The best way to think of it is that a load with a low power factor will move a lot of electricity back-and-forth in the power lines without actually consuming the energy. You get billed for the amount of power the load uses, but a higher amount if moving back-and-forth, and being disipated as heat in the power lines, transformers and so on. So, there's a real cost to the electricity company, but it doens't show on the meter. That's why larger industrial users with poor power factors will be charged for it, and why some install local capacitors to act as reservoirs to restrict the back-and-forth to their own premises, thereby avoiding all the waste in the power transmission system.
No, power meters measure the real power, so that won't happen.
Installing power factor correction at the load will actually give you a small reduction in power used. That is because it will reduce current for a given power delivered, so the resistive losses (I^2 R) in the wiring will go down.
If you study how a mechanical killowatt-hour meter works, you'll find that it depends on the voltage and current being in phase. Usually phase-shifting loads (transformers, motors, CHLs) are negligible (their resistive loads are much greater than their reactive loads) and their effect is ignored. Put a big enough reactive load (that shifts the phase between voltage and current
90°) on the circuit and the old-fashioned, mechanical, killowatt-hour meter will do what?
It will stop. Or run backwards.
Specifically:
"Some combinations of capacitive and inductive load can interact with the coils and mass of a rotor and cause reduced or reverse motion. All of these effects can be detected by the electric company, and many modern meters can detect or compensate for them.[nudge-nudge, wink-wink]" ["Detection" is usually accomplished by looking at the WTF? box attached to the distribution panel.]
Power Factor is related to inductive or capacitive loads. It is best seen if you take it to an extreme with a load that is 100 capacitive. Lets say you put a capacitor across the line and measure the current at 10 amps. This current is not doing any work and is returned to the circuit. It doesnt show up on your electric bill and is not read by your power meter. This is only more or less true. The more or less part come in because the cables that carry the current to and from this capacior are not perfect conductors, they are resistive. The increased current caused by the capacitor increases loss on the lines. These losses turn into heat which you will have to pay for. For resisdential use it wont be very much for industrial use it could be quite a bit. PoCos also have extra charges for places who have a highly reactive load because it causes greater losses on the PoCo's power lines. Their are lots of myths that you can add capacitors or inductors to reduce your eelctric bill and even get free electricity. Neither are practical for residetial users. The free electricity myth isnt true for any type of user.
I agree with other comments - particularly hr[bob], Wayne, George and trader.
Accuracy of watt-hour meters comes up at alt.engineering.electrical. Both mechanical and electronic meters accurately measure the real power (watts). There is no question. (If anyone is interested in how mechanical watt-hour meters work details are in a thread on alt.engineer.electrical starting 11-21-09 and titled "Balancing the Breaker Box". Much of the thread is forgettable, but look at posts by snipped-for-privacy@shawcross.ca and daestrom , particularly starting 11-30. This is only readable by techies.)
Adding to hr[bob]'s post - the current through an inductor (as in a motor) stores energy in a magnetic field. As the current is increasing, additional current is required to store the energy. As the current is decreasing the energy comes out as current that flows back into the grid. This shifts the peaks of the current flow away from the peaks of the voltage. For a motor, the overall current is increased over the current that does mechanical work.
In a capacitor, energy is stored in an electric field. As with an inductance, the energy flows into the field and back out to the grid, shifting the voltage and current peaks.
Watt-hour meters ignore reactive currents (inductance and capacitance) and measure only real power (watts). (They record energy - watt-hours.)
Energy storage in capacitors counter balances energy storage in inductances and can return power factor toward 1. Utilities have racks of PF correction capacitors to raise the PF toward 1, which reduces currents, which reduces utility resistance losses.
Utilities can meter several things. One is real power (energy), which is what watt-hour meters measure. For commercial and particularly industrial facilities they may also measure "demand" and "VARs".
"Demand", which is in Daring's posts, is the peak power consumed (max of watt-hours measured over a small time period). High peak power means the utility has to have capacity to supply that demand. If usage can be shifted, like cycling air conditioning when a facility is using a lot of power in other areas, the capacity the utility has to provide is reduced and the facility is rewarded by lower "demand" charges. IMHO motor starts are too short to change demand much. On a mechanical meter demand is a dial around the top of the face of the watt-hour meter.
"VARs" are volt-amps - reactive. This is reactive power, and peaks when voltage and current are at 90 degrees. If V and A are in phase (resistive load) the VARs are zero. It is measured with a separate watt-hour meter (could be combined in an electronic meter - don't know if they do). This reactive power is not "used" - it flows from the grid and back to the grid 120 times per second. But it increases the resistance losses for the utility, and the utility can charge a big penalty for VAR 'use'. That provides an incentive for facilities to reduce the VARs using PF correction capacitors which, as someone said, have to be switched in and out depending on motor load. PF correction at motors reduces the resistance losses within the facility.
Since residential users pay no VAR penalty "black boxes" to increase PF are a scam. Residential users pay only for power that is used.
Equipment that includes a DC supply distorts the current, with high current near the peak voltage and low or zero current the rest of the cycle. This includes switch mode power supplies (computers, CFLs) and variable speed drives. The V & A peaks are not so much shifted as the current wave form is non-sinusoidal. I think this is referred to displacement power factor. (Power factor is defined as power divided by volts times amps.) I believe the European Union has limits on this.
Umm, haven't you ever noticed the large banks of capacitors housed outside many industrial buildings? THOSE are the ones that are correcting for the PF in that building. The power company does not correct for unknown power factors and couldn't if it wanted to. I think you're misunderstanding the purpose of whatever it is you're seeing that you think are cap banks.
I wonder what kind of IR losses are going to be in the pole pig transformers when you get a low enough PF to get free electricity. Ive seen what happens to an engine /generator set when it was feeding a UPS with a PF of .57. I couldnt convience the D... A.. enginneer that it OK to disconnect the bank of PF correction caps, that it wasnt written in stone that you had to use ALL of them. All the smoke started coming out, 1200 amp breaker tripped.
Don't know about where you live, but around here I often see racks of PF correction caps on utility poles - 3 phase distribution voltage. Utilities certainly DO install them. Utilities may also switch PF correction caps [which can cause bad surges].
Another good post by George. Another bad one by Twayne.
Utilities -sometimes- may install them in certain areas, I don't know. I've never seen it in Coronado, San Diego, Chicago, Aspen, Fort Worth, St. Louis, Boca Raton, or upsate NY and NYC. Anymore it's all underground anyway except for smaller cities and rural areas. I've seen a lot of things on power poles but never a capacitor bank. Once the plans are approved for their installation by the powerco, a contractor installs them any where I've ever been. Then they're inspected by the powerco if it's a big system and they go into use. One of the things you do often see on a power pole is a repeater for sending the RF received electrical usage down down the hi-voltage wires for charging for power purposes.
I'd appreciate it if you could find a URL or similar source to verify that they'll put capacitor banks on a power pole. You do realize how much even small ones weigh, don't you? And what the value of "small" would be? I'm guessing you don't, but it's easy to calculate. Actually I'm wondering now if you would even recognize a capacitor bank as capacitors anyway. But, if I'm wrong, I'd certainly like to see some evidence of it.
I first saw a rack of PF correction caps about 5th grade. The utility was installing one on a utility pole next to my school. I asked a lineman what it was and he told me. Even explained what it did, but in
5th grade it didn't entirely make sense - current when there is no voltage???
That rack, and the racks I see about every day, look a lot like the .htm from HeyBub. The racks may have 3, 6 or 9 caps.
Gotta be way lighter than 3 pole pigs for 3 phase.
ooh - nobody is as smart as Twayne. I have know what PF correction caps look like since I was about 10. Maybe you don't know what they look like.
HeyBub to the rescue after a difficult google search.
But the power company commonly corrects for PF and does install capacitors to do it. They know practically none of their customers have a unity PF and are usually lagging. Their base charges already include an allowance for that. Not sure why they couldn't correct PF if they wanted to since all they need to do to correct the typical lagging load connected to them is install capacitors just like a large industrial facility might if they want to avoid a PF penalty.
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