RE: Newby

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Michael Brooks" <mbrooks-at-perrytech.edu> 

Thank you for the input; I am very interested in creating a little
monster of my own.
As far as my background I teach Electrical Technologies at Perry
Technical Institue. We train students for their Journeymen Electrical
License. I don't have any engineering background per se (though I am
working on that)
Primarily I teach basic theory behind caps, inductors, 1 & 3 phase AC
generation, sine wave characteristics, transformer theory and
connections, 3 phase power and PF correction.
Some of what I have read on the list so far is well beyond the capacity
of my noodle at this point but I am confidant I can figure it out in
time.
Again I appreciate the information and I will continue to learn and most
probably patronize with many questions!


Michael Brooks
Instructor
Perry Technical Institute
mbrooks-at-perrytech.edu
509 453 0374 xtn 234


-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Tuesday, July 27, 2004 12:08 PM
To: tesla-at-pupman-dot-com
Subject: Re: Newby

Original poster: "Paul Nicholson" <paul-at-abelian.demon.co.uk>

Michael Brooks wrote:

  > I have just recently signed up for the list

Great!

Your description of power factor correction of an inductive load
is essentially the same thing as occurs when a coil is tuned to
some required frequency by adding capacitance at the top.

If you picture a source of AC driving into the *top* of the coil,
(with coil base grounded) the source will see a lossy inductive load.

(At least it will if the drive frequency is below the lowest self-
resonance of the coil).

Then adding shunt capacitance (by way of the self capacitance of
a toroid or sphere) to the top of the coil is having the same
effect as power factor correction.   The PF correcting caps are
forming a parallel resonant circuit with the load inductance.

However, this doesn't reflect the way that toroid sizes are chosen
when coils are designed.  Instead coilers (should) choose the
toroid (or whatever topload shape is employed) size that best suits
the generation of streamers  - if that's the intended application.

They fit this chosen topload to the coil and then look for the
frequency at which the power factor correction naturally occurs,
ie the resonant frequency of the coil/topload combination.  So it
is kind of like the PF correcting process in reverse - start with
the cap and find the frequency at which correction occurs!

  > Is this similar of the same as the calcs you may be using to
  > get to reasonance?

Yes, when you've finished calculating the PF correction cap, you
should find it resonates at the line frequency with the load
inductance, ie Xc has the same value as the Xl of the load when
calculated at 60Hz.  In general,

    (Xl = 2 * pi * Freq * L) = (Xc = 1/(2 * pi * Freq * C))

which leads to Freq = 1/(2*pi*sqrt(L*C)).

Welcome to the list Michael - and as you're obviously involved in
elec eng you won't have any trouble figuring it all out.  All the
usual laws of physics apply (with the odd subtlety to make life
interesting) so your existing EE knowledge applies 100%.
--
Paul Nicholson
--