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Participant

Join Date: Jan 2009
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Do You Pay for Watts or Volt-Amps?

02/09/2009 4:56 PM

When pay your utility bill. ARE YOU PAYING FOR WATTS OR VOLT AMPS per HOUR

My understanding is watthours.

A co worker tell me it is VA hours.

We can leave out the hours.

Watts or VA?

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Guru
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#1

Re: Do You Pay for Watts or Volt-Amps?

02/09/2009 5:28 PM

Look at your bill.

It says "kWH", not "kVAH", does it not?

Your friend is wrong.

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#2

Re: Do You Pay for Watts or Volt-Amps?

02/09/2009 5:47 PM

I guess it would depend on your location, i know up here we pay by the watt/hour, which I thought was the standard for residential and light industry. There is also a demand meter which has a sweep pointer, metering was never my specialty though, I just had some exposure to it. I do have a demand meter here about someplace, maybe I should hook it up and see how it works.

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#3

Re: Do You Pay for Watts or Volt-Amps?

02/09/2009 6:23 PM

droframps: you pay for kilowatt hours, many customers pay a penally if their K.V.A. falls below 90%, or if they are late paying their energy bill. perry

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Guru

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#4

Re: Do You Pay for Watts or Volt-Amps?

02/09/2009 9:35 PM

After 23 years as a Utility meter tech I can assure you it is WATTS X hours (you are in the Philadelphia area, USA) that you pay for.

Since Volt-Amps are greater than the watts, and based on power factor may not even do you any work (watts), the Utility would love to charge you for VA. Instead, the power authority requires that they only charge for the energy that does work for you (watts), measured by a Watt-Hour meter.

If you are a major user of industrial energy, then the VA required to enable your demanded watts becomes an issue. Then the VARs are measured (still not Volt-Amps) and the tariff charge applied for that also.

Volt Amps that you measure with a voltmeter and an ammeter tell you nothing about the timing between the volts and the amps, which is the key to the energy you can actually put to work.

Have you have ever played with a certain toy paddle that requires you to hit a small rubber ball tethered to the paddle with a rubber band? Then you will understand that lots of paddle movement (amps) with force (volts) transfers very little energy (watts) to the ball if your timing is off.

I guess you could say that by charging for watts rather than volt amps we are getting mercy for not being perfectly coordinated (at least our appliances are).

Regards, CJM

P.S. I am guessing there is a reason your co-worker has given you faulty information, care to share that with us?

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#5
In reply to #4

Re: Do You Pay for Watts or Volt-Amps?

02/09/2009 10:56 PM

Exactly right. You are billed for 'real power : kW' not 'imaginary power : kVA", the difference being the phase relationship between voltage and current at the point of load. The distinction is usually negligible at the consumer level but can be appreciable on the industrial scale.

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#11
In reply to #4

Re: Do You Pay for Watts or Volt-Amps?

02/10/2009 5:02 AM

Its nice to know that the utility supplier is doing what it says on the packet - kWh!

We have similar in the UK with heavier users (non domestic / residential) having targets and potntial charges for low P.F., I believe.

I have one question regarding the current. Its my experience that many current measuring devices are not so good at accurate RMS values for non-sinusoidal current, mainly drawn by rectifier loads in electronics. These harmonics are often in phase (displacement factor near unity) but also cause high readings on some equipment. Have you seen typical domestic voltage/current and displacement out of interest and is the current sinusoidal?

Do you know the capability of the meters in terms of true RMS with high frequency response as I've been tempted to fit chokes to see if the current shape improvement (which reduces the RMS current) has a beneficial effect on the electricity costs if the meter is 'over-reading'. In the case of high harmonic content loads, this would be worthwhile.

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#16
In reply to #11

Re: Do You Pay for Watts or Volt-Amps?

02/10/2009 11:32 AM

First I will qualify my answer, in that there is a deep science within the technical world of measuring electricity, just as there is within any field of science such as medical specialties.

A brain surgeon might have an osteopath (bone specialist) at his elbow while repairing a damaged head since they specialize in different things, and even though they overlap, there are too many small details to be certain of that neither surgeon would choose to do the task alone.

That being said, I do understand due to experience most of the answer to your question, but would welcome clarification from a specialist in the field (which is where I got my queries satisfied a few years back), which I will now share with you.

Metering was an analog function for the most part until recent decades where most metering is becoming partly or completely digital. There are differences in the method of capturing the values.

With an analog device, the metals, clearances, thickness, gaps and permeability were all engineered by these specialists to achieve high degrees of accuracy with changes in temperature, waveform, harmonics, spikes in volts or amps (welding, x-rays, elevators etc.) Some devices work better with different challenges as any metrologist could detail, but once a device is validated for the stated purpose it can then be relied upon to perform accurately as stated.

With the increasing number of electronic devices in use, and the increasing of 'dirty' waveform generation sources (wind or solar through rectifiers etc), there has been a greater need to address the science of accurately measuring to account for these issues.

A modern digital electric utility meter samples the waveforms of voltage and amperage ten thousand times per second or more and does the math to produce highly accurate measurements. There have been physical improvements since the beginning of electronic meters to account for the increase of harmonics, DC saturation and spikes etc, and we have now meters that are even more highly accurate than previous analog devices could attain.

The short answer is that you can trust that your electric meter has been designed to accurately account for all the modern challenges, and that even the older meters are highly engineered so that very few things present them a challenge either.

As for harmonics, I understand that only high values of the odd harmonics (3,7,9) cause trouble, but not usually significant trouble. When these are identified, they can be corrected with the science available. Harmonics have small values in the first place by nature, decrease with the increasing harmonic number, and after the 9th harmonic the values are simply insignificant.

Dirty waveform presents a problem mainly for timing devices such as clocks, since many of them rely on the 60 cycle per second value to keep time, and must accurately see the cycles. Since meters sample many thousands of time per second, the waveform is not such a problem as you might imagine. Same with spikes.

Regards, CJM

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#18
In reply to #16

Re: Do You Pay for Watts or Volt-Amps?

02/10/2009 11:54 AM

Its interesting to hear that the meter response is so fast (10kHz), I wouldn't have thought that of a standard domestic meter before.

I raised the question as a well known RF filter manufacturer (with substantail test equipment and expert resources) tested within their own premises and found a significant reduction using chokes but I hardly believe it without testing myself. I've had similar feedback from a biscuit manufacturer but again its anecdotal and I'd like to see it myself.

I do know that some VIP instruments are quite limited as I've used one at work but found the results to be nonsense (400Hz), more recently, with a high speed power analyser everything makes more sense but these are an expensive luxury (£2000+) in day to day life - still not compared to the 'consumption' at the meter.

Thankyou for the care and information you've taken in your response, I'll still probably test out of curiosity when I get a chance to resolve the different viewpoints on this issue. I suspect you're absolutely correct and the wattmeter indeed measures active power so I'll hope for confirmation of this.

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#12
In reply to #4

Re: Do You Pay for Watts or Volt-Amps?

02/10/2009 7:30 AM

Hi McGill,

As being expert on Utility Meters can you please tell us regarding performance of new Digital Meters (Chinese Make) which are now introduced in our city Mumbai, India. Many people are complaining that their electric bills have shot up. Are they accurate or just filling pockets of Utlities companies?.

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Guru

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#17
In reply to #12

Re: Do You Pay for Watts or Volt-Amps?

02/10/2009 11:45 AM

An older analog meter got to be a customers friend as it aged, like an older car they simply begin to slow down with age. Many customers that suspected and complained of tiny inaccuracies in their analog meter were highly disappointed when the new electronic replacement did a much more accurate job and accounted for all the usage the older meter was missing.

Without actually testing the values metered, I cannot address a particular meter, Chinese or otherwise, but I can state with authority that very good metering science exists. I suspect that replacing older analog meters with new electronic meters will have the same effect as replacing old metal water pipes with new plastic ones - less water (or watthours) goes unaccounted for.

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#6

Re: Do You Pay for Watts or Volt-Amps?

02/09/2009 11:12 PM

Could not have said it better Stevem luckily it is not in VolT-Coulomb

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#8
In reply to #6

Re: Do You Pay for Watts or Volt-Amps?

02/10/2009 1:02 AM

Just adding little spice! here in India we pay both ,the installations are divided as High Tension and Low tension depending on Load requirements and supply Voltage (220V for LT and 11Kv to 66Kv for HT)Low tension installations are billed for KWH and a fixed Kva or demand charges.

High tension installations are billed for Both KWH known as energy charges and for KVA known as Demand charges

crm

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#14
In reply to #8

Re: Do You Pay for Watts or Volt-Amps?

02/10/2009 9:12 AM

crm, do not tell the world, how funny we (India) are.

We pay some portion as Fuel Surcharge. I wonder, how the distribution companies generate electricity without use of any fuel. Thus, I was expecting to pay only for electricity consumed (which includes fuel used). But, we pay for electricity consumed, as well as fuel.

Then, even if we use our pwn generator,with fuel purchased from our pocket, we still pay to distribution company, for the electricity we generated.

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Guru

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#7

Re: Do You Pay for Watts or Volt-Amps?

02/10/2009 12:28 AM

In Hungary there are two groups of customers.

"Residential costumers" pay simply for kWh and can get electricity from 0.4 kV grid. They can get discount for off-the-peak consumption.

"Industrial customers" have a more sophisticated invoice. They have to pay also for the consumed kWh-s but they have to pay extras for the peak Amperage, the inductive load, etc. and they can get discount for regulated capacitive load, the off-peak consumption and for accepted consumption limitations. They can be connected either to 0.4 kV or to 10 kV grid.

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Participant

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#9

Re: Do You Pay for Watts or Volt-Amps?

02/10/2009 1:18 AM

Dear friend,

The utility bill is paid base on the real power consummed, not the apparent. Depending on your load (Whether more inductive or resistive); if it's more resistive your power factor will be good and there will be less power loss in your electrical system; but if your load is more inductive, then your power factor will be poor which will result in much power loss and so will cost you more than necessary.However, power factor correction can be made by means of capacitors or synchronous motors.

I hope this clarifies the matter.

Cheers

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Participant

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#10

Re: Do You Pay for Watts or Volt-Amps?

02/10/2009 3:45 AM

we pay for watthours, but watt is nothing but product of volt and amp. and power factor. so in other words we can say ,we pay for VA

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Associate

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#13

Re: Do You Pay for Watts or Volt-Amps?

02/10/2009 8:33 AM

A question about Demand Charges related to this thread.

How is demand measured and billed?

Best explained with an example.

Say I have a Demand meter and demand billing on a single phase 120/240V electric service. The loads are 120V 1kW heaters.

Case 1: If I put two 1kW heaters on Phase A and no heaters on Phase B.

Case 2: If I put one 1kW heaters on Phase A and one 1kW heater on Phase B.

What will the measured demand be for Case 1 and Case 2?

What will the billable demand be for Case 1 and Case 2?

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#19
In reply to #13

Re: Do You Pay for Watts or Volt-Amps?

02/10/2009 12:03 PM

There will be no difference since the meter will be designed to account for either load.

Usually the load you are describing will not require any demand measurement, since the power factor will be near unity, and the demand will be easily calculated from the kWh.

Demand metering records only one specific point in the billing cycle - the point at which you draw the highest average current for 15 minutes, or the stated interval measured, multiplied to equate to the highest per hour usage, which is useful in determining the size and cost of the distribution equipment your needs demand.

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#15

Re: Do You Pay for Watts or Volt-Amps?

02/10/2009 11:02 AM

Meter manufacturers are working on meters to charge for kVA, but politics are getting in the way. They've found a way around it, however, by charging varying rates as a function of power factor. Residential customers generally don't cause power companies any heartburn with regard to low p.f.'s.

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#20
In reply to #15

Re: Do You Pay for Watts or Volt-Amps?

02/10/2009 1:22 PM

Hey Bill, I hear your suspicion clearly, but perhaps it will be of some consolation that I and many other meter techs and meter designers have spent a career, each with a personal commitment to extreme accuracy, not favoring either supplier or consumer, but deriving a great deal of professional satisfaction in the science of metering accuracy.

Also it must be stated that kVa, kWatt and KVAr are the three inseparable elements of your electricity. All three have always been easily metered, nothing new to design. For the supplier to have what you personally need available in kW, there must be a certain amount of kVa and kVAr in exact proportion to the kW.

With the use of trigonometry, metering any two of the three would be just as accurate as metering any of them individually.

I guess what I am saying is that you can be comfortable that you will be fairly dealt with no matter the method of metering chosen. As for the cost of energy, that is mainly in the hands of energy traders and governmental interest (interested in getting your money) and less a function of the Utility.

CJM

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#21
In reply to #20

Re: Do You Pay for Watts or Volt-Amps?

02/10/2009 1:58 PM

It isn't a suspicion -- I consulted with Sangamo years ago to help them design an electronic meter which included peak demand metering, kVA/kVAR vs time of day, etc.

Power companies in this state (as well as most others in this country) are public utilities, and as such must follow agreements with state governments all the way down to municipal governments. Industry lobbiests are the major roadblock to power companies getting paid for having to produce enough power to supply low p.f. customers, although the power companies are making progress via slick negotiations with political liasions. It's one of those cases where they're not charging customers directly for kVAR's by calling it something else. But, if it walks like a duck, and it quacks like a duck, then . . .

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#23
In reply to #20

Re: Do You Pay for Watts or Volt-Amps?

02/10/2009 5:45 PM

Regards.

<meter techs and meter designers >

No doubt they worked hard to bring as true as possible in the past & somewhere in a corner of this world, but not in under-developed countries where all are looting public.

And even the Hi-Techs are not aware what pilferages being made.

Supply COs using un-calibrated & uncertified Meters & Meter readers are advised to show lower readings for a month or two & in the 3rd month bill goes to higher Rates of bill.

eg instead of billing each month correctly to a consumer say 150/155/160 Units 110/105 units are billed for 2 months & actual reading which is much higher than 200 is billed which in higher Tariff rate. [in excess of 200 units]

And ....

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#24
In reply to #23

Re: Do You Pay for Watts or Volt-Amps?

02/10/2009 6:28 PM

I must admit that recently in the little community where my wife's mother resides, there is a local municipal utility, and they did just that. In order to increase revenue they delayed meter reading for a week, which increased the total kWh usage to a level that reached the next higher billing tier for many customers, increasing revenue in a sly manner.

They were called on it by an alert customer, but made excuses, called it a mistake, and only reversed the overcharge to the few who pushed for it.

This is one of the areas that improve when an oversight body with visibility, clout, and public accountability has authority over the energy suppliers. This requires a clear and extensive understanding of the science, and experienced staff dedicated to protect the consumers. This is what was lacking in the disaster that was called 'energy deregulation' in California, and it cost well over 10 Billion $US to learn the hard way.

However, in keeping on topic, at least the ability to meter extremely accurately does exist in spite of the technical challenges. Perhaps a company could make a good income providing independent electrical meter validation at the main panel to provide a means of comparison and control, while also adding energy management tools for the consumer. CJM

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#22

Re: Do You Pay for Watts or Volt-Amps?

02/10/2009 4:53 PM

Regards.

It depends in which part of the world you are living.

For example it was KWHs in the past here in Pakistan as the Bills showed PF 80% & Actual-reading of Meter [KVA] was multiplied by 0.8 & amount calculated & billed to consumers.

Now PF column has been deleted from bill & Reading[KVA] X Tariff is billed

I know [may be outdated] that energy meters read KVA not KW.

RMS reading meters are quite dear & have sophisticated in circuitry.

I know the price of a True-RMS Multimeter was quite higher than an Average-reading one.

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