Do we need to be concerned with power factor?

Discussion in 'General Electronics Chat' started by chipwitch, Mar 15, 2014.

  1. chipwitch

    Thread Starter Member

    Mar 29, 2013
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    The title says it all.

    I realize why it's important to the power company, but when we design circuits, are there any advantages to trying to keep the PF at unity? Do high frequency circuits make it any more or less important?
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    P.F. correction as far as incoming power is concerned is usually a concern for larger industrial users, where the cost factor can be considerable.
    For the average residential user, it is most likely not practical to try and correct any small difference that may occur at the supply level.
    Max.
     
  3. chipwitch

    Thread Starter Member

    Mar 29, 2013
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    Thanks. That's what I thought. I was reading a pdf file put out by one of the chip manufacturers on SCRs and Triacs. In it they were speaking specifically to how one goes about designing a circuit for a light dimmer to keep the PF high. It's actually a benefit to the consumer, as I understand it, to have a low PF. The way they described it, it was an essential design element. I guess they're just being responsible corporate allies.
     
  4. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    Not a fvreq issue. Unity power factor significantly reduces the AC RMS current drawn from the mains for a given amount of load power.
     
  5. crutschow

    Expert

    Mar 14, 2008
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    Many countries now have requirement for the minimum power factor of home appliances and electronics that are sold. That's the reason for the dedicated chips to help power factor, it's a created market.

    Sorry to disappoint but few companies are so responsible that they design chips from the goodness of their heart. The only do it if there's a profit to be made. :rolleyes:
     
  6. bountyhunter

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    Sep 7, 2009
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    Power companies "correct" commercial users PF by putting large capacitors on the power poles. Most homes look inductive.
     
  7. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    That's because they learned from experience that consumers won't pay a nickel more for a product that is "green" or "environmentally friendly" if there is a cheaper one.
     
  8. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    There must be nice power companies where you work. My company just had to do your own.
     
  9. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    There are alway A few people willing to buy a hybrid so they look environmentally friendly (because neighbors and customers can see their cars). Very few will pay extra for renewable sourced electricity.
     
  10. MaxHeadRoom

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    Jul 18, 2013
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    I just attended a seminar put on by the Provincial service supplier in order to educate local industries to encourage them to have an evaluation done of the plant, and show the potential saving, often the ROI of PF equipment is recouped in the 1st year. But it is the companies responsibility to have the evaluation.
    A large culprit now is the prevalence of VFD's and other high frequency switching power devices.
    I was asked to attend by one of my customers in order to establish a plan.
    Max.
     
  11. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    They aren't nice, it saves them money. Keeping the PF closer to unity makes their transformers RMS current go down, and keeps the power delivcered a lot more Watts and less VARs. Most commercial users get billed for the Watts only, so the power company gets more money by correcting the PF. I have heard of cases where they installed a VAR meter when the user was running way off, but not typically.
     
  12. MaxHeadRoom

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    The saving is by the customer, not the service company.
    Max.
     
  13. bountyhunter

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    As far as power switchers: the ones we built to run off AC mains single phase typically had PF's about 0.58 ballpark, the ones with three phase AC input got up to close to 0.85 so that was a big advantage for users who had three phase AC available. Any power supply above about 2kW had to use 3 ph because the input current would have been too high otherwise.
     
  14. bountyhunter

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    No actually, the power company saves too. As the power factor goes off unity, the RMS current you have to draw from the transformers increases substantially to support a given amount of load Watts. That RMS current is what heats the transformers and causes power losses and limits the power that can be delivered.

    You are correct the power company usually gives a customer a break on the bill if he will implement better power factor: and they do it because it saves them money. The power company would prefer unity PF, most residential homes are in the 0.85 - 0.9 ballpark. But commercial can drop a lot lower because they have so much inductive hardware running, so power companies incentivize them correcting the PF because it saves them money.
     
  15. MaxHeadRoom

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    Jul 18, 2013
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    Of course the power company saves also, but the incentive for companies to employ PF correction has to be seen in real $$ and it is not because of a 'break' by the power company it is because of Real metered savings in the cost of power.
    Max.
     
  16. #12

    Expert

    Nov 30, 2010
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    Not a peep (from the power company) about PFC here in Florida.
    Once upon a time, I tried correcting a 1/4 HP refrigerator compressor. It needed about 80uf. Then I wondered how long it would be until the relay contacts welded shut, so I removed the capacitors. :D
     
  17. ronv

    AAC Fanatic!

    Nov 12, 2008
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    LED lights and switchers. Imagine the usage.
     
  18. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    The "incentive" for the the customer company to save $$ is very simple: the power company is going to charge a lot more when their PF drops too low because it causes power losses at the source end and they are going to charge for that. The power savings at the customer end isn't really that much, the cost savings is from avoiding being socked with the low PF surcharges by the power company and getting a VAR meter installed:

    http://www.reliableplant.com/Read/13339/power-factor-correction
     
    Last edited: Mar 16, 2014
  19. chipwitch

    Thread Starter Member

    Mar 29, 2013
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    ronv... that photo's a fake!!

    It's never night over the entire EARTH at the same time! Plus, you'd have to have an awful long arm for a selfie THAT big!
     
  20. #12

    Expert

    Nov 30, 2010
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    At least it proves the earth is flat. :D
     
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