What are we paying for? Watts or VA?

[WB2CAU]

I've been connecting various different devices in the house to my "Kill-A-Watt" meter.  Typical incandescent lamps being almost purely resistive show almost identical power and VA readings as they should.

My 27" CRT TV measures around 100 Watts but around 160 VA.

A typical CFL measures 13 Watts and 22 VA.

Since there is a difference with any reactive load, I start to question whether the meters that measure our power consumption from the grid are truly measuring power in Watts or the higher-reading VA.

Has anyone else ever wondered whether we are paying for Watts or VA?

Okay, call me a conspiracy theorist!

[Ed/KB1HYS]

easy enough to find out.  Pull your mains, then make sure the meter doesn't spin.
Power up one circuti - attach a known load for about an hour. See what the meter reads.

Use a CFL or similar for max differntial W vs. PA.

[WA1GFZ]

Or run a bunch of inductive stuff. While watching the meter. plug in a cap across the line and see if the speed changes.

[VE3GZB]

What you pay for on your hydro bill is VA. But it's only watts that do actual work.

That's why big companies put PF correction caps on their power distribution systems. When it comes to thousands of watts versus thousands of VA, the difference is significant.

[WD5JKO]

Or run a bunch of inductive stuff. While watching the meter. plug in a cap across the line and see if the speed changes.

I have always wanted to take a utility meter and play with reactive loads... I wonder if the new smart meters record differently than the old versions with no active components? My neighbor had his old meter replaced with a smart meter, and his utility bill doubled!!

  A lightly loaded induction motor is very reactive with a lagging power factor. The amps are about the same between full and no load, but the phase angle is what changes. Remember that watts = VA Cosine theta. So a perfect loss free induction AC motor unloaded would have a phase angle of 90 degrees, and since the cosine of 90 is 0, we have zero power. This could be true even though the motor pulls 10 amperes! A real motor will have losses though, and will always consume some real power.

   I have a swimming pool with a 2 HP water pump. The pump also has a switch to cut the RPM in half where the rating is 3/4 HP. When I run at 2 HP, my electric meter spins pretty dam fast. When I switch to low speed, I can barely see any change at all from the pump being OFF. I have always wondered what the difference between VA  versus W between HI/LO speed is. Running on low speed at twice the time pumps the same amount of water, yet the impact to my utility bill is minimal. Running at HI speed adds about $100/month to my utility bill. This assumes 8 hours a day on HI, versus 16 hours a day on LO speed.  Any pump guru's have an explanation?

Jim
WD5JKO

   

[WA1GFZ]

Power factor correction is a big deal with switching regulators. One option would be to tune each inductive load with a cap to correct the phase. Say stable loads like a fridge would be easy to tune. My class e rig has a 340,000 uf filter so maybe I get a deal when it is on.

[WD5JKO]

Here is a good answer to what are we paying for:

http://in.answers.yahoo.com/question/index?qid=20070818090016AAFPMFL


Update: See attached file. This suggests to me that we pay for KWH as long as the power factor is close to 1. If the PF drops below 0.9 we pay KVA??? Maybe the new smart meters follow the examples in the attached file. Then again, for residential usage, maybe the power companies don't care. I like the reference in the first link that CFL's have a PF of 0.5!!

[k4kyv]

Since most home appliances present an inductive load, maybe it would pay to install PF correction capacitors at the service entrance. How would you measure the PF of the load?

[W3GMS]

Don,
You can calculate the power factor by measuring the VA and then measuring the wattage.  Divide the wattage by the VA and you have the PF.  Example, 700W/1000VA = .7PF. 
Joe, W3GMS.     

[Tom WA3KLR]

You pay for True Power, not Apparent Power (VA).  Those old electro-mechanical electric meters on the outside of your house (with the spinning disk) are true-power meters, temperature compensated too.  Any of you with the big thick Electrical Engineers handbooks at home (that you don't normally look in) can look up the electric power meters section and read about them.

Of course some meters today are all electronic.  High speed A-D samples the voltage and current at/almost the same instant, does a multiplication, and does the math for integration and totaling for energy use.  Same result, no conspiracy.

[N4LTA]

You pay for Watts. Utility meters are very strictly calibrated - Utilities are very strictly regulated.

Actually you are paying for energy - KWh.

Some industrial customers are penalized for low power factor - I have never heard of a residential customer penalized for power low power factor.


Pat
N4LTA

[W1RKW]

The "Kill-A-Watt" meter that Eric/CAU mentioned in the original post measures power factor of the device that is plugged into it.  It's a handy little device.  

Take all the appliances and devices that are plugged in in your home that appear to be OFF and measure the power consumption of all the standby power supplies and don't forget wallwart devices too.  You'd be surprised at what you're drawing 24/7.

[k4kyv]

Don,
You can calculate the power factor by measuring the VA and then measuring the wattage.  Divide the wattage by the VA and you have the PF.  Example, 700W/1000VA = .7PF. 
Joe, W3GMS.   

So, I can measure the VA drawn by my washing machine or big screen TV, using a voltmeter and an ammeter.  But how do I measure the actual wattage these appliances draw, if they don't happen to present a purely resistive, non-reactive load? Is there a simple instrument available on the market capable of taking this measurement?

[WB2CAU]

 Is there a simple instrument available on the market capable of taking this measurement?

Yes, there is.  I mentioned it in the first post:

http://www.newegg.com/Product/Product.aspx?Item=N82E16882715001&nm_mc=OTC-Froogle&cm_mmc=OTC-Froogle-_-Electronic+Gadgets-_-P3+International-_-82715001

It's $20, free shipping at this time

[W3GMS]

Hi Don,
As Eric mentioned true watt meters are available.  We had one in our Switch Mode Power Design Lab at work and it was regarded as the standard many years back.  The meter came from Japan and the name was something like "Sangawana" or something like that.  It was an analog meter.  As Eric pointed out they have much cheaper ones these days.  The old switching power supplies had a horrible PF.  They looking into a Cap input filter and the current pulses off the line were typically very narrow but high in amplitude.  They created a lot of Harmonic distortion and the EU (European Union) came up with a standard dealing with Harmonics.  The solution to that problem was to develop an active power factor corrected front end.  That resulted in since wave current waveforms which took care of the harmonic problems.  Most if not all switch power supplies today have active PFC corrected front end.  The topology is typically a boost converters.  The beauty of that is you now have a regulated DC rail which allows one to operate the supply on both 100V and 200V AC service.  Line regulation is not an issue since the HV rail for the switches is now regulated.  Kind of like a pre-regulator prior to the main switching converter.    With the PFC front ends, sometimes conducted EMI components can be a problem, but with common mode chokes and differential type front end filters things can pass pretty well.
Regards,
Joe, W3GMS         

[WB2CAU]

The meter came from Japan and the name was something like "Sangawana" or something like that.  

Was it a Yokogawa, Joe?  

At my last employer, the piece of equipment that I liked most to measure power was made by a company called "Valhalla Scientific". It was a digital VAW meter. VAW = Volts, Amperes, Watts.  http://www.valhallascientific.com/

I bought a rather large Fluke (analog) VAW meter at a hamfest many years back.  I had wanted to fix it up and use it but after buying the inexpensive yet effective Kill-A-Watt, there's less incentive to do so because of the Fluke's greater bulk.  I might just sell off the Fluke.

Eric

[W3GMS]

Hi Eric,
Yes that's it!  It's been a long time since I heard that name but that is it.  It was the top of the line during its day. 

Later we used power monitors that calculated and displayed everything for you.  The tech's used those in the lab exclusively and liked them.  They were pretty expensive units but I would have to email some of my techs to find out who made them.   
During the last 10 years of my career they moved me up the engineering management chain and I had no where near the fun.  I really missed the time I spent in the lab.   

Joe, W3GMS     

[The Slab Bacon]

You pay for Watts. Utility meters are very strictly calibrated - Utilities are very strictly regulated.
Actually you are paying for energy - KWh.
Pat
N4LTA

Maybe so, but they are not above doing whatever they can to maximize profitability.

The one line they hit us with around here in the summer with is:
"We had to cut the voltage back due to the increased demand"

With air conditioners and other heavily inductive loads now drawing more current due to the decreased voltage, Isn't this kinda like the butcher having his thumb on the scale while he is weighing up your pork chops? ?   

If anything, they should increase the voltage to reduce the current load. (At least I would think)

The other thing that they do is if you are a commercial customer, the more electricity you use the more per KWH they charge you for it   

To me that seems to go against all principles of economics. The more you buy, the higher the unit price   In everything else you buy, the ability to buy more product is always a bargaining chip to get a better unit price. Not with BGE/Constellation Energy.
Rather than upgrading their infrastructure, they offer "reverse incentives" to use less

also if you are a commercial customer here in Baltimore, they charge you an additional, healthy surcharge during the summer months. They will tell you it is to cover the "additional cost of air conditioning" even if you dont use A/C in your business.

The bottom line is that they have you by the BA's and wont hesitate to remind you of it! !

                                                                 The Slab Bacon

[KB2WIG]

Round here the local electrical transportation provider ( dont make 'lectricity, they move it) has a 3% a year for ten years push to reduce electrical consumption.

"

If we all reduced our energy consumption by
3% a year for the next 10 years, the impact would be huge.

But everything starts with you.Do it for your checkbook. Your grandkids. The polar bears. But just imagine if we all did it.

It's easier than you might think. So get your Personal Energy Evaluation, then take the 3% Pledge to use less energy. And National Grid will show you how.

https://www.powerofaction.com/

"


klc

[WB2CAU]

Thank you to all who responded to my query.  It appears that the answer is somewhat inconclusive.  Some say we are paying for Watts, some say VA and from what I'm gathering, there's even an area averaged between (maybe I misunderstood that last conclusion, not entirely sure).

If we do not pay for actual wattage, then we are misled by the energy saving claims stated in advertisements. 

Eric

[N4LTA]

Watts are Watts

Watts time time is energy.

That's what you pay for  - there is NOTHING inconclusive -

Lowering the line voltage is not what the utilities want to do - they don't turn a knob - there is no knob

When the load increases - the line voltage drops - just like in a radio.

The utility grid is a very complex network and you can't just turn a knob to lower the voltage to screw your customers.

Look at the utility grid as a net of "nodes" each contributing power  - if one node lowers the terminal voltage (if you could easily do so) the network current flows into the lower voltage node until things equalize and power flows into the node.


Reactive power does no work. It is easily corrected at the generator.  A utility generator generates only real power at the generator node (unless the utility had some really unusual reason to run the generator less efficiently)  - the field of a synchronous generator is set to cancel any reactive current. What happens down the line due to load and line reactance is a different problem and utilities use capacitors to help correct power factor problems.

A utility would NEVER want to reduce line voltage because doing so would reduce power and reduce revenue.

Running a low delivery voltage would put the utility in a situation where they could and would be legally responsible for damaging equipment.

I have been working with many differently utilities since 1973 in over 10 states and i have never seen any tricks and I have never seen any utility charge for anything other than energy (KWH) and demand (KW)

I have seen power factor penalty clauses in rates schedules (not residential rate schedules) but in almost all cases - the utility warns the customer and gives them ample time to correct the problem before any penalty is enforced.

Rate schedules are public information - published on the net - I challenge anyone to show one that charges for reactive power as a metered commodity. Not saying it is impossible somewhere in the world -  but pretty darn unlikely - it is not a matter of opinion.


Pat
N4LTA