Joe,
As i was i child i played with some 10 kV transformers which are used as
ignition transformers in oil ovens. Also some HV TV cascade experiments
were done. To discharge the loaded C's i took a motor (out of a cassette
player) and applied a wire on its axis. When spotting some ligh from a
hand lamp to a photo diode that opens a transistor the motor begun to
rotate and closes a contact gap of several cm, good for 100 kV if
necessary ;-) Maybe something in that way would be an alternative to
switching usual mains relays in series. Then your 50 kV are no problem.
The contact forces is another thing of course...
73, Stefan
Am 12.10.2011 10:59, schrieb James Moritz:
Dear Joe, LF Group,
Feeding this into 3 mH (X=2500 ohm at 137.8 kHz) gives 11.2 kV (17 kV
peak) so relays in series as suggested by G8FZK and G3NYK should work
well.
It is a bit more complicated than that... if you have a number of
relays in series, when the contacts are open there will be one or more
isolated "floating" sections of conductor linking the open contacts.
To ensure that the voltage is evenly distributed between the relay
contacts, you would need to take steps to ensure that the potentials
of these isolated sections are equal divisions of the total antenna
voltage - this would mean adjusting the distributed capacitance in the
relay wiring somehow. Also, the relay at the "hot" end will have the
entire antenna voltage between contacts and coil, so coil-contact
breakdown voltage would need to be much higher than the voltage rating
for the contacts.
I'm puzzled by the 6pf/metre rule for monoploes. It seems the
capacitance
of the monopole is much higher.
This is a good first-order estimate for wire antennas - it is
reasonably accurate for wires up to a few mm in diameter, but if the
antenna element is a conducting mast, the diameter will be much
larger, and C significantly higher too.
Cheers, Jim Moritz
73 de M0BMU
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