Power Factor

[WGB]

Here is one for all the engineer types.
What about tying one of these with our generator sets?
I know someone selling one very similar to this unit, but it also supposed to clean up distortion, noise, spikes, you name it.
He also has a pseudo test instrument that shows the before and after results in a good / bad type response.
Power factor I buy, what about the other claims, smoke and mirrors?
This is one company below that wants me to sell there products.
They also have solar and other products.
I could see an old farm or business with a lot of old induction motors and equipment.
If you had one or two energy star appliances it isn't going to do anything for you right?

http://www.power-save.com/1200.html

[WGB]

This is a good explanation of PF in a PDF file:
http://app.bronto.com/public/?q=ulink&fn=Link&ssid=5214&id=acje58pywz3gp55a3284gswx90iq3&id2=h6s9kpwp5l3xribq7fipegrwhhkqn&subscriber_id=ayskplmuhgtaywfkjnyacyjuhodabbe&delivery_id=bsjezqymickoqsidxbttchzeivhhbhk

[cschuerm]

I'd say your skepticism is well-founded and your assumptions are right on.   PF correction certainly isn't smoke and mirrors, but I think their claims for savings are not realistic. Likely little more than a pair of motor run caps in a box for $300.  I can imagine a small savings for a typical residence, but not 25%.  If you could cut your utility bill that much by simply hooking up a little box, everyone would have one already.
A big shop, with lots of motors....sure.  Done all the time.
Chris

[mobile_bob]

i personally am glad you posted this scheme/product  (i don't mean that in a negative way at all)

powerfactor and powerfactor correction is a pet research project of mine now for many many years.

if you want to get an arguement going try and get a civil discussion going amongst EE, electricians, and diy'ers

my bet  is if you get 3 different EE together you will have agreement in principle but widely different explanations
of all the "whys" involved.

here is my take on that unit, that is if it works as it should

for a typical residential grid connected home, you will see no reduction in your electric bill, because the power company
does not typically charge a residential customer for poor power factor. those amp reduction shown are reactive current
that circulates back and forth between the power source and the load, without real work being done. so while they
exist those extra amps a residential customer is not charged for them.

on the other hand if you have a business, or are unlucky enough to live in a region where the utility charges you
for poor power factor, then yes it will save you money.

for an offgrid guy that produces all his own power, power factor of his system is of huge importance, or at least it can
be if your system exhibits poor powerfactor which my bet is many such installations do, unless they are using modern
energy star appliances and pf corrected lighting, new pf corrected computers etc.

poor power factor uses up generation capacity without doing more work, in some cases one can significantly increase the
amount of load that he can service having good powerfactor over a system where he had poor power factor.

the question comes down to, at least for me, is this product as good as advertised in powerfactor correction?
if so then it might be a useful addition to "some" offgrid systems.

my opinion only, ymmv

bob g

[BruceM]

WGB's link is a  good explaination of PF.

The "power save" product is an outrageous fraud, but not a new one.  As Bob says, this won't save you penny on a typical residential power meter.  

Buy Bill Roger's book, "Home Power Producers Guide to Electrical Reality" available through Utterpower:
http://www.utterpower.com/home_power.htm

It explains PF in detail, and how to add the right amount of capacitance to get optimal performance of your genset.  For the off grid homeowner, this means adding motor run capacitors to your frequently run motor loads so that each has optimum PF.

PF of 1.0  just means that voltage and current waveforms are perfectly in phase. A device that gulps current out of phase with voltage will have a lousy PF, like 0.5, such as some POS compact fluorescent (CF) bulbs. PF correcting chips on switching supplies can solve that problem- they spread the bulk DC current draw throughout the rectified halfwave in a series of little gulps, using boost converter techniques to up convert the voltage of each little gulp.  

It isn't uncommon to find an induction motor with a PF of 0.75.  Adding the right capacitance (by measuring voltage and amps) can save you 25% fuel costs on that motor.

It would be possible to make a device which would do what the power co. does- dynamically switch in and out capacitors to keep PF closer to 1.0.

If would require a microprocessor to dynamically compute PF from the AC voltage and current waveforms, and then switch in/out motor run capacitors, at zero cross time.

The "power save" device shown is unlikely to actually do dynamic PF correction properly;  because that could be sold without lies and deceit.  In the technical specifications, it provides almost none, but I'd guess it's just a fixed value of metalized film (motor run) capacitor, with a bleed resistor, and a MOV surge suppressor.  In the installation manual, it's use on generator sets is specifically prohibited.  

[WGB]

WGB's link is a  good explaination of PF.

The "power save" product is an outrageous fraud, but not a new one.  As Bob says, this won't save you penny on a typical residential power meter.  

Buy Bill Roger's book, "Home Power Producers Guide to Electrical Reality" available through Utterpower:
http://www.utterpower.com/home_power.htm

It explains PF in detail, and how to add the right amount of capacitance to get optimal performance of your genset.  For the off grid homeowner, this means adding motor run capacitors to your frequently run loads so that each has optimum PF.

PF of 1.0  just means that voltage and current waveforms are perfectly in phase. A device that gulps current out of phase with voltage will have a lousy PF, like 0.5, such as some POS compact fluorescent (CF) bulbs. PF correcting chips on switching supplies can solve that problem- they spread the bulk DC current draw throughout the rectified halfwave in a series of little gulps.  Adding capacitance won't fix this particular crappy CF problem.   It isn't uncommon to find an induction motor with a PF of 0.75.  Adding the right capacitance (by measuring voltage and amps) can save you 25% fuel costs on that motor.

It would be possible to make a device which would do what the power co. does- switch in and out capacitors to keep PF closer to 1.0.

If would require a microprocessor to dynamically compute PF from the AC voltage and current waveforms, and then switch in/out motor run capacitors.  

The "power save" device shown is unlikely to actually do dynamic PF correction properly;  because that could be sold without lies and deceit.  

I have understood the simple explanation of PF for years.
I have Bill's book, it was a bit over my head the first time I read his explanation on PF.
I had never seen it explained with vectors and such.
I'm getting the just of it now, thank God for youtube LOL.

I'm not bad with motor controls, wiring, transformers, components, and such. Theory, math and building electronic circuits from scratch I'm lost.
I have taken some formal electrical and electronics classes long ago, but if I don't use it I loose it!
After digging in again, I'm absorbing the basics.

I have been following the many in-depth discussions on the forum, some of it is starting making sense.
My goal is to tune my generators and power system as efficient and electrically clean as possible.
I think I'm wanting to get an oscilloscope now.
Thanks for all the help and info from the forum!

[BruceM]

WGB, To get a visual picture of PF with a dual trace scope-  set one channel to see the AC voltage.  For current, put a 0.01 power resistor in line or better, use a current transducer like this:

http://www.allspectrum.com/store/product_info.php?products_id=788

to get the current waveform.  Put current on the second trace, superimpose them, and now you have a nifty visual PF monitor.

An oscilloscope is a very important learning tool- being able to "see" the waveform makes a world of difference in understanding, I think.  A dual trace scope is also a big plus, as seeing the timing relationship between two signals is often essential.

[mobile_bob]

i would also add this

if you have a motor load that is at .75 power factor and you improve it to .95 (which is about where one should target for)
you will not save 20% in fuel with your genset, but maybe 1 or 2%.

bad power factor just limits the load capacity of the generator and perhaps the transmission lines, but because it is power that
is basically bouncing back and forth the only losses are that which are in covering the risistance.

power companies do it because they can get better utilization of their generators and there distribution lines and transformers.

which is also the case for the independent power producer, you just don't save as much fuel as it would appear at a specific load.

bob g

[BruceM]

Thanks, Bob, guess I'd better go look at Bill's book again. 1% isn't enough to worry about, I thought it was more.

[mobile_bob]

Bruce:

i think there are some conditions where it is more, but probably not more than a couple percentage point
in the vast majority of cases.

this took a very long time for me to get a grasp of the concept

when George told me he had just received the first box of Bill's book, i made a b-line to his place
and was there for the grand opening

nearly tore my hip pocket of buying the first copy, and went straight for his treatment on the subject of
power factor and its correction.

Bill's book was the first that explained it in a clear and concise manner that a diy'er can understand, even if it
takes a few times rereading.

prior to that i had gotten so many explanations and arguments both for and against power factor correct
that i was getting really confused, so it was nice to see how Bill's explanation and specifically his practical approach
clarified what was once a very murky subject for me.

i knew enough about power factor to know it was important, but could not quantify it until recently
that being in what does poor power factor do to your bsfc numbers.

one or two percentage points is not much surely, unless you can find several places where one or two percent can be
found and incorporated,, much like picking up pennies, over time you have enough for a nickle then a dime
and all of a sudden it becomes important.

bob g

[BruceM]

I'm confused, now.

I have always assumed that apparent power was what what you had to generate in a home power system, regardless of how much of it was reactive. In looking at some technical papers online, I find that PF correction for self powered industrial facilities is claimed to provide significant cost savings for power generation.  This isn't consistent with the 1% figure.

From Bill's book I did not get the impression that reactive power took an insignificant amount (1%) of energy to generate.  Maybe I missed it? 

So my question is-  how much engine power DOES it take to make 1000 watts of apparent power with 500 of it being reactive (PF 0.5) vs 1000 watts of apparent power with zero reactive (PF 1.0).

[mobile_bob]

the extra fuel need to generate the reactive power is only that which is needed to overcome those I^2R losses
of the conductors in the circuit.

which in a huge system loaded made up of large generators, huge step up transformers, miles of transmission line, followed
by another step down transformer, more miles of local distribution lines, local step down transformers and finally the motor load
being served, add up to significantly more than a percentage point.

when i speak of a percentage point of so, it is based on our micro generation systems, lack of stepup/stepdown, miles of wire
and only a single point of use motor being generally the big offender.

our circuit is relatively small in comparison  with proportionally lower resistance to have to pay for with power.

this topic comes up all the time in other forums, the latest i am aware of, and it has what i think is a fairly good breakdown
of an offgrid powerfactor example can be found at

http://www.fieldlines.com/story/2009/12/28/182850/44

if someone comes up with something different i am always up to learning more on this topic

bob g

[mobile_bob]

Bruce:

just wanted to add the following

if it can be shown that correcting power factor for a typical appliance such as a washer or drier, refrigerator
or freezer such as is used in a home, works out to improving the fuel consumption numbers over a percent or two

i will be the first inline to want to know!

one single percent improvement to me at this point is much like finding the holy grail, finding the first 10% is easy, the next 5% difficult
the next 2% extremely difficult, and at this point getting another 1% anywhere is becoming nearly impossible.

at least for me.

sort of like a ww2 fighter plane, which might do 300mph with 1500hp, to fly 350 mph took 2000hp and to fly 360mph took 2500 or better
not really a linear return on investment

one gets to a point of rapidly diminished returns.

so yes, i guess for me the short answer is yes, i am interested in determining if the savings in fuel is appreciably more than
a percent or so in a typical offgrid installation using a typical appliance.

hope that clears things up, i just didn't want to come off as some sort of expert on this topic, because sadly i am no expert in this subject
but an avid student with far more questions than answers,  just ask Bill Rogers!

i am sure he will tell you he is more than tired of answering my powerfactor, and powerfactor correction questions.  i have probably asked him
at least a dozen since the book came out, and maybe more... likely even a few more if i can frame the question clearly so he knows what it is
i am asking.

thats the problem with this topic for me and i suspect many other diy'ers, it is a relatively complex subject and without a pretty good basic understanding it is very difficult to be able to formulate and ask a coherent question.

again at least that is the way it is for me!

for the life of me i have been trying to find my lab notes, i did a quick bsfc test with a motor load that had poor power factor
before and after, i can't find the results, but
iirc the results were very discouraging

i guess i will put that on my list of things to do next time i get out to do some testing
perhaps a few others could do similar testing and we can compare notes to see exactly what
the penalty in added fuel consumption really is going from poor power factor load to a corrected power factor load.

i suppose that is where the rubber meets the road?

bob g

[BruceM]

I read the thread at fieldlines...thanks Bob.  It sounds believable, but I'm not confident.

It just seems odd that Bill Rogers wouldn't spend time explaining and recommending PF correction for off grid power generators, if the fuel benefit was 1% or less.

Likewise, power co. billing for low PF.  I they were that concerned about 1% efficiency, we'd be seeing big toroidal transformers on every pole and pad.

I still vaguely remember Bill explaining that for the home power folks, we have to generate the apparent power, thus making PF correction important.  I probably made this up- my bogus memories are often stronger than the real ones.

So I'm in my usual state- uncertain, somewhat baffled.

BruceM

[mobile_bob]

Bruce:

its important to have high power factor in order to utilize the generator to its best capability
far better for it to be maxed out making real power than it would be having to reduce capacity
in order to make a bunch of reactive power.

its just that the reactive power doesn't cost as much in fuel as does real power,

i got to thinking about my assertion of a percent of two, and remembered something that might also
come into play

my calculations are based on a generator running at near peak load,

the following is for illustrative purposes only, actual numbers will vary depending on all sorts of factors:


if we have an ABC 20hp engine driving an st10 head, if we were to test it we might find it takes
a 1/4 gallon just to run the head at no load for an hour, we can call this the baseline fuel consumption for this
setup.

at full capacity the genset might well get to 1/8 gallon per kwatt/hr,

taking a look at the numbers we have to assume the following

in order for the engine/generator to provide that 1/8gal/kw/hr it must be producing 10kwatts or full load
that fuel consumption number starts out with 1/10th of the baseline, or .025 gallon so the balance attributed
to the 10kwatt average amounts to about .100 gal/kw/hr

stepping back to the other extreme,

if we only generate on kwatt, we then have the .100gal/kw/hr owing to making the power, but also "all" of the baseline
of .250 gallon for the hour, for a total of .350 gal/kw/hr

from this analysis we can see that the first kwatt generated is the most expensive kwatt/hr produced, and the 10th the least

so....

in my assertion about 1% improvement in fuel economy was based on a genset running at near peak load
we can now see that on the other end of the spectrum, the improvement may well amount to a significantly larger
improvement.

from this one could take away a couple of things, not the least of which is

1. it is far more efficient in fuel consumption to run at near full load than it is at very low loads, and

2. power factor becomes more important at low loads because of better fuel economy, and

3. power factor is very important at near peak load so that we can get most all of the st10's 10kwatt rating
(a poor power factor load, might well reduce our st10's ability to provide for real work to 7.5kwatt or even less
with the balance going to produce reactive power and cover line losses associated with it.)

now this is my understanding of the principles, but i may well be off the mark.

bob g