From: "Terrell W. Fritz"
Date: Wed, 30 May 2001 12:46:34 -0600
Subject: Re: [TSSP] Secondary in motion
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. 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. 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'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. 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.