PF correction devices, again

[charlie b]

Good point, Jon. Too often we believe whatever our instruments are telling us, without understanding how they make their measurements, and what their readings actually mean.

 

[PowerQualityDoctor]

Plausibility question:

I know that a residential KWH meter is supposed to measure _power_ consumption. The theory of the meters that the torque applied to the spinning disk is supposed to be proportional to the instantaneous product of voltage and current. However I have never tested this.

Is it possible that an improved power factor will result in a reduction in the meter reading even if the 'true' power consumption remains the same?

-Jon

Electromechanical meters measure kW, not kVA. In older times, utilities used another electromechanical meter that measured kVAr (by shifting the current by 90 degrees). Nowadays, when PF reading is required, utilities use electric meters.

There are some utilities that do measure PF for residential customers, sometimes it is offered as an option (for time of use tariffs).

That is misleading too, the impact these have on the POCO's efficiency is so minor, would take many years to make up the energy used to produce the actual device, not to mention the energy that is consumed by the magic box of capacitors.

The main issue for low PF for utilities is not the efficiency. It is the generation capability (and thus the network security). In addition, as reactive energy cannot be transmitted for longer distances (as active energy can), the risk for blackout is higher (see, for example, the August 2003 blackout investigation).

 

[winnie]

Electromechanical meters measure kW, not kVA. In older times, utilities used another electromechanical meter that measured kVAr (by shifting the current by 90 degrees).

I know that electromechanical meters are _supposed_ to measure real power, not apparent power, and are supposed to integrate to get kWh.

My question is how much error is introduced by 'quadrature' current and non-unity power factor.

-Jon

 

[PowerQualityDoctor]

I know that electromechanical meters are _supposed_ to measure real power, not apparent power, and are supposed to integrate to get kWh.

My question is how much error is introduced by 'quadrature' current and non-unity power factor.

-Jon

Meters are calibrated without harmonics for power factor of 0.50 leading to 0.50 lagging. This means PF should not affect the accuracy but harmonics can. To what level? Normally, they measure mainly the fundamental frequency.

The biggest inaccuracy of meters is due to temperature. They are calibrated at 25 [FONT=&quot]?[/FONT]C/77 [FONT=&quot]?[/FONT]F. When the ambient temperature changes, their inaccuracy changes. Some utilities check this, some base of the standard only. I personally attended a test which showed more than 10% change of accuracy at 40 [FONT=&quot]?[/FONT]C/104 [FONT=&quot]?[/FONT]F.

 

[gar]

100407-1317 EST

A theoretical discussion of an induction watthour meter is given on p586-588 in "Electrical Circuits and Machinery", Vol II, Hehre and Harness, 1942.

There is no integration error. Integration comes from a mechanical gear box. There are errors from friction and the means of calibrating the wattmeter part of the mechanism. This is an analog devices so there will be some linearity and magnitude errors. But fundamentally it does measure power and ignore reactive components of the current.

See
http://www.usbr.gov/power/data/fist/fist3_10/vol3-10.pdf
In particular 6.1 METER ACCURACY for a rough idea of accuracy. At unity PF about +/- 0.3 % of load at certain load levels, and somewhat less accurate at PF = 0.5 .

This was found by using the search words --- accuracy of a spinning disk watthour meter --- in Google.

.

 

[K8MHZ]

You are joking right?

Well, laws to make more work for us have to start somewhere you know, and I need the work.

Some of the stuff I post here is serious and some is all or partly in jest.

You just need to learn how to sort.

:roll:

 

[winnie]

Gar,

Thanks.

My google search for 'electromechanical power meter power factor accuracy' just went the wrong way quickly

-Jon

 

[WinZip]

100407-0745 EST

WinZip:

There is no possible way for the device you mentioned to produce the the electrical energy savings you describe.

With any reasonable knowledge of electrical theory about circuits you would never propagate such grossly inaccurate information and try to sell what is a fraud.

There is no reason to use a KWH meter to do the test. A far quicker and more useful test is with a wattmeter. You connect the wattmeter, then connect and disconnect the so called power saving device and see how much the power changes. Note: essentially a KWH meter performs an integration of the output of a wattmeter. Integration means summation. In an ordinary rotary type watthour meter the counter (dials from a gear train) is the integrator. The rate of rotation of the disk is the wattmeter.

Do you work for some power saver device company?

.

No I do not work for any power saver companies,was just telling you what I did for a friend who bought it off the Internet an he is convinced his savings are because of that PS unit,and as far as what I meant about testing I think you might see something different in readings with a 2 week test or a 1 day test.
Again I seem to have posted something I should not have.

WinZip

 

[StephenSDH]

No I do not work for any power saver companies,was just telling you what I did for a friend who bought it off the Internet an he is convinced his savings are because of that PS unit,and as far as what I meant about testing I think you might see something different in readings with a 2 week test or a 1 day test.
Again I seem to have posted something I should not have.

WinZip

It took me a long time to wrap my head around PF. It doesn't help that there is a lot of miss information out there, even from large scale manufacturers. It is easier for someone to show they work then it is to disprove that they don't. I would recommend reading up on it a little bit. Once you get over the hump of understanding KVAR/KW/KVA/PF everything electrical becomes alot clearer.

 

[LarryFine]

The company I work for sell real energy optimizers which provide measurable kWh reduction . . .

Please tell us more.

 

[zog]

No I do not work for any power saver companies,was just telling you what I did for a friend who bought it off the Internet an he is convinced his savings are because of that PS unit,and as far as what I meant about testing I think you might see something different in readings with a 2 week test or a 1 day test.
Again I seem to have posted something I should not have.

WinZip

If I sell you a gizmo to bolt on your car to promise better gas mileage for $29.95 with a money back gaurentee and the next week you use less gas than the previous week do you think you have a miriacle gadget sold by Zog.com that will solve the worlds oil issues or do you think you may have driven less?

50% chance you drove less than you did the week before, so now zog.com posts your review as proof of gas savings. The other 50% that drove more will use more gas, a few of those will call and complain and demand thier money back but that is OK, I accounted for that when I set the pricing for my scam device that cost me $1 to make but I sell it for $29.95. So maybe I give 10% of the people thier money back and I have 50% of my customers telling thier friends to go buy this thing at zog.com.

Same deal. How can you read the study from NIST that I posted and still think this PF gadget works? It defies all basic electrical principles, but it is sold by some smart shifty guys. Don;t you think your magic box would say GE (Or Eaton, Siemens, ABB) on it if it really worked?

 

[gar]

100407-1513

WinZip:

To evaluate the effect of a power factor correction capacitor it is far better to use a wattmeter than a KWH meter. This I described in a previous post.

Following are some results from using a "Kill-A-Watt" meter. This is a very inexpensive instrument but works quite well within certain limits. Quantized to 1 W. One limit is that it does not work when the voltage is less than 105 to maybe 90 V. I have three of these and they all have different voltage failure points. Also my sample "Kill-A-Watt EZ" performs less well than the standard unit at low load powers, but it is better in voltage range.

These measurements are all at about 123 V.

1. A GE oil filled capacitor 12.5 mfd.
..... 0.58 A, 0 W, 0.01 PF . Calculated reactance is 212 ohms at 60 Hz.
....... This checks with 123/0.58 = 212 .

2. 5000 ohm 5 W resistor calculated dissipation 3.02 W 0.024 A.
..... 0.02 A, 2 W, 0.84 PF ------ I would have expected a higher PF near 1.0..... Although wire wound there should not be enough inductance at 60 Hz to be a problem. I am estimating the inductance is 16 mH or less. This is 6.5 ohms of inductive reactance or less.

3. 15 W tungsten filament incandescent bulb.
.... 0.11 A, 14 W, 1.0 PF

4. 27 W CFL regular type (not designed for dimming).
..... 0.32 A, 27 W, 0.59 PF

5, Same as 4 but added a shunt load using the 12.5 mfd capacitor of experiment 1.
..... 0.74 A, 27 W, 0.30 PF

Note: the CFL has a very peaked current waveform starting at about 60 deg and tapering down to zero at 90 deg.

6. Load is the series combination of 212 ohms resistance and 12.5 mfd.
..... 0.42 A, 37 W, 0.71 PF, 86 V across R and 88 across C.
..... Calculated power from V*I = 86*0.42 = 36 W
..... Because the capacitive reactance equals the resistance at 60 Hz
....... we expect PF to be 0.707 . Good correlations.


Number 1 experiment demonstrates that the instrument does a good job of ignoring the reactive component.

.

 

[WinZip]

ZOG,

I never said I sold them all I said is I Installed one for a friend an he claims it has saved on his electric bill over the last 14 months an he uses his equipment the same as he did before this was Installed.

I will tell him you think he is nuts - point is he still uses all that equipment same as he did before an his bills have reduced quite a bit over the 14 months,other than that I don't know.

 

[LarryFine]

The theory of the meters that the torque applied to the spinning disk is supposed to be proportional to the instantaneous product of voltage and current.

Is it possible that an improved power factor will result in a reduction in the meter reading even if the 'true' power consumption remains the same?

If the motor's moment-to-moment speed (by motor, I mean the meter) is dependent upon instantaneous voltage and current, it seems that improving the power factor would increase the speed of the meter for a given voltage and current. Hmmm.


Added: Maybe that's why the POCO charges more for poor PF.

 

[zog]

ZOG,

I never said I sold them all I said is I Installed one for a friend an he claims it has saved on his electric bill over the last 14 months an he uses his equipment the same as he did before this was Installed.

I will tell him you think he is nuts - point is he still uses all that equipment same as he did before an his bills have reduced quite a bit over the 14 months,other than that I don't know.

See, that is the problem, there is no way to explain the physics to someone with no electrical knowledge (Heck, it is hard to explain to many woth electrical knowledge). All your friend thinks he knows is this magic box made is electrica bill go down, so he is spreading the myth to others. Dang things are like the plauge.

Your firend Winzip, and your customers look to you as the expert beacuse you are (I assume) an electrician and should know how these thing work (Or don't).

Now, you want to buy my gas saver thing? Only $29.95

 

[iwire]

Now, you want to buy my gas saver thing? Only $29.95

Yes as long as you include a Slap Chop


Maybe Vince could make PF correction devices sound fun and cool.

 

[don_resqcapt19]

... The company I work for sell real energy optimizers which provide measurable kWh reduction but we spend so much explaining the results. I wish I could just show some tricks... I have just finished few hours of analysis, got an impressive 15% saving in kWh, sent to the customer, and started to get requests for further explanations... I think the difference is between selling to layman vs. engineers.

I hope that you are not talking about the PowerOptomizer which claims to use "specific wavelengths of infrared light to stabilize the vibration state of "spinning" electrons.
Stabilizing the electrons, which form electric current actually reduces the heat-emitting and power-robbing collisions that normally occur as the electric current moves from the source to the desired load."

 

[zog]

Yes as long as you include a Slap Chop


Maybe Vince could make PF correction devices sound fun and cool.

Didn't he get busted for punching a hooker in the face after he was done with her?

 

[PowerQualityDoctor]

Don_resqcapt19,

I am talking about sinusoidal voltage controller which controls the voltage supplied to loads sinusoidally. Since it does not create any harmonics (and in fact filters significant part of them), it allows providing the most optimal voltage to loads.

We have two solutions:
- for lighting, we provide the lowest voltage level allowed in the spec (normally -10% from nominal). At this point the lux/watt ratio is maximal.
- for electric motor, we change the voltage on partially loaded motors to improve their efficiency and power factor.

Both solutions are field proven with real measurements (at least I think so - I do most of them). I always measure before the unit (so all internal losses are inside the calculation and the harmonic filtration is from the network side) and base the results on kW, PF and THD/TDD. I use the current reading for calculating saving on line losses (which are significant in industrial sites). I wish everyone would do the same - I spend so much efforts explaining the differences. Competitors use current to show saving and our sales people ask how we provide "only" 15-35% saving while competitors provide 25%-60% saving. I wish sales people will be engineers...

You can learn more at http://www.powersines.com.

 

[EcoTroll]

power factor misdirection

power factor misdirection

I think the key here is application. If you stick a cap on a motor, yes, you will reduce line losses. If it is a really big motor it isn't a bad idea. But to mount a bunch of caps at the panel is just stupid. You can't reduce line losses unless you put them at the other end of the line. It's really telling when you look closely at their promotional videos. They tout the drastic amperage reduction, but if you look closely at the meters, you can usually see the kw reading which barely changes if it does at all.

but remember ... avoiding the true is not the same as a lie, as long as you customer is an idiot and you get paid in advance.

note: I'm not lumping voltage controllers, actual line conditioners, and VSD into this observation. Just those ridiculous "Kvar" units.