PTO Generator Question

[Industrial Toys]

Thought maybe some kind of kool Data logger.

 

[ptsg]

Volt-Amps (VA), Watts, Vars:

Only watts do the real work.

Volt-Amps is the beer mug, Watts are the beer, Vars are the foam.

Sometime you need a 16 oz mug to drink a 12 oz beer.
Power factor would be 0.75.

We learn this stuff on schools with that same exact analogy. :drink:

Of course, if you speak about beer on a class full of male students, we all know they will actually pay attention.

 

[Industrial Toys]

What is a VARS? I have never seen such a confusing analogy.

Now, can someone explain Power Factor? I know the utility may be charging you too much or not enough based on power factor. The not enough, I have heard they are upset about. The too much, not so much.

 

[CobyRupert]

What is a VARS? I have never seen such a confusing analogy.

Now, can someone explain Power Factor? I know the utility may be charging you too much or not enough based on power factor. The not enough, I have heard they are upset about. The too much, not so much.

Loosely:
ONE simple way to describe power factor is to say it represents how out of phase the (AC sinusoidal) voltage waveform is compared to the current waveform.
...but that leads to the question: Why is the voltage out of phase with the current?

Electrical Resistance is just one type of Impedance.
(Simplistically) Impedance comes in 2 parts: 1) Resistance (i.e. resistors) and 2) reactance (i.e. capacitance (capacitors) and inductance (inductors or coils). With resistance, energy is transformed into heat; with reactance it is stored and then released, but the voltage & current waveform relationships to each other has been altered.

"ELI the ICE man"
When an AC voltage (E) is applied to a coil (inductor(L)) or capacitor (C), energy is stored, then released with each cycle. The capacitor plates charge then discharge, the inductor coils get magnetized, then polarity is reverse, etc..
For an inductor (L), the voltage (E) waveform will lead the current (I) waveform that is produced by 90 degrees ("ELI"); for a capacitor (C) the current (I) will lead the voltage (E) by 90 degrees ("ICE").
A capacitor or inductor in a circuit provides current blocking impedance like a resistor does.

So...(simplifying) say you have an old lighting dimmer switch (inductor) that develops an impedance and (by Ohms law) develops a voltage across itself, thus reducing the voltage downstream available to the light and making it dimmer. If the dimmer switch consumed REAL power it would get hot like a resistor (heating element).

So, imagine our dimmer in a 120V light circuit, cuts the voltage to lamp to 60 volts so current is 2 amps: 60 volts at 2 amps is developed across the dimmer, 60 volts at 2 amps is across incandescent light. The dimmer ISN'T throwing off (60volts x 2amps) 120 Watts of heat, but the bulb is!!

We call the 60V at 2 amps across dimmer "reactive power" or "volt-amps reactive ("VARS") as opposed to the "real power" (120 Watts) at the bulb; as opposed to the total 120V x 2 amps = 240 Volt-amps (VA) the total circuit is passing.
So:
Total circuit "Complex power" Volt-Amps = 240 VA (Mug)
"Real power" Watts at light = 120 Watts (Beer)
"Reactive power" VARS at dimmer = 120 VAR (Foam)
:drink:

Because the real power (Watts) at light is 50% of the volt-amps the circuit is conducting, the power factor is .5 or 50%.

Notice that the utility had to supply 240 Volt-amps (VA) because of the power factor, but they only measured/charged you for 120 Watts.

 

[vsteel]

Another way to think of it is assume we plug in a coil of wire to make heat and it has a .5 PF. This coil of wire is also an inductor. The .5 PF means that half of the energy supplied is making heat and half is in the field generated but it gets released back into the wall plug. While only half of the energy is doing work, the circuit breaker sees 100% of the energy and must be sized appropriately.

 

[Industrial Toys]

I was an apprentice electrician and went to school three times, took a digital electronics course and worked in the field pretty much all my life. Also a HAM. Never heard of VARS. Is it an american term?

Math has never been my strong point. I know about reactive circuits and voltage lagging current and so forth, but the implictions of it in electrical distribution are still lost on me, sorry.

 

[Industrial Toys]

Happened to be looking at the specs on a generator I hope to pick up. So PF claims 1.0. OK, so is that good or bad?

 

[John_Mc]

Happened to be looking at the specs on a generator I hope to pick up. So PF claims 1.0. OK, so is that good or bad?

1.0 PF is good - It doesn't get any better. However, it's not clear to me what that gets you in a generator, since the PF of the load can still throw things off.

 

[pmsmechanic]

Interesting reading. The understanding part is not so great. Great illustrations.

 

[buickanddeere]

Happened to be looking at the specs on a generator I hope to pick up. So PF claims 1.0. OK, so is that good or bad?

1.0 PF on the generator doesn’t mean anything . What matters is the amperage , both real and reactive does not exceed the capacity of the generator . This is why prospective generator purchasers should ignore the watts and instead add up the amps .
Causation advises to not mixup 120V and 240V amperage . 120V using on elite and 240V using both lines .