Power factor correction..

Discussion in 'Math' started by bill4807, Nov 26, 2014.

  1. bill4807

    Thread Starter New Member

    Nov 15, 2014
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    Hopefully someone with PFC knowledge can help me out here.
    A formula of mine is not coinciding with A sizing Capacitor chart from a local distributer. And I am curious why?

    This Formula:
    C = KVAR / (2 * pie * F * V^2) Translation: 2 times 3.14 times frequency times voltage squared.

    Assume KVAR= 10.188, F= 60, and V= 480.
    This formula should come out with an answer in Micro Farads.

    The data sheet from a local distributor is saying a 10KVAR cap rating shoulds read/measure Min: 57uF--MAX: 66uF.

    Can anyone clear this up for me?
     
  2. bill4807

    Thread Starter New Member

    Nov 15, 2014
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    Rereading this I thought...Should I post this in the Electronics Forum? I know it is a simple math problem but getting to the answer may be more in the electronics field than math? I know I did not include many details about how I came up with the 10.188 but that should be irrelevant.
     
  3. Ramussons

    Active Member

    May 3, 2013
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    A fast mental workout says the manufacturer 1s correct.
    Where did you get the formula from?
     
  4. #12

    Expert

    Nov 30, 2010
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    I get 56.3 uf.

    Look carefully: Is the sizing chart from the distributor or the manufacturer?
    Motor quality has changed a lot in the last 20 years. A distributors chart might be way out of date.
     
  5. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    If the the 10 kvar is delivered by a single capacitor @ 480V working then the equivalent capacitance would be ~115uF.
     
  6. #12

    Expert

    Nov 30, 2010
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    @t_n_k The title of the thread is about power factor correction for an inductive load, not total power delivered by a single capacitor...or am I missing something important?

    Then I look at my math and see that I did not square the 480 volts.

    Therefore, some doubt remains.
    I hope we have been helpful in some way.
     
  7. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    The OP hasn't presented the question with great clarity.
    Irrespective of that, a capacitor with a specific kvar "value" will have a capacitance value commensurate with the nominal kvar, operating voltage & frequency. What else could one conclude?
     
    #12 likes this.
  8. #12

    Expert

    Nov 30, 2010
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    Thanks. I was trying to draw a conclusion from the small scale work I do, and it doesn't stretch that far.
     
  9. WBahn

    Moderator

    Mar 31, 2012
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    I get that a single cap needs to be 117 uF to have that reactive power under those conditions (i.e., same as t_n_k). What conditions does the data sheet apply to? I could envision it being intended to size a set of caps in a three phase system, for instance.
     
  10. bill4807

    Thread Starter New Member

    Nov 15, 2014
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    Thanks for the replies everybody!
    I kept coming up with around 115 Micofarad also.
    This is the manufacture datasheet.
    It does specify 480V 60Hz 3 phase on the datasheet, so this is why then the formula I posted is for a single cap?
    So how are they then coming up with the round abouts 56 Microfarads?
    They must not be wired in parallel because i come up with 18 Microfarads?
    They are wired in series parallel?

    Or do you have to multiply the 480 x 1.73 before hand?
     
  11. bill4807

    Thread Starter New Member

    Nov 15, 2014
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    Sorry did the parallel calculation wrong. I calculated it for series capacitance.
     
  12. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    Did you post a link to the data sheet?
    Hard to comment unless one can view the manufacturer's information.
    Even if the 10kvar is distributed across three phases the value of 56 uF remains a mystery.
     
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