KWH Meter

[jwilson3]

A local company has approached my client with an offer to install a "device" that increases power factor to reduce KWH consumption thereby reducing utility cost. They claim that PF improvement lowers current, which is true, but that it also lowers KWH usage by the same percentage which is not true. They assert that the utlity meter, which they claim was verified by GE, "computes" KWH based on volts X amps, while in fact it's based on volts X amps X PF.

I haven't been able to explain the details of the workings of the meter to adequately convince my client, so if anyone can suggest a resource I can used to support my position, I'd appreciate it.

 

[wfowfo]

Here's another forum where you might try for an answer.

http://www.themeterguy.com/

Click on the "Tailboard" section at the top of the page.

 

[jwilson3]

Thanks, I've done that also. I'm on both forums to get all the experts involved.

 

[waross]

When power factor penalties are assessed the scale is invariably so onerous that the payback on correction is a very short time.
As you know, the money to be saved is on power factor penalties, not consumption. If there are no power factor penalties there are no savings to be had. In fact, with reduced currents, you will have reduced line loss and the possibility of slightly higher KWHrs due to higher voltage exists. The actual amount would probably be negligible.
I suggest that you advise your client to ask for guarranties and to negotiate a payment plan where payments for the work done are made out of real savings.
respectfully

 

[jghrist]

I'd have your client call the electric utility. Their word should be convincing.

 

[jraef]

Here is another good resource, from Mark Empson (Marke) a member of this forum as well. He doesn't specifically state what you want to hear, but he does provide decent examples that lead to that conclusion.

http://www.lmphotonics.com/pwrfact.htm

Marke runs another forum associated with that website, and in there he has addressed this issue. It comes up a lot, but here is where he makes the specific statement to your point.

http://www.lmpforum.com/inforum/index.php?showtopic=856

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[stevenal]

kWh meters look at the instantaneous values of current and voltage to accumulate energy usage. There is no power factor in this measurement. Pf is a convenience for using rms values rather than instantaneous. If the meter reports pf, it is a derived rather than a measured quantity. For a reference, see the Westinghouse Distribution Systems Reference Book, Chapter 11.

In a way they are right, pf is not used directly. But since capacitors not only lower the instantaneous peak current value, but also shift the whole current waveform in time; then the measured energy should be similar both with and without pf correction. The only difference will be in losses.

Utilities will usually charge industrial customers for energy use plus demand charges and pf penalties. First thing is to see how a particular customer is being charged.