RE: Ok, what is an LTR cap.

["David Dean" <deano-at-corridor-dot-net> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

> -----Original Message-----
> From: Tesla list [mailto:tesla-at-pupman-dot-com]
> Sent: Friday, August 25, 2000 11:24 PM
> To: tesla-at-pupman-dot-com
> Subject: RE: Ok, what is an LTR cap.
>
>
> Original poster: Terry Fritz <twftesla-at-uswest-dot-net>
>
> Hi Deano,
>
> 	The real key here is that in an NST the primary to
> secondary coupling is a
> little loose so the secondary is sort of free to ring up.
>
> 	In a pig, with very tight coupling, this degree of freedom
> would have to
> be the ballast.  So if you rang the secondary up into ultra high voltages,
> the primary would follow via the turns ratio.
>
> 	It all sounds sort of nasty.  Personally "i" would try in
> on a computer
> first ;-))
>
> 	Off hand, I would think you would divide the ballast
> inductance by the
> turns ratio squared to get the transformed impedance value of the ballast
> as it looks on the secondary side.  Then choose your capacitor to resonate
> at 60Hz with that value.
>
> At 220VAC and 10kW at 60 Hz, we could choose a ballast of Xl =
> 4.84 ohms or
> 12.84mH.  With a 14400 pig that transforms to 3uH.  To resonate at 60 Hz
> the cap value is 2.34F.  An impossibly high cap value...

Try 4.84 X 3600 = 17424ohms = 152.2nf
or 5.76 X 3600 = 20736ohms = 127.9nf
(actually 6 ohms works out to 40 amps at 240 volts)
so 6 X 3600 = 21600 ohms = 122.8nf
remember that high voltage = high impedance,
low voltage = low impedance

> So it would appear that there is no chance of getting resonant or LTR
> charging from a pig.  However, if I should have multiplied the square of
> the turns ratio instead of dividing, I would get 127.5nF...  If I
> have made
> that error (which the book on my lap says I didn't...) then the resonate
> case would be easy...  Perhaps others could please double check my
> reasoning and math here...
>
I don't know what book you have, but weather you multiply or divide, well...
That would depend of course on how you look at the ratio, 1/60 or 60/1.
I just take the number "60" and then apply the rule to see if the answer I'm
looking for should be larger or smaller. Then multiply or divide
accordingly. A fine example to remember and help keep it straight is a plate
circuit in a vacuum tube amplifier (high impedance) driving a loudspeaker
(low impedance) through a stepdown transformer.

> I would think such a resonant system would make one darn good bang!!
>
> Cheers,
>
> 	Terry
>
>
>
> At 10:22 PM 8/25/00 -0500, you wrote:
> >Hi Everyone,
> >
> >I have been following this thread with some interest.
> >
> >snip
> >> >  > > however (and OBIT's), can use LTR's. Could you imagine the
> >> joules for a
> >> > pig
> >> >  >
> >> >  > > using an LTR? I see smoke, fire, wooosh!!! Well, for most
> >> of us, not
> >> > Greg,
> >> >  > > Bill, Hull, etc... or you Chris (yet?).
> >> >  >
> >> >  > Actually, Terry's MMC Calc gives me .351uF.
> >> >
> >> >  For a 240/14.4kv, 694mA, 20,749 ohm pig? Terry is .351uF
> >> correct? I though a
> >> >
> >> >  matching reosnant cap size should be 0.128uF. Maybe my math is
> >> wrong here.
> >> >  Someone please clarify?
> >> >   >>
> >> > As I found out the hard way, you can also get into a 60 hz
> >> resonant condition
> >> >
> >> > with probabaly any cap by varying the inductance in the
> primary used as
> >> > ballast.  I am using .05uf with a 14.4  5 kva distribution
> >> transformer and it
> >> >
> >> > was resonant with the particular welder that I was using.  It was an
> >> > uncontrollable condition.  Maybe with a sync rotary gap, but
> >> not with my non
> >> > sync rotary.
> >> >
> >> > Ed Sonderman
> >>
> >>
> >>
> >>
> >> Yes, I remember the situation. Your transformer is resonant at
> >> .064uF, so you
> >snip
> >
> >So what would happen if one hooked up a pig to a TC primary
> circuit with a
> >"resonant" cap,
> >say 0.064 for a 5KVA or 0.128 for a 10KVA, then hooked the low
> voltage side
> >to a 240V source,
> >and did not put any ballast in the circuit, just depended on the
> "impedance"
> >of the pig as if it were a NST?
> >
> >Hint:
> >(excerpt of a post on the subject from Malcolm)
> >
> > <          resonant charging calcs really only apply to a
> >ballasted system. The faceplate rating on a pig might be 10kW
> >but there is nothing to stop you drawing 100kW from it on a
> >transient basis as the leakage inductance is so low (well it
> >should be - it's supposed to mimic a voltage source with the
> >mains behind it).>
> >
> >"I" think the fuse or circuit breaker, whatever over current
> protection is
> >upstream would blow.
> >
> >For my money, the distribution transformer (AKA pig) is close
> enough to an
> >_ideal_
> >transformer to not worry about any of its parameters (that is DC
> resistance,
> >inductance of the windings, coupling coefficient, etc. etc.)
> except for the
> >turns ratio.
> >Of course if you are planning to overload it for a long time,
> then you might
> >want to
> >consider the "% impedance", but that would be a rarity for our
> application.
> >
> >"I" think that the only meaningful impedance seen by the TC
> primary circuit,
> >spark gap, etc.
> >is the impedance of the ballast as "reflected" by the transformer.
> >
> >Suppose someone wanted to run in "Mains resonance mode". In
> order to match
> >the pig to the tank circuit, an inductor with X(L) = X(C)/n^2

> where n is
> >the turns ratio of the transformer, and C is the tank cap, the
> reactance's
> >of course calculated at line frequency) would be inserted in
> series with the
> >low voltage winding of the pig.
> >If the inductance were larger, then it would be a LTR cap. situation.
> >If the inductance were smaller, then it would be a STR cap. situation.
> >
> >For the record, I try to run mine LTR.
> >
> >Just my humble opinion,
> >later
> >deano
> >
> >
>
>