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The Shifting Climate of Power Factor Correction

You'll presumably pay a lot more in power utility bills if you're charged for so-called “reactive power” as an industrial customer who uses banks of “uncompensated” motor loads facing the AC mains. But as so many articles over the years have pointed out, the typical residential consumer won't save much by swamping out all that inductance at his house. That's because his “power” meter keeps track of the total energy actually consumed, not reactive power or apparent power. Beyond that, various environmental and medical concerns over such issues as greenhouse gas emissions from the power plant are beginning to creep into the consumer's head, even those who aren't particularly sold on global warming.

Up to now, power-factor-correction (PFC) has been largely about how much money Joe Average saves each month. But in practice, the critical economics derives from the utility's perspective. So what's the direct savings to the utility, whose rates determine — albeit in an unknown, indirect way — what residential customers pay for energy per kilowatt-hour? And what would be the plant's overall transmission efficiency if PFC were applied universally?

The utility might save about a penny a day per household appliance, as suggested in National Institute of Standards & Technology (NIST) Technical Note 1654 by Martin Misakian, et al. But even that number is rather buried in the article's last sentence, and we're still awaiting answers to what the integrated savings might be for a utility serving tens or hundreds of thousands of customers, each of whom uses appliances that present something other than a resistive load to the utility's power source.

Oddly enough, representative numbers are hard to come by and maybe don't even exist. None of the majors in the big-energy business — from state utility commissions to the Department of Energy (DoE) to Electric Power Research Institute (EPRI) to NIST — have yet offered me a methodology to answer the big question. Perhaps the lack of a ready response owes partially to the perceived sensitivities of manufacturers in the business of providing power-factor-corrected equipment and the various marketing over the years focused on increased efficiency and cost-savings. On the other hand, is an accurate analysis truly doable?

“The study would be worthy of a Ph.D. thesis,” says William Rynone, whose 2007 article “Is Power Factor Correction Justified in the Home?” (Power Electronics Technology) did some number crunching to conclude the resident doesn't gain directly from PFC. “I don't know if it's possible to do,” he said, underscoring the complexity of even defining an “average” household. “I believe you would need teams of mathematicians, engineers, and systems/maintenance personnel to figure it all out.”

Rynone's article, from the resident's perspective, looked at several motor-driven appliances based on a 1-HP motor, which included a refrigerator, washing machine, air conditioner, and well pump. He calculated the residential system losses — basically the power losses in a given two-conductor, 25-foot section of #12 copper wire leading from the main panel to the various appliances with unity power factor. Then he determined the difference in power loss for the appliances with a lagging PF of 0.75 (current flow increases), suitably scaled over time of use per day and over a month.

The difference to the resident was 8 to 14 cents a month for the major appliances (this did not include the air conditioner) for a typical electric bill of $60 to $80 (at 10 cents per kW-h, includes use of unity PF devices such as lighting, toasters, electric stoves). That represents a savings of about 0.2 percent in the total monthly bill.

Misakian's group, looking at the issue from the utility's standpoint, similarly calculated how much energy would be saved because of lower resistive losses in a distribution system corrected by placing suitable capacitance (108μF) across a central air conditioner. Assuming a distribution system that looks back at the utility and sees a system resistance of 0.05Ω, Misakian's group calculated the utility would consume 4.4W less as the result of a reduction in I2 R losses. The resulting energy savings for powering the air conditioner, which they assumed would run for 12 hours a day over a little less than half the year, was thus 52.8W-h/day. At 20 cents per kW-h, their calculated cost savings for the utility would be about $1.80 for that approximate half-year period. The issue of using active or passive PFC didn't come into the discussion in either Rynone's or Misakian's article.

But given the new focal point on PFC and the various new ways customers can save on energy — even sell it to the power utility –would a working power-delivery characterization now be that important? Curiously enough, PFC marketers' initial “low-profile” argument for PFC — cutting down on greenhouse-gas emissions from the power plant — has seemingly become its ace-in-the-hole. Beyond our breathing cleaner air, it's to some degree about global warming, which is becoming more serious an issue than paying a relatively small bill in a fiat-based monetary system. Global temperatures have certainly been higher since the earth formed, but today's rate of change in the modern world looks unprecedented.

I've been unsure about much of the science in those studies, and a number of skeptics make some noteworthy criticisms. On the other hand, I now hand it to you by way of a null hypothesis: Keeping in mind a 2°F increase in 100 years is considered rare at this point in our evolution, discuss the last time the average (smoothed) yearly temperature increased 2°F over just a 20-year span in a virtually untouched environment — for example, as measured at my rural locale and in line with similar sites around the country. Then, assuming you agree that global temperatures have gone up, tell me the naturally-occurring causes you believe are responsible for such an increase — reportedly greater for the US than around the rest of the world.

15 comments on “The Shifting Climate of Power Factor Correction

  1. Steve Taranovich
    June 14, 2013

    Two comments:

    1. Beware of home power factor corrector devices—I have had numerous instances when sales people tried to sell the idea of PFC for the home, and the first question I asked was “How much power does your device draw from the utility?” They usually walk away. There may be good ones out there though, I'm not sure. As the author mentions, it doesn't amount to much savings for the homeowner.

    2. As far as the utility savings, the author mentions that it could be significant there. My feeling is that the responsibility needs to be on the manufacturer/designer of the refrigerator, pump, A/C compressor, etc. PFC ICs are ubiquitous and relatively low cost to embed into a design for a motor controller.

  2. kendallcp
    June 14, 2013

    The idea that you can correct power factor by applying some compensating reactive components is not realistic with today's loads.  It used to be that synchronous motors were the main source of phase lags in otherwise fairly sinusoidal currents.  These days, the majority of electronic items have power supplies that don't take sinewave currents from the line, but something spikier.  This results in a degraded power factor that can't be corrected with reactive components.

    Absolutely the worst thing in the home for producing poor-PF current waveforms is the ubiquitous phase angle dimmer.  I think it's quite risible that the market is rushing towards 'dimmable' LED light bulbs, which when used at full output have a relatively clean current draw, just like a filament lamp.  Stick them on a phase angle dimmer, which seems to still be standard equipment in the US home, and the power factor is just as awful as it would be with old-school bulbs.

    Correction is impractical, but what /is/ feasible is measurement.  It's possible to derive a tarriff extension for power factor shifts.  If you really want to capture the additional costs, both real money costs to the utility and burden costs on the environment, set up a tarriff that gently penalizes / dinsincentivises the user for poor-PF loads.  Engaged consumers have an option to change their behaviour by intelligent purchasing and usage decisions, and the majority who don't really care will just pay an extra 10% or so if they want to use poorly performing loads.  implementing the split tarriff in a modern smart meter is simple, it just requires collective will to permit this change of approach.

    That's the conclusion i came to when I was looking into power measurement a few years back, anyhow.

  3. bjcoppa
    June 14, 2013

    NIST- HQed in Maryland- was noted in this article for helping set the standards of this technology. NIST is a national lab along with Los Alamos, Oak Ridge and others. The national labs have taken a hit in terms of funding over the last 4 years and been constrained in their ability to hire and expand programs. Most have been under budget freezes since the recession and sequestration reduced budgets at some facilities. It is time for a new federal budget so that engineering organizations within can plan for the future and carry out a long-term vision.

  4. Vishal Prajapati
    June 15, 2013

    It is very true that todays' instruments or electronics doesn't consume the current in sine wave pattern. So, Simply putting capacitor or inductor for correction doesn't work.

     

    This was encountered first when I was designing LED driver. It consumes current at voltage peak like a spike. I searched on the internet and found a correction technique called Velly fill Power correction circuit. I tried to simulate the circuit and provided adaquate results but only by trial and error. Till date I haven't found its theorical explanation. I don't know how to select components values. Can someone point out good reading about it?

  5. DEREK.KOONCE
    June 17, 2013

    Vishal – take a look at the paper https://www.coilws.com/Publications/ImprVF.pdf . It may help answer your question. At least get you started in the analysis.

  6. Brad Albing
    June 17, 2013

    @KCP – thanks for that reminder that PF is degraded from unity by not only simple reactive elements or networks connected to the power line, but also by capacitor-input filter networks following a bridge rectifier and by “phase-cut” triac dimmers.

  7. Vishal Prajapati
    June 18, 2013

    @Derek, Thank you very much for your reply. I think the trial and error simulation can be the only option for this thing. But this has cleared most of the theorical part. Thanks again.

  8. Etmax
    June 19, 2013

    You mention unprecedented temerature rise, and this isn't strictly true, the temperature has risen like this a few times in the past and each time it has been accompanied buy mass extinctions. If I put my hand in the fire and it burns and I do it a second time and it burns I would suggest I would be an utter fool to try it a third time, so each time in the past that temperatures rose dramatically it was a disaster I don't think we need to be surprised as to what the outcome will be this time.

  9. Brad Albing
    June 20, 2013

    OK, so it's a “precedented temperature rise.” But, as you've noted, the outcome will likely be unpleasant.

  10. vbiancomano
    June 20, 2013

    @etmax—Without quibbling too deeply over what constitutes “unprecedented” in the context of what we call modern times, I think it's most important to determine at what point the apparent acceleration in temperatures brings us to the point where our planetary system can be classified as being in thermal runaway. Indeed, we may have already arrived and don't know it yet. One initial confirming signature could well be mass extinctions, as you've brought up.

    With air-sea interactions a very important part of the feedback loop, some of the more recent research cuts to the chase in examining why frogs and sea life, among other species, are right now disappearing worldwide.

  11. Brad Albing
    June 20, 2013

    @Derek – that paper does help explain some of this PFC stuff  – thanks.

  12. Etmax
    June 20, 2013

    The frogs may be more related to a virus they have discovered but then the virus may climate related although I doubt it. What's happening in the oceans is significant in that CO2 is absorbed acidifying the oceans and adversely affecting shell fish. What is even more scary is that common foods become toxic in the presence of higher CO2 levels as the plants spend less effort growing. Examples are Yams and apricots produce cyanide and wheat and other grains produce less protein and more carbohydrate. They reckon by 2050 we may not be able to make bread due to low protein content. Further on this apparently locusts swarm more in years when proteing levels are lower so we have a many sided whammy. My main comment really was that it isn't unprecedented, only unprecedented in living memory. Yes interesting times and running out of time to do something. Every years delay increases dramatically the cost of doing something about it. We may get to the point where we no longer have the resources to combat it. That's the game over scenario

  13. vbiancomano
    June 21, 2013

    Epidemiology and climate change have been closely linked in recent years, and thus researchers have not yet ruled out viruses as a “product” of that relationship. Indeed, they rule them in. In any case, in keeping to point, I do not see that we disagree on the issue of climate change and man's contribution to it. It's a matter of degree. There are many variables, their relationship as you know is nonlinear in many cases, and thus the grand system is very difficult to analyze.

  14. Etmax
    June 21, 2013

    Here I agree on all points, 🙂 I must also appologise for drifting so far away from power factor correction. I don't normally do that. Sorry guys.

  15. Brad Albing
    June 24, 2013

    Not a problem. Sometimes that's how the best discussions develop.

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