Power factor

[Sahib]

A watt is an instantaneous value.

WHAT?!

Just joking.

You are also right. You are referring to the instantaneous power whereas power used in practice is average power.

 

[Sahib]

I agree here. But lets say the capacitive or reactive impedance is increased, wont watts go down since voltage will begin to dip at the resistor? Think of a lighting ballast...

You are correct.

I had in mind power factor improvement application in a building with a fixed active power demand with an effective resistance 'R'.

If R is fixed and power factor is varied and so is the impedance, the watts is also fixed.

 

[Smart $]

Not to stray off, but for this series circuit what would the watts be at 120 volts? Ditto for the impedance?

Given...

R = 1 ohm
Xl = 1 ohm
Xc = 1 ohm

...except on energization, the effective Z is 1 ohm. Power factor is 1.

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/rlcser.html

 

[Besoeker]

WHAT?!

Just joking.

You are also right. You are referring to the instantaneous power whereas power used in practice is average power.

Average infers a time dimension and many probably think about it that way. But a Watt is just a Watt. Named after a Scotsman - we have our uses you know!

And, for a Scot, Watt and what aren't pronounced the same way. The "wh" matters...............:thumbsup:

 

[mivey]

It's not a problem when referring to a voltage or current plot.... or even a power plot when there truly is a DC component.

Then it shouldn't be too hard to imagine since the average results in the same accumulated energy being transferred over time as you get with a constant DC power line. The point is it is not uncommon the refer to the offset component on a sinusoidal as the DC and the varying component as the AC. You could even call it direct component and alternating component if you wanted but there should be no confusion about what component is being discussed, slang or not.

 

[mivey]

I certainly agree with that with respect to a voltage or current waveform. Does the same apply to a power waveform? That would mean that every power waveform in an AC system has a DC component (unless the power factor is zero).

It has a constant component and alternating component (some call it the intrinsic power IIRC). Doesn't seem too confusing to identify them as DC & AC components, even if it is not the current or voltage waveform. It is still a sinusoidal and the underlying math works the same way.

I don't really know what is standard, that just sounds a little confusing to me. So in the case of a power waveform, I think it would be clearer to call it a constant component.

Probably clearer but I do not see it as confusing. To each his own.

The phrase "DC component of the power wave form" suggests to me the constant power attributable to the DC components of the current and voltage waveforms.

It indicates to me it is the same power you would get with a DC signal. Not that much different in concept.

 

[mivey]

Wouldn't falling be a better word than decaying?

No. Decaying is correct. However, I should have used growing instead of rising.

I think of decaying as something discharging like a capacitor

Correct.

not a generator switching direction in polarity.

Don't know what you are referencing.

 

[mbrooke]

Given...

...except on energization, the effective Z is 1 ohm. Power factor is 1.

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/rlcser.html

I know the math doesn't lie, but why isn't it 2 ohms? What would happen if you short circuited the resistor?

 

[mivey]

but Id never use the word decaying for a reversal in current flow depicted across a graph.

Me neither. What are you talking about?

 

[Smart $]

Then it shouldn't be too hard to imagine since the average results in the same accumulated energy being transferred over time as you get with a constant DC power line. The point is it is not uncommon the refer to the offset component on a sinusoidal as the DC and the varying component as the AC. You could even call it direct component and alternating component if you wanted but there should be no confusion about what component is being discussed, slang or not.

You are correct... it's not hard to imagine... and all I'm going to do is imagine it.

 

[mivey]

I agree here. But lets say the capacitive or reactive impedance is increased, wont watts go down since voltage will begin to dip at the resistor? Think of a lighting ballast...

But we have an ideal source! If we don't, we at least try to get close to one when we can.

 

[mivey]

Average infers a time dimension and many probably think about it that way. But a Watt is just a Watt. Named after a Scotsman - we have our uses you know!

And, for a Scot, Watt and what aren't pronounced the same way. The "wh" matters...............:thumbsup:

I know your better half can teach you the correct pronunciation. Why not two "tt" in Scot or one "t" in Watt? You guys...

 

[mbrooke]

But we have an ideal source! If we don't, we at least try to get close to one when we can.

Im confused. How would source make a difference?

 

[Besoeker]

I know your better half can teach you the correct pronunciation. ...........

Not for Ecclefechan................

 

[steve66]

What determines low power factor or more precisely why some loads have varying power factor compared to others? Say I had an inductor. The current lags by 90*, and no other load. My power factor would be zero, correct? But if I add a resistor in parellel drawing equal current my power factor would be 50%? And if I add a capacitor of equal current (in parallel) my power factor is 100%? Does this accurately represent what goes on in most loads being a mixture of capacitance, inductance and resistance hence VA?

Sorry if someone has already mentioned this, but there were too many responses to read.

Going back to your original question, has anyone ever shown you the power triangle before?

http://www.allaboutcircuits.com/tex...ent/chpt-11/true-reactive-and-apparent-power/

https://en.wikipedia.org/wiki/AC_power

 

[mivey]

Not for Ecclefechan................

Oh yeah, that would be "fetchin". Similar to "She was fetchin the water when she went and fell in the crick!". Ask the Belle, she knows.

 

[mivey]

Im confused. How would source make a difference?

An ideal supply has no drop to the load so the voltage is steady. Or were you talking about unequal C & L ?

 

[Besoeker]

Oh yeah, that would be "fetchin". Similar to "She was fetchin the water when she went and fell in the crick!".

Not at all. It's like the "ch" in loch that everyone else pronouces as "lock".

Ask the Belle, she knows.

She does.

 

[mbrooke]

An ideal supply has no drop to the load so the voltage is steady. Or were you talking about unequal C & L ?

Ok, lets say C goes down, does voltage not drop across a series R?

 

[mbrooke]

Think of it like this. A small C is used to help drop the voltage across a resistor (fluorescent tube) @ 1:20:



https://www.youtube.com/watch?v=NtzAVlucpqQ


The same concept hold true for a "capacitive dropper" voltage reduction circuit which has the ability to substitute a transformer:



http://ww1.microchip.com/downloads/en/appnotes/00954A.pdf