What is the difference between power factor 0.85 lagging and 0.85 leading, in terms of value and graphical representation?

 

poornimah,

Here's a link to a site which I have found to be very helpful to many:

http://www.the-power-factor-site.com/

If you still have questions, feel free to ask them here. Do try to provide some context for your question (power generation; power transmission; course learning/explanation; etc.) so that we can be most helpful. (There are some differences depending on the location where a power factor is being measured/monitored, specifically into/out of a substation.)

Hope this helps!

 

A leading power circuit is mostly capacitance; a lagging power factor circuit is mostly inductive. Adding capacitors to a lagging power factor inductive circuit increases the power factor reducing the apparent power.

 

Thank you for your valuable reply sir. I will check out the site you've provided.

 

A power factor of 1 is when the current timing (i.e. phase, waveform) matches the supply voltage timing (i.e. phase, waveform). A leading power factor simply means the current timing is ahead of the voltage timing, while a lagging power factor means the current timing is behind the voltage. Assuming both parameters have a sinusoidal waveform, leading and lagging refer to the same point in each of the respective parameter's cycle, such as peaks and zero crossings when plotted.

With AC cycle timing being measured by angle, a full cycle being 360 degrees, a 0.85 power factor is the cos of the angular difference between the current and voltage. Arccos 0.85 = 32 degrees... So the values provided have a current that leads or lags the voltage by 32 degrees.

 

A general PF definition includes Harmonics:

- PF = Active RMS Current/Total RMS Current
- Total RMS Current =(sum(I1^2+I2^2+...+In^2))^0.5
- In = order "n" Harmonic Current.

Here there is no precise "Lag" or "Lead" angle.

Regards-
amadeo

 

>- PF = Active RMS Current/Total RMS Current

As the term is <i>power factor</i>, you should be discussing this in terms of power:

PF = Real Power/Apparent Power

Also, while non-linear loads "blur" the lead or lag angle, there is still a lag or lead angle when the discussion is based on the power triangle...

Apparent Power (S)
Real Power (P)
Reactive Power (Q)

S, P, and Q are vectors which form a right triangle, where the vertex of P and Q are the right angle, and S is the hypotenuse. Pythagorean Theorem applies:

S = sqrt(P^2 + Q^2)

Cos(theta) = P/S = <b>PF</b>

BTW, here's a link for the OP'er, Poornimah, and others as need be:
http://www.the-power-factor-site.com/Power-Factor-Triangle.html

 

It's all about the timing of current and voltage, and load (which is the inverse of impedance).

pf=1 is a 'real' load, e.g. simple resistor. Hit it with a voltage, and current happens, at the same time

Where you have leading/lagging power factor, is where there is a non-real load, i.e. reactive impedance. This is where the impedance X can be described with a real and imaginary component X = a + jb

Just remember lagging is inductive load, i.e. motor, inductor, transformer. Hit it with a voltage, and because the magnetic field isn't built up yet it is initially an open circuit - it takes some time for the current to build up. Therefore the current lags the voltage. Graphing the phasor of impedance (A + jB) yields a positive angle theta=arccos(pf), so the phasor is in the first quadrant of a real/imaginary plot

Leading is capacitive load, i.e. a capacitor. Hit it with a voltage, and since there aren't any charged particles on the plates of the capacitor yet, it is initially a short circuit - it starts off with infinity current which eventually goes down to zero as charges build up and voltage in the capacitor increases. The current wants to lead the voltage. Likewise when you connect a charged capacitor to a load, the current goes out of the capacitor before the voltage can drop. Graphing this phasor of impedance yields a negative angle theta (A - jB), so it's in the 4th quadrant of a real/imaginary plot

The angle theta in both cases is the phase difference from voltage waveform to current waveform, at whatever frequency. Just a phase difference between two sine waves. The voltage can be leading or lagging the current

You can also graph the phasor of Power on a real/imaginary plot, with the same angle as that of the impedance plot. The length of the vector is the apparent power, which has components on both the real and imaginary axes. If pf=1, it's a purely real load. Loads with a power factor <1 have a component on the imaginary axis as well as the real, thus they consume imaginary power, a component of the total apparant power (that is supplied by a generator) that does no work. This leads to inefficiencies

 

leading power factor will provide you a negative angle (more conductive), in other others negative reactive power, lagging will provide you a positive angle (more inductive), in other words positive reactive power.

lagging pf = 0.85 --> cos-1(0.85) = 31.8 that will provide S = P + jQ
leading pf = 0.85 = - cos(0.85) = -32, that will provide you S = P - jQ

Hope it helps.