Return to KLUBNL.PL main page

rsgb_lf_group
[Top] [All Lists]

LF: Possible VLF HV problems, or not?

To: rsgb_lf_group@blacksheep.org
Subject: LF: Possible VLF HV problems, or not?
From: Stefan Schäfer <Stefan.Schaefer@iup.uni-heidelberg.de>
Date: Tue, 09 Mar 2010 17:35:15 +0100
In-reply-to: <9afca2641003090337t4062bb3avc9b952612014c0ba@mail.gmail.com>
References: <9afca2641003090337t4062bb3avc9b952612014c0ba@mail.gmail.com>
Reply-to: rsgb_lf_group@blacksheep.org
Sender: owner-rsgb_lf_group@blacksheep.org
User-agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; de; rv:1.9.1.7) Gecko/20100111 Thunderbird/3.0.1
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


<Prev in Thread] Current Thread [Next in Thread>