From: Bert Hickman
Date: Sun, 05 May 2002 21:59:10 -0500
Subject: Re: [TSSP] Secondary voltage stress factor
Paul and all, Those are some VERY interesting animations, with many implications. However, I don't think the transients will be as nearly great as the model indicates for arrested leaders (in-air leaders not arcing to ground). In addition to adding capacitive loading, the streamer channel is also quite resistive. Charge transfer from the toroid to the leader should cease once the topload voltage declines to the point where ionization can no longer be maintained at the leader tip(s) due to terminal voltage drop and voltage drop across the leader. A relatively small (10-20%?) drop in terminal voltage would likely be sufficient to stop any further leader propagation until the terminal voltage can recover sufficiently to resume leader growth - this implies significant residual charge is left in the toroid after the leader propagates. The present model used in the animations is a fair approximation for a power spark to ground, but is not an accurate model for an arrested leader that doesn't reach ground. Perhaps an uncharged capacitance (to represent the leader and streamers), in series with leader channel resistance, suddenly connected to the topload the instant the leader propagates. Terry has done some measurements (quite some time back) that may be useful for plugging in leader R and C parameters for a model... Best regards, -- Bert -- -- Bert Hickman Stoneridge Engineering Coins Shrunk Electromagnetically! http://www.teslamania.com > Paul wrote: > > > One very odd thing is that the resulting step is so small. > > I've fixed this. The model was only working with the lowest 22 > resonant modes - not enough of a basis to reconstruct the response > to such a sharp transient. The model was just doing the best it > could with the available modes. > > I've re-run the response using 60 modes, and the plots below > start at the foot of the final 1/4 cycle rise before the discharge, > so we've skipped a couple of cycles from the start of the bang. > > http://www.abelian.demon.co.uk/tssp/pn040502/tfsm1-h1d2.wave.gif > > The transient is now almost of the expected size. The animation > is > > http://www.abelian.demon.co.uk/tssp/pn040502/tfsm1-h1d2.anim.gif > > which is long enough to see the pulse travel down the coil, reflect > from the bottom, travel back up and reflect from the top. > > The model is predicting that the pulse maintains a substantial > amplitude all the way down the coil. Dispersion due to different > velocities of its components is scattering the pulse, so that by > the time is has travelled the length a couple of times, the coil is > awash with small wavelets reverberating back and forth. > > Note the initial drop in voltage near the top of the coil in the > frame straight after the discharge - this is due to the coil-toroid > distributed capacitance which is able to couple the transient > directly to all parts of the coil, although the most effect is near > the top. > > The question is - are the discharge transients really this big? If > so, why don't we see sparks popping out of the secondary whenever > the topload discharges? > > This is one of those situations that calls for an experimental test. > Something like a solid state gap, modest bang voltage, earthed > electrode brought up to the toroid for a low voltage discharge. > Base current CT, and something to pickup the top volts. We can look > at the size of the base current transient which occurs 1/4 cycle > after the discharge to see if it's consistent with the model. > > One possibility is that the nature of the simulated discharge is > unreal. The program simply removes the stored charge from the top- > load in between two time steps of the model, ie within around 30nS. > Thereafter the top voltage is no longer clamped to earth and is free > to rise again - perhaps in the real coil the discharge can continue > for much longer, clamping the topvolts down, and altering the > characteristics of the transient. > > -- > Paul Nicholson, > --
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.