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Thread: Power Factor

  1. #11
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    Jul 2008
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    We have been called by some of our customers who have had "power factor salesmen" contact them about saving them big time money on their power bills by installing this "black box" inside their plant or building. All that we looked at were scams!! Now, it has been our experience working in many large office buildings that those buildings having "power factor correction capacitor banks" installed at the end of each bus duct riser and they are turned "OFF" ???? Some that we checked had blown fuses??? From what we see there is a place for them, but very limited to large factory type areas???

  2. #12
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    May 2003
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    Quote Originally Posted by charlie View Post
    If you look closely at the bill, you will find an adder for poor PF OR a credit for PF better than XX% OR everything on the bill in kW and then the numbers change to kVA and a charge for the kVA used (kVA can be reduced with PF correction).
    While I did not review all the bills the ones in Maryland I have seen and saw no penalty noted I looked fairly close.
    Brian John
    Leesburg, VA

  3. #13
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    Quote Originally Posted by brian john View Post
    Several different projects, on some a single PF correction was installed at the main service.
    On others point of use was installed.

    In all cases the customers had little or no idea it was part of the design. With the PF off the measured PF with the site up and running was between .82 to .92. Not sure there was any benefit to the end user as the local utility had no PF penalty.
    Even without the PF penalty, with correction installed at the load, you will reduce heat losses, lower the voltage drop, and reduce supply equipment size needs. As you know, correction at the meter does nothing for you if there is no PF penalty.

  4. #14
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    Quote Originally Posted by charlie View Post
    I just don't understand how the serving electric utility can require anything in the way of a PE stamp.
    Agreed, unless they were willing to forgive past sins and associated charges and/or demand levels.

  5. #15
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    Quote Originally Posted by brian john View Post
    While I did not review all the bills the ones in Maryland I have seen and saw no penalty noted I looked fairly close.
    around here, on a poly phase service of 400A. or larger, there is a demand
    meter with a captive needle that the meter reader resets every time he
    reads the thing... the unit price on the KW is based on the demand meter.

    high motor starting loads will peg that meter, and that means a higher rate
    paid for all electricity used that month.

    in the late 70's and early 80's, all grocery stores had interlocked compressors,
    so they couldn't start more than one refer compressor at a time.... if the
    tumblers lined up, and a bunch of them hit at once, and pegged the demand
    meter, the cost of electricity for that 50,000 sq ft supermarket would be $5,000
    higher for that month, and that was in the late 70's.
    “Give a person a fish and you feed them for a day;
    teach that person to use the Internet and they won't bother you for weeks.”

  6. #16
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    Quote Originally Posted by Fulthrotl View Post
    around here, on a poly phase service of 400A. or larger, there is a demand
    meter with a captive needle that the meter reader resets every time he
    reads the thing... the unit price on the KW is based on the demand meter.

    high motor starting loads will peg that meter, and that means a higher rate
    paid for all electricity used that month.

    in the late 70's and early 80's, all grocery stores had interlocked compressors,
    so they couldn't start more than one refer compressor at a time.... if the
    tumblers lined up, and a bunch of them hit at once, and pegged the demand
    meter, the cost of electricity for that 50,000 sq ft supermarket would be $5,000
    higher for that month, and that was in the late 70's.
    I remember we used to call the power company when we pegged a meter when we would cut stuff back on after working.

    I'm not sure that the PF correction would help for an inrush as the down-line capacitive/inductive couple would still have to be charged. I'm not sure what the response time was on those old meters. It saves now because the meters integrate over time and the initial charge is a small piece of the interval.

  7. #17
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    Feb 2003
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    Indianapolis
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    6,102

    Smile

    Quote Originally Posted by charlie View Post
    . . . If you look closely at the bill, . . OR a credit for PF better than XX% . . .
    Quote Originally Posted by brian john View Post
    . . . and saw no penalty noted I looked fairly close.
    I am assuming that you are talking about larger services that have demand and reactive meters. The smaller commercial services are normally treated the same as residential services with respect to PF.

    If the percentage for no additional charge for poor PF is 85% and the customer is running 85%, it would appear that the serving electric utility doesn't charge anything for poor PF. In the vast majority of cases, the serving electric utility will give a credit for correcting past 85%. In other words, there is a charge for any PF less than 100%. It is necessary to check the rates of the serving electric utility and the rate the customer is on. The 85% that IPL uses (page 1 and top of page 2) may be 90% or 80% for your electric utility. :smile:
    Charlie Eldridge, Indianapolis, Utility Power Guy
    Responses based on the 2011 NEC, unless stated otherwise.

  8. #18
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    Jan 2009
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    ORLANDO FLA
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    Well i disagree with the pre engineered power factor ,heres why and iam just a simple electrician from the south we are real slow down here but i know you all will correct me .
    I feel we need to test the system as a whole break it down meaning tune that capacitance to that inductive load resonant frequency circuit wise.

    Meaning each wire length to motor each motor itself has a power factor issue alone meaning a good motor manufacture to a cheap motor of manufacture which is to me a power factor correction at motor or motors itself .

    We also understand the HID or ballast flor lighting issue in a building but any capacitance added will help NO i think not.

    I see a need to test or monitor the loads to get a record of PF at the load then you can calculate what you need by PF formulas .

    What iam saying is test the actual load then calculate the capacitance needed no one knows what PF is until it is tested in the field . take care comments ?
    Last edited by ohmhead; 03-29-09 at 05:19 AM.

  9. #19
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    Jul 2008
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    774
    Ohmhead,
    Just curious--what type of power monitor do you have?

  10. #20
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    Feb 2005
    Location
    Charlotte, NC
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    Quote Originally Posted by charlietuna View Post
    Now, it has been our experience working in many large office buildings that those buildings having "power factor correction capacitor banks" installed at the end of each bus duct riser and they are turned "OFF" ???? Some that we checked had blown fuses??? From what we see there is a place for them, but very limited to large factory type areas???

    Pf correction cap banks are common to see turned off in large industrial plants. Reason is that 20 yers ago they needed them, poor Pf from all the motor loads resulting in big fines from utility. Over the last 20 yers the VFD has become commonplace, you see VFD's all ove these plants, and the caps they use correct the low Pf's from each motor load. So in many cases those big PF correction caps are no longer needed.

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