Watts vs volt amps, what does power meter count?

Status
Not open for further replies.
Originally Posted By: Garak
Make them use just joules and scientific notation. I'm sure that would create loads of fun for manually read meters.
wink.gif



I loathe having to report "heat rate", the inverse of efficiency, in "GJ/MWhr"...having a factor of 3.6 in there feels so...."imperial"
 
Originally Posted By: ARCOgraphite
Are you sure it doesn't draw 1800VA? - You have to put a load on it; like a big fat lasagna in there:)
Oh, I just saw the "not in use". Sorry. I typ dont care about standby power, as the big power monsters like the electric drier and my wife's crockpot I can try to minimise use and this will swamp any "irritating and inconvenient to employ" savings by disco'ing the littler nibblers throughout the house.

Suggestion - get a clothesline and try to use for 3.5 seasons.
 
You should just look at the watts when toggling the KWH/Watt button. If it's off and drawing any watts that is standby usage.
 
http://en.wikipedia.org/wiki/Power_factor
also google power triangle

things get lost in translation.
the basic premise is watt = volts x amps, and watts is a measure of power. and power over time = energy in watt-hours or kilowatt-hours which you see reported on your electric bill.

but you and any company that uses electricity actually pay for "apparent power" which technically is based on the amount of current drawn and "used" and that is why a big deal is made about power factor correction,
because when a factory has poor power factor like when they have all induction motors that are only 50% efficient, that means there is high high reactive power and a lot of current drawn by the load is not used to do any useful work. That higher current draw results in higher transmission loss from the power plant to the load, which the power plant has to supply to begin with.
the power plant can't supply that extra current (power) without using extra fuel, which costs them money... which costs you money.
So they charge you for apparent power, as in kilo-voltamps (KVA) technically and not kilo-watts, even though is says kw-hours on your bill.
and is also why you will see many things especially in industry have a KVA rating instead of a KW rating, because the amps of the KVA is what will trip a circuit breaker.
 
Originally Posted By: 1 FMF
http://en.wikipedia.org/wiki/Power_factor
also google power triangle

things get lost in translation.
the basic premise is watt = volts x amps, and watts is a measure of power. and power over time = energy in watt-hours or kilowatt-hours which you see reported on your electric bill.

but you and any company that uses electricity actually pay for "apparent power" which technically is based on the amount of current drawn and "used" and that is why a big deal is made about power factor correction,
because when a factory has poor power factor like when they have all induction motors that are only 50% efficient, that means there is high high reactive power and a lot of current drawn by the load is not used to do any useful work. That higher current draw results in higher transmission loss from the power plant to the load, which the power plant has to supply to begin with.
the power plant can't supply that extra current (power) without using extra fuel, which costs them money... which costs you money.
So they charge you for apparent power, as in kilo-voltamps (KVA) technically and not kilo-watts, even though is says kw-hours on your bill.
and is also why you will see many things especially in industry have a KVA rating instead of a KW rating, because the amps of the KVA is what will trip a circuit breaker.


This is what you get when someone reads Wikipedia then thinks they're an instant expert.

In general, nobody pays for VARS especially not residential. There can be penalties in industrial for a power factor lower than contract. KVAR does not translate to torque and does not cost the generator extra fuel. The gen exciter has to be turned up and the rating is reached sooner with less KW left in reserve. I'm not going to go on. You need to go to school for at least a couple of years.

Anyway it's a complex system. Reading the internet and thinking you're an engineer is just like reading it and thinking your a doctor and diagnosing your disease.
 
Originally Posted By: 1 FMF
http://en.wikipedia.org/wiki/AC_power


Posting a wikipedia link doesn't help your argument much. turtle is right, in most residential cases, you are only charged the real power, or the real component of the total complex power.

When you see your bill in kWh, the units are correct as charging just the real power.
 
Originally Posted By: EdwardC


in most residential cases, you are only charged the real power, or the real component of the total complex power.


you say most residential cases,
then what are the other types of cases?
 
Originally Posted By: 1 FMF
Originally Posted By: EdwardC


in most residential cases, you are only charged the real power, or the real component of the total complex power.


you say most residential cases,
then what are the other types of cases?



I suppose I meant all residential cases (at least that I know of). I more so meant that for commercial buildings, like noted in some of the previous posts, can be billed separately for low power factor.
 
Originally Posted By: turtlevette

KVAR does not translate to torque
yes but i don't think that was the initial topic
and does not cost the generator extra fuel
i disagree, yes it does because that extra "power" on the hypotenuse of the power triangle is extra current being drawn by the load... which is drawn on the conductor coming from the generator which also is turned into heat via transmission loss... which the generator has to supply... which requires more fuel for the generator to produce it in the first place since it's called for by a reactive load.


You need to go to school for at least a couple of years.
i meet this requirement, but that does not mean someone who did not go to school for 2+ years can't understand this


if you have an expensive Fluke meter that does RMS, are you measuring real power or apparent power with it?

what causes the most heat, true power or apparent power?

for arguments sake lets assume that power companies want to make money and be profitable,
or any company for that matter wants to be profitable,
you can't be profitable by bad accounting practices and mismanaging money spent vs money received... power generated and fuel used vs power accounted and billed for at the power meter. The reactance Q on the triangle varies constantly based on the types of loads turning on and off on the power grid, such as the high inrush of current on an electric motor when it first starts up... that is apparent power not true power. your saying the power company doesn't measure that at the meter, and that high inrush of current i don't get billed for? that's awesome, i take back everything bad i ever said about my electric bill... or maybe that's why i have all those extra charges/taxes beside generation charge and transmission charge?
 
Originally Posted By: 1 FMF
Originally Posted By: turtlevette

KVAR does not translate to torque
yes but i don't think that was the initial topic
and does not cost the generator extra fuel
i disagree, yes it does because that extra "power" on the hypotenuse of the power triangle is extra current being drawn by the load... which is drawn on the conductor coming from the generator which also is turned into heat via transmission loss... which the generator has to supply... which requires more fuel for the generator to produce it in the first place since it's called for by a reactive load.


You need to go to school for at least a couple of years.
i meet this requirement, but that does not mean someone who did not go to school for 2+ years can't understand this


if you have an expensive Fluke meter that does RMS, are you measuring real power or apparent power with it?

what causes the most heat, true power or apparent power?

for arguments sake lets assume that power companies want to make money and be profitable,
or any company for that matter wants to be profitable,
you can't be profitable by bad accounting practices and mismanaging money spent vs money received... power generated and fuel used vs power accounted and billed for at the power meter. The reactance Q on the triangle varies constantly based on the types of loads turning on and off on the power grid, such as the high inrush of current on an electric motor when it first starts up... that is apparent power not true power. your saying the power company doesn't measure that at the meter, and that high inrush of current i don't get billed for? that's awesome, i take back everything bad i ever said about my electric bill... or maybe that's why i have all those extra charges/taxes beside generation charge and transmission charge?


RMS for what? A meter measuring voltage is just voltage, same as current. It doesn't mean anything without the phase angle. It's been a while since I took my power courses, but I understand that even that inrush of power has a phase angle, and that you still only pay for the real component. Reading some of the articles I found, it seems pretty easy for the utilities to assume that at an average, residential households have some known power factor. I doubt that changes much, so they can just account for that in what they charge per kWh.

I just assume those additional fees and taxes were there just to pad the pockets of the politicians!
smile.gif
 
http://s29.postimg.org/v2kbedbp3/va0.jpg
http://s15.postimg.org/qpo0x9vbv/va20.jpg
http://s1.postimg.org/eavx8t6jz/pwr.jpg










for pic of 0° at any given point in time the power is volts x amps, because the volt and current wave are in phase those values of volts x amps result in the highest magnitude.

for second pic of 20° phase shift which is PF = 0.93, the result is a reduced magnitude of volt x amp which is why there is reduced power that the load can use, as shown in pic 3 by the 20° power curve having lower magnitude.
So for loads having low power factors, they still need to draw the needed power to perform at their expected power level and this happens by increased current draw to make up for that diminished power peak level.
the term "real power" is mathematical and is backed out afterwards, and looking at the 2 power curves you see the small bump at time = 170, this makes up for the diminished peak and area under each curve over time is the same, this is the "real power" value. but that is not real world, because of the diminished peak of the 20° power curve that red current curve in pic 2 must go higher and that extra current makes up the reactance.

so if you want to think your power meter is measuring "real power" and not "apparent power" go ahead, if someone works at a utility company and scoffs that the meters measure real power then my question is who told you that and where/when did they get their information? because i would argue they use an emotional definition for "real power" in order to placate the dumb customer who is not going to want to hear they are paying for "apparent power". over time as the meter measures wattage (volt x amps) i'm saying the reactance value is included and accounted for and mathematically and technically it is apparent power or VARS that you are paying for.

some more "random" internet links:

http://www.aptsources.com/resources/pdf/True vs. Apparent Power.pdf

www.tek.com/dl/55W_28941_0_MR_Letter.pdf == see page 6, this is why i say your utility meter is measuring apparent power, how can everyone's utility meter know the nature of the load and calculate "real power" ???

http://www1.eere.energy.gov/manufacturing/tech_assistance/pdfs/mc60405.pdf
The U.S. Dept. of energy states on page 1 to improve your power factor and reduce your electric bills... if the meter is measuring real power then this document is false, and all the money spent by factories to improve their power factor is in vain.

one last thought,
start your 5000 watt gas generator and plug in an inefficient single phase electric motor having a power factor 0.5 or less without capacitive start. the power rating on the electric motor is whatever hp and it's less than the electrical output rating (1hp = 746 watts) of the generator, but when the motor goes to start it trips the generator circuit breaker. why is that? it's because of the inductive load which has high reactance and it is drawing more "apparent" power which is that extra current that the generator can't provide... without requiring a bigger horsepower engine and using more fuel... the principle goes all the way back to conservation of energy.
 
I understand complex power, and I'm positive the utilities can also measure the power factor of the energy supplied to a house. Page 6 of that pdf says that the meter can read apparent power, but that doesn't mean that the real power isn't know. All the references are describing what apparent power is. And that power factor correction can reduce electricity bills.

I'm not disagreeing with the concepts of complex power, or that transmission losses can be reduced with power factor correction.

My argument is just that utilities charge residential customers the real power. Utilities can and do charge/penalize commercial and industrial customers for having poor factor. Their bills have a separate demand charge line item for KVA. Residential homes are almost always relatively close to unity, and as such, just billed for the real power, in kWh.
 
when ever a meter samples voltage and current on an alternating current (AC) line, and you multiply volt x amps that is apparent power because the reactance is on the line. and what you are measuring is what's "apparent". You do not know the lead/lag of the waveforms like in the pics i posted unless you use equipment and sample & average over time to know what that time difference is between the magnitudes of the voltage & current waveforms, to then calculate the angular difference based on frequency which then gives you power factor. to know and do all this takes extra equipment, extra electronics = extra money.
the true or real power as it's called is after you do the math to pull out the reactance and is the amount of power used at the load which is doing the actual work.

why would utilites charge for just real power when it is not accurate and representative of what the utility has to produce?
21.gif
that is not logical.
why would they put all that extra complexity and cost into the utility meter? please answer me this, i mean i know they are not that bright to begin with but to claim only real power measured does not make sense.
there is no "apparent" reason to do it in the first place
crackmeup2.gif
 
oh but the power company told me i get charged for real power.

I had a discrepancy on my electric bill a few years ago and the lady on phone said, but your kilowatt hours value on the statement has nothing to do with what your bill amount is in dollars.... don't believe this if you choose... what do i know i'm just some internet expert.

how's ethanol working out for everyone?

on cnn right now... "The Whole Truth, A challenge to the account of bin laden's death"

http://www.cnn.com/2015/05/11/opinions/bergen-bin-laden-story-a-lie/index.html

i don't want to play anymore.
 
Originally Posted By: 1 FMF
i don't want to play anymore


Did you tell your mommy people weren't being nice to you? Why do I suspect she's never told you you're wrong once in your life?
 
1 FMF I see you're putting a lot of effort into these posts, but I must joint turtlevette and EdwardC in setting the record straight - a generator's fuel consumption is related almost entirely to true power, and the power factor and apparent power have almost nothing to do with it aside from a very small effect on alternator efficiency (on the order of ~0.9% difference between PF of 0.8 and 1.0) which is due to higher temperatures in the conductors increasing resistance.

Remember, the "extra" apparent power is taken from and returned to the circuit every cycle resulting in no net work being performed. No work = no power = no more fuel required to produce it.

I have a presentation here by a PE at Progress Energy (utility company now part of Duke Energy) discussing this subject, it closes with this:
"BOTTOM LINE ON Understanding Power Factor and How it Affects Your Electric Bill
- Very small charge with penalty most customer have no Power Factor Penalty
- None or very small savings or possible increase cost when using Power Factor Correction Devices"

If fuel consumed was related to power factor as you suggest, these two points would not be true.

FWIW for 3-phase AC I use PowerSight PS2500 power loggers and an AEMC 8335 power quality analyzer in my work. They'll tell you whatever you want to know - volts, amps, PF, KVA, watts (real power, really), and the PQA will also provide THD and other info.

More FWIW - generator set specific fuel consumption curves are given vs. real power output, irrespective of power factor. Why do you think that is?

Here is some good reading on this exact subject:
http://www.eng-tips.com/viewthread.cfm?qid=35570
http://www.eng-tips.com/viewthread.cfm?qid=310797
http://www.eng-tips.com/viewthread.cfm?qid=76677
http://control.com/thread/1307586278

jeff

ps. you really lost us with the ethanol and Bin Laden non sequiters
 
Status
Not open for further replies.

Similar threads

A
Solar Powered Weed Wacker
Replies
19
Views
1K
Astro_Guy
ctechbob
Short Review of the new style Wen 56477i 4000/4800 Watt Inverter Generator
Replies
13
Views
6K
ctechbob
R
"Large" parasitic loads - what affect on "smart" battery maintainers?
Replies
18
Views
2K
SubLGT
SubieRubyRoo
More EV power requirement calculations
Replies
14
Views
1K
Slow Car Sport Mode
ctechbob
Tracking Heat Pump Water Heater Power Consumption (1 Year)
Replies
11
Views
2K
dlundblad
Back
Top