KWH Meter Myth?

Discussion in 'General Electronics Chat' started by CDRIVE, Feb 16, 2012.

  1. CDRIVE

    Thread Starter Senior Member

    Jul 1, 2008
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    Gentlemen, I moderate quite a few lathe and machine shop groups. One of the discussions that pop up regularly is power distribution to these machines. Besides the inherent benefits of lower voltage drop when configuring a dual voltage motor (120V/240V) to 240V and load balancing the two 120V lines to minimize voltage drop on any single conductor, there's a dubious claim that keeps popping up in these discussions that has little to due with these issues. If it weren't for 'Myth Busters' errant cannon ball it would have made a good episode.

    Anyway here is the claim:

    There are those that believe that the power companies are ripping off the customer via inaccurate measurement of your KWH use. The claim further states that if the load on the meter (itself) is not ballanced the meter will lie. As usual with these claims, the error always benefits the power utility.

    We have great minds here at AAC and we also have dirt green novices. Please leave this discussion to the knowledgeable. Merely posting something like "It's true" won't cut it. Any intelligent discussion about this (pro or con) must include solid knowledge of the KWH meter's workings and why current draw off one leg would manifest this. From the little that I've read it follows some of the same principals of a common 'Electrodynamometer' better known as a 'Wattmeter' that measures true power regardless of reactive loads.

    PLEASE, NO CONSPIRACY BABBLERS!
     
  2. GetDeviceInfo

    Senior Member

    Jun 7, 2009
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    single phase 3 wire meters sum the current from both phases. If say 1 amp was flowing in L1, but not L2, it would have a 'torque' value of say '1'. If that current was flowing in both L1 and L2, it would be summed for a 'torque' value of '2'. The question then becomes of the accussers, what magical combination of numbers can't be summed? Voltage is measured across the supply at full voltage, so I can see the question of phasing being raised. If I draw a single phase motor on one leg (120 v) but a resistive heater on the other, is my meter being fooled. The question can be restated as, can a single source produce multiple phase angles.
     
  3. Wendy

    Moderator

    Mar 24, 2008
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    I'll freely admit I can't discuss the issue intelligently.

    However, if it could be proved, or even questioned, the class action lawsuit would be unbelievable. To me the real risk is similar to the gas pump, calibration. That one would be hard to prove. That is why there are independent state inspector checking that 10 gallons is really 10 gallons. I don't think the equivalent exists on the electric company level. There may be a business opportunity there perhaps.
     
  4. Lundwall_Paul

    Member

    Oct 18, 2011
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    As far as power companies ripping consumers off I strongly doubt it. But on that note I am not 100% sure but I would think the meters would have to be checked of by the National Bureau of Standards. If this was any other business or manufacture the meters would require periodic calibration. How do the power companies get around this?

    My take on this is that the power company does not and cannot balance the loads. This 100% up to how the end user attaches loads and the equipment that is attached to the lines. If a three phase motor has three identical windings the circuit is balanced. If the motor was manufactured wrong or if the windings are intentionally different the load is not balanced.
     
  5. CDRIVE

    Thread Starter Senior Member

    Jul 1, 2008
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    Bill, this is the same argument that I pose whenever one of my members rekindles this argument. Unfortunately, the conspiracy theorist crowd remain undeterred. :rolleyes:

    Chris
     
  6. tedanderson

    New Member

    Feb 14, 2012
    5
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    I've been wondering about that in the back of my head for quite some time. I share my house with a couple of other people and we split the bill 3 ways so it's really hard to tell who uses what, when, and how long. But one thing that I notice is that the bill shoots up a good $250 to $300 when I have 15 consecutive days of using my space heater. Even though it's 1500 watts, I can't see it adding that much to the bill if I use it for 30 days straight.

    Typically around this time of year I'll run it 8 hours a night and that's it. If I do a liberal estimation at 12¢/kWh that should increase my bill by only about $45 to $50.
     
  7. CDRIVE

    Thread Starter Senior Member

    Jul 1, 2008
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    This is not relevant to the issue. Balancing loads on both legs is a good thing for the reasons I already stated but it's irrelevant to the topic.
     
  8. CDRIVE

    Thread Starter Senior Member

    Jul 1, 2008
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    While I sympathies with your situation it's not relevant to the topic and can only serve to sidetrack it. I would gladly participate in a discussion about it in your own thread though. ;)

    Chris
     
  9. Wendy

    Moderator

    Mar 24, 2008
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    This does post a second question though, verification. How would you install a personal meter (hopefully without having to use an electrician). Ideally it would be something that could record use over time, so you could compare your use with their data. Especially when the rates change.

    You can not convince conspiracy theorists of anything. The moment you argue against them you are either a fool or one of the dark protagonists.
     
  10. CDRIVE

    Thread Starter Senior Member

    Jul 1, 2008
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    GDI, all good points and we both know the answer to that.

    Chris
     
  11. JMW

    Member

    Nov 21, 2011
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    While this may or may not be true, I posit that a great deal of energy could be saved if the line voltage entering your residence was limited to 220 VAC.
     
  12. CDRIVE

    Thread Starter Senior Member

    Jul 1, 2008
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    No argument there. 1/2 the current per X wattage load equates to lower voltage drops which, in turn, equates to less wasted power dissipated as heat on the conductors. Unfortunately, in the USA 240V is treated as some sort of special power. Ridiculous? I think so! ;)

    Edit: See bold. They already are. The problem is that the outlets are all 120V because only a small percentage of plug in appliances are manufactured for 240V.
     
    Last edited: Feb 16, 2012
  13. Papabravo

    Expert

    Feb 24, 2006
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    Two questions come to mind

    1. How accurate does the measurement have to be to avoid the "charge" that the power company is "ripping you off"?
    2. Can you think of a suitable experiment to measure the discrepancy?
    If your <snip> friends cannot answer those two questions, then they have no business opining on any technical issue related to power distribution.

    The killer reply is of course. "If you're so smart, how would you improve the measurement technology and how much would you be willing to invest to save whatever amount this technology might indicate?"

    Lastly the meters don't calculate or charge for reactive power which does no work.

    See the following for more details
    http://www.nlcpr.com/Deceptions1.php
     
    Last edited: Feb 16, 2012
  14. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Australia has promoted adding an electronic energy meter to the switchboard (in addition to the standard energy meters owned by the power company). They did a national campaign and the govt paid a subsidy to help install the units, total user cost was $50 I believe. It uses RF to send data to a display box inside the house.

    The idea was that if people can see their energy usage it encourages being conservative, ie turning things off.

    Bringing that back on-topic, I have not heard of a case where the new independent high tech energy meter gave a significantly different reading to the power companies energy meters, I'm sure that would have made it into the media.

    In the past I read somewhere (possible just forum gossip?) that if you draw high frequency pulses of current from the AC mains it does not efficiently activate the old mechanical mains energy meters (as they are high inducance, lossy magnetic cores etc) so the energy meter reads lower than the actual. I'm not sure if that is going to be an issue in the future with so many CFL lamps and SMPS devices in everyone's home.
     
  15. CDRIVE

    Thread Starter Senior Member

    Jul 1, 2008
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    Yes, you make very good points but I must correct you about something. My friends are machinists and machinist aren't usually stupid. Stupid people can't create objects with dimensional tolerances to < thousandths of an inch. On the up side I'm getting good ammunition here and it will enable me to just give them the link to this thread. In fact I'm going to make it permanent in our links section.

    Thanks for the ammo,
    Chris
     
    Last edited: Feb 17, 2012
  16. Papabravo

    Expert

    Feb 24, 2006
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    They still need to answer the questions if they expect to move the debate along. I did not, I repeat not use the word stupid in any context and I'll thank you not to put words in my mouth. They have however advanced allegations with respect to the power utilities and their measurement equipment for which there is no factual basis.

    If it makes a difference I am also a machinist in addition to being an graduate engineer.
     
    Last edited: Feb 16, 2012
  17. BSomer

    Member

    Dec 28, 2011
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    This is a good point. I do know for a fact that the local power company here does monitor industrial and commercial customers power factors. If your power factor does not meet certain requirements you have to make some changes to your equipment or electrical service to increase it. Otherwise you pay extra fees for how bad your power factor is. To my knowledge they really don't bother the residential customers about power factors. I don't think that it would be cost effective to do so. Especially considering that the power companies here in Nebraska are publicly owned and any changes to rates or what-not must be approved for by the public.

    This may or may not have anything to do with these allegations or myths about power companies ripping off their customers.
     
  18. Papabravo

    Expert

    Feb 24, 2006
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    Any new technology is bound to attract additional myths.

    Apparently the new digital "smart meters" with no moving parts are believed by some to be even more insidious than their mechanical predecessors. As with the pf correction mythology this also has no factual basis.
     
  19. SgtWookie

    Expert

    Jul 17, 2007
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    I'm afraid I won't be of much help either. I've never had a reason to do anything with a meter.
     
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  20. CDRIVE

    Thread Starter Senior Member

    Jul 1, 2008
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    No, you didn't but please be honest with yourself. Referring to my membership as "your little friends" was what, if not condescending?.... Elves, Dwarfs, children, small minds? Was I supposed to regard that comment as an inconsequential adjective?

    PB, as I see it, you've posted the most compelling arguments thus far. I really do appreciate your participation in this thread and I totally agree that my membership must be equipped to answer the questions you raise. Please don't let this thread regress into you said, I said.

    Thank you,
    Chris
     
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