My Power Bill

What your meter records is the product of volts times amps time hours time Cos Phase angle.

For example if you were running an electric heater on a 230v supply taking 4.35 amps (the phase angle would be zero° for a resistive load) your power consumption would be at the rate of 1 KW and your supply meter would record 1 KWh (unit) for each hour.

Hi Syphrum,

Industrial utility customers go to a lot of trouble installing power-factor controllers just to make sure the utility bills them only for energy actually consumed, simply because watt-hour meters can't tell the difference between actual and apparent power. The situation may have improved since I last dealt with the problem, with utility companies installing intelligent watt-hour meters that take phase angle into account. But some years ago I worked on an experimental automated transit system which, overall, presently a highly inductive load to the system. We were billed for apparent power, not actual power, so I know phase angle wasn't being considered.

-e

Reactive, or "apparent" power is a problem for supply industries as it increases the losses in their supply cables. To illustrate, a power cable connected to an ideal capacitor will dissipate some heat, whereas the ideal capacitor will not. The utility supply company will incur some energy loss to feed the capacitor, the value of which it recovers by charging the customer.

Very few domestic users are charged for reactive power; the relationship to resistive power is so weak in cash terms it is usually not worth bothering with charging directly. Why go to the bother of measuring reactive power for domestic consumers, when one may make a stab at the losses from reactive power for an average home, and bump up the charge for a unit of resistive power by that amount (rhetorical question)?

Power factor correction becomes valuable for big users of power, because they are charged for reactive power as well as resistive, and altering the load characteristics by introducing (usually) capacitance lead is often a very attractive investment. It can often reduce the need to re-run and increase cable sizes when a cable is approaching the limit of its rating to dissipate heat. Power factor correction can be cheaper than digging the cable up and replacing it.

It all depends on circumstance.

Without regard for phase angle.

So if your net electrical load is purely resistive, the phase angle is zero and you're being billed for actual energy consumed. If your phase angle is not zero, you're being billed for apparent energy consumed which will always be greater than the actual energy consumed. The net reactance of the load returns some of the power back to the system, but your typical simple-minded electromechanical watt-hour meter doesn't know the difference. Watt-hour meters can be made to accommodate phase angle and show actual energy used - the technology certainly exists and can be mass-produced - but what's in it for the Power Company?

-e

In my country, Argentina, homes pay per KWh despite power factor. The industry pay KWh more one plus per inductive KVARh minus bonus per capacitive KVARh.If industrial power factor fall under 0.9 inductive the bill is really expensive.

The mechanical watt hour meters work by using the voltage and current being consumed to rotate at disc.

http://en.wikipedia.org/wiki/Watt-hour_meter

A simple volt or current meter use source in combination with a fixed magnetic filed to produce the torque that moves the needle so individually they can't show you the angle between the two.

The mechanical watt hour meter on the other hand uses a combination of the current and voltage simultaneously in conjunction with a fixed magnetic filed to produce the torque that rotates the disk. Since the both are used together the phase angle is automatically taken into account the number of rotations is a pretty close representation of the power being consumed rather than just a simple multiplication of the voltage and amperage.

Large consumers of power are billed in a more complex way than just energy consumed. Firstly the rate they are charged at depends upon the peak instantaneous consumption. In other words if they use more than a certain number of watts the rate they are billed per kilowatt hour is increased. Secondly if the power factor or phase angle gets bad enough they are also billed at a higher rate for a given period. Finally the pay different rates during peak demand and low demand periods. As a result of these complex billing practices its in the users best interest to do thins like reducing peak usage by load shedding, correcting the phase angle and delaying operation of equipment till low demand periods.

Until recently suppliers have only billed domestic consumers on the amount of energy they have consumed as it would be too costly to implement the complex metering that is used for large consumers. With the introduction of mass produced microprocessor based meters that can monitor things like peak demand etc. they are starting to offer domestic consumers similar incentives to those offered to large consumers.

Basically it depends on your supplier and whether they have decided to implement the complex metering and billing systems, but in general for domestic users you are only paying for the actual energy you consume and nothing more.

The power you draw is being measured in Watts. The energy you are being charged for is being measured in Watt-hour which is an incorrect way of saying joules. Technically, you should have a value that says this is how many joules of energy you are using. It is only called watt-hours because it has become industry standard not to do what would be correct. It would be more correct to break the hours into seconds (since watt is a joule per second), the time unit of seconds would then cancel out leaving you with joules (energy unit). Watt-hour is an energy unit too, but the term contains two terms for time which should cancel out. It is just easier not to do that math, and industry is lazy on this one.

If I had my way, everyone's electric bill would state the number of kilojoules consumed.

Guest writes: "...Watt-hour which is an incorrect way of saying joules."

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Equivalent, perhaps, but not incorrect.

-e

"If I had my way, everyone's electric bill would state the number of kilojoules consumed."

This has come up before on several other threads especially when it comes to comparing things like gas and electricity bills. As Jaba-Jabba said any engineer should now how to convert watt hours to joules. Interestingly the gas company I use charges me for gas in Kj. They are about to get into supplying electricity so it will be interesting to see if they stay with the trend and show how many Kj of electricity they are charging for.

Great, another Kilowatt-hour post, I've seen three here in the past two days! The concept of units of measurement are older than the hills, please search wikipedia or Webster or Google or even maybe search the forum you are about to post in for explanation of what units are.

Quit beating a dead horse!

In reality you are being charged for ampheres, not volts. 220volts (.5 the amps ) is always cheaper than 110 volts. Better yet is three phase electricity if you can get it. Numerous voltages with a transformer, the same amp (or current ) draw.

no, you are being charged for energy. There are costs connected to the ammount of power you need at any given time to cover the wire and equipment needed to provide service.

sounds like the blind leading the blind in several threads. I thought this was an Engineering forum! Any engineer should be able to do unit conversion equations.

Here here!

Please people, if you are not ABSOLUTELY SURE of what you are going to say, please refrain from posting. That previous post was complete jibberish! You are NOT charged for amps only, you are charged for WATTS based on the amount of time used! The voltage and ampereage are interrelated only in the fact that their product is watts. Why is this such a complex issue for some people???

I thought that's what I was saying, (WATTS * time) is a unit for energy... I didn't want to use any unit name in fear of confusing someone so I just said energy.

I went on to say that there may be other charges based on your power needs; which was probably a mistake to do.

It depends on where you live, local utility supplier, regional power supply utility, transmission utility, local type meters, size and type of customer, local laws (time of day charges, daily peaking charges, monthly peak, size of customer, voltage and phase of customer). Large customers with clout and capability to verify calibration accuracy can bargain for accurate measurement. Local home owners have not clout except, roughly speaking, to throw off all switches and verify whether the meter continues to spin. If so, request a recalibration. If not, what option do you have?

Some utilities are phasing in "remote" reading that may be more accurate. Some utilities only read meters bi-monthly with visual odometer type readouts with plus or minus 5% accuracy. New metering may be 0.5% accurate.

The short answer is phase angle is not within the accuracy capability of most any local home meter.