Power Factor in a distribution system

Discussion in 'General Electronics Chat' started by Cerkit, Sep 21, 2015.

  1. Cerkit

    Thread Starter Active Member

    Jan 4, 2009
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    Why is that in a distribution system the operator tends to want to run at a lagging power factor?

    If the network was primarily inductive shouldn't it be running at a leading power factor in order to counteract the inductance (and to be lagging if it was a primarily made of capacitance) ?? Is this correct?

    I am confused, can someone please explain.

    Thanks
     
  2. crutschow

    Expert

    Mar 14, 2008
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    A power line usually has a lagging factor (current lags the voltage) because some of the loads are motors, which look like a partially inductive load.
    Sometimes the power company will add large capacitors to the distribution system,which generate a leading current to cancel the lagging current, so the rest of the power line and generator do not have to supply it.
     
  3. john*michael

    Member

    Sep 18, 2014
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    From a power company's standpoint, a power factor of one is desired. This is because when the power factor is one, the power delivered is P(watts) = VxA (volt-amperes).

    With any other power factor it takes more current at a given voltage to provide the power. for example, if the power factor was 0.5, P= .5xVxA, so since the voltage is fixed by the power company, it takes twice as much current to deliver the same power.

    The line resistance is the major contributor to loss in a power distribution system, and the losses are proportional to current squared. In the example, twice as much current means four times as much resistive losses in the power lines and connections, which is lost power that the power company cannot bill for.

    For this reason, power companies sometimes charge industries a penalty for low power factors, hence the capacitor banks.
     
  4. umphrey

    Member

    Dec 1, 2012
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    Last time I talked to an industry guy he said the power company doesn't care what PF you run at, they just bill you based on VA. Also I know a lot of power factor correction customers are consumers rather than suppliers. Maybe it is different in my area?
     
  5. crutschow

    Expert

    Mar 14, 2008
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    Home electrical meters measure actual power delivered to the house, not VA.
     
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  6. umphrey

    Member

    Dec 1, 2012
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    Also leading power factor causes increased voltage at the tie point, which is one reason to prefer lagging PF
     
  7. crutschow

    Expert

    Mar 14, 2008
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    What "tie point"? :confused:
     
  8. john*michael

    Member

    Sep 18, 2014
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    You are probably right umphrey and thanks. I was a lineman before I determined I was college material, but this was way back in the 1970's when power meters weren't so smart.
     
  9. crutschow

    Expert

    Mar 14, 2008
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    Here's a discussion of home electric meters.
    As you can see all the AC units measure actual power consumed, not volt-amps.
    Whatever "industry guy" umphrey talked to doesn't know what he's talking about. :rolleyes:
     
    Last edited: Sep 26, 2015
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  10. umphrey

    Member

    Dec 1, 2012
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    "Although there is no universally accepted standard for how Electrical Utilities charge their customers for a low power factor, it appears to be common practice to apply power factor penalties within the demand charge [2]. Most Utilities charge their customers for energy supplied in kilowatt-hours during the billing period plus a demand charge for that period. The demand charge is based upon the peak load during the period. The demand charge is applied by the Utility because it must provide equipment large enough for the peak kVA demand even though the customer’s real power demand may be much lower. If the power factor during the peak period (often a 15 minute sliding window) is lower than required by the Utility (usually 0.9 or 0.95), the Utility may also apply a low PF penalty charge as part of the demand charge portion of the bill."

    http://www.mirusinternational.com/d...buted to Many Power Factor Misconceptions.pdf
     
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