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Re: New Transformer/Gap Quenching
Hi Boris,
I am cc.'ing this to the list in case others have
comment or find it useful:
On 6 Jul 00, at 6:36, boris petkovic wrote:
> Hi Malcolm,
>
>
> > and a high
> > magnetizing current (about 6A) due to fewer than
> > optimal
> > primary turns for the core which was the result of a
> >
> > successful attempt to boost its output with a fixed
> > secondary.
> ------
> I have an access to 220V/ 6000V-at-800 mA rated power
> transformer here.Logically, I'd like to employ it for
> TC powering project.
> Quick estimation for 2XFmains (=100BPS) discharging
> cap frequency and rated power output would give Cp
> needed in access of 0.5 uF!!
You can only calculate it like that if the transformer stats
result from leakage inductance. If the transformer has k ~1
between primary and secondary, such calcs don't work. In that
case, you can suck what you like from it until you burn the
windings up or blow fuses.
> .So,it would be totally inadequate for resonant freq
> of planed TC,and for my expenses,and Xp would be to
> low and not to mention other problems.
> .
If the transformer does provide the mechanism described above,
I see no reason why 0.5uF shouldn't work but you would need a
very high Lp and hence very low Fs to make it happen
efficiently. Large coil in other words.
> The problem for rational pushing P>4kW into TC circuit
> is too low secondary voltage of course..
>
> With increased output voltage the problem would be
> history..Due to very good insulation properties (it
> was tested for 20 KV+) of the transformer , I have a
> wild thought of pluginn primary to 380V (=220XSQRT(3)=
> phase to phase distribution network voltage) in
> order to get higher secondary voltage-then Cp=0.2 uF
> cap would be satisfactory value I would accept to use.
> However,we live in a real world and there's no perfect
> and ideal transformers.I'm aware that magnetic cores
> may react badly to increased magnetizing currents (the
> worst consequence is final saturation) .
> I know that bigger transformers can work without
> problems at even 40% increased voltages.
> Am I in dangerous zone (1.73 V rated)?-your off hand
> opinion please.
My guess is yes.
> How that can be simply checked for this particular
> transformer (msm) ?
Run the primary from a variac and monitor the primary current
with the secondary open circuit. As the core approaches
saturation, primary current will increase sharply.
> ------
> > Operation with a static gap is smooth and
> > well-behaved even
> > with a LTR cap.
> -----
> What kind of cap is LTR cap?
Larger than resonant. See list archives for acronyms.
> -----
> > I tested this transformer on the coil a couple
> > of days
> > ago and noted the following (apart from the obvious
> > such as
> > increased output from the coil and far less heating
> > in the
> > transformer windings: whereas operation had been
> > previously
> > very touchy with regard to airflow through the gap
> > (too much
> > and the gap couldn't fire
> -------
> This appears somewhat strange to me.You mean gap
> couldn't fire at all with a strong airflow through it?
Correct - when it was set to fire at the peak the transformer
could deliver with the particular cap that was connected to it.
There are transient conditions involved. If the transformer
does manage to fire with a marginal setting, the short that
the gap places across the secondary allows some extra energy
to be stored in the core which in turn allows a higher output
voltage on subsequent firings.
> That was temperaturely colder airflow stream than
> surrounding air or ordinar?There is Paschen's low for
> breakdown voltages of uniform fields with respect to
> pressure ,temperature ,moisture.I think that pressure
> is factor that affect the most here but it should be
> checked.
> Also:0.1 uF cap was reso cap?
Not at 50Hz.
> -----------
>
> ; too little and the gap
> > power-
> > arced), the increased stiffness of the supply
> > coupled with the
> > higher voltage at the same (best for the previous
> > transformer)
> > gap setting allowed me to use a much wider range of
> > airflows
> > including quite a stiff breeze for a variety of
> > quenching
> > effects. As expected, too much air did decrease
> > output but
> > smoother operation resulted with more than the
> > gentle wafts I
> > had been forced to use previously and the coil is a
> > much
> > better behaved overall. In fact the airflow can in
> > effect be
> > adjusted as yet another "tuning" parameter for best
> > output.
> -----
> Yeah,that is a topic I'm interested in.
> ------
> >
> > FWIW - the transformer secondary incorporates a
> > variety
> > of inter-layer insulation (mostly paper/varnish but
> > several
> > single layers of PTFE tape at more-or-less even
> > intervals) and
> > a reasonably thick coating of a rubber compound
> > which comes in
> > cans, contains a variety of nasty solvents and used
> > to go by
> > the name of "Colorguard" or something similar.
> > Excellent stuff
> > for coating high voltage components and I have used
> > it for
> > 20kV EHT windings in the past. More conventional use
> > includes
> > dipping the handles of pliers etc. to insulate them.
> > It needs
> > to be applied in a number of coatings as applying it
> > too
> > thickly leaves gas pockets. There is also a double
> > layer of
> > PTFE tape between the phenolic bobbin and the core
> > and which
> > stretches an inch beyond each end of the bobbin so
> > allowing
> > self-suspension of the bobbin between the top and
> > bottom core
> > end legs. The core itself is ungapped.
> ----
> Same in my case - the transformer core is ungapped .
But is it a c-core? You find that k has more to do with
relative placement of the windings and the degree of core
coverage than whether it is gapped or not. Gapping simply
allows it to store far more energy (in the airgap) before flux
density reaches a saturation level. Think of the gap as a
magnetic capacitor.
Regards,
Malcolm