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Power factor

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MikeMl

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Sure, that is why they are put across inductive loads to cancel some of the inductive reactance. Inductive= jX; Capacitive = -jX.
 

Electronman

New Member
I want to know if Power factor exists for both capacitors and inductors? Besides after reading several sentences about caps I can not understand if power factor for a capacitor is another name for ESR too?
power factor formula for a capacitor = (loss energy inside the capacitor)/ (saved energy)?
so what about an inductor?
 
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Electronman

New Member
What's your opinion of this formula?:
power factor formula for a capacitor = (loss energy inside the capacitor)/ (saved energy)?

I seem to misunderstood the above formula with Z formula or so? or maybe both state one thing?
 

MikeMl

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That definition does not quite jive with this one...
 

BrownOut

Banned
I want to know if Power factor exists for both capacitors and inductors? Besides after reading several sentences about caps I can not understand if power factor for a capacitor is another name for ESR too?
power factor formula for a capacitor = (loss energy inside the capacitor)/ (saved energy)?
so what about an inductor?


I think that's the definition of the capactor's Q. In fact, it's 1/Q.

Edit: By Q, I mean the quality factor, not the reactive power as defined in the linked article.
 
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RCinFLA

Well-Known Member
Q of a capacitor is Xc/ESR, where ESR is series resistance of capacitor.

This term is used for RF circuit design. It varies with frequency so Q statement without frequency of Q measurement has no meaning.

The inverse of Q is the dissipation factor as tan(D) = ESR/XC

In first approximation ESR stays relatively constant versus frequency so Q goes up as frequency goes down. As frequency gets higher the surface currents of capacitor plates and dissipation within dielectric can drive ESR higher but the biggest deviant is the self inductance which will cancel some of the Xc to point at higher frequency where self resonance occurs. This point is actually used for selection of capacitance for RF bypass function.

Usually all this has little to do with circuit power factor since capacitor and inductive losses are usually much less then power consumed by device (motor) in run mode.
 

BrownOut

Banned
I know it has little to do with power factor. That's my whole point. 1/Q is synomonous with the OP's definition of
(loss energy inside the capacitor)/ (saved energy)

The reason Q is specified is because the definition of Q is:

Q = 2Π*Peak EnergyC/Dissapated EnergyC (1)

The numerator is 1/2C(V(peak))^2 and the denominator is ∫1/R(v(peak)sinWT)^2dt|0 - 2Π

= WRC.

So, the frequency dependence on Q derives directly from (1), which is much closer to the OP's definition than power factor.


That was my whole point. There is some confusion on the OP's part of Q and power factor, IMO.
 
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BrownOut

Banned
Sorry for the sidebar. I didn't mean to change the discussion to Q. I only thought part of the OP's confusion might come because he's getting Q confused with power factor. Hope I didn't exaerbate the confusion.

Did the Wiki article help?
 

MrAl

Well-Known Member
Most Helpful Member
Hello,

Do Capacitors have so called POWER FACTOR too?

Thanks

Hi there,


To add a little to the other posts already here...

We usually dont refer to capacitors as having a power factor when
they are the only load in the system because they effectively have a
zero power factor or very close to it and anything with a zero power
factor wont do too much by itself.

Power Factor is a phrase usually used when a load draws more current
than it should in order to work properly due to the current being out of
phase with the voltage, in which case the cost of the system goes up
(sometimes very substantially) due to the cost of the more robust parts that
have to be used to carry the extra current. In some cases power factor
correction is employed in order to help this situation and in other cases even
mandated by law.

"Power Factor" therefore is usually applied to some kind of load that
is known to draw current out of phase with the voltage in an AC
power circuit of some kind, and not to a capacitor alone.
You will see writings like, "That load draws 1000 watts and has a
power factor of 0.7", or similar, but never see something like, "That
capacitor has a power factor of X", because it simply doesnt really
come up in practical real life probably because the capacitor always
has a 'power factor' of zero or close to zero.
What else you will see a lot is, "Power factor correction capacitor",
which simply means that capacitor is used for power factor correction
for some load.

In the strictest sense, it is true that a capacitor, a real life capacitor that
is, can have a power factor all it's own because it must use some real
power as well as act mostly like a capacitor does and mostly store energy.
However, rather than rate the capacitor in terms of "Power Factor" they are
typically rated in "watts lost per kvar". This terminology relates more closely
to the overall effects the actual capacitor in question has on the system.
 
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