# 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

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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!