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Re: Transformers, pole
Hello there!
I have been a lurker on the mailing list for some time now. However, I
decided to shed my inhabitions and post a few lines...
First, I would like to express my deepest gratitude to those who are
responsible for establishing this discussion group. I have been privilaged to
read your technical prose concerning a subject of a long time interest to me,
that being Tesla coils. At one time I believed I was alone in the world of
amateur scientific experimentation. Now, thanks to you, I know I am not alone.
Now that you know how much I appreciate being involved in your group, I
would like to begin active participation by offering some assistance on a
recent post by Ed S. about those mighty Pole Pigs. As a student in Electrical
Engineering, I was lucky enough to recently acquire a Pole Pig on loan. The
one I have obtained was designated as scrap by the source, and I was allowed to
borrow it for a time if I promised to return it when my experiments were over.
The pig is a 4800V/8600V 15kVA. A tag on the side showed a diagram of how to
rewire the primary for 8600V. I pulled of the cover and found 4 very heavy
copper leads that were bolted internally to the 3 insulated low voltage
connectors that feed through the can (one was case ground, the other two
are for the 240V feed). The transformer apparently has a dual low voltage
winding. I paralleled the two windings and bolted their lugs back on to their
insulators.
I wanted to make sure the modification was done correctly, so I decided to
test my handywork. I plugged in a filament transformer (about 7V output) and
connected this to the pole pig (Do NOT use regular line voltage for this test).
I then connected my Voltmeter across the Hi Voltage output of the pole pig. If
I wired the low volt correctly, I would get about 250-300 Volts reading on my
meter going by the ratio: 8600V/240V = 36; so 7V * 36 = 252 Volts...
Well, I am very glad I tested my wiring because I got a zero reading.
Who knows what would have happened if I had tried it with 240V! I changed my
wiring again (boy are those wires stiff!) and again applied my 7 Volts.
Voila! 280 Volts or so were displayed on the meter!
I measured the voltage on the high voltage winding of the pig and divided
this figure by the voltage on the low voltage winding and came up with the
ratio of 40:1. Thus for a 240V input I should get out 9.6kV (unloaded). I am
now in the process of making a 240V extension cord for the pig so I haven't
put it on line yet (It needs to be filled with oil, too). I feel confident that
It will deliver something close to my measurements.
Also, I was concerned that the output voltage of the pig might be a little
low, so I am planning to buck-boost the voltage to the main capacitor by using
at least one microwave oven's transformer as you folks use an RF choke (in
series with the pig's secondary). I think I can calculate a capacitor value
to be used with the uwave transformer that will allow for the boosting at about
120Hz but will block any reflected RF power from entering the pole pig.
I am currently enrolled full time as a student, so my experimentation is
progressing more slowly than I would like. I would gladly accept any suggests
or comments from the group, as I am trying to learn as much as I can from you
guys. By the way, I have found that simulating circuits like this on your
computer is very informative, and I am trying to model mine on PSPICE.
Thank you for letting me throw in my copper.
Sincerely,
Brian