Power factor correction for the home?

1. It's too long pay-back period for power factor correction device in home using. Because reactive power of home sets is small enough.

2. It's uncomfortable for using. If consumer switchs on iron there is necessity to go to power factor correction device to compensate added reactive power and after switching off to compensate again.

IMHO

But how do we know? I've got three fluorescent lighting fixtures (ballast is an inductive load), a refrigerator, an air conditioner, iron, tv, other stuff with transformers in them. Switching in a capacitor would not be too much of a problem effort wise though I would have to invest a little money.

Has anyone tried measuring the power factor in a typical home? How much, in terms of kwh would it improve if corrected? A payback time of five years is good enough for me.

I don't know what price for 1kW in your country. Therefore it's difficult for me to estimate return. But I know the price of 1kW is 2 cent only here. So get profit is difficult enough.

Homes do not have a significant enough inductive load to warrant the use of power factor correction capicators. Motors running at full load, such as fans and air conditioners are not inductive loads. Flourescernt lights are the only inductive loads in the average home.

There really is no benefit to the homeowner to correct power factor unless it were so great that the utility decided to meter the VAR usage and bill the customer for it. Only then would it be worthwhile to do an economic evaluation to determine which is more economical, paying for the VARs or installing power factor correction capacitors.

there are some "power saver" products on the market that uses the power correction bases, just plug it in a outlet, but I dont know if those units works http://www.minisunpower.com/

http://www.tradekey.com/product_view/id/115278.htm

It is an idea to reduce emmission, but you will not save money by installing capacitor in the house application. Industrial customers pay in both demand KVA (demand meter) and energy consumption (KWH meter). For residential customers we pay for energy consumption based on KWH meter and the line loss is structured in a billing system in agregated average price not per our demand KVA. The industrial users installing capacitors to reduce the demand KVA, capacitor does not help to reduce your energy KWH.

I hope this helps

You wrote: 'residential customers we pay for energy consumption based on KWH meter'

You are right, In fact, I believe that KWH meters do not accurately measure power when used in an inductive (lagging) circuit. I believe the meters use 'apparent' power for their calc, and this is less than actual power in lagging circuits. There is no benefit to correcting a lagging power factor at home, except to the power company.

Please correct me if I am wrong-

Please do not forget that the power companies do not enjoy it when they have to buy power back from you, or even just reduce the bill they send you monthly...

Good quality fluorescent light fittings have a load balancing capacitor in them so if you use these much of the problem is already eliminated. It also brings about a simple solution and that is include the power balancing circuitry in each individual appliance that way you avoid the problem of measuring the and trying to compensate for the current lead or lag.

The meters in your house calculate the energy you use in and I am told already take the angle that the current leads or lags into account when calculating the power consumed. The only financial advantage of balancing the power factor would be to the electricity supply utility since you only pay for the Watt Hr not the Volt Amp Hr that you use.

If your cos phi factor goes below a certain value, electricity companies charge you a fine because you use more power than you actually pay for. To avoid this fine, you should keep your cosinus phi value above this value. To obtain this you should put condensors in your system.

So : if you want to be holier than the pope, put condensors in your home, so you can get a bigger electricity bill and sleep better ...

paulvandenbossche@monti.be

I had read that the reason they charge more for uncorrected power factor is not because you use more power than is apparent, apparent power is apparent power. However in a situation where the power factor is uncorrected, the must provide larger current capacity to supply the same amount of real power than when the current and voltage is in phase. When current and voltage are out of phase, more peak current is required to supply the same amount of real power and it is real current that the equipment has to supply even though less power is being consumed than would be consumed if the same current were in phase with the voltage. It puts extra strain on all their equipment but with no extra power showing they can't bill for it.

Thanks guys for the Truth about power factor correcting! I have some evil competition that was running around telling everyone that by lowering the apparent power by capacitance on a reactive load, that you would save KWH... NOT, especially when NO demand meters were present at any location in question!

A simple watt, Volt, Amp meter with true RMS will tell the TRUE story, with or without capacitance the wattage never fluctuates at all.

I hope something I said didn't confuse you. If the current and voltage are not in phase you cannot simply multiply amps times volts that you read off meters to acurately calculate power. You will get an erroneously high reading that you could correct if you knew the phase angle between the two but you can't determine that with your volt and amp meter.

Okay, looking at all the replies, I can't seem to get a clear picture of whether there can be savings (however little they may be) or no savings at all. This is what I know about pf correction.

If you put them at the load (switched on when the load is switched on), the current capacity of the cable to the load is increased. Basically, it means that the current going to the load is less when the capacitor is connected than when it is not connected or installed (at least I think that's what it means).

Putting the capacitors in a centralized location and switching them in and out with a pf controller, there is no current capacity increase in the branches but the central location and control makes for a simpler installation.

That capacity increase is what caught my attention. If the current goes down, doesn't that mean that the power consumption is decreased also?

Am I making sense here?

The current does go down. The reason it goes down is the capacitors counter the inductive components and the current and voltage are adjusted to be in phase with each other. Consequently, to achieve the same power less current is required. When the current and the voltage are in phase you can calculate power by the RMS current and voltage measurements. When they are not in phase the calculation from the RMS measurements will come out higher than the actual power being consumed by the device because the peaks of the current waveform and the voltage waveform are not occurring at the same time. In other words, some of the current is flowing when the voltage is zero and visa versa. No real power is transfered at that point. It is because the load is reactive. In theory, a perfect inductor placed across an AC voltage will draw no power even though you will measure voltage across it and current flowing. It is because the voltage and current are 90 degrees out of phase. The energy consumed during part of the cycle is returned on the next so no net power is consumed. I know this may seem strange but it is so. In fact if you over correct you essentially create the same problem but with a capacitively reactive load instead of inductively reactive.

As usual I believe the best way to understand what is going on is a picture so here we go.

What you have is a representation of the instantaneous voltage (shown in red) and current (show in green) for an inductive load. As you can see the current is not in phase with the voltage and since the power used is the current times the voltage you don't get a lot done.

By adding a capacitor in parallel with the inductive load you will bring the current back in phase with the voltage and hence you get more power out of the same current. Since you are already paying for the power and not the just the RMS voltage times the RMS current then there is little point in trying to balance the load.

Wow, there is some misinformed discussion going on here.

Power factor correction for the home offers NO benefit. PERIOD. End of discussion.

You are NOT charged for poor power factor in your home. You are ONLY charged for kWH consumed, NOT current. The only possible (and by that I mean incredibly remotely possible) additional power losses due to poor power factor are IF your wires are undersized for the load AND it has a poor power factor, the wires will heat up, and that heat represents wasted power. The amount of those power losses, even IF it happened, would be so small as to be almost immeasurable, and besides, your wires should have been bigger anyway. Bottom line, PFC does NOT change the kWH consumed. PERDOID. End of discussion.

Utilities do charge industrial and large commercial customers for poor power factor because it represents an amount of system capacity that they must create and maintain, but for which they cannot charge with a kWH meter, because A kWH METER CANNOT READ THE EFFECTS OF POOR POWER FACTOR! What that means is that there are losses in the transmission equipment (transformers, loooooong cables, etc.) associated with the higher current carried to supply VARs, which means THE UTILITY is spending more to deliver it. So the utilities must install ANOTHER METER that reads kVAR (reactive power consumption) and charge the customers sepratelyately for that. For the little tiny bit of system capacity that residential users represent to the overall capacity of a power utility, the cost of installing, maintaining, reading and billing all those kVAR meters in residences would exceed the revenue that the utility could generate from them. So that is why utilities don't care about residential power factor. PERIOD. End of discussion.

People selling PFC correction schemes for residential users are SCAM ARTISTS! They prey upon the inability of most people to understand how they are charged for power, thinking that current is the only important thing. They rig up meters to show how current is dropping, and it is, but what they do NOT show is that the kWH meter feeding the entire demo has NOT changed at all. PERIOD. End of discussion.

Sheesh...

Calm down please .

As I said in my original post, I'm not that knowledgeable with electrical stuff, particularly these kinds of stuff.

For the most part of my working life, I've dealt with DC electronics. Though we studied phase differences in high school, it wasn't given much emphasis in electronics classes. This concept of KVAR and peak demand is something new and I'm learning quite a bit here, and not just about the posted question.

What have I learned?

The standard kWh meter in the home is not affected by poor pf. PFC is good for factories/facilities with larger electrical loads (motors in particular) since these places are charged for poor pf. I take it that if a factory does not have a kVAR meter, they are not charged for poor pf. From the discussion, however, all large factories are required to have this, right?

Further, the poor pf of factories puts an added load on the power distribution system since it decreases the current capacity of the existing electrical cables, transformers, etc. Hence, it makes sense for the electrical utility to charge for poor pf in an effort to convince these large consumers to install pfc and thereby prevent or delay future capacity increase requirements for the utility.

Motors are not the cause of poor power factor. Motors running at rated load usually have a power factor of 0.9 or better. Poor power factor generally results from a large flourescent lighting load or any type lighting that employs ballasts which remain in the circuit after the lamp is ignited. Factories office buildings, hospitals and schools have very large inductive lighting loads.

Factories that employ large motors have an alternate option for correcting power factor. An over-excited synchorous motor has a capacitive reactance characteristic. The amount of capacitive reactance can be varied by varying the field voltage to the motor. This is a good option to consider during the design phase of a new factory. However, there may not be as great an economic advantage over an auto switched capacitor bank if it requires replacing an existing induction motor unless an existing motor has to be replaced anyway due to irrepairable failure.

Most heavy industrial power users are billed from 3 meters:KWH, KVAR, and Peak Demand.The best performance is attained when current and voltage are in phase.If the current is not in phase with the voltage, it requires more current to do the job.The utilities must provide this current, even though it is not performing any "work" The wiring size must be increased to carry this reactive current, because it does generate heat in the conductors.In addition to capacitors, some industries use synchronus motors, which can correct low power factors.Imagine a room of 4 acres in size, with 1500 ea. 2 hp motors. That's a lot of reactive current to deal with. Without KVAR capcitors, the wiring cost as well as the operating cost would be much higher.

As for home use, capacitors for reactive current correction are not cost-effective.

Most residential air conditioning compressors have "start" and "run'' capacitors which help correct power factor.The utilites also mount capacitor banks on poles to help keep losses to a minimum. A feeder feeding a subdivision may have one bank to correct power factor "en masse" for all the homes.

The old days of "reading" the meter are long gone for industry.All data is now recorded by the power companies in real time, and most energy concious companies have a link to the utility to monitor and control their "peak" load.

Once a "peak" is achieved, the company is billed at a higher rate for the entire billing cycle, sometimes months, sometimes years, so it is very beneficial for them to manage peak loads and KVAR amps.

Finally, someone who got the gist of the problem, and it right. P.F. correction is not only performed for the utility company's and utility bill reduction, but also to maintain the efficiency of other motors within the physical plant. Some facilities forget the reason for PF, and the possible advantage of using sync motors (although this is an old method) that provides motive energy while alos correcting PF.

So if a capacitor in parallel with an inductive load does not improve the billing by KWh, can adding a capacitor across a non-sinusoidal load (dimmer) decreace spike current noise on the supply lines? It wouldn't save any money but it could improve the performance of electronics that are susceptible to power line noise.

Yes, but this capacitor is usually incorporated into the trigger circuitry for the Triac, which requires very little extra cost.When you turn the brightness knob, you are varying the duty cycle of the triac, in the case of a dimmer.Trigger voltages are very small, usually less than 1 volt, so very cheap to filter.Most electronic circuitry has built in filtering on the power supplies.The most damage done to electronic parts are done by high-voltage spikes, causing a puncture of the PN junctions(on diodes, transistors) or the capacitors-on-chip (on CMOS devices).These spikes can be arrested somewhat by MOV's of proper rating across the line.The best suppressors have 3 mode protection:

1: line to line(220 vac)

2: line to ground (for each hot wire on 220 vac)

3:line to neutral (+ neutral to ground on 120vac)

I have constructed my own MOV filters on remote instrumentation and have been very successful in providing lightning and surge protection.This required protection at every voltage level into and on-board to be effective.

Also important to have a single grounding point, and bond all ground rods together, that way the current only has one place to go.Multiple grounds create unpredictable fault currents.

A few bucks worth of componets= thousands of dollars of protection.

I seem to have strayed a bit from the original topic, hope I didn't bore you.

Hi,

I ran across this after I typed in Power Factor Correction. Check out Ebay, BobM7694 and go to the ebay store on that seller's site. Power Factor Correction is legal and described. Bob owns one for his home to save on electricity in south Florida. The item described has surge protection as well. Note that we determined size of the power factor correction unit by the number of square feet in the house. Bob is not an electrician or electrical engineer. He owns one for his home along with a tankless water heater for heating hot water inexpensively. Good luck.

RM

Interestingly when I looked on E-bay for the item you listed it had been removed. Could it be that CR-4 taught him the error of his ways or did he just decide to cut and run?

Interestingly enough, these "home" devices are probably based on a patent by NASA that was published many years ago. There was even a construction article in I believe either Popular Electronics or Radio Electronics or whatever it was called at the time. The premise was as was mentioned in an above post that it monitored PF and lowered the voltage when it was high since this occurs when the induction motor is lightly loaded. The problem is there is only one appliance I can think of that would have a variable load presented to the motor and that would be a clothes washing machine. Refrigerators have an induction motor but if designed properly is operating at pretty close to full load whenever it's on. So the opportunity for any significant savings is pretty slim which is why it clearly never caught on. I guarantee you if someone had something that cut your electric bill by some tens of percent people would be crawling over each other to get their hands on it. Sorry, but once again, no free lunch.

Well guys, I should say that this has been a very informative thread, at least for me. I wasn't aware of pfc products for the home that were being sold and, had I not asked this question, I might have bought one of those things!

I'm still a little in the dark about the KVAR thing and how correcting the pf can lower the current and yet not change the power consumption. I'm gonna look for a good text book or find someone to explain it to me in simple terms.

Thanks a lot!

Ok, lets try this: Presume a series circuit consisting of a capacitor, an inductor and a resistor.The circuit is supplied by an a/c supply.Presume also that the capacitive reactance, and the inductive reactance are equal.Since they are equal, they cancel each other out.The only thing determining the current in the circuit is the resistor.

The resistor will receive the full power of the supply if the XL and XC are equal.(There will also be some very high voltages across C and L if XL and XC are high values, and the resistor is low value.This voltage can exceed the supply voltage by many times!)

If either one is greater, the total resistance of the circuit increases.The resistor receives less power.Some of the power is absorbed by the Inductor, or capacitor, as the case may be.The resistor in this case is analogous to the load.

The inductance is the field windings in the motor.The capacitance is the power-factor correction capacitor.The power meter on your home can only measure resistive load.The current circulating in the circuit that is out of phase is not measured, yet the power company had to provide it, the wires had to be sized to carry it, and this current does produce some heat,meaning larger wire, transformers, etc.When power factors are low, it is nescessary for the power companies to recoup this loss , as they do with heavy industry.

As previously stated, the power companies mount remote banks of capacitors to compensate for homes and at key points in their system where power factor is low.

You pay for this correction on every bill, as this cost has to be passed on to the customer.

Hope this helps clear it up a bit, but I don't know your level of electronics training, and I may have made it worse.

Thanks for the explanation hitek.

I'm a radio/tv technician by training (vocational, two-year course) but I only worked in that field for about 4 years. After that, I went into process control and instrumentation and I've been at it for 21 years. I learned on the job but, as what usually happens in these cases, I learned only what's necessary at the time or what got my attention/curiosity. My involvement in electrical stuff was mostly limited to starting/stopping motors. Sizing the motor is not within my range of knowledge but I had to learn how to select wire size.

I know about inductive and capacitive reactance but only with regard to getting the proper values of capacitors and inductors or determining the operating frequencies.

You're explanation made sense except for the series connection because I thought pf capacitors were connected across the load and not in series with it. Putting it in series would indeed lower the current since it's an added resistance.

You did fine with one minor correction. When I and E are out of phase the reactive elements don't dissipate the power that does not go into the resistor. Some power is lost due to inherent resistive components in any real reactive component but with "ideal" components any power gained in one part is returned in another and hence no power is dissipated. Although your example used a series configuration, in PF applications it is parallel. The same idea applies but when Xc=Xl (resonance) in a parallel circuit you have high impedance vs. low for a series circuit.

I understand what you are saying, and agree, but I figured it would be easier to explain in a series circuit without any graphics., very easy to visualize.Did not know the questioner's training level at that point.

Common practice in KVAR capacitor sizing says that once at or above 90 percent PF, there are diminishing returns on going any higher.

Too much KVAR can result in a much higher than designed voltage on the system, and premature component failure.I have seen this happen when a large inductive load was eliminated from a manufacturing plant.The 575 volt 3 phase went up to over 625v, and motors and starters began to fail prematurely.

Turns out the power company had to remove some of their capacitors from their substation(This plant had a dedicated substation, fed by 113Kv, stepped down to 13,200v and the plant bought it at this voltage and did their own stepdown stages as needed.7200,4160, 575, 240,120, ect.).

As always, there can be too much of a good thing.

Oh my God! I've died and gone to heaven! It's me, "Capacitor Bob", and I am so thrilled there are people out there who actually get it. The formula for watts is Volts x Amps x power factor. If I lower the amps by 20%, the PF goes up by 20% and therefore the watts are the same. Every black box scam involves capacitors and convincing the uneducated that Volts x Amps = watts. They will show you with a basic ammeter that the amps went down, on the line side, when you turn the capacitor on and therefore you are saving that percentage reduction in watts. If you don't ... well it must be the utility company scamming youand certainly not their black box.

If you have a power factor of 80%. It means that 80% of the amperage used is doing work (real power) and the other 20% is needed for magnetic fields that are required by inductive devices such as motors and transformers. Household meters only measure real power. As an experiment, and hoping I was wrong, I turned on every fan, pump, and compressor (AC and Fridge) I had in my house and measured 2 KVAR (kilovolt amperes reactive). I added a 2 KVAR capacitor (hey, it's what I do) and turned it on. Believe me, the meter didn't slow down.

If a 1000KW demand industrial customer has a power factor of 80%, the utility company is providing 20% more amperage to the customer and must size their distribution equipment accordingly. It used to be that they just threw capacitors on their lines to supply it, so they gave the customer a break and didn't charge for it. That thought is absolutely horrifying to Capacitor Bob and I'm relieved to say that utility companies are no longer going to give free reactive power.

The moral of the story is... you large commercial and industrials buy your own capacitors, but only if you are billed on apparent power. If you see KVA or power factor somewhere on the bill, you probably need your own capacitors. Just be careful how you apply them as you can create other problems with over voltages and harmonics.

You homeowners stay away from the scammers! You won't save a watt.

Thanks for my thrill of the week. Pray I get a life someday.

Yeah, I'm thinking we all should get out more.

I guess I am over the hill, myself.Heck, my back goes out more than I do.I know I am on the downside now, but I can't remember hitting my peak....

I've read all the way to the bottom and no one has risen to the bait and thrown in about the capacitance of the supply lines or the big inductor supplying the power in the first place. Believe me, the more you go into this PF stuff the more interesting/in depth/scary it gets!

Very interesting... Please feel free to enlighten us. What do you calculate the line capacitance to be? And I am eager to hear more about this "big inductor" that supplies the power. Sounds fascinating. I guess I'm "rising to the bait" but it smells kind of fishy.

Don't forget about the inductance in the transmission lines, then there is the resistance and conductance to ground and don't forget the capacitance between the windings in the generator plus the resistance and inter winding conductance then there is the hysterisis in the cores of the transformers and generators and the eddy currents and the conductor interaction on 3 phase transmission lines and….

If I remember correctly it takes about a year to cover all the topics and that's after you master the mathematics.

Oh my Lord, this thread is still alive!

Dear friend .

actually there is an IEC standard for low power home appliances and lights concerning power factor specifications .In low power systems mostly active power factor correction which is some kind of switch mode power filter is used .Switched capacitor systems are mostly used in factories where active power factor correction is not feasible .

To sense the need for power factor correction , you have to sense the current and voltage and compare them if there is any phase difference then the electronic circuit considers adding capacitors or reducing them to minimize the phase difference between current and voltage .

Best Regards.

Faridani

That has to do with reducing the harmonics. it has nothing to do with trying to save power. It can't. Capacitors do not save power.

Let it die already...

Sorry, I have to disagree about not saving power.The reactive current creates heat in the conductors,even though it is doing no actual "work". as previously stated. Having a high power factor can reduce losses in the conductors, reduce conductor size required, and free up utility capacity for other uses. In a single home, this loss is negligible, but en mass it is huge. Most large industries have 3 meters: KV,KVAR, and Demand, all recorded on cassette at the meter, as well as the standard meter config.Most all industries also have a computer connection to the power company that gives second-by-second analysis of usage in all three areas , and a power management system to adjust peak load and power factor, sometimes using a Synchronous motor for PF corrections.This can function as a variable capacitor to correct PF. By the way, what is your level of training and experience in Power Distribution?You do not seem to have a firm grasp of the facts at hand. Don't go hunting bear unless you are well armed. HTRN