Re: OLTC II Initial calculations

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Malcolm Watts by way of Terry Fritz <teslalist-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi Stephen,

On 6 May 2003, at 17:56, Tesla list wrote:

 > Original poster: "Stephen Conner by way of Terry Fritz 
<teslalist-at-qwest-dot-net>" <steve-at-scopeboy-dot-com>
 >
 > Hello list,
 >
 > I've been doing calculations for my next OLTC, which I name Steve's Folly.
 > This is the first acceptable design I got (with some help from FANTC)
 >
 > Primaries:		Two single turn, 15" diameter, 3" copper strip.
 > Tank cap:		10uF 1000V MMC
 > Switch:		Two IGBT Bricks (Powerex CM600HA-24H 1200V 600A)
 >
 > Secondary:		10" x 20", 1500 turns
 > Toroid:		6" x 20"
 >
 > Resonant freq:		65.3kHz
 >
 > Bang energy:		10J
 > Peak primary current:	4100A (2050A/brick)
 > Top voltage:		625kV (if lossless: 450kV if 50% efficient)
 >
 > Output -at- 120bps:	58"
 >
 > I have a question for the more experienced tesla-teers on the list. I heard
 > there is a relation between the top voltage and the secondary length i.e.
 > if the secondary is too short for the voltage it will flash over and be
 > ruined. What is that relation, and do you think I am the wrong side of it?
 > I'm a bit uneasy given that if you apply the 1.1kV/mm rule, the sparking
 > distance for 625kV is 27" which is longer than the secondary! Plus, I don't
 > want to be striking the primary/control box too often. I could easily make
 > the secondary taller/thinner if I have to.
 >
 > Another thing, do you think the resonant frequency is too low? I heard that
 > streamers don't grow so well at low frequencies. Again, I could probably
 > raise it a bit without running out of peak current.
 >
 > Any input much appreciated,
 >
 > Steve C.

Spark distances in air are different for those where surface tracking
may occur. The minimum I'd use is about 8'/MV.

Malcolm