to a 20hp motor the airgap would be ridiculously small.... more sensitive to small manufacturing variations and possibly would create vibration/noise. This larger (relatively speaking) air gap on smaller motors would contribute to the higher magnetizing current that you mention.... which would contribute a portion of stator I^2*R that doesn't change as much with load. (Although I don't think it could be said that a large air gap increases core losses.)

 

[Marke]

True, there are many reasons, not just one, however, don't forget, when you shink the core size, a) you need more turns, and b) your winding window is reduced, so the result of the smaller core size is increased copper loss as well as iron loss.
Mark Empson

http://www.lmphotonics.com

 

[cbarn24050]

Hi Marke, I think you are missing the point, a motor in an unloaded state represents a total loss, that is all the electrical input power is lost as heat, it therefore makes sence to reduce the input to the minimum required to keep the motor spinning at its rated speed. This is what energy saving units do and as such will save reasonable emounts. Typicaly the phase current can be cut down to 20% of no load current.

 

[Marke]

Hello cbarn24050

No argument from me at all.
My point is not whether you can save energy on an unloaded motor, it is simply how much you can save. The example quoted to me showed savings in the order of 3KWE when in reality, the savings would be less tha 1kw, I would expect more like 700W under open shaft conditions. If we apply your 20% suggestion, then that would be about 20% of say 2KW which would be 400W.
A saving worth having, but the payback would be a long time, not the "Less than 12 months" often quoted.
If you look at the paper referred to at the begining of this thread, the statement is made, that you can only save a portion of what you are wasting. I believe that many are claiming to save that portion of the motor rating!!
Best regards, Mark Empson

http://www.lmphotonics.com

 

[cbarn24050]

Hi, actually thats an 80% reduction not 20% in line current.

 

[Marke]

Hello cbarn

An 80% reduction in line current is achievable on small open shaft single phase motors, but would be rather optomistic in a real three phase installation, - not impossible, just not the norm. An 80% reduction in line current does not necessarily mean an 80% reduction in kw. I have seen excessive voltage reduction bring the KW back up again, however getting back to the quoted example, the quoted energy saving was higher than what I would expect the real motor losses to be, and no one has yet come up with a reason as to why the losses at no load should be higher than the full load losses, which was the original question asked.
Best regards, Mark Empson

http://www.lmphotonics.com

 

[electricpete]

From my perspective Mark's paper seems very reasonable.

A recurring theme is that the Nola-type control cannot save more energy than is lost in the normal motor (without Nola control). That is hard to argue with.

It would appear to me that the latest round of argument from a third party on Mark's board is to attempt to minimize the significance of the above fact by inflating the actual losses in a normal motor at low-load far beyond what anyone would consider reasonable.

 

[busbar]

MarkE — Apologies for my Aug 10, 2002 entry. Clearly, I had not read the originally posted links. The emergency colosincipital {sphincteriosincipital?} extraction went well, and I’m feeling a lot better.


It seems like your original detractor may have gotten cold feet. The resurgence in glowing promotion of the “miracle” Nola invention cycles about each decade in various forms.

I remember the original article in NASA Tech briefs. Clearly the work intended for small 1ø HVAC-type motors has been repeatedly blown out of proportion.

 

[jraef]

Marke,
You and I have crossed paths on this on other occasions and forums, and we have like minds in this matter. I too am a skeptic when it comes to the "new" versions of Frank Nola's circuit cropping up on the internet. I have linked people to your website on many occasions as a good resource for the truth in this matter. As I work for a soft starter manufacturer who can provide this feature in our products, you would think I would be biased TOWARD it. Quite the contrary. I recommended, and accomplished, removal of this feature from our standard products as it was essentially a waste of money and a source of poor customer relations. That is not to say that it never works, just that what users expect and what they achieve are separated by a chasm of disappointment.

Years ago I latched onto someone's formula that the motor needs to be at least 50% unloaded at least 50% of the time in order to achieve any appreciable savings. The truism that correlated to this is that if a motor is 50% unloaded 50% of the time, why is it even on? I now use this concept as an indirect way of selling soft starters: If you can turn it off, there is no better energy saver. Having a soft start then eliminates the objection to restarting only when needed.

15 years ago I worked for the old Nordic Co. before it was absorbed into obscurity by Furnas and then killed by Siemens. In those days, we sold the energy savings concept to the Bowling industry. Bowling pin resetters run all day long, then a clutch engages once in a blue moon to operate the mechanism. In THAT application, the concept worked. We saturated that market and I have not found another one since.

I have read several "papers" on how these wunderkind have rediscovered the long lost secrets of the Nola circuit. Some have even claimed that they were squelched by the "powers-that-be" because of their world-altering benefits that may cause the demise of the money grubbing power industry blah, blah, blah. Although I have never personally challenged their math or measurements (I suppose because I already know the answer), my suspicion is that they tend to prey on the fact that most buyers will assume that they could not make the claims if untrue, ergo they MUST be true! Warped logic, but unfortunately all too common.

I'm glad that you present the facts the way you do. Negative? Maybe. Beneficial? Definitely. The other guys argument? Suspicious, and my suspicion is validated by his lack of response.

By the way, jbartos might be onto something when he mentioned voltage waveform distortions affecting measurement accuracy. Phase angle firing of SCRs to reduce voltage causes significant harmonic distortion. For soft starters, we get away with it because we are a transient distortion source. When the Nola circuit is activated, the distortion is as continuous as the reduction, hence the possibility that harmonic distortion is skewing their measurements. This distortion, by the way, is one of the reasons why I recommended removing this feature from our products. It tended to cause more harm than good.

Electricpete: I bow in humility to the thoroughness of your endeavor. You are unbiased and open minded to a fault. Wow!
Subvert the dominant paradigm... Think first, then act!

 

[jbartos]

Suggestion: Please, notice that Frank Nola's patent expired in 2001, see

http://nctn.hq.nasa.gov/innovation/Innovation64/door.htm

http://history.msfc.nasa.gov/book/appendg.pdf

(for the patent award; historical info)

http://www.sti.nasa.gov/tto/spinoff1997/er5.html

(here, it is called a voltage controller)

http://www.ucan.org/consumer_info/Elec Bill/consguidestuff/pplanner.htm

(addresses the displacement power factor and harmonics)
etc. for more info

 

[Marke]

SNAP jraef!!

I likewise come from a background in this area, being one of the first to develop and patent a three phase implementation of the NASA algorithm. We got out of the energy saving side in the early 80's because of the b...s... put out by others creating unrealistic expectations, like the refigeration engineer from another side of the planet who rang me on the recommendation of Frank Nola, to look for units for his chest freezers. He had been guaranteed 50% saving on these 50Hp units running at half load, and tried several types, none of which achieved the savings. I told him that I wouldn't sell for the application because there were no savings. Why he cried?? Because to achieve 50% saving, you would need to add a gnerator of some form. Check your motor efficiency at half load and you will see why. This he did and found an efficiency of over 80%. How can you save 50% energy without exceeding 100% I asked? This was so typical and it keeps recurring every few years.
As I have said before, you can only save a portion of what you are wasting. How a motor fitted with these magic things can save more energy than switching it off, beats me, new technology or not!!

Best regards,
Mark Empson

http://www.lmphotonics.com

 

[jltx51]

Energy Saver for Induction Motors
We also developed a three phase implementation of the NASA algorithm in the early 1980's. We successfully inmlemented the design in hardware and software. Our test application was a pumping application with a varing load. Innitially our results looked good as the motor was significantly oversized for the load and the mechanical balance was off. After resizing the motor to match the load and correcting the mechanical balance we experienced saving comparable to what the motor manufacturing predicted using power factor correction. We did find some applications where the controller did a fair job enough to warrent a decent return on the consumers inversment. After recently reading your thread on this subject I concurred with the comments as they pretty much match our experience with the technology. Mentioned early in the thread was a comment about possible legislation that may make these devices illegal. Please give me information about this legislation as we would like to know the current status. Thank you, Rosborn

 

[jraef]

jltx51
// Harmonic legislation will probably make these units illegal soon anyway. \
//Mentioned early in the thread was a comment about possible legislation that may make these devices illegal. Please give me information about this legislation as we would like to know the current status. Thank you, Rosborn\
I believe that what was refered to was some proposed (maybe only discussed) changes in IEEE 519 with regards to how harmonics are measured. It is not legislation, but many engineers abide by IEEE and manufacturers who ignore them are likely to find a shrinking market.

Right now, we are concerned with THD (Total Harmonic Distortion) at the Point of Common Coupling in a system, usually the main incoming bus off of a utility transformer. The result of this is that when one mitigates harmonic distortion created by a device such as a VFD or Energy Saver, it need only be done for the effect it has on the system as a whole. This also means that when something else changes in a system, i.e. loads added or removed, the mitigation effort may become less effective. This has become a problem that IEEE sought to address.

As I understand it, the new change will be to look at Total Demand Distortion, meaning that each device will be responsible for mitigating the harmonic effect it has on the system based on the load it represents. I know this sounds the same, (and I may not be describing it correctly) but the gist of it is that harmonics will need to be addressed at each controller, not just at the Point of Common Coupling. VF Drives are already dealing with this by adding 18 pulse or active front ends, and harmonic nuetralizers are available that can be used on anything. The point is though, that if you bought an Energy Saver just for that purpose and then had to spend additional money to mitigate the harmonics it generates, the payback will become too long for consideration.

I hope I got this right. Maybe some others in this group are more directly connected to the IEEE committee that is working on this. Quando Omni Flunkus Moritati

 

[jbartos]

Suggestion: The harmonic mitigation performed locally at the harmonics causing load is preferable; however, it may become more expensive than one harmonic mitigating device at the utility service system point of entry. Also, one upstream harmonic mitigator may leave harmonic distortions untreated downstream within the power distribution system. This poses a low quality power supply to the power distribution loads downstream, which may be negatively affected by the low quality power supply that includes harmonics.