[Prev][Next][Index][Thread]
[Fwd: This phase shift stuff... - Plane Wave]
Hi all,
I always understood that the issue is simply one of a standing wave - we
*do* design our coils to be effectively quarter wave resonant at the
operating frequency. The length of wire needed is not that much, after all,
we do have trouble finding enough wire in on piece to complete our mad
designs! In addition, the self-capacitance and top-loading effectively
increase the electrical length of the winding. In that case, I do think
that there may be just cause for the transmission line model - although
obviously in a system of this nature other elements have to be taken into
account - ie the capacitance of corona discharges, leakage and winding
resistance etc. I think when someone talks about the 90 degree phase shift
in a TC sec, they are not talking about a shift between the top and bottom
of the coil but instead the near-90 degree shift between the voltage and
current waveforms along the sec; as I understand it the phase shift could
never be completely 90 degrees as this would imply our top terminal being
at an infinite voltage with no current whatsoever. I know this may be
simplistic, but I cannot help but think that simple is sometimes best!
Oh, also re: Capacitor ideas, etc, everyone building bottle caps seems to
be using glass - this would seem to be counter-intuitive as all the facts
point to this being high-loss material. I personally wouldn't trust a bank
of beer bottles to withstand anything more than a kilowatt, and I would
have thought that in the US you have as many plastic soft-drink bottles as
we do here in the UK! OK, they may need to be connected in series, but I'm
sure they would give better results! A safety gap across them and you're
away anyway...
Safe and happy coiling everyone,
Alex Crow
PS My custom-built neons are lovely - I got a Jacob's Ladder running as
soon as I got them, and I was getting the arc to climb about three feet
with that lovely fizzing hum - I can't wait to get those caps charged! They
even threw in free power factor correction capacitors!
----------
From: Tesla List <tesla-at-pupman-dot-com>
To: tesla-at-pupman-dot-com
Subject: Re: This phase shift stuff... - Plane Wave
Date: 22 February 1999 06:20
Original Poster: Terry Fritz <twf-at-verinet-dot-com>
At 09:28 AM 2/22/99 +1200, you wrote:
>Hi Terry, Antonio, all,
>
snip..........
>
>My apologies for a snip of such interesting material. I am beginning
>to think that models that assume the influence is propagated up the
>coil via wire conduction have not taken the turn-turn coupling into
>account. For each turn and its immediate neighbours, the coupling is
>very tight indeed. Terry's results seem to me to indicate that the
>wave is propagating turn-turn at nearly the speed of light. That
>being so, a lumped model is entirely appropriate to describe these
>coils. Furthermore, currents should be largely identical at top and
>bottom. There should be a proof that says the coil is, in effect,
>tightly coupled from top to bottom despite the almost zero direct
>coupling of the bottom turn to the top because of the inter-turn
>coupling. Alternatively, there should be a proof that says this is
>not true. Perhaps Jim's students might care to have a look at this.
>Anyway, if the turn-turn coupling has been disregarded in modelling
>the secondary then the Tx line model used has a fundamental flaw in
>it.
snip,,,,,,,,,,
>
>Malcolm
>
>
Hi Malcolm,
I also feel that the capacitive charged region around the coil (Cself) is
also acting as a stabilizing force that is helping to limit any out of
phase effects. Consider the instant in which a free standing secondary
(primary has quenched) has converted all of its energy into capacitive
charge stored in the volume around the coil and the current is zero. At
this instant, the oscillation continues and the charge is reabsorbed back
into the coil and converted once again to current. Imagine what a mess
this system would be if parts of the charged volume around the coil were
not in phase. In one area of the coil there would be high current and
little Cself charge storage while at the other end of the coil the
situation would be reversed. If one considers how such a system would
work, it appears simply that it would not unless the distance was so great
that the propagation speed of light would isolate the regions. In the
typical dimensions of our coils, light can reach across the coil length in
say 3 nano-seconds. The propagation affects can be considered just about
zero. Thus we are left with a coil that has magnetic and charged fields
around it that either must be in phase or transferring energy in the
direction of the coil instead of in and out from the coil.
We always tend to think in terms of magnetic energy. However it must be
remembered that the entire energy of the secondary is stored completely in
Cself many times during the oscillation just as it is stored completely as
magnetic energy a moment later. Imagine a coil with no current in it but 5
joules of energy stored in the E-field around the coil. 16pF charged to
say 400000 volts is a lot of power! This charged volume around the coil
would have a very difficult time if the lower half were charging at the
same instant the upper half were discharging as the high phase difference
case would suggest. Really, you can't explain that situation without
seeing that the regions would rush towards each other and try to cancel the
effect and bring the entire system back into phase.
The current in the secondary is in phase from top to bottom, however the
magnitude of the current decreases drastically across the length of the
coil. This is due to energy being sucked out of the secondary and
transferred into space charge in the volume around the coil. In the dark,
you can see the corona indicating that the current is leaving the secondary
along its length in a powerful system.
I am not disagreeing with you or anything. Just babbling mostly to
myself... :-))
Terry