Dear LF,
I have had some thoughts about HV problems when operating a vertical
antenna wire at some 10kV.
Normally, e.g. in a 50Hz system there will flow a current into the air
(capacitive with a restistive component) due to the ionisation of the
air when partial discharges occur.
This is due to exceeding the maximum E field strange on the wire (a
function of its radius and geometry and insulation and the gap between
wire and insulation and the epsilon r of the insulation and and and ...
;-) ).
In the special case of a VLF antenna there might be some special
conditions that can limit the influence of the partial discharges. For
example, the Z (sqrt (L/C) of such an antenna is very high, so the
resonance is quickly lost if C is changing slightly. The presence of
partial discharges will apparently increase the C since the surface is
virtually increasing. There will be additional resistive losses but
since a change the C will bring the circuit out of resonance (what would
reduce the voltage at the wire), there might be a limitation of the
momentary value of the voltage. This will be anything else than a stable
process but there might be the effect, that the voltage will be limited
like with a varistor or a spark gap in series with a resistor. So,
theoretically, there will be many harmonics and my signal might be
better visible at its harmonics than on the ground wave ;-) So, have
some of you, perhaps on LF, have experiences with theese effects??
73, Stefan/DK7FC
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