Reactive Power Absorption

Discussion in 'Homework Help' started by Stereoblind, May 15, 2015.

  1. Stereoblind

    Thread Starter New Member

    Mar 10, 2015
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    Hey guys,

    I'm having a few issues understanding the following statement:

    "A capacitor bank generates lagging VArs and absorbs leading VArs".

    My understanding is that if we have a lagging power factor our current is behind our voltage, indicating an inductive load. So surely a capacitive bank would absorb lagging VArs since the leading/lagging relationship has been flipped?

    Apologies if this is a dumb question but I just can't get my head around it for some reason. We have a similar section relating to generators and it's confusing me :/ .
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    use the Mnomenic CIVIL

    capacitor current leads the voltage ,

    inductor voltage leads the current
     
    Last edited: May 16, 2015
  3. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    Where did you read that statement? Hopefully you didn't hear it from your professor.
    Your doubts are well founded and your proposed ammendment to the statement is correct.
     
  4. WBahn

    Moderator

    Mar 31, 2012
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    By your own description, an inductive load has a lagging power factor when it is absorbing power, so wouldn't it be reasonable to say that an inductor absorbs lagging VARs?
     
  5. crutschow

    Expert

    Mar 14, 2008
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    I would say (and I think the convention is that) an inductor generates lagging VARs and absorbs leading VARs, the opposite of a capacitor.
     
  6. WBahn

    Moderator

    Mar 31, 2012
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    I have a feeling that it's a matter of terminology and that I may well have it mixed up.

    I think of "generating" and "absorbing" in terms of power and energy transfer and from that perspective both an inductor and a capacitor "absorb" reactive energy though that is a poor description since they are constantly absorbing it and releasing it and the phase relationship is constant for either case. None-the-less, from that perspective, if you are going to use a phrase saying that it is either absorbing or generating VARs, associate absorption with the phase relationship that it operates at. But it has been a while since I've been exposed to this terminology and I think, thanks to your response, that the mindset leading to the conventional terminology is weird and comes from a weak and superficial analogy in that if you have an inductor, in which the voltage is leading the current (so a lagging power factor since voltage is used as the reference), that the inductor is somehow "generating" the lagging VARs associated with that situation. That seems like a bass-ackwards way of looking at the concept of power generation, but from the perspective of someone managing power factors is probably not too unreasonable and is probably quite useful.

    So I agree with you and t_n_k.
     
  7. Stereoblind

    Thread Starter New Member

    Mar 10, 2015
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    It's in the notes beside an example. Thanks guys, my head was scrambled trying to understand what was going on.
     
  8. crutschow

    Expert

    Mar 14, 2008
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    I think the terms "absorb" and "generate" make more sense when used in relation to the VARs involved, and not considering the energy flow.
    Thus a logical definition is that the VARs that get larger with a larger inductor means the inductor is generating them and the VARs that get smaller with a larger inductor are being absorbed.
     
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