Didn't we look at this before?

http://www.power-save1200.com/1200?gclid=CMKs8NvjzJICFQGCxwod33IFbg

A local resident had on installed and said his monthly electric bill is about $10.00 lower.

I am trying to convince him that it can't be true.

Thanks for the input.

John

IF it is actually lower (and thst is a ginormous IF) it is likely to be because he is conscious of his usage and is being more conservative.

Have him dig out his bills for several years and compare the KWH of comparable periods.

Thanks Bryan.

That is exactly what I told him. 3 months of data at this time of year is useless. A comparison to last year at the same time of year is an absolute minimum.

It is power factor correction and it might save a little money if you have the right kind of loads but 10% is a lot.

I have a wattmeter on my house. My understanding is that I wouldn't save anything with power factor correction.

My guess is power correction too possiblty caps. Residences are "poor" when it comes to power factor. Friges, freezers, air conditioners, any motor loads like hand held appliances have "poor" PF. I would imagine that is one of the reasons why residential kW rates are higher. Large commercial users pay for the PF issues.

Back in the 1950s there seemed to be a lot of interest in secondary capacitors for residential services. For example, Sangamo offered the "Secovar" line of 240V 2KVAR caps for installation at the meter location. They came in three versions: a separate box which connected to the meter box by a nipple, a box with male and female meter jaws on opposite sides which was inserted between the meter and the meter box, and a meter box with the caps inside.

Several companies also produced pole-mounted secondary caps.

The way I understood the article when the "green plug" was being tested is a lightly loaded motor is very inefficient but a properly sized motor in something like a fridge or HVAC runs at very close to unity and these things are a waste of money for that. You notice when they do demonstrate these things they like to use a fractional HP motor with no load at all.

Except that these are only a very small %, and mostly intermittant- you're not going to save any money pf correcting a garbage disposal or garage door opener for the few seconds a day they're running. The vast majority is simply resistive or of a nonlinear sort that wouldn't be helped by a pf cap- lighting, water heater, stove, clothes dryer, electronics, etc. The only load that would really be helped by this is the AC compressor. And with natural seasonal variations, you're never going to be able to prove anything without a GIANT study.

Residential pf is typically .92-.96. Here's a small poco study actually looking at the effectiveness of residential power factor correction caps:
http://www.kvarhydrosave.com/sites/kvar/gfx/Residential_Power_Factor_Porrection_Project_2005.pdf

Redsy: did you point out to your friend that electic bills are all an estimate based on past useage, and that his "$10 savings" is actually reflecting the month's usage BEFORE he got the pf correction, and more likely just because the weather is more temperate right now than any of the snake oil he wasted his money on?

ARGH, bitten by the short edit window again! I wanted to point out that residential meters are measuring kW not kVA. If the pf was .2 and 5kVAh/kWh or 1.0 with 1kVAh/kWh, it wouldn't matter, you'd pay the same per kWh regardless.
Looking more closely, this was a very poor study. They only ran it for 2 months, and didn't have a control. Ironically, it looks like the pf correction caps actually made the pf worse, because while it would correct a poor pf while the motors were running, it would overcorrect and increase current while the motors were not.

Their conclusion was that the poco may recoup savings on the pf cap due to reduced overall transformer, generator and line current loading, but an individual HO would not see any cost savings.

Agreed. I guess my post was not clear enough. A residence is full with equipment that have potential pf issues. Anything with a motor, ballast, or transformer is a candidate. It all comes down to how often you use them. For example in my hose right now, I have a flourescent light on (ballast) the frige is cycling and my lap top is running off it power unit (transformer). All my electronis have a little transformer in them and a couple of motors. Seperatly they do not amount to much. Combined, they could add up. In hot areas, you have fans and AC running all day. Colder areas you have blowers and fuel pumps running. It is dependent on on what you got and how often you use it.

I personally find it hard to believe that a 10% savings is possible on a residence unless you have a mansion or you are just running a bunch of electrical equipment all the time. If residential pf correction was cost effective or profitable, the POCO's would be all over it.

IIRC, a residential kilowatthour meter measures only real power consumption, and ignores reactive power (the inductive or capacitive current draw). So a homeowner won't see any difference on the electric bill. The POCOs just figure that residences have about the same power factor, and it's just figured into the rates they charge.

Yep, exactly.

So NONE of these devices are going to save the homeowner one single cent!

Interestingly, the units nameplate says "7-amps" @ 240-volts".
I put a meter on the main and the current dropped 6 amps when the unit was turned off.
The branch breaker feeding the unit did the same thing.
My question is...

Is this thing actually consuming 1440 watts, or am I measuring 6 amps of capacitive current from the unit charging and discharging back into the line?
If so, what is the net consumption of the unit, if anything at all?

Thanks,

John

You'd know it if that was consuming 1440 watts, it'd be making a lot of heat. Burning up, almost. It's just charging and discharging back to the line, as you said in the 2nd half of your question.

POCOs don't like it when you draw current without consuming real power, it means that they have to have heavier wire and transformers without selling more energy.

Industrial users sometimes have, as part of the metering, a measurement of reactive power, as well as real power. That reactive power is usually inductive (motors and florescent light ballasts) and adding capacitors to that reduces that reactive power seen by the POCO's reactive power measurement. That's where money would be saved. Most homeowners don't have reactive power measured by the POCO, so they would not save any money with this thing. The POCO won't mind someone volunteering to reduce their reactive loading; they just won't know who is doing that (and how much) to be able to offer any money savings.

On a different aspect of the topic: looking at the cap banks on aerial distribution primary lines, I'm surprised by how many have one or two of the three cutouts open, and have been in that state for quite a while.

Since not all of the cutouts are open, I'm assuming the openings are due to fuses blowing rather than intentional switching operations (i.e. I don't *think* cap switching is done on a phase-by-phase basis). This would imply that keeping the caps operational is a relatively low priority.

The 1950s seemed to be the heyday of automated primary capacitor switching, with controllers activated by time, temperature, voltage, current, remote signals, alignment of the planets, etc. in any imaginable combination. That's probably still true for substation caps, but out on the lines around here, all I see is manual switching.