Source PF

Discussion in 'General Electronics Chat' started by fromeout11, May 13, 2014.

  1. fromeout11

    Thread Starter New Member

    May 13, 2014
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    I have a question regarding the terminology used when specifying power factor for sources vs. loads. For inductive loads, the power factor is assumed to be *lagging*, with positive Q, and "absorbing" VARs. For capacitive loads, the power factor is assumed to be *leading*, with negative Q, and "producing" VARs. This much makes sense.

    What I don't understand (or haven't been able to verify) is the terminology regarding the source - let's say a generator - that is powering these loads. If there is a net lagging load, then the generator is set to be overexcited, i.e. *lagging* or "pushing VARs", and vice versa.

    This seems contradictory to me. Given that a *leading* capacitive load will balance out a *lagging* inductive load for power factor correction, why is it that a *lagging* generator will balance out a *lagging* inductive load? Is the terminology just reversed when discussing the source vs. the load?

    Additional question: assuming my statement above is true, does the current exiting the generator lead or lag the voltage for correcting an inductive load?
     
  2. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    One must be consistent. What the load absorbs, the generator supplies. If the load absorbs reactive power this must be supplied by a generator or alternative passive (e.g. PFC) reactive power source.

    Not sure what your question about excitation current relates to. Do you mean the AC generator DC field excitation?
     
  3. fromeout11

    Thread Starter New Member

    May 13, 2014
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    My question is in regards to the lagging/leading terminology - if a capacitor or a synchronous generator are both supplying VARs to an inductive load, why is the capacitor considered "leading", but the generator is considered "lagging"?

    I didn't ask about excitation - read "exiting". Ignoring terminology, what does the voltage/current waveform relationship look like exiting the synch. generator when balancing an inductive load?

    Thanks in advance.
     
  4. fromeout11

    Thread Starter New Member

    May 13, 2014
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    Bump? I'd love a good answer to this.
     
  5. studiot

    AAC Fanatic!

    Nov 9, 2007
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    You need to be clear whether you (or your text) is using the source or generator convention or the sink or load or motor conventuion, and not mix them since they are duals.
     
  6. fromeout11

    Thread Starter New Member

    May 13, 2014
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    The source of the "lagging" description for the generator output when pushing VARs is the D-Curve/Capability curve for the generator.
     
  7. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    Last edited: May 26, 2014
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