Power Factor Correction.

Discussion in 'General Electronics Chat' started by Vasanthkini, Jun 24, 2010.

  1. Vasanthkini

    Thread Starter Member

    Jun 9, 2010
    40
    2
    Can some one theoretically explain how is power factor correction done?Most of the on line documents end up defining what power factor is which i am well aware of,but then how do we correct it or shall i say obtain a better power factor close to 1(one).

    Thanks!:)
     
  2. timrobbins

    Active Member

    Aug 29, 2009
    318
    16
    Improving PF of a load means either (a) introducing leading or lagging VARs (ie. inductive or capacitive net reactance), or (b) introducing harmonics to counteract the harmonics generated by a non-linear load.

    Do you have an application/problem?

    Ciao, Tim
     
  3. Vasanthkini

    Thread Starter Member

    Jun 9, 2010
    40
    2
    @Tim

    Hey Thanks for you time.Let me see if i have got it right.We use leading or lagging networks depending on whether the voltage or current is leading right?If i have got it right,how do we implement it?let me be more precise,how will i theoretically calculate the leading o lagging network components?

    And yes,i am basically working in Research and development in power supply.Getting the power supply work is one issue but understanding the concepts very well is what i believe in and hence the question.

    THANKS!
     
  4. timrobbins

    Active Member

    Aug 29, 2009
    318
    16
    If you have X VAR leading, and you add X VAR lagging then you end up with VAR = 0, as seen from the power source. The only load remaining is purely resistive (W=VA), and this gives PF=1 for a linear load (no harmonics).

    Ciao, Tim
     
  5. dsp_redux

    Active Member

    Apr 11, 2009
    182
    5
    For example, if you have a room full of motors, the load will be pretty inductive, so the current might be lagging vs the current (I hope that's the term you use in english). Hence, S=P-jQ where S is in VA, P in Watts and Q in VAR. See the negative sign on Q. What you want is introduce a capacitive load in parallel to your circuit so you compensate the lagging effect (+jQ). If you can get up to Qcap = Qindu, then your circuit becomes purely resistive and the PF = 1.
     
  6. Vasanthkini

    Thread Starter Member

    Jun 9, 2010
    40
    2
    Wonderful !

    The above explanations where good enough for me to understand! Between,how do we differentiate the load as linear and non linear?

    Thanks !
     
  7. dsp_redux

    Active Member

    Apr 11, 2009
    182
    5
    If you look at the graph (V vs I) of a linear load, you'll see Z will vary linearly (for exemple, a simple resistor). That's not the case for diodes for instance since V vs I will vary following the diode equation I=I_S (e^{\frac{V_D}{n V_T}} -1) where I_S is the saturation current, V_D the voltage accross the diode, n is the emission coefficient (=1 the majority of the time) and V_T the thermal voltage (about 26mV at room temperature).
     
    Vasanthkini likes this.
  8. timrobbins

    Active Member

    Aug 29, 2009
    318
    16
    Thanx DSP.

    The best example of a consumer non-linear load is the generic switchmode power supply, which draws a current from the mains that is not a pure sinusoid. It's only more expensive larger powered switchmodes for industrial applications, or for more expensive computor power supplies, that deploy special input circuitry that electronically achieve a sinusoidal input current waveform, and hence achieve PF=1.

    Flourescent electronic lighting ballasts are almost entirely not PF=1, which is a growing problem.

    Ciao, Tim
     
    Vasanthkini likes this.
  9. Vasanthkini

    Thread Starter Member

    Jun 9, 2010
    40
    2
    The explanations were just too good for anyone not to understand.Thanks a ton guys ! These informations were handy enough !

    Thanks! :)
     
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