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Re: [TCML] PFC Question (again)--more



DC, all,

I "kind-of" use transient protection on my pole transformer.
By "kind-of" I mean a 36 kV OCV rated distribution arrester
attached in parallel across the high voltage output of my 14.4
kV pig. At one time, I was using an 18 kV rated one but it
actually failed as a short on one occasion when I was firing
my coil outdoors on a windy day. One of the streamers was
"blown" back into the side of the secondary and/or the primary
circuit and this transient surge found its way back through
the 50 ft. of transmission line from the tank circuit to the trans-
former and took out the 18 kV arrester. The 36 kV rated one
has not failed in about 3 years now. I suppose the arrester did
its job though as I would much rather have killed it than my
transformer or the primary capacitor!

David Rieben


----- Original Message ----- From: "DC Cox" <resonance@xxxxxxxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Thursday, May 29, 2008 10:20 AM
Subject: Re: [TCML] PFC Question (again)--more


This is another reason why even pole xmfrs should have some transient
protection.  I use a network of 12 parallel resistors, 600 Ohms each, 200
Watts, in series with the output. After the resistor network I always use a
3" ID x 10" long air core choke wound with #14 600 volt PVC wire.  This is
insulated from ground on a pair of stand-off insulators.  I have this data
in schematic form is anyone should need it.

I know many people don't but good engineering practice dictates they
should. Even robust pole xmfrs don't like harsh transients for long periods
of time.  Lightning strikes, by contrast, are very short duration as
compared to running a xmfr for 1-2 minutes.

Dr. Resonance

On Wed, May 28, 2008 at 10:00 PM, bartb <bartb@xxxxxxxxxxxxxxxx> wrote:

Hi John,

Your right. The inductive ballast on PIGs and PTs do change the LTR/STR
scenario. I however always look at this as based on the transformer alone. But your right, the ballast changes that scenario. Even though JAVATC states that LTR is intended for internally ballasted transformers such as NST's, I
still personally look at LTR as a general transformer situation (which I
probably should not). You've done well to point out the issues. This isn't the first time! We've been down this road in the past as you know. I agree with all you've said in this post and in the other posts that I missed out on replying (had to take wife to hospital the last couple days, so TCML was
just not possible).

Anyway, great postings on this subject. I could not agree more. But I will
say that all of us (you included) really don't know if PIG's are truly
running LTR, STR,  near or at resonance. I've always assumed STR given my
personal situation and how I likely relate to the coiling world. The fact
is, we might be running STR. When you hit that STR value near 1.4, your
basically riding the edge of resonance, but just enough to allow a little
voltage calming. Were all likely hitting that area. I honestly doubt LTR in
pig (just a hunch). Not just from a massive cap size scenario or even the
ballast inductive affect on what is or is not LTR, but the fact that when
you run a coil in slight resonant charge mode (always near resonance in
either direction), there are always some good sparks to be  realized if
there is sufficient "power" regardless.

I run STR on a small coil and get great spark lengths, but I have the power in the transformer to make it happen. This would not have been possible if the coil was not running near resonance at a 1.4 ratio. Well, maybe I speak
too soon. I haven't tried a larger ratio and maybe I should. But, it does
incredible for it's situation. Who's to say that Kevin's larger coil would not do as well scaled appropriately. That is my rub. Even though PIG's and PT's are externally ballasted (not always), doesn't indicate that they must be running LTR. They can certainly be running well in STR mode as well. BPS
is certainly part of their efficiency, but when it comes to power and
sparks, efficiency isn't always the winner. Considering the costs and size
of components, it's probably economical to do the great spark lengths
inefficiently. I hate to say that (as I'm into alternative energies and the
like), but the cost of reality probably dictates that situation more than
anything else.

My bottom line is that I'm not sure and I'm pretty sure no one else is
either. If I had the resources and funds, I would strive for efficiency in
spark length. I know you would also. We all would if we could.

Bart

FutureT@xxxxxxx wrote:

 In a message dated 5/27/2008 4:22:54 P.M. US Eastern Standard Time,
FutureT@xxxxxxx writes:



David,





I didn't do the calcs lately but I think it's  close to  resonant,
maybe slightly LTR.  He's running at 120  bps.  At 120  bps,
you pretty much have to use resonant or  LTR to get good power
throughput.




John




Also (adding to my posting here).  Resonant and LTR have  a
different meaning for pig and PT coils than for NST coils.  For an NST
coil the resonant sized cap or LTR value cap is
a certain value.  For a pig or PT coil, the setting of the  ballast
determines if the coil operates in STR, resonant, or LTR  mode.
At the pig or PT's rated power, there may be a particular  value
cap for LTR or resonant.  But such a coil can be run at  more
or less than it's rated power. For example at 120 bps, a small cap could
be
installed on a pig coil, a certain amount of ballast can be  cranked
in to make it resonant, and it will run, but at less than  the
transformer's rated power.  For example let's say the  resonant
value is 0.3uf.  A cap of only 0.03 can be installed, and the  correct
amount of ballast can be cranked in to give resonant  operation,
and the coil will run.  It won't draw much power, and sparks  will
be short, but it will be running in resonant mode.  Also an  "LTR"
value cap can be installed on the pig coil, and the needed  ballast
can be cranked in to give resonant operation.  Perhaps  the
transformer will draw twice it's rated power, but it will still be
able to operate in resonant mode, despite having an "LTR" value
cap.  Sparks will be very long in this case.  In any case  resonant
operation depends a lot on the ballast setting for pig and PT  coils,
unlike for NST coils which have a fixed leakage inductance,  and
a fixed resonant cap value.  If a pig or PT coil is run with a  small
cap at high bps, then the ballast L has to be reduced to let  in
more power (if long sparks are desired).  Then the coil is  truly
running in STR mode.
 John









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