What's the difference between power factor of 1 VS .7 ?

[Billy Mayo]

What is the difference between a product/unit with a power factor of 1 VS a product/unit with a power factor of .7?

Power factor of 1 is KV
Power factor of .7 is KVA

Power Factor of 1 means it's 100% Power/watts
Power Factor of .7 mean it's 70% power/watts and 30% the current and voltage is Power LOSS

Power Factor is the PEAK or RMS? Power factor is the True Power?

Power Factor of 1 is Voltage X current
Power Factor of .7 is Not Voltage X current, why is that?

 

[Ratchit]

Billy Mayo,

What is the difference between a product/unit with a power factor of 1 VS a product/unit with a power factor of .7?

Difference with respect to what?

Power factor of 1 is KV
Power factor of .7 is KVA

What have you been drinking? PF is a number between 0 and 1, and has no units.

Power Factor of 1 means it's 100% Power/watts

What does that above sentence mean?

Power Factor of .7 mean it's 70% power/watts and 30% the current and voltage is Power LOSS

Power factor is not a measure of power loss. Better get a new textbook.

Power Factor is the PEAK or RMS? Power factor is the True Power?

Peak or RMS of what? The power factor is not true power.

Power Factor of 1 is Voltage X current

V x I is the same so matter what the PF is.

Power Factor of .7 is Not Voltage X current, why is that?

Because that is not how PF is defined.

Ratch

 

[ronsimpson]

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

If you have a resistive load the power factor is 1.
Some loads are inductive like a motor or capacitive and PF<>1
Some loads are non linear where the current and voltage are very different. example: where the current=0 for most of the cycle but is very high at the peak of the voltage. PF<>1

 

[Billy Mayo]

So power factor doesn't mean Power? or True Power or RMS Power?

Why are some circuit designs a power factor of 1 and others circuit designs a power factor of .7? how are they different? I don't understand the difference or what makes them different from a power factor of 1 and .7

Why would a circuit design need a power factor?

 

[ronsimpson]

The attached picture is of a power supply like in a PC or radio. The current has a very high peak and is not sign wave!

The power company wants a PF=1.
In the case of the picture the current is much higher (PK) and the resistance loss in wire is more. You can only get about 10A average through a 20A breaker. Same problem with wire heating in the walls. 10A not 20A The power company has loss in the lines that they don;t charge you for.

If you have a motor the current lags the voltage. It is hard to deliver power when the current and voltage peak ARE at different points in time. So the power company might have to add capacitors to correct for the phase shift.

With the push for "green" we have to make large devices have a good PF. (TV and computer)

 

[MrAl]

Hi there Billy,

Most circuits do not 'need' a power factor, they end up having a power factor because some of the load is reactive which means it stores some energy and dissipates energy while a purely resistive load (power factor 1) does not store any energy.

So that's the main difference. If the power factor is less than 1 then the load has capacitors and/or inductors in it as well as resistors. If the power factor is 0 then it only has capacitors and/or inductors and no resistance to eat up any energy.

So a little table:
PF=0, no power dissipation, capacitors and inductors only.
PF=1, no reactive elements like capacitors or inductors, resistive only.
Between 0 and 1 but not including 0 and 1, there is some reactive and some energy being dissipated.
So a PF like 0.7 means there is some energy storage and some energy dissipation. We can use math to figure out how much of each.

 

[KeepItSimpleStupid]

The utility wants a PF of 1. The "green guys" want a PF of 1. Why? The power company might have to deliver more current because the PF is not one and it ends up not doing any useful work, The power lines heat up, etc.

You migt want to read this application note on Power Factor Correction: https://www.google.com/url?sa=t&rct...dQHbcbbrUOBZguQ&bvm=bv.49967636,d.dmg&cad=rja

 

[Billy Mayo]

The power factor of 1 or .7 or .8 , can be an AC sinewave, I just don't understand the difference between them and how are they different?

If the unit is 3000 Watts output 120VAC output

3KVA X power factor of 1 = 25 amps
3KVA Watts X power factor .7 = 17.5 amps

Power factor of 1 outputs 25 amps
Power factor of .7 outputs 17.5 amps

What does this mean? the power factor is a Current Limiter? the power factor is a phase angle? what is a power factor?

 

[MrAl]

Hi,


The main idea with the power factor is that when we have a load connected to the line we see a current I flow, and normally when we compute power in a circuit we multiply current times voltage:
Power=Current*Voltage.

But if the load has a power factor then we have to multiply by the power factor to get the real power being actually dissipated in the load (because some energy is stored as i said before). So the real power then is:
Power=Current*Voltage*PF

This is often because the current is too high to be used to calculate the power because the current is a result of both resistive and reactive elements.

To illustrate, we can use a 1000uf capacitor and a 3.12 ohm resistor in series, powered by an AC source of 1 volt at 50 Hertz.

The current through these two comes out to 0.2243545 amps, and if we multiply that by 1v we get 0.224 watts approximately, which is wrong.. So we usually call this volt amps (VA) and say that we have 0.224 VA not 0.224 watts.
Now we multiply by the power factor which is 0.7, and we get as true power:
0.224*0.7=0.157 watts, and this is real power. This is the power being dissipated in the resistor while the capacitor just stores energy.

So you see the power factor allows us to calculate the power knowing the VA, and of course vice versa.

Now if we only had a resistor in the circuit the power factor would be 1 and that would mean that the watts equals the VA. But the presence of a reactive element changes the power factor to something less than 1.

Power factor correction circuits try to raise the power factor to get closer to 1, but first it is a good idea to understand power factor in normal type loads before jumping to power factor correction.

 

[ronsimpson]

If the unit is 3000 Watts output 120VAC output

3KVA X power factor of 1 = 25 amps
3KVA Watts X power factor .7 = 17.5 amps

Power factor of 1 outputs 25 amps
Power factor of .7 outputs 17.5 amps

What does this mean? the power factor is a Current Limiter? the power factor is a phase angle? what is a power factor?

Where did you get these numbers? Something is not right with the numbers. I can't explain wrong information. Through these numbers out and read the links above.

 

[MrAl]

Hi again,


We multiply VA by the power factor to get watts:
VA*PF=Watts

or divide by the power factor to get VA:
Watts/PF=VA

So if you have a 100KVA load at 0.7 power factor then you have true power:
100KVA*0.7=70KW (which is seventy killowatts)

So the power factor has units of Watts/VA if you want to call it that. So we would then have:
100KVA*0.7W/VA=70KW

 

[Billy Mayo]

If a Unit is a power factor of 1, I CAN NOT hook up any kind of load that is inductive or a capacitive load?

 

[Billy Mayo]

So power factor is the Real Power or True Power?

Power Factor is for Reactive loads

Where do they come up with the .7 ? why .7 ? what is the .7 ? is this a phase shift of .7 from voltage to current leading and lagging?

 

[Billy Mayo]

The power factor has nothing to do with the design of the circuit? is only has to do with the LOAD? the load has a power factor of .7 ? it's not the circuit / design of the unit that has the 0.7 power factor?

 

[KeepItSimpleStupid]

If you had a load that was 500 W with a 0.7 PF, you would need a 500 W/cosine(0.7) or ~653 W capable unit to drive it.

Now you see, how it costs more money for a higher power device to drive your load. If the voltage were a constant 120, then guess what parameter goes up? Current, because P=VI. So, the wiring has to be sized for 653 W and not 500 W.

---

IF (Big IF) you were a designer of a continuously online UPS, it would be wise to employ power factor correction so that the wall power sees a resistive load, otherwise the power company police will come after you in a commercial environment.

If your UPS auto-switches from line to UPS, you can't design it that way and the user (the 0.7 PF load) as to buy a bigger UPS to run his gizmo. In the first case, he would have to buy a bigger UPS as well, but the "power police" will be happy.

Tis article may be a "little" simpler: https://www.dteenergy.com/businessCustomers/largeBusinesses/electric/powerFactor.html

A business that uses a lot of standard motors and not VFD's could very easily benefit by installing PF correction at the service entrance. This device switches in capacitors to improve the power factor, Where I used to work, we had 36 heat pumps which translates into at least 72 motors, each messing up the power factor especially if they were all on at once. Thus power factor correction was employed.

Variable Frequency drives would have power factor correction at the front end, nearly eliminating service entrance power factor correction.

The utility has to do some, so it's transmission lines don;t exceed the allowable current. When you look at power generation, neuclear can provide a base power, but it's difficult to turn off. Wind provides power as it sort of feels like it and you can't turn it off easily too because the rotor will spin out of control. Solar using inverter technology can do local power factor correction. e.g. It can do things like output 4000 Amps at zero volts, thus it can correct the power facor. This info basically came from a presentation that I attended and is very brief.

And capacitors can also provide power factor correction. The inverter technology can fine tune the correction.

 

[Ratchit]

Billy Mayo,

The power factor of 1 or .7 or .8 , can be an AC sinewave, I just don't understand the difference between them and how are they different?

An AC sinewave of what? Voltage or current? You have to know both to see the PF difference.

3KVA X power factor of 1 = 25 amps
3KVA Watts X power factor .7 = 17.5 amps

Where did you learn math?

(3000*1)/120 = 25 amps
(3000*0.7)/120 = 17.5 amps

Power factor of 1 outputs 25 amps
Power factor of .7 outputs 17.5 amps

Don't those different numbers tell you something about the difference between PF's?

What does this mean?

It means there is a phase difference between the voltage and current in the PF=0.7 circuit.

the power factor is a Current Limiter?

No, just increase the voltage to compensate for the lower current. Just because the current is lowered does not mean the current is limited.

the power factor is a phase angle?

No, it is the cosine of the phase angle.

what is a power factor?

It is the cosine of the real power/apparent power. You should not have to ask that question because there is plenty of material about this subject in textbooks and the web.

Ratch

CORRECTION: Looks like you pulled one over on me. The calculations you made above to determine currents are bogus, because the AC current in a series circuit is the same throughout. The correct calculations should be 3000*1= 3000 watts and 3000*0.7 = 2100 watts. So the circuit with the lower power factor will dissipate less power.

 

[Ramussons]

What is the difference between a product/unit with a power factor of 1 VS a product/unit with a power factor of .7?

Power factor of 1 is KV
Power factor of .7 is KVA

Power Factor of 1 means it's 100% Power/watts
Power Factor of .7 mean it's 70% power/watts and 30% the current and voltage is Power LOSS

Power Factor is the PEAK or RMS? Power factor is the True Power?

Power Factor of 1 is Voltage X current
Power Factor of .7 is Not Voltage X current, why is that?

Billy Mayo,

Useful Power (Watts) = Volts (Volts) x Current(Amperes).

There is no problem in calaculating power with this Equation in Direct Current DC.

But in Alternating Current, AC, the Phase Difference between the Voltage and the Current plays a critical role.

The Phase Difference occurs due to inherent Inductance or Capacitance in the Load. Inductance causes the current to Lag, Capacitance to Lead.

Here, Useful Power = Volts x Amperes x PF = "Volt Amperes" x Phase Factor (PF)
PF is the Cosine of the Phase Difference (a number without units); = 1 when phase diff = 0° and = 0 when phase diff = 90°.

So, PF = 1 means that the Current and Voltage are in Phase, 0.7 means there is a Phase Difference of 45.5°.

An ideal Inductor or Capacitor will cause the Current to Lag or Lead the Voltage by 90°, the PF will be 0; which means that even though we have a Voltage across the load and a Current through the load, the Useful Power is Zero.

Ramesh

 

[samovar]

0.3

 

[crutschow]

If you had a load that was 500 W with a 0.7 PF, you would need a 500 W/cosine(0.7) or ~653 W capable unit to drive it.

...................................

Not exactly. You need a source capable of providing the amount of current that a 653W load would require but it still only needs to supply 500 W of power.

 

[KeepItSimpleStupid]

Not exactly. You need a source capable of providing the amount of current that a 653W load would require but it still only needs to supply 500 W of power.

In the details, yes. One could also say that the source has to be within the SOA (Safe Operating Area) of the load, The point I was trying to make is a source with a higher current capability is required.