From: "Malcolm Watts"
Date: Thu, 28 Jun 2001 10:08:41 +1200
Subject: Re: [TSSP] Toroid breakdown voltage indirect meas.
Hi Marco, On 27 Jun 01, at 9:24, Marco Denicolai wrote: > Hello all, > > Before getting a discharge to the primary and blowing the CCPS, I was > using Thor to measure (indirectly) the voltage required to get streamers > from the toroid. I was used to think the threshold value was above 12 kV > feed, i.e. 390 kV (calculated from the MicroSim model) but this > measurement proves that this value is much higher. > This time we were operating in complete darkness, besides some small red > warning lights on the safety fence around Thor. The measuremnt was well > repeatable, but indirect for two reasons: > > 1 - I was not directly measuring the feed voltage, but rather its > setpoint (i.e. desired value) > 2 - I was not directly measuring the secondary top voltage, but > calculating it with the MicroSim model of Thor. The voltage > predicted by the model, BTW, is the same that what Antonio Carlos > program (TeslaSim) predicts. > > Anyway, here are the results: > > - Feed voltage 18 kV or less (i.e. toroid 585 kV or less): no streamers, > NO CORONA anywhere. > - Feed voltage 18.35 kV or more (i.e. toroid 598 kV or more): streamers, > NO CORONA anywhere. I wonder whether it is possible to observe "ghostly" cold streamers emanating from the terminal under the breakout threshold? It requires *very dark* conditions to do this. You won't see anything looking like typical streamers. Instead, you will see a "ball" of very faint light (which on closer examination looks like faint streamers emitted in all directions) extending well beyond the terminal. The first time I saw it, I thought it was a trick of the light (like reflected gap glare or some thing else). Then I had a closer look......... Truly one of the most beautiful phenomena I have ever seen. I didn't see this when Electrum was being tested as mentioned in another post. However, it was hardly that dark during the tests and the terminal was a couple of stories high. > The toroid had no bumps or sharp sticks applied, as well as there was no > grounded rod nearby it. We really couldn'r see any corona on the toroid > preceeding leader formation. Of course, the red light were a little > glittering on the toroid surface, and the RSG was also making some light > (but not much). If you can mask off those sources of light (gap in particular) you may be in for a rare treat. I first saw this phenomenon occuring on a coil with a spherical topload a few years ago and Bert Hickman has spotted it since. It is the closest thing to an aurora you will see at STP. > I would say that the precision of the setpoint (i.e. feed) voltage > measurement was within 5-10%. Bang rate was about 300 BPS. This was also > the first time we were running in full darkness, instead of being under > the light of powerfull halo lamps. Can you adjust the power level of your supply so that you can get it down to, say, 1 BPS with the gap sitting idle? Just wondering. I've built that sort of capability into the flyback supplies I've used. Turns out to be very useful and much easier on the caps of course. My apologies to the list for wandering off the strictly scientific with this post. I couldn't pass up the opportunity. Best Regards, malcolm
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.