According to :

DoN. Nichols wrote:


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.


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,
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.

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?

I am open to any arguments you have on why the imaginary current would
change with load.

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 do agree the power factor changes with load, but
only because the real current changes, not because the imaginary
current changes.

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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Email: | Voice (all times): (703) 938-4564
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--- Black Holes are where God is dividing by zero ---