Just got a call about power factor device?

Seems they think I need one of these.

http://www.kvar.us/about.htm

I told the guy that a typical residence would not benefit from it. Was I right?

From the site:

"...now reduced to a compact unit, to reclaim and recycle electrical energy."

Baloney alert.

1) residential meters only charge for real current, not
reactive current.

2) it's a capacitor. (SWAG)

3) you can buy a bigger capacitor, cheaper then they
sell this thing. (SWAG 2)

Jim

Yes and NO

Its certainly not voo doo like the magic bracelets or the magnet on your cars fuel line.

The old style power meters had some power factor compensation built into them, my old one said 80% on it. The new electronic meters I am told have none of that and in reality was just a rate hike that they didn't have to get approval for. With digital clamp on amp meters put in various places (the service, at the capacitors, and at the load itself) it is plain to see power factor correction works if applied correctly.

My father has been playing around with the concept since back in late winter/early spring and has made some findings. For most folks there are only a few things within a household that would warrant the use of a power factor correction device and that being the furnace and air condition units, and maybe well pump, etc. The more motors the more likely you would benefit from the device. Right now my father only has his home built unit set up to come into play when the furnace/ central air is running and he figures he is saving 10.00 per month.

The bad deal is if the capacitors stay connected to the power they can actually have a detrimental effect on your meter (running it up) as the connected capacitors fool the meter into thinking there is a load. That is why he is using the humidifier enable contact on the furnace to bring his capacitor bank on only when the furnace is running.

I have been collecting parts and maybe this winter will set about building up a capacitor bank. My thought is to use current relays at the panel so that when certain loads are in use the current relay will pick up and bring the right amount of capacitors on line.

tim

Bovine gastrointestinal effluent.
Utilities charge for watts, not amps. Residential customers pay nothing extra for poor power factor performance, only larger 1 phase commercial installations and 3 phase customers pay, and how they pay is a "penalty" for PF below .95 that ends up as a multiplier on their basic bill. The utilities must install a kVAR meter in order to even know what the PF is for them, a regular kWH meter will not see the difference. So you were right, for a residential customer in the USA, you will see no perceptible benefit.

You were right that a person in a normal household would not benefit, but there is good reason to correct power factor in certain domestic situations and the best place is close to the source of the reactance, near the meter will do nothing to improve the power bill or cabling costs.

Some reasons are.

Running lots of fluorescent lights, on a 240V system the average 40W light has a PF of about 0.45. I have 2000W of them running off a 10A circuit which I had to power factor correct to 0.9, the correction is done in the fittings. No point doing it elsewhere as the wiring still sees the reactive current.

Running heavy welders, mine are partially power factor corrected to reduce the circuit load which would be 40 amps at 415V, capacitors in the welder knock 12 A off that.

I once did a test and put a 20A purely reactive load on the end of a 100ft run of 4mm sq cable just to see what transmission line loss I had, 300W was what the meter said.

Correcting power factor on long cable runs will save power provided the correction device is near the source of reactance and is turned off when the reactance is turned off, left in line it will waste power just like a highly reactive load will.

Usually the power lost though reactive current is only a tiny fraction of total power draw, for Utilities because they have long cable runs the reactive power is a significant loss and that is why they charge commercial users for reactive power.

I doubt the device mentioned would be of any use and the main reason that I power factor corrected some of my equipment was that the capacitors were free.

jim rozen said:

From the site:

"...now reduced to a compact unit, to reclaim and recycle electrical energy."

Baloney alert.

1) residential meters only charge for real current, not
reactive current.



Jim

Click to expand...

Wattmeter readings are not indications of current drawn but simply the watts
dissipated.

Last time I checked there was a fairly straightforward
relationship between the two.

I tend to tell folks that watthour meters only measure
real current, and ignore reactive current, because there's
a subset of folks who tend to go MEGO when you start
discussing real vs. imaginary power.

Jim

You could have a load that is highly reactive yet the wattmeter is very low.
The load current could exceed the rated value but your watt meter will not
indicate the situation. In theory if the load were purely reactive the wattmeter
reading could be zero but your device would be burning up due to the high
current drawn.

Another issue is power factor correction. It is only useful when the load is
operating at one point. If you are say operating a welding machine and the
unit is idling most of the time then power factor correction is not worth it and
you end up paying more for electricity.

Since we are talking about such things, the power company recently installed a kvar meter at my carwash. I cannot understand what is going on anymore. It used to be that they read the meter and obtained the kwh and demand, then computed the bill. I pretty much got that ok. Now, here is a copy of my latest bill:


Can any of you gents explain to me what is going on.

About 10 days before this bill came out, I read the meter myself. It gives 3 numbers or readings. Here were my readings:
#1 3521 kwh
#2 9.07 kw
#3 4.54 kvar

Now, I get that the 3521 kwh is my total use, to date. The bill has them estimating my total @4,032, which is probably a little low (I haven't read the meter lately). The bill states my load is "7.0", where they are getting that is beyond me. It is not a reading that is available to me, unless it is somehow calculated from the 3 numbers displayed. It may also be that the #2 reading of 9.07 is the load, what say you.

I hear you talk about PF in relation to kvar, but is there any indication of what my PF is, based on these meter readings or billing information?

sounds like a call to the power company is in order.

without knowing how you power company calculates these things I have no idea, ask them.

#2 9.07 kw
#3 4.54 kvar

Click to expand...

These 2 readings are instantaneous readings. the power factor at the time these readings were taken was 9.07(9.07 + 4.54) = 0.66. That is poor, 0.8 or 0.9 is a good number to aim for, capacitors are cheap putting 3 kvar leading (capacitors) on the offending appliances is a cheap fix. I would suspect discharge lighting is the cause. Motors usually run at 0.8 pf 0.9 if they are large. elements are around unity pf.

The key may be in your "peak demand", and worst power factor.

if your peak demand over a short time (often 15 or 30 minutes) is considerably larger than your average, you may get billed for more power than you use.


I know this is the case, as I have seen the billing differences, but have not had to deal with the details of the bills vs loads etc, so I can't comment on your numbers directly.

You may be socked for some period AFTER you stop drawing long peak demands or poor power factor......

it's possible that if you know your billing rate details, you can install some sort of timer etc which can evade the peak demand billing. But your need for hot water etc on demand may trump that sort of activity.

Poor power factor can be dealt with by capacitors, or VFDs with PFC front ends.