From: mystuffs@orwell.net (Metlicka Marc)
Date: Thu, 31 May 2001 00:34:26 -0400
Subject: Re: [TSSP] Secondary in motion
terry, "Terrell W. Fritz" wrote: > > Hi Paul, > > The most interesting part of the movies I see is at about 65% of the first > cycle: > > http://hot-streamer.com/temp/Vgrad.jpg > > It does appear there is more pent up voltage ready to arc near the base in > the k=0.2 case. Since racing arcs occur when the voltage is really high > anyway, maybe this little difference is all that is needed to push it over > the edge and arc. yes this could explain arcing upwards or to the primary, and if you look just at or a little past 75%, we see that the voltage at the very base is low with very high voltages above. this could be a downward race? I find it interesting that if you drag the slider across each point of zero crossing of the primary currents, the voltage gradient differs so much between each? also if we look at 49% of k=.20's first cycle, we see a very sharp point of low between two peeks on the lower 25% of the secondary. i am thinking that this potential difference in such a short area could be enough to start an arc? > > Racing arcs also tend to occur more on mistuned coils. I assume that is > because the voltage is "trapped" in the secondary coil more and does not > get out to streamers as easily. hmmm, sounds good? > > There is also a possibility that the change in voltage (dV/dt) at the lower > part of the coil is allowing greater current into the space capacitance at > that point which is helping ionization to occur. Since this is a "surface" > arc phenomena. It can occur at far lower voltage gradients than 26kV/cm. > > I wonder if dirty or dusty coils that have a lot of arc points on the coil > are more likely to arc than clean coils? If racing arcs are a very > temperamental thing, then dirt and other contaminants that promote arcing > would have a big effect. i have seen this, i commented to the other list about drywall dust on my 3k turn coil causing racing arcs that almost drove me crazy, until i wiped it clean. I'll write the other list for more info. > > It appears that racing arcs are a little more complex than "I" expected. > However, the clues are pointing in the right places. beautiful mpeg's, i will be studying and sliding them around for some time to come. marc > > Cheers, > > Terry > > At 06:37 PM 5/30/2001 +0100, you wrote: > >More movies. > > > >This time showing voltage *gradient*, both around 1.7 Mbyte, > > > > http://www.abelian.demon.co.uk/tssp/tfsm2-pdv-k=0.12.mpeg > > http://www.abelian.demon.co.uk/tssp/tfsm2-pdv-k=0.20.mpeg > > > >The vertical FSD for both movies is 0 to 425 V/turn for a primary > >bang voltage of 10kV. The gradient has been full-wave rectified, > >so its always +ve on the graph. I've left off all the trimmings they > >considerable increase the mpeg size. > > > >Trace duration, both movies, is 0 (bang) to 31uS. > > > >The corresponding static plots (with 100V firing voltage) are in > > > > http://www.abelian.demon.co.uk/tssp/tfsm2-p-k=0.12.gif > > http://www.abelian.demon.co.uk/tssp/tfsm2-p-k=0.20.gif > > > >and the secondary voltage movies, which you've already seen, are in > > > > http://www.abelian.demon.co.uk/tssp/tfsm2-p-k=0.12.mpeg > > http://www.abelian.demon.co.uk/tssp/tfsm2-p-k=0.20.mpeg > > > >The actual peak gradients are, > > > > k=0.12: max=400V/turn @ 24% height, 17.75uS, frame 59 > > k=0.20: max=410V/turn @ 90% height, 11.29uS, frame 37 > > > >Not a vast difference there in the peak turn/turn voltage. > > > >You have 17.72 turns/cm on this coil, so if you exceed 1.47kV/turn > >you will be exceeding 26kV/cm longitudinally. > > > >With some naive reasoning along these lines, you should be comfortably > >immune from turn/turn breakdown (insulation permitting?) up to a firing > >voltage of 10kV * 1470/410 ~= 36kV. > > > >Would be interesting to find someone who's having real trouble with > >racing arcs - a well tuned, bottom heavy coil that has an aggressive > >primary, and put their setup through the mill - see how that comes out. > > > >PS, by 'bottom heavy' I mean a coil that has a fair amount of its > >distributed capacitance near the bottom of the coil, resulting in a > >more rapid rise in voltage in that region, as illustrated by the > >exaggerated artifical example #5 in > > > > http://www.abelian.demon.co.uk/tssp/pn1710/ > > > >So far, to me, it doesn't look like k=0.2 is a problem for your > >coil Terry, I'll attempt to contrive a k=0.3 arrangement and run > >that one. > > > >Cheers, > >-- > >Paul Nicholson, > >Manchester, UK. > >--
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.