From: Paul
Date: Thu, 09 May 2002 22:22:40 +0100
Subject: Re: [TSSP] Secondary voltage stress factor
Boris wrote: > Once,I had been ready to think just like you but > changed my mind after seeing real scope > discharges of several units. Well you have the advantage there because I've never had a close look at the discharge currents. Perhaps I'm thinking too much like the characteristics of a primary gap arc. Maybe the toroid-ground discharge arcs are more fragile, in that the current path doesn't survive the initial zero crossing, except for the HF currents which you describe, whose ringdown will be short compared to an Fres 1/4 cycle. > problem being here that these violent > transients occure at 5 ,10 ,20 Mhz or more and EM > theory not yet imbeded in a software starts to play > important role. Yes, if we say that our upper frequency limit for the quasi-static approximation is when the coil is 5% of a free space wavelength, we are limited to considering modes up to around 30Mhz. The highest I've actually used is 24 Mhz. Therefore we may expect to come up against features that we cannot reproduce with the model. The arc discharge itself I'd guess would be dominated by a ringdown at the resonance of the arc's self-inductance and the toroid capacitance. For a 1 metre arc and a Ctop of 50pF this would be around 20 Mhz, so this may also be a factor. I think we should just apply some simple discharge models to begin with, accepting the frequency restrictions, ignoring the reactance of the arc discharge loop, and just see how well these compare with observations. When we see from the scope the character of the discharge, we can put this into the model to generate a base current prediction. Then we can compare the base current to test the model. Then the model can be used to look for transients big enough to contribute to secondary voltage stresses. I guess that counts as a strategy. Cheers All, -- Paul Nicholson, --
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.