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Energy Savers for Induction Motors
3

Energy Savers for Induction Motors

Energy Savers for Induction Motors

(OP)
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

RE: Energy Savers for Induction Motors

Hi, an interesting article which does seem a bit negative, it seems you have selected a few bad examples to illestate your point.There are a number of benefits from using these softstarters, apart from the energy saving aspect, which you fail to mention at all. Also your pricing seems a bit out, a 7.5kW unit should be around $250 not the $3K+ you mentioned. Harmonic legislation will probably make these units illegal soon anyway. The latest craze is to use an inverter for enery saving, this is a great improvement, and coupled with new "green" tax laws these units have a faster payback time.

RE: Energy Savers for Induction Motors

What can possibly cause losses to increase as load decreases? I can only come up with two ideas:

#1 - Core losses. As load increases there is less voltage drop across the series leakage reactances.  Clearly this will increase the flux in the rotor iron, which would tend to increase rotor losses.  Although there will be a competing effect that the frequency of the rotor field decreases (as we decrease load) which tends to decrease the rotor losses.

What about stator core losses? I have to think a little bit about the meaning of the equivalent circuit parameters to decide whether portions of stator core are exposed to higher flux. What do you think?

#2 - Friction/windage. For a high-slip motor (Nema design D), there might be a substantial change in speed between full-load and no-load. This will increase the friction and windage losses. For a NEMA B it would be less.... in that case we are assured the change in speed is less than 5%.  I don't know if there is a formula relating friction losses to speed (friction ~ speed^2?).

None of the above was very reasonable. Here is I think a more likely explanation for that data. The data gatherer simply measured the current and assumed a constant power factor. At no-load the current decreased to about half of full load so he calculated about half power. I would ask him to tell you the power factor as function of load to see if he measured it (if he accurately measured power input he must have measured power factor).

RE: Energy Savers for Induction Motors

I still think measurement error (not measuring power factor) is most likely cause.

But, trying to keep an open mind, I can imagine one more possibility. Perhaps if this motor is supplied from an electronic drive, the characteristics of the voltage may change with load (not so difficult to imagine). A change in the high frequency content of the voltage might influence the core losses dramatically.  (It's a stretch)

RE: Energy Savers for Induction Motors

One more related item... a change in waveform can introduce measurement errors also.  (still in the not-very-likely category).

RE: Energy Savers for Induction Motors

One thing that should not be obscured by my discussion of remotely-possibly explanations is the most-likely scenario:  This person simply assumed power factor was constant for all power levels.

RE: Energy Savers for Induction Motors

(OP)
cbarn24050 Thank you for your reply. The article is not about soft starters, just the energy savers. I appreciate that a number of soft starter manufacturers include this functionality as an added feature. My comments are really aimed at the marketing people making sweeping claims based on tests on very small single phase motors. The examples quoted are from manufacturers datasheets and are typical of the claims that I have seen.
Soft starters have many other advantages. I have spent the last 23 years working on soft starter designs, so don't worry, I do believe in them!!

electricpete You sort of confirm my theories in that it is hard to come up with an explanation. I was informed that this is the norm for induction motors and was why there were good savings to be made, and my estimates were unacceptable.

I will keep looking, perhaps someone can give me a good explanation, till then, from what I have seen with induction motors, I remain a sceptic!!

Mark Empson
http://www.lmphotonics.com

RE: Energy Savers for Induction Motors

I will open up my mind to the possibility that your source may be correct. Here is an interesting excercize that I was surprised at.

IEEE 738-1995 (IEEE Recommended Practice for Energy Management of Industrial Facilities) figure 5-12 and MG10-1994 give “typical” efficiency vs load curves for 1hp, 10hp, 100hp motors. I read (guessimate) the values for efficiency from those curves at 25%/50%/75%/100% load as follows:

    efficiency        
                100hp    10hp    1hp
100% load:    84    79    62
75% load:     81    74    53
50% load:     77    65    45
25% load:     70    55    33
            
The I compute losses using the formula     
    Losses (%)=output (1/eff - 1)    
    
                   100hp    10hp    1hp
100% load:    19.0    26.6    61.3
75% load:     17.6    26.4    66.5
50% load:     14.9    26.9    61.1
25% load:     10.7    20.5    50.8

I’ll admit I was floored to see  no significant increase in losses with increasing power as we might expect from the I^2*R component.  Also I was surprised at the high losses on the 1HP.  And your 50% data point (2.5kw losses=17%) and 100% data point (3.5kw=23%) falls between the 10hp and 100hp results as expected (if anything, the 50% losses of 2.5kw reported represents even a little lower than would be predicted by the above data, indicating better efficiency and more of a decreasing loss with decreasing load than shown above).
 
But that NEMA data is still not even close to consistent with what your source reported for no-load losses.
 
First you’ll notice that computed losses do in fact stay roughly constant or decrease as load decreses toward zero.  Second you’ll notice that your motor should fall between 10 hp and 100hp (closer to 10hp).   If we generously place your 15hp motor in the 10hp category, we still see the losses should not exceed approx 27% at any load which would be at most 3.75kw for your 15kw motor. (we have been generous also in not following the trend of decreasing losses with decreasing load).

One thing missing is a zero-power data point. The efficiency figure cannot go to zero load (undefined efficiency) and in my curve stops at 25%.  But with the shape of the curves at the known data points and physical reasoning there is no reason I would suspect a sudden jump in losses going from 25% load  to 0% load.
 
So the NEMA/IEEE data seems to contradict your source’s observation of >8kw losses at zero power and increasing losses with decreasing load.
 
The only points that might have lead me toward incorrect conclusion:
- perhaps newer motors behave differently than the older motors in this pre-1994 data (but I would expect them to be more efficient at all loads)
- perhaps I am mistaken in assuming there is no abrupt change in the curve between 25% and 0%?
- perhaps this is a large single-phase motor which might have some special characteristics?

I still say that it should not be unreasonable/insulting for you to ask your source for his power factor readings.  The data seems fairly consistent with the pattern expected with an assumption of constant power factor vs load. In the meantime if I get time I’ll see if I can come up with a more quantitive demonstration of that hypothesis.

RE: Energy Savers for Induction Motors

I will clarify that "losses (%)" is intended to represent losses in percent of rated output power.  ie for the 15kw motor, 1.5kw losses at a given power level would be 10% losses.

RE: Energy Savers for Induction Motors

If I go back and re-read the 1hp 75% load point I see it's closer to 55% which gives losses of 61.5% which gets rid of the anomaly in the curves.

Now a pattern becomes evident:
Losses are approx constant over the range of 50%-100% for these 1hp and 10hp typical motors. (smaller range of flat losses as horsepower increases)

But we know the I^2*R components increase substantially between 50% to 100%. Not quite quadruple but surely at least double for a high-speed motor with low exciting current..  So.... is the I^2R so small in comparison to other losses that it's increase doesn't show up? Or is there another loss component which significantly decreases as load increases to counteract the increasing I^2*R?

Perhaps whatever phenomenon is responsible for my inability to explain this nema data is responsible for our inability to explain Mark's friend's test data.

RE: Energy Savers for Induction Motors

Here you will find data sheet for a 20hp 400v motor:

http://www.reliance.com/pdf/pdf/aced/PD16-G7473.pdf

At the no-load point they have 9.9A, 4% power factor
gives real power input = 9.9*sqrt(3)*400*0.04=0.3kw if I have done my math right.  (although that does sound terribly low).

At the 1/4-load point they have 11.6A, 51% power factor
gives real power input = 11.6*sqrt(3)*400*0.51=4.1kw total input.  Subtracting out 3.75kw input gives ~ 0.4kw. This is an order of magnitude lower than suggested by the NEMA.

Just to check the 100% point they have 28.1, 83% power factor, 92.6% efficiency gives real power OUTPUT = 28.1*sqrt(3)*400*0.83=*0.926=15KW (confirms the math and voltage etc).

I got to that motor data sheet by selecting motor parameters at this page:
http://www.reliance.com/cgi-bin/mtrquery.pl#modelchar

Draw your own conclusions. I think perhaps these are simply quite a bit more efficient than the older NEMA data. The published full-load efficiency of 93% confirms that (they had only 84% for 100hp motor!).

So really this new data about more efficient modern motors pushes your clients claims further out of whack.

Note in particular there is no dramatic change in losses between 25% and 0%

(by the way don't forget to ask for the power factor data).

RE: Energy Savers for Induction Motors

(OP)
Hello Electricpete

This one has really got to you hasn't it!!

With small motors, the magnetising current can be very high, sometimes as high as 70% of the full load current. Under those circumstances, the I2R will change very little between full load and no load, so the info above is quite as expected and easily explained. On very large motors, the magnetising current is in the order of 20% so I would expect to see a much larger variation between losses at full load and no load due to copper loss variations.

Additionally, the leakage reactance is higher on small motors than large motors so the voltage regulation across the magnetising component of the equivilent circuit would not be as good as with a larger motor. There fore I would expect to see a small increase in iron loss at no load, but certainly not a multiple of 3!! An increase of 10% - 20% on small motors would be acceptable in my book.

I prefer to use the equivilent circuit model to explain the losses and when you look at this, there is no way that I can see for such a massive increase in iron loss!!

Unfortunately, I asked too many questions of the other party and he is now ignoring me completely, so no further information is available.
Best regards,
Mark.

Mark Empson
http://www.lmphotonics.com

RE: Energy Savers for Induction Motors

Yes, it is an interesting one for me.  I was coming to the same conclusions as you have mentioned, although not yet 100% confident in them.   

I stumbled upon the fact that small motors have much higher percentage of no-load losses through an interesting side-track....  The shape of the efficiency vs load curve can be used to estimate the relative no-load and load losses, as follows:

Assume the losses are of the from
L=NL+LL * P^2  
where L=total losses, NL=no-load losses, LL=load losses at full-load, P=output power from 0..1

divide by P:
L/P = NLL/P + LL *P

Max efficiency occurs at the minimum of the quantity L/P which is found by taking derivative of L/P with respect to P and setting it to zero:

0 = -NLL/P^2 + LL
Pbep = sqrt(NLL/LL) where Pbep = "best efficiency point"... peak of the efficiency vs power curve.

LL>NLL => Pbep<1 (np) <=> peak eff within op range

NLL>LL => Pbep >1 (np) <=> peak eff above op range

Looking at the NEMA efficiency curve for larger motors indicates that peak efficiency occurs perhaps around 1.0 or slightly. Indicates these large motors have LL>NLL

Looking at the NEMA efficiency curve for smaller 1hp motors indicates that efficiency is still increasing at the point where P=1.  Pbep>1 indicates these small motors have NLL>LL.

I am still thinking about the stator core losses. I understand your thought process that increased current causes increased voltage drop across stator leakage reactance and reduced voltage applied to magnetizing branch.  I have heard people imply before that voltage across magnetizing branch is directly related to flux.

But, I struggle a little with the physical understanding of that. Let us say that we operate the motor at no-load so the rotor is an open circuit.  The exciting current flows through series combination of L1 and Xm. It is really the series combination of L1 and Xm that represent the magnetizing inductance in this case.

If we add load and allow rotor current to flow, then some of the flux does not couple the rotor which leads to the need to separate L1 and Xm. But the same voltage is still applied across the series combination of L1 and Xm. We distinguish them to separate the flux which is not coupled to the rotor, but does that in any way reduce the stator flux?  i.e. the "voltage drop accross L1" that we propose is reducing our voltage available at Xm is STILL creating stator flux in L1... it just isn't linked to the rotor.

I'll think some more. Any thoughts?

RE: Energy Savers for Induction Motors

my discussion of comparing NLL and LL neglects the effect of magnetizing current, but near full load where the peak occurs, the error is not severe.

RE: Energy Savers for Induction Motors

Regarding the shape of the efficiency vs power curve and resulting inferences about LL vs NLL.  The inductive current does introduce some error so the results should be considered qualitatviely, not quantitatively accurate. (It is not exactly true that LL=NLL at the point where efficiency curve peaks... but fairly close).


I am still thinking that perhaps physical view of the equivalent circuit does not support the view that stator core losses decrease with load.  The stator flux will need to satisfy Vapplied=N dPhi/dt, regardless of secondary load.  That seems to apply that total stator flux does not change with load (although local distribution may change).  

It is true that the flux linking the rotor decreases. That is why we need to separate the total primary reactance into X1 (not linked to rotor) and Xm (linked to rotor). But from my perspective that does not provide a mechanism for decreasing stator flux. Maybe I am missing something?

As for rotor flux, it will decrease, which would tend to decrease core losses with load. BUT, the rotor frequency increases with load which would tend to increase rotor core losses with load (core loss proportional to f^2).


RE: Energy Savers for Induction Motors

I think maybe I have the answer to my question about effect of load on flux.  (just thinking... not sure).

There are at least two different (series) contributors tof the stator leakage reactance: stator toothtop leakage reactance and end-turn leakage reactance.

I believe the stator toothtop leakage reactance acts the way I predicted.... current flow through it does not reduce flux to stator. That is because the associated flux does magnetize the stator.  It bypasses the rotor but not the stator core.

I believe the stator endturn leakage reactance acts the way you predicted.... current flow through it does reduce flux to stator. That is because the associated flux does not magnetize the stator.  It bypasses both the stator core and rotor core. Equivalently imagine that the stator was energized by a very long pair of leads representing the leakage reactance. As current increases a voltage drop is created which reduced voltage available for flux production in core.

So bottom line is that there is some reduction in flux due to increase in load. But I don't think it is as large as we would predict if we considered the entire stator leakage reactance X1 to create a voltage drop which does not produce flux in the core (the portion associated with tooththop leakage reactance does produce flux in the core).

At this point the discussion wanders pretty far from the original point. I'm just trying to learn a little in the process.

RE: Energy Savers for Induction Motors

Just for completeness, I believe that in the case of a transformer, virtually all of the leakage reactance acts the way you described, which is similar to the motor-end-turn leakage reactance in that the associated voltage drop reduces the flux in the core.

For the core form transformer with core insdie of LV winding inside of HV winding, tany flux which does not link both windings must be outside of the LV winding (mostly in the space between windings). If it is outside of the lv winding it is outside of the core. Any associated current contributes to voltage drop without magnetizing the core.

In contrast for the stator tooth top portion of motor winding leakage reactance, the majority of the flux path is in the stator core. The current associated with this leakage reactance creates a voltage drop which limits rotor voltage, but also contributes to magnetization of the core.

RE: Energy Savers for Induction Motors

Just for completeness, I believe that in the case of a transformer, virtually all of the leakage reactance acts the way you described, which is similar to the motor-end-turn leakage reactance in that the associated voltage drop reduces the flux in the core.

For the core form transformer with core insdie of LV winding inside of HV winding, tany flux which does not link both windings must be outside of the LV winding (mostly in the space between windings). If it is outside of the lv winding it is outside of the core. Any associated current contributes to voltage drop without magnetizing the core.

In contrast for the stator tooth top portion of motor winding leakage reactance, the majority of the flux path is in the stator core. The current associated with this leakage reactance creates a voltage drop which limits rotor flux, but also contributes to magnetization of the stator core.

RE: Energy Savers for Induction Motors


Maybe this has been adequately covered in other threads { Thread238-21978  Thread237-19632 } but does the validity of the NASA/Frank Nola/power-factor controller and related claims bear discussion here?  
  

RE: Energy Savers for Induction Motors

I have another question to throw in... why is it that smaller motors tend to have a higher fraction of no-load losses than large motors?

RE: Energy Savers for Induction Motors

(OP)
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

RE: Energy Savers for Induction Motors

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.

RE: Energy Savers for Induction Motors

(OP)
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

RE: Energy Savers for Induction Motors

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.)

RE: Energy Savers for Induction Motors

(OP)
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

RE: Energy Savers for Induction Motors

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.

RE: Energy Savers for Induction Motors

(OP)
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

RE: Energy Savers for Induction Motors

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

RE: Energy Savers for Induction Motors

(OP)
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

RE: Energy Savers for Induction Motors

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.

RE: Energy Savers for Induction Motors


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.  
  

RE: Energy Savers for Induction Motors

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!

RE: Energy Savers for Induction Motors

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%20Bill/consguidestuff/pplanner.htm
(addresses the displacement power factor and harmonics)
etc. for more info

RE: Energy Savers for Induction Motors

(OP)
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

RE: Energy Savers for Induction Motors

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

RE: Energy Savers for Induction Motors

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

RE: Energy Savers for Induction Motors

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.

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