Home PF Correctin

[ATSman]

I went to a local energy conservation fair last Saturday, and there was a guy there selling a power conditioning box for homeowners. It was basically a box of capacitors that maximizes power factor, compensating for the low power factor of electric motors. He claimed that this would reduce utility bills. I said he was wrong, because the home owner isn't charged by the power company for low power factor. Industry is, because the peak currents are large and the line resistance loss in the grid is significant. But the homeowner only pays for the part of the current that's in phase with the voltage. He insisted, claiming that he timed the rpm of his meter rotor and found that the meter turns slower when his bix is connected. I said maybe something in the house switched off when his box was attached. What do you guys think? Scam or not? :-?

 

[bsh]

it is a scam

 

[mikeames]

Already discussed several times. consensus is SCAM/ snake oil...etc...

 

[charlie b]

Scam, big time, and for the exact reason you named. Do a word search on this forum, and you will see several similar discussions.

I would tend to reply, to the saleman's description of his own experiment, that if he can connect a device to a residential service, and if that device can, with all else remaining the same, cause the meter to turn noticeably more slowly, then that device probably contains some component that is illegally altering the way the meter operates.

 

[Besoeker]

I agree. It's a scam.

 

[weressl]

I went to a local energy conservation fair last Saturday, and there was a guy there selling a power conditioning box for homeowners. It was basically a box of capacitors that maximizes power factor, compensating for the low power factor of electric motors. He claimed that this would reduce utility bills. I said he was wrong, because the home owner isn't charged by the power company for low power factor. Industry is, because the peak currents are large and the line resistance loss in the grid is significant. But the homeowner only pays for the part of the current that's in phase with the voltage. He insisted, claiming that he timed the rpm of his meter rotor and found that the meter turns slower when his bix is connected. I said maybe something in the house switched off when his box was attached. What do you guys think? Scam or not? :-?

I have a bridge for sale. I picked it up at a similar 'home improvement seminar' where I picked up my device for my home electricity bill saving. It works great, but the POCO must be raising their prices. The bridge has a sign 'Brooklyn' on it if this helps..........

 

[Dennis Alwon]

Read what Mr. Electricity has to say- click here

Here is some of his comments

Here's why I don't think this saves any appreciable amount of electricity:

• A utility company employee writes:
  
  I work for a utility in Ontario and we have tested these devices in our shop, and these devices are a scam for residential billed customers. They do correct the power factor but since residential customers are only billed on kw.h they do nothing to reduce a customer bill. That is loads use watts, and residential customers are billed on watts, so it doesn't matter what the PF is. Our tests not only proved this but that these devices actually use a small amount energy, which ironically drives the customer bill up.
  PF only comes into play with larger commercial customers who are billed on Peak Demand. The theory is that customers use Watts and the utiltiy supplies VA, so for the same load (watts), the lower the PF the more the utility must supply in VA. To combat this the utility bills is the higher of Watts or 90%*VA, thus the customer is charged more for a low (bad) PF, thus they can reduce their demand charge by raising (or fixing) their PF. PF is lowered by inductive loads, thus adding capacitance raises it. These little expensive devices are just capacitors.
  I read the white papers on these devices, and they did not report anything that was untrue, but the advertising is very misleading. Some of the technical people at our work were fooled, until it was explained and our results revealed.
  Only for motors and transformers. The reduction isn't for every device in your home, only things with motors, transformers, and fluorescents which need reactive power.
• Modern appliances have power-correction built in. Ancient appliances were wasteful, but modern appliances (like fridges) already have this same kind of power-correction technology built-in. For those devices, there are no more savings to be had.
• People from two different utility companies wrote in to tell me that these devices don't work for home users. The person from Ameren in Illinois says, "Our residential meters don't measure reactive power. You can't save money by plugging in a reactive power correction device." And Greg from Canada writes, "I work for a utility in Ontario and we have tested these devices in our shop, and these devices are a scam for residential billed customers. They do correct the power factor but since residential customers are only billed on kw.h they do nothing to reduce a customer bill." See his more complete comments at right.
• I've never measured any savings when testing an actual unit. No manufacturer has ever sent me a unit to test (could it be they know the product would fail?), and the ones I purchased myself or which were sent to me by readers failed to save any energy.

 

[ATSman]

Read what Mr. Electricity has to say- click here

Here is some of his comments

Thanks guys and sorry for the repeat, I will search next time.
Dennis, thanks for the link!

 

[celtic]

He insisted, claiming that he timed the rpm of his meter rotor and found that the meter turns slower when his bix is connected.

I'm sold.

BTW, just how long did he stand there counting the revolutions of meter?

 

[broadgage]

Similar scams have been tried here in the UK.
Residential customers here are billed for KWH just as in the USA and no financial saving is possible by improving the power factor.

Large industrial users who pay a maximum demand charge based on peak KVA, not peak KW may achieve a saving, though large installations are often equiped with power factor correction already.

 

[Ass't Lord-High Commish]

Ignorant?

Ignorant?

OK...I'm going out on a limb here! Was I asleep in apprenticeship, or is there actually a loss of power delivered when PF goes out of synch? If true, then correction would improve power delivered thereby reducing total consumption...right? The guy who brought up the fact that modern motor-driven appliances contain PF correction from the factory reveals the validity of that concept (even though he goes on to argue against the validity of the correction devices?)! So, help me out here! Rather than re-stating the 'scam' claim; provide an intelligent explanation. If you feel that the residential meter doesn't see PF, explain why...and then how the 'commercial' industry metering differs to include that. Let's be thorough and scientific! Thanks

 

[LarryFine]

Okay, Commissioner, try this uneducated explanation:

Watt-hour meters do not read the reactive power component. A meter is basically an electric motor whose speed depends on voltage and current. When the voltage and current peak at different times, less than the full voltage times the full current is measured.

The meter does not compensate the POCO for the poor PF, and it does not compensate the end user for the improvement in PF. In other words, the meter will never read less for a given power usage with an improved PF.

Plus, people forget that capacitors have to be charges between discharges. The boxes get warm, which is a waste of power. Commercial metering provides surcharges for poor PF, and there, the improvements do save money.

Added: Besides, PF improvement is not a one-size-fits-all kind of thing. The amount of correction needed must be determined. You don't want to over-compensate for when reactive loads are turned off.

 

[charlie b]

So, help me out here . . . provide an intelligent explanation.

I?ll give it a try. To start with, power factor does not ?go out of sync.? It is what it is. There is ?real power,? and there is ?reactive power,? and the two add up (in a trigonometric sort of way) to give you ?apparent power.? The thing that causes ?reactive power? to come into the picture is anything that involves magnetic fields, such as the windings of motors, ballasts of fluorescent lights, and welding machines.

I don?t really like the ?beer and foam? analogy for power factor. But here it is anyway. Real power is like the liquid that fills most of a glass of beer. Reactive power is like the foam at the top of the glass. What you really want is the liquid, but the foam is there and you can?t avoid it being there and it doesn?t change the amount of liquid at the bottom. Suppose you start with a glass with some amount of liquid, and a little foam at the top. In order to contain both, the glass has to be a bit larger than necessary for the liquid alone. Suppose you can generate some extra foam, and suppose you pour it into the glass. You haven?t changed the amount of liquid, but you need a bigger glass to contain it all.

Now back to electrical stuff, and a bit of trigonometry. Take a sheet of paper, and draw a horizontal line about one inch long. Label the left hand end of the line as point ?1? and the right hand end as point ?2.? From point 2, draw a vertical line upwards one inch. Label the top of that line as point ?3.? Finally connect points 1 and 3 to form a triangle. Line 1-2 represents the real power, and it is a measure of the ?real work? being done by the load equipment. Line 2-3 represents reactive power, and is a measure of the energy being exchanged (you might even say ?wasted?) between the magnetic field of the utility generator and the magnetic field of the customer?s motors and other inductive loads. Line 1-3 represents apparent power, and is a measure of the power that the utility has to provide, in order for the customer to run the motors.

Power factor is a measure of the angle located at point 1. In terms of trigonometry, PF is defined as the cosine of that angle. If that angle is zero degrees (which happens if line 1-3 has no length at all, so that line 1-2 and line 1-3 lie one on top of the other), then PF is unity. If that angle is large (which happens if line 1-3 is long), the PF is considered ?poor.?

What would happen to that triangle, if you drew the vertical line as 2 inches long, instead of 1 inch? The real work, line 1-2, does not change. But the apparent power provided by the utility (line 1-3) is now much longer. Thus, in order to allow the customer?s motors to do the same amount of work, the utility has to provide more power.

What would happen to that triangle, if you drew the vertical line as 1/2 inche long, instead of 1 inch? Here again, the real work, line 1-2, does not change. But the apparent power provided by the utility (line 1-3) is now much shorter. Thus, in order to allow the customer?s motors to do the same amount of work, the utility has to provide less power. You can see why the utility does not like the customer to have a lot of reactive power in their loads. You can see why the utility will charge some customers (large industrial plants, for example) a penalty for having a poor power factor.

What a power factor correction device does is to reduce the length of line 2-3. It does that by adding a reactive power load of a type that is opposite to that in the customer?s loads. Usually, a customer?s loads are motors and other inductive loads. To that, you add a capacitive load. What that does to the triangle is like starting at point 3, and drawing a line downwards towards (but not as far as) line 2. Call the end of this new line point ?4.? Here?s what you get: Line 2-3 is the customer?s inductive loads. Line 3-4 is the power factor correction capacitors. Line 2-4 is the new value of total reactive power. Line 1-4 (I didn?t tell you to draw that yet, did I?) is the new value of total apparent power. You will note that line 1-4 is shorter than line 1-3. So the amount of power supplied by the utility has gone down.

What is physically happening in the power factor correction device is that, where you used to have an exchange of energy between the between the magnetic field of the utility generator and the magnetic field of the customer?s motors and other inductive loads, you now have an exchange of energy between the magnetic field of the customer?s motors and the electric field of the power factor correction capacitors. The utility company meter does not record that energy exchange, because it takes place entirely within the customer?s facility.

 

[wasasparky]

If you feel that the residential meter doesn't see PF, explain why...and then how the 'commercial' industry metering differs to include that.

First of all, the utility has watt-meters not power-meters.
By definition they do not factor in power factor.
That is why large energy users get penalized for bad pf...

 

[wasasparky]

I...claiming that he timed the rpm of his meter rotor and found that the meter turns slower when his bix is connected...

I've seen them. I've always wondered if the watt-meters were maybe wired incorrectly, and act more like an ammeter. (or a VA meter)

Bad power factor will increase the amount of current drawn, since V and A are now out of phase...

 

[Besoeker]

First of all, the utility has watt-meters not power-meters.

A Watt is a unit of power.

 

[wasasparky]

Yes, but there is true power, and apparent power.
It's important to know the difference...

 

[Besoeker]

The guy who brought up the fact that modern motor-driven appliances contain PF correction from the factory reveals the validity of that concept

Valid it is.
The capacity of your supply is limited by its current carring capability.
Improve the PF and you need less current for the same power. Or you can get more power for the same current.
But it makes little difference to the power and thus energy consumption which is power times time, of course - kWh.
Domestic consumers pay for kWh.

 

[Besoeker]

Yes, but there is true power, and apparent power.
It's important to know the difference...

A Watt meter would show true power.

 

[LarryFine]

Line 1-2 represents the real power, and it is a measure of the ?real work? being done by the load equipment. Line 2-3 represents reactive power, and is a measure of the energy being exchanged (you might even say ?wasted?) between the magnetic field of the utility generator and the magnetic field of the customer?s motors and other inductive loads. Line 1-3 represents apparent power, and is a measure of the power that the utility has to provide, in order for the customer to run the motors.

And, unless I'm mistaken, watt-hour meters only respond to the Line 1-2 power. The POCO has to go out of their way to measure the Line 2-3 power, which they can use to calculate the Line 1-3 value.