1 to 3 phase converter power factor question

On completion of a 3 phase converter and after adjusting the voltages with caps what effect does adding the power factor corrections cap have
on the commercial power meter reading.Does it add more or less power to the power bill? My guess is that it would add more power to the bill as the power factor approached zero(voltage in phase with the current) Hence according to my ramblings it would be better not to correct power factor and let the power company worry about it.
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snipped-for-privacy@yahoo.ca wrote:

I have a friend who bought an electric forklift for his collision shop. He has a 3 phase converter in his shop for his milling machine. When his electrician came out to set up the charger (which is three phase) he told him "you're going to wear your meter ot with this charger" I would ask the power company, may just be a matter of how much juice your pulling. (disclaimer: all this was hear-say and not my experience, just passing along what i heard... and we all know how "they" can be)
walt ps. do you need an electric forklift with the charger? i know a guy who has one and is willing to sell it cheap : )
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    It depends on what you mean by the phrase "commercial power meter". If you mean the average home meter, it would result probably in a tiny reduction -- corresponding to the extra power wasted heating the wiring from the higher out-of-phase current.
    However -- at least *some* commercial *users* of power -- especially those with three phase to their shops -- are charged "demand" metering, which can be sensitive to the out-of-phase current so they are charged based on that -- and on the *peak* demand during a given period. So -- run a high-current heat-treat oven (for example), for an hour or two, and you wind up paying a *lot* more *per* *month* for several months, until they are sure that it will not repeat. (You are being charged for the worst-case power which you *might* use, not what you are actually using on the average.)
    Since you've built a rotary converter, I presume that you don't have an industrial power contract, so you will get a very small improvement in your power bill -- but you will get fewer nuisance trips of your circuit breakers. (Depending on how close to the trip point the "imaginary" power takes you.) The breaker works on the vector sum of the real and imaginary power, while the home meter works only on the real, so it is mostly a good thing to add the power factor correction, especially if you are going to be running other (single-phase) equipment off the same breaker.

    Not so. The power which you draw doing actual work is the real power, and you'll be charged for that in any case. ("Actual work" can include things like the heating of wiring by the out-of-phase component of an uncorrected power factor.)
    Now -- another factor comes into the game here. The power factor correction is only good for a single level of load. As you increase or reduce the load level, the power factor will be somewhat less well corrected.
    So -- if you are likely to spend more time with the rotary converter idling than actual machining time (e.g. you turn on the converter when you come into the shop, and turn it off when you leave for the day), but only run the machines say 20% of that time, you are better off with the power factor correction tuned to the unloaded converter. But, if you turn on the converter just before turning on the machine, and then turn it back off just after you stop the machine, it would be better tuned for the converter plus the machine running a typical cutting load. (However, you draw more current when starting the converter, so you will probably save more running with the converter on most of the time you are in the shop, ready to start the machine.

    My opinion is that it would be better to correct the power factor to save wear and tear on your breakers and wiring -- *and* heat buildup in the idler motor as well.
    Good Luck,         DoN.
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DoN. Nichols wrote:

Don, I would disagree with you here. I think the power factor correction is good for correcting the imaginary current. And the imaginary current does not change with load. The real current changes with load.
I am open to any arguments you have on why the imaginary current would change with load. I do agree the power factor changes with load, but only because the real current changes, not because the imaginary current changes.
Dan
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    Well ... when you switch on a load (typically a machine motor), you are adding predominantly an inductive load, and it will probably work out to close to resistive only when the motor is near full rated power -- that is heavily loaded -- so you would need more capacitance to tune out that additional inductance during most of the time. (Do you always push your machines to the maximum that their motors can handle? Even when taking finishing cuts?

    It is with the switching in of an additional motor, which (as above) will be predominantly inductive -- thus worsening the power factor somewhat -- even if you have already tuned the rotary converter to have a neutral power factor with just the idler connected and running.
    If your motor in the machine were in the circuit full time, and you just had a clutch to connect it, and a variable speed pulley (or step belts) to change speeds, then as long as the motor was connected and spinning, I would expect the power factor to be pretty much constant. But most of us have machines in which the motor is switched to start and stop the spindle. (Yes -- an old Monarch 10EE with the motor-generator setup would probably qualify, and some versions of the Clausing lathes (though not mine) have a variable speed belt and a clutch.
    The electronic versions of the 10EE might well improve the power factor when switched on but not spinning the spindle, as the power supply would probably look more capacitive. The same for a VFD hung on a rotary converter.

    I could accept this if the load motor were connected full time. But I don't think so with the load motor being switched.
    Enjoy,         DoN.
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If the meter measures actual power consumption, then hear output of the running idler (and wires) should be equal to measured power consumption, without a load that is. Let's keep that in mind.
i
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    Yes -- which is why I was predicting a slight improvement in power costs for a tuned converter over an untuned one. How slight is a function of how much of that energy is going to heat the wires.
    Enjoy,         DoN.
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All the improvements will be tough to see in a converter that is actually loaded with machines being used.
In my case, combine that with the de-humidifier running in the shop and it's pretty much down in the grass.
Jim
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Thanks for explaining your thoughts. I agree that switching in an inductive load would worsen the power factor. But if you correct the power factor for a motor while it is idling, and then load the motor, only the real current changes and there is no need to change the amount of capacitance used for power factor correction.
I don't think it is important to correct power factor in most cases. The exception in my thoughts is fairly large welders which have very low power factor when energized and no welding is going on. In that case one can get by on a smaller breaker. Breakers over 60 amps jump in price.
Dan
DoN. Nichols wrote:

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snipped-for-privacy@yahoo.ca wrote:

No. Uncorrected power has a real (resistive) component, which you pay for, and an imaginary (inductive or capacitive) component, which your meter ignores. If your power bill is the only issue, there is no reason to use power factor correction caps. However, both kinds of current really flow in your cabling, so if your wire is anywhere near its rated current you can feel much safer if you use PF correction caps.
Grant
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snipped-for-privacy@yahoo.ca says...

For residential meters which measure only the in-phase component, they have no effect whatsoever.
Jim
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"jim rozen" wrote: For residential meters which measure only the in-phase component, they have no effect whatsoever. ^^^^^^^^^^^^^^^^^^^^^ The I^2R losses in the circuit are based on the vector sum of the in-phase component and the quadrature component. If the power factor is not one, this resultant current is larger, so the meter reading goes up accordingly. The electric company is not going to let you heat your wires for nothing.
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Lichtman says...

The ohmic losses in the wires are small compared to the (real) windage losses in the converter, which are themselves small. To put this in perspective, the real power consumed by my 5 hp idler is about 200 watts. This is bearing and windage loss in the idler itself.
The magnitute of the reactive current is about 7 amps, so for a loop resistance of, say, one ohm, that would be another 50 watts. Not much. But it makes sense to over-size those wires anyway, true.
Jim
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Yes they are, unless you are a commercial customer paying for KVAR (KVA reactive). They would like every customer to have a better power factor but it's just not cost effective to meter the out of phase component in residential and small commercial accounts.
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