# Power Factor (Leading or Lagging)

Discussion in 'Homework Help' started by xiahbaby, May 21, 2009.

1. ### xiahbaby Thread Starter New Member

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How do you know whether it is leading or lagging in Power Factor?

I was told by my lecturer that if the sin θ is positive then it is lagging
And if it is sin θ is negative then it is leading

However, in this case, the answers that I got is all positive but it has a variation of leading and lagging.

I am confused.

Does he means that if the θ is positive then is is lagging and if it is negative then it is leading ?

I try to google up on this and this is what I get ...
But I practically do not understand a thing from the Mnemonics

From the Mnemonics

"ELI the ICE man" or "ELI on ICE"  the voltage E leads the current I in an inductor L, the current leads the voltage in a capacitor C.

CIVIL  in a Capacitor the I (current) leads Voltage, Voltage leads I (current) in an inductor L.

P/s: I have also upload the solution if you need more detail on the solutions.

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2. ### mik3 Senior Member

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You calculated cos() and not sin().

Another way to find it is to look at the angle of the current relative to the angle of the voltage.

If the currents leads the voltage (greater angle than voltage) then the power factor is leading (capacitive load).

If the current lags the voltage (less angle than voltage) then the power factor is lagging (inductive load).

3. ### t_n_k AAC Fanatic!

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If the resulting current phase angle is more negative in relation to the driving (source) voltage phase angle, then the power factor is said to be "lagging".

If the resulting current phase angle is more positive in relation to the driving (source) voltage phase angle, then the power factor is said to be "leading".

So if the driving voltage phase angle is $\theta$ deg and the resulting current phase angle is $\phi$ deg.

If $\theta$ > $\phi$ power factor is lagging.

If $\theta$ < $\phi$ power factor is lagging.

Then if $\theta$ = $\phi$ power factor is unity and neither leading nor lagging.

The driving (source) voltage phase is often assumed to be zero (for convenience) and in that situation it is immediately obvious that a lagging power factor condition is indicated by a negative sign for the current phase angle. Similarly a positive sign for the current phase angle indicates a leading power factor.

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4. ### t_n_k AAC Fanatic!

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If $\theta$ < $\phi$ power factor is leading.

5. ### xiahbaby Thread Starter New Member

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Thanks for the explanation ! I understand it nw XD

6. ### hitmen Active Member

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Thanks for clarification. Is it safe to say that constant 240V = 240<0 V (phasor)

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Yes it is.