From: "Barton B. Anderson"
Date: Sat, 11 May 2002 14:25:24 +0000
Subject: Re: [TSSP] Topload breakout potentials
Hi All, Yes, my toroid is smooth (from the last bulk buy of spun alluminum toroids). I don't use a breakout point at all. I have no trouble breaking out. My typical mode of operation is to turn up the voltage to about 180V input (a habit) on a 14.4kv 10kva pig. I then increase current via variac ballasting. Like I said, breakout is no problem at all. Without racing arcs, I would begin increasing voltage to max and then increase current again. The racing arcs are occurring a second or two after breakout and streaming all the way down the secondary from the top. I'll run it tonight and recheck voltage, current, where breakout is occurring, etc... I am getting several streamers at this point. It seems I'm getting just the opposite of what one might expect. I'll recheck tuning as well. It's possible the toroid is slightly higher than the coil would like and may need to add a bit more shielding to the top windings. I'll check that out as well. I don't plan on changing coupling at this time. I'll work with everything else first. Take care, Bart Paul wrote: > For John's TT42 that we're looking at the voltage stresses on, tcap > computes a maximum surface gradient of 0.051 V/cm/V occuring on the > outer surface of large (upper) toroid at a point 24 degrees below > the 'equator' of the tube's cross section. > > With an estimated 590kV peak topvolts for a 4J bang, that gives a > peak surface field of 590 * 0.051 = 30kV/cm. > > For Bart's coil which we're also looking at on another thread, a > 15.3 kV firing evolves 460 kV on the topload. The max surface gradient > for Bart's topload is 0.026 V/cm/V at an elevation of +20 deg, which > gives a field strength of 0.026 * 460 = 12kV/cm. > > These figures suggest that John's coil would break out much earlier > than Bart's, and would perhaps produce more but shorter streamers. > Assuming a smooth toroid and a 26kV/cm breakdown threshold, it looks > as if Bart's topload shouldn't be breaking out at all without some > assistance from a breakout point. > > I wonder if these characteristics are bourne out in practice? > > -- > Paul Nicholson, > --
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.