Power factor Correction

[2rlp]

Hi,

Is it possible to use Power Factor Correction in a residence having a 230 V single phase supply. Will power factor correction reduce the usage of power (in short will the amount in the bills be reduced). How does one do this power factor correction.

Ron

 

[kamenges]

Unless you are currently paying a premium rate due to poor power factor (which is unlikely), power factor correction will not help you. Most residential power metering equipment only records real power anyway. This is one of the reasons that utilities get so upset about bad power factor. The infrastructure needs to support the total power but the utility only bills on real power.

Power factor correction will not change the amount of real power you use in your home so it won't directly effect your bill.

Keith

 

[Tom Jenkins]

You can correct power factor on single phase residential service.

It probably isn't worth doing.

Look at your energy bill. Unless there is a line item that identifies power factor penalty you aren't being penalized for poor power factor. In fact, since residetial loads have a lot of incandescant lighting, which is generally resistive, your power factor is probably pretty good anyway.

Power factor penalties are usually for large industrial users with a lot of motor loads and high usage. The penalty is usually for total plant power factor less than 85% and is applied as a multiplier to peak demand charges. Residential billing is usually a constant $/kWh for total use only, and time of day, peak demand, and power factor don't usually apply.

 

[Lancie1]

Tom,

Perhaps in the midwest, lighting is a significant factor. Here in the humid South, air conditioning motors are a large percentage of the load for 9 months of the year. Besides I have no incandescent lights in my house anyway.

It is interesting to see how the power factor penalty level has gradually crept up over the years from 0.6 years ago to 0.85 now in most places.

 

[g.robert]

Going off memory here but you correct a bad power factor by adding KVAR. Power factor is the difference between real power (KW) and apparent power (KVA) or KW / KVA. You would like the value to be unity (1) or as close as possible. The lower the percentage of PF (<90-95%) the bigger problem you have. This "problem" is caused by inductive loads. They cause you to use more power than you really need for the load. If you know your KVA and KW, you can solve for KVAR which is the sq rt of the KVA sqd - KW sqd. There's more to it like leading / lagging power factor, figuring the existing capacitance, ETC.

The whole thing is further compounded by the fact that most inductive loads are intermitent.Power factor correction capacitors can create havoc in establishments that have ASD / VFD (not likely in a home). Power factor correction is a specialty all in itself and not to be treated lightly.



I've heard it argued that if you want to save money on your light bill, oversize all wires. Sounds odd and I would not do it but P= I(2) X R so the lower the R the lower the P. Sorry I got off topic.

 

[allscott]

Sorry for the hijack but does anyone have any idea what % of utilities in North America (or the U.S) actually require a certain power factor level.

I am looking at installing PFC equipment in our plant (our pf is about .65) Ours utility doesn't require a minumum pf and the demand charge isn't bad so the payback for this project isn't quite what the company is looking for.

I'm just curious to know how many utilities require it and if there is a trend that might make it a requirement here.

 

[jraef]

The OP is in Mumbai, India. I have heard that they do in fact charge residential customers for poor power factor, so a capacitor based system may work but as others have said, only for induction loads, i.e. motors. Fluorescent lighting often presents a poor pf, but that is usually a distorion pf, not a displacement pf, so correction is a lot more complicated and can run in to ressonance issues.

For allscott;
No idea on the percentages, but there are a significant number of utilities who do not charge pf penalties in all service areas. It really depends on that issue though. If you are in a service area where there already is a poor pf, they may enforce penalties to keep you from making it worse, even if they don't bother in other service areas. PG&E, the bigest utility here in California, is like that. Most of us do not have penalties for poor pf, so the PFC capacitor sales reps are always hungry. But that is not universal; some PG&E customers do get hit with it.

 

[2rlp]

Thanks guys for all the replies. Someone is marketting a product which claims to reduce the amount in your bills by about 15 - 20%. One has to install this unit at the incomming point of the supply.

Now I think that there can only be 2 ways of reducing the bill amount.
1) By reducing the incomming voltage, by means of a Thyristor switch. But this is not being done as the unit is universal & caters for any load current.
2) By correcting pf.

May be I am wrong. If there exists any other way, pl let me know.

Bottom line is that there exists no proof of any saving, as results are known on monthly basis and the load usage also varies depending on areas & the month.

Thanks

 

[brucechase]

Thanks guys for all the replies. Someone is marketting a product which claims to reduce the amount in your bills by about 15 - 20%. One has to install this unit at the incomming point of the supply.



Bottom line is that there exists no proof of any saving, as results are known on monthly basis and the load usage also varies depending on areas & the month.

The only thing that I know that will definately reduce your power bills by 20% is an OFF switch. Turn if off 20% of the time and your bill is automatically reduced by 20%.

Just think, if it really were this easy, electric companies would require these on all installations, global warming would turn into global cooling, nuclear reactors would be shutdown, there would be no need for "green" incentives by the utilities, and dogs and cats would be sleeping together (oops, too far).

By the way, our utility SCE&G does have a substantial penalty if our powerfactor falls below .75. Lots of motors (all oversized by the MEs and running less than full load) is the primary cause.

 

[Mark Buskell]

Thanks guys for all the replies. Someone is marketting a product which claims to reduce the amount in your bills by about 15 - 20%. One has to install this unit at the incomming point of the supply.
I have heard of this scam here a few years back. The device is completely worthless. The only one making money on this is the con artist.

 

[rdrast]

Not the thing from This Thread...?

Thanks guys for all the replies. Someone is marketting a product which claims to reduce the amount in your bills by about 15 - 20%. One has to install this unit at the incomming point of the supply.
I have heard of this scam here a few years back. The device is completely worthless. The only one making money on this is the con artist.

 

[Tom Jenkins]

Sorry for the hijack but does anyone have any idea what % of utilities in North America (or the U.S) actually require a certain power factor level.

Virtually all utilities charge for power factor, but most only do it on large users.

Residential charges are usually for kWh only at constant rate $/kWh

Small industrial users pay time of day charges, at a high rate $/kWH for on peak (daytime weekdays) and a low rate for off peak (night and weekends)

Large industrial users pay time of day plus demand charges, where they add a cost $/kW for the highest peak power used during a month averaged over a 15 minute period.

Even larger industrial useres pay time of day plus demand plus power factor penalty which is usually a multipllier on demand charges for power factor lower than their target, usually 85%.

Remember if the power company is going to bill you, they need to meter the various factors. It isn't usually worth the higher meter cost to keep track of time of day and demand and power factor on small users.

Look at your power bill and find out what you are paying for before you start spending any money on energy reduction programs. Call your electric utlity - they usually have a staff of engineers on hand that will come to your place at no charge and do an energy survey and make recommendations on savings programs. They don't do this because they are nice guys - they want to avoid building more peaking generator plants, and many states legally mandate them to provide this service.

 

[leitmotif]

I was on Seattle City Light citizen rate advisory committee. Basically we came up with a customer recommendation when City Light needed to change rates. Residential customers were 60% of customers and drew only 20 or 30% of the total load - don't quote me on this it is off top of my head.
City Light ran up a comparison of comparable utilities in NW who charged for pf. All utllities charged for it but only for larger loads ie large commercial to heavy industrial. NEVER to households. Interestingly City Light reserved the right to refuse service if PF was less than .75.

Industry installs power factor correction when they get in the megawatt range more likely is 1000 megawatt. That is off the top of my head also.

As mentioned previous several times residential is mainly resistive load. Even with the compact fluorescent and other fluorescent lighting being used in homes more frequently there is probably not enough impact on residential power factor from them when you compare to large resisors ie hot water tank, stove, dryer, electric heat. Price (utility cost) of a home meter is around 25, price for a power factor meter is around 200.

You will save a little electricity if you do power factor correction however the reactive load is so small in homes it is not worth your time or to put it another way
if it is not worth it to the utility to meter it
then why waste your time??


Dan Bentler

 

[milldrone]

Interestingly City Light reserved the right to refuse service if PF was less than .75.

Dan,

It would be interesting to know if they ever used this feature, and the real reason they were using their option.

 

[leitmotif]

Dan,

It would be interesting to know if they ever used this feature, and the real reason they were using their option.

I don't remember if they ever used the option. I suppose they used it to club someone into installing PF correction, however from what I saw (industry concerns and efforts) the money charged on PF correction alone was enough incentive for them to install correction.

I know the steel mill here in town gets a HUGE discount if they run the furnace after 1 am. Any other time of day they get "beat to death" on the dollars.

Also Boeing has to call City Light before starting the wind tunnel (13,000 HP) so City Light can switch in capacitors.

City Light is a city owned utility
the advantage for them is they have no oversight from the state utilities.
DOWNSIDE they deal with a lot of politics ie irritated customer can call mayor or City Council who then run City Light thru the political wringer and in some cases screw up good engineering or utility practice.

Dan Bentler