Re: Small, slow AC machines: surface to volume ratio?

To droll on a bit, and expand the discussion:

Clearly a motor is an inductive load. Without argument we may take that
a motor is an inductive source, when used as a generator. We're talking
AC motors here....

What the hell is an inductive source?

Well, a transformer could be one, but there's this issue of impedance
reflection, so let's leave that out and *not* assume a classic linear
AC-tranformer-AC-diode-capacitor power supply is an inductive source.

I do know one motor sucks at driving another, so we'll just go with
that. An inductive source is one which "doesn't like" inductive loads.
And so we may presume it does like resistive or capacitive loads.

Now, universally, what is done with an AC induction motor to turn it
into an SEIG is "to slap some caps on it". This is power factor
correction, making the generator system more happy with resistive
loads, which predominate.

How does this work?

Well, I understand resonance and I think I have a pretty good
explanation:

The stator winding inductance and slapped on capacitor bank need to
form a *resonant tank* with frequency "somewhat less" than the
frequency desired.

How much less? Or, a better question, why *less* and not *more*?

Oh, that's easy....

The driving source, the prime mover, is essentially along the X axis.
And output, a function of resonance, is along Y.

Now, what do you *not* want a generator to do when you load it?

You *don't* want it to sag, that is, lower its output. And that is
precisely what will happen if you're operating on the low-frequency,
inductive side of the Q curve:

A little load, a little less speed (conservation of power or energy). A
little less speed, a little *less* output. A little less output, well,
you get the idea. dy/dx > 1.

A positive feedback system, right? Remove the load, it overspeeds,
blowing out the prime mover. Add load, it sags, stalling or lugging the
prime mover.

So what happens on the other side?

Easy. Negative feedback. dy/dx < 1.

More later....

Doug

.

Relevant Pages

  • Re: Flywheel on a rotary phase convertor
    ... > An induction motor is a consumer, ... > induction generators have to be excited by overdrive from ... > The RPC is a load on the mains, not a supplier to the mains. ...
    (rec.crafts.metalworking)
  • Re: Frequency and Voltage
    ... Frequency affects induction, and if induction ... >affects affects power, then frequency affects power. ... load does not draw any power (not counting any losses due to the tiny ... Low power factor loads tend to be inductive, so a bank of capacitors ...
    (alt.home.repair)
  • Re: 7-1/2HP 3-Ph. MTR on Single Phase
    ... and power factor. ... Perhaps my description of a load being reflected ... Users of big induction motors sometimes used another induction ... motor to correct power factor. ...
    (rec.crafts.metalworking)
  • Re: very low voltage -- dangerous?
    ... appliance plugged into that particular circuit. ... It might, or might not, affect the voltage reading, ... depending on the wiring between the "load" and the point ... induction is exactly the same. ...
    (alt.home.repair)
  • Re: very low voltage -- dangerous?
    ... It might, or might not, affect the voltage reading, ... depending on the wiring between the "load" and the point ... induction is exactly the same. ...
    (alt.home.repair)