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Re: More Tuning/Debugging
Tesla List wrote:
>
> >From richard.quick-at-slug-dot-orgWed Sep 11 22:32:50 1996
> Date: Wed, 11 Sep 1996 03:03:00 GMT
> From: Richard Quick <richard.quick-at-slug-dot-org>
> To: tesla-at-poodle.pupman-dot-com
> Subject: Re: More Tuning/Debugging
>
<big SNIP>
>
> Sooo.... And I tuck this down here where few will probably really
> read it... I admit defeat. The 25KVA 7200-120/240 pig is not
> satisfactory when run saturated to supply 14,400 volts. A major
> change is in the making and I have a question or two to pop out
> for those whom I have not yet put to sleep.
Richard - I can't believe you would admit defeat at anything having to
do with Tesla coils! :?) Many of us have come through the ranks of being
observers, lurkers, and finally TCBA members and coilers with your help.
The LAST thing your well-written posts do is put me to sleep!
> 1) Pros and cons on: a) plunking down $335 for a 14,400 10KVA pig
> and using that for the standard lab supply; b) plunking down a
> similar amount for another 7200 volt pig and running two pigs
> with the HV windings in series to get the 14,400 volts needed.
>
I'd recommend option A, unless you want to run at SUBSTANTIALLY higher
than 10 - 15 KVA power levels. At these power levels, a single 14.4 KV
pig would give you the same performance in less than half the space. The
ONLY reason to consider option B is if you really wanted to explore the
20 - 30 KVA realm. You're just going to have to migrate to a 24" coil or
a PAIR of out-of phase coils like that fella in New York. :^))
You just might get a few complaints from your neigbors when you start
flickering THEIR lights as well as your own and THEIR fluorescent lights
started eerily glowing.
> 2) Since I have already have an investment in the 25KVA pig which
> is rewired on the low voltage side so that both 120 volt windings
> are in parallel ("Star")... If I plunk for another 7200-120/240
> pig, would it be better to rewire the second pig to match the
> first, and run the two "Star" wired LV windings in series to get
> to 240 volts input... Or, should I rewire my existing pig so that
> the LV windings are back to the Delta configuration (both LV
> windings in series for 240 operation) and place the LV windings
> on the two pigs in parallel. Would it make any difference?
>
I think either option is equivalent. Since one pig will need to get
re-wired, I'd select the 25 KVA one, since you know exactly how to undo
what you did. Since one pig is a 25KVA and the other a 10 KVA, the
short-circuit surge impedances will probably be different. Since you'll
always be running with a current-limiting ballast, this should'nt be a
major concern except under heavy (>25 KVA) loading. If you can, try to
get a 10 KVA transformer with an impedance % at least as large as the 25
KVA pig. Also, I wouldn't recommend tieing the HV side "center tap" to
the RF ground with this pair, since mismatching between the two will
result in unequal output voltages under various load/transient
conditions.
Minor shift to tutorial mode... skip if you bore easily:
For the benefit of those not familiar with impedance percentage, in
addition to voltage and KVA ratings, distribution transformers also
carry an impedance rating, expressed as a percentage. This represents
the percentage of the full rated primary voltage (on the HV side)
necessary to draw full rated primary current when the secondary is
short-circuited. This means that, with the secondary shorted,
(100%/%Z)xRated Current would be the primary current drawn if full rated
primary voltage were applied.
During a secondary fault, a transformer with a 2% rating would draw 50X
its rated current, while a 4% rated transformer would draw 25X its rated
current. Transformers are sometimes paralleled to increase total
capacity - in these cases, power companies will try to match impedances
to prevent mismatching and current overloading of the lower impedance
pig. In Richard's application, matching impedances will better insure
that the pig output voltages are more evenly matched under heavy loading
conditions.
> Richard Quick
>
> ... If all else fails... Throw another megavolt across it!
> ___ Blue Wave/QWK v2.12
Or another Megawatt! Good luck and safe (Mega)coilin' to ya! :^)
-- Bert --