From: Bert Hickman
Date: Mon, 04 Nov 2002 23:12:52 -0600
Subject: Re: [TSSP] Top Voltage
Hi Boris, all, Comments below... boris petkovic wrote: > Hi Bert, > > >>Streamer and leader propagation should occur only as >>the top terminal >>has an increasing potential - i.e., during ringup - >>and not during >>ringdown. > > --- > Can you always put your money on this ? > I wouldn't.It is a rare event I guess ,butI saw > scoping pic of TC where arc attached to a grounded rod > during ringdown period .It is indication to me that > arc can propagate during ringdown in some > situatuations as well. > What about leader propation in a natural lightning ? > Source (pocket charges of cloud ) doesn't rise > difference of potential with respect to ground as > leader propagates.The electromagnetic thing (except > avearage leader current field)which is increasing is a > field at ground surface since leader by its' evolution > carries its' strong space charge field. > --- I guess never say never... :^) The specific case I was thinking about was for Tesla Coil air streamers and leaders. If a TC leader and streamers have already propagated most of the way across a gap to ground, are close to bridging the gap, and the gap is now significantly overvolted, your observation indicates that it is then possible to make the final "jump" during a lower voltage peak (i.e., during ringdown). Generally, leader/streamer propagation requires that the E-field at the tip of the conductive leader is kept sufficiently high so as to support further electron avalanches and additional streamer formation, and that the resulting current pulses are sufficient to keep the leader channel conductive. Normally the sudden charge transfer associated with leader/streamer growth reduces TC topload voltage, and the combination of the reduced leader tip E-field (the injected space charge from the preceding leader step reduces the effective E-field) combined with the sudden reduction in terminal voltage chokes off further leader/streamer progression until the charge (and terminal voltage) can be restored/surpassed (via continued resonator ringup). The huge reserve of charge in a cloud, the replenishment of charge via internal storm activity, and the comparatively long (DC-like) period of voltage overstress makes lightning a distinctly different system than a Tesla Coil. > If we haven't seen evidence of breakout > >>during a given >>ring-up, we'll likely not see any evidence of >>breakout during the the >>subsequent ring-down. If we generated corona or >>corona streamers, we've >>injected space charge into the region near the >>terminal. > > snip;-) > --- > Yes,this seems to be a problem.According to base cap > readings ,OLTC doesn't generate injected space charge > if clearly visible breakout happens (or if generates > some it must be very small or just diffuse from cycle > to cycle).Formed streamers the observer doesn't report > in dark either. > Therefore it should be a weak ,low energy corona,not > being capable to develop in streamers. > Perhaps,some minimum space charge density and flux > area & shape avilable in vicinity of electrode are > necessary as Paul and I suspected are necessary (read > our earlier posts)? Regarding small diameter spherical breakout ball, there's some evidence in the literature that the divergence of the E-field affects the length of initial streamers - larger ROC terminals generate longer streamers in part because the E-field doesn't drop off as rapidly as you move outwards. I need some more time to digest the huge batch of technical papers I've recently obtained - will distill them down to a smaller subset of relevant ones to share... > > regards, > Boris > > __________________________________________________ > Do you Yahoo!? > HotJobs - Search new jobs daily now > http://hotjobs.yahoo.com/ > Best regards, -- Bert -- -- Bert Hickman Stoneridge Engineering "Electromagically" (TM) Shrunken Coins! http://www.teslamania.com
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.