Residential & PF

Don't sweat the power factor. Residential metering is based upon kWH and the metering equipment does not register the reactive or harmonic parts.

There is a tiny 'second order' effect when dealing with constant power loads (motors and switched mode power supplies). The additional current drawn as reactive power will produce a small power loss due to branch circuit I^2R losses. You can make some assumptions about R and calculate this, but the return on investment for p.f. correction isn't economically viable.

I added another newsgroup that might be of interest for this topic, but the traffic there is practically nil.

Killa Watt is a great window into measurements that were previously inaccessible to home owners. As you found, it provides a tidy little tidbit of information that may be useful for you to understand just how much an appliance is bleeding from your purse, and thus the nation and the world.

For safety reasons it is probably better that one does not go about modifying appliances to get closer to a resistive load but I understand where you are coming from. You are enlightened enough see your appliance is throwing 54 watt hours per hour to the "terrists" who provide the fuel for our polluting power plants.

Considering that the power delivered to you appliance by the electric utility is a fraction of the energy required to make it and pump it through the distribution system for your appliance to consume, correcting the power factor could save

100 watt hours per hour or close to a megawatt ( 24x365x100W) of prime mover energy per year from being consumed.

If there were ten million of these appliances on line 24x7 that little power correction, to all of them, could prevent the need for one more nuclear power plant. Ten million is how many appliances there would be if one in thirty Americans owned one of them.

peace dawg

No it's not. The reactive power does not require fuel into the power plants. Reactive power is energy that is "traded" back and forth between your appliance and the power grid, but almost as much is passed back in one portion of the cycle as was taken in another portion of the cycle. It's not real power.

It's not *entirely* free. If the PF was 1, that appliance would draw only 1.74 A, not 2.2 A. The "extra" 0.46 A causes extra resistive losses in the house and utility wiring, and that wastes real power - but only a few watts, not 64 W. (269 - 205 = 64, not 54).

Also, "watt hours per hour" is simply Watts. Why invent a new but useless unit?

Again, reactive power isn't real power and doesn't need prime mover energy, other than the small amount of real-power losses. And the extra current in the wiring happens only between his home and the utility's closest facility that corrects line power factor, not all the way back to the alternator.

Dave

You are apparently confusing "power factor" and "efficiency", which are two different things. The ratio of power delivered over power produced is the efficiency, not the power factor. In fact, the power delivered to your home is a fairly large percentage of the generated power.

Power factor is the ratio of real power (W) to apparent power (VA). Improving power factor reduces reactive power and therefore apparent power, but has theoretically no effect on real power. In reality there is a small effect on real power due to a slight reduction in the conductor losses because the current is reduced. Therefore it has only a small effect on the prime mover energy or your residential meter reading. For a typical residence that operates at fairly high power factor it is insignificant. For large factories operating at low power factors it is much more significant.

If the load needs 269 VA at .78PF and the generator can only generate 205 watts would the load be getting all the power it needs? Would the generator have to deliver 269 watts to satisfy it?

peace dawg

Although, in the case of thermally-generated power, the power delivered to your home is apparently only about 30% of the original heat energy produced by burning fuel (or fission of atoms, concentrating the sun, or whatever source of heat was used). That's because the process of converting heat into electrical energy is inherently inefficient.

So burning fuel to generate electricity which is transmitted to your house and then converted back to heat takes about 3 times as much fuel as if you burned the fuel in your house in a 90% efficiency furnace. Electric resistance heating is 100% efficient, and the transmission grid is pretty good too, but the fuel->heat->electricity step is not. And "efficiency" depends a great deal on what you choose to measure as the input and output.

Dave

Yes, the generator only needs to generate the real power, although the current flowing in the wires (and thus the resistive losses due to that current) is about 30% higher than it would be with a power factor of 1.

Think of the reactive power as energy that is oscillating back and forth between the motor (or whatever inductive device is in the appliance) and the grid. The motor "borrows" it for part of a cycle, then "returns it" in another portion of the AC cycle. It doesn't contribute to useful output, but it doesn't load the generator either.

Dave

Would a 205 megawatt generator set be able to drive 269 MVA load?

does 205 W @ .762 PF = 296 VA?

is that the same as 205W @ - 40.35 degrees?

is that the same as (205 -j174) watts load?

peace dawg

LOL! Wow, this is an interesting thread to greet a newcomer with. It only took one post to identify the egos, louts and misfits even if a few of them do know what they're talking about. Obviously several participants are parrots and the others like their buzzwords and guess a lot, while a few actually know what they're talking about. That tells me, don't ask a question here if you really want a professional and accurate response to most things.

Maybe I'll see you all again, dunno.

Twayne

Aha! A newcomer. I'm surprised that some of the folks here didn't try to sell you on the latest financial scam or flat earth theory.

You've got to lurk on a newsgroup for a while in order to figure out who the goofs, trolls and troublemakers are. In the final analysis, the advice you get is worth every penny you pay for it.

Flawless.

lol, well, then again, there is the experience factor. Like I said, several personalities stood out immediately; much faster than on most groups. So, no, one doesn't necessarily have to lurk in a group to figure out who the goofs, trolls, etc. are. But I do admit it's a LOT faster to happen here than on any other group I've worked on. Now, about that flat eart theory: How could something so sensible and so obviosly evident be debatable in any way? Heck, every high school kid knows the earth isn't round; far from it, in fact! But I digress, don't I? Well, don't I? I've decided this group does have some value after all, BTW. Reading through tonite's episode was truly amusing, even somewhat interesting in a comedic sort of way. At least I haven't heard anyone make any snips about hole theory being dismissed; now, that would be funny. How many electrical engineers participating in this group does it take to change a lightbulb? None. All but one don't know how and the other person is too smart to bite. How many electrical engineers participating here does it take to kill someone? None. Anyone standing too close to this group will die by default.

Were there ever any real, actual electrical engineers in this group? Are there now? Stand up and identify yourself if you are actually an electrical engineer. Here's a test question for you: Does an electrical engineer's career ever encompass nothing but digital transmission circuits? I'll bet over half of you don't know the correct answer, or if you do, you don't know why it's the correct answer.

Cheers all, & thanks for making me feel so much a genius by inference,

Twayne

Yes & yes. Real and actual ones too.

I have some paper that says I am actually one, so I guess I am. Sometimes I even get to sound the train whistle.

Ooh, a test, and I forgot to study. Can I make it up a different time?

Big deal! They sell clocks that do that on the hour. My retired dad has one with a steam locomotive & whistle. :)

Sure, when you finish building that time machine. ;-)

------- Yes there are real electrical engineers lurking on this group. Paul H is one, Daestrom is another, Ben Miller is one. I also am one. There are others and some definitely are not engineers- wecandoit, and the guys who spend their time in infantile insults are not.

Do we deal with digital transmission lines? - I don't and some of the others don't- power transmission and utilization is far more fun.

You got a good answer to your question from Paul and Martindale pointed out some facts. In considering residential service, the charges are based on energy as read by a KWH meter which actually measures the real power* time. Your KWH meter, at .38KWH over 1.62 hours indicates an average real power of

380/1.62 =230 Watts (rounded to 2 significant figures). This meter doesn't give a hoot about power factor Your killawatt indicates 205 Watts - The KWH meter is actually more accurate by a fairly large margin (money is involved).

In determining your costs- consider only the real power as that is all that the KWH meter cares about. The power factor as found from watts/Volt amps =205/269 =0.76 as opposed to the measured 0.78 . Your voltage times current indicates 259VA not 269VA so there are a few discrepancies but this is to be expected. The measured Volt-amps includes the effect of reactive volt amps which is a measure of energy put in during part of the cycle and returned in another part of the same cycle =average of 0 (in every 1/60 second) so it doesn't register in the watt reading. This is what gives the power factor which is the ratio between true power (watts) and the apparent power or volt-amperes. Using your measurements the reactive Volt amps =174VAR The power factor of different loads will depend on the load. A light bulb or heater will be unity power factor as they are pure resistance loads. A single phase motor will have a power factor at full load of the order of 0.7 or so at full load and about 0.5 at no load because it is inductive. Fluorescent lamps have inductive ballasts so they will also have a power factor less than unity.

All this tells us nothing about the efficiency of the generator, the transmission line or even the appliance itself. At this power level trying to correct power factor (at the appliance- not at the house service entrance) might save a couple of watts (line losses as Paul had indicated) but would cost more than it saved so why bother.

Does this help?

Oh well, there goes my job. Replaced by a machine.

There are several.

I am.

Of course not. Other parts of the career include things like going to meetings, training new managers, and other more difficult stuff.

"Feel" like anything you want, though you must be a Democrat.

Electric train, I hope. Otherwise you'll get the steam union mad.

Don't worry. It's open (note)book.

What can I say? It happens to us all, sooner or later. :(