Re: OLTC update - primary IGBT loss

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

Original poster: "Paul Nicholson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <paul-at-abelian.demon.co.uk>

Terry wrote:

>  Paul predicted a Q of 45 when "we" thought it should be 200...

Ah, the '45' isn't a prediction - its a measured value extracted by
tcma from your secondary ringdown.  My best Q prediction is 79, which
is obtained by considering the wire AC resistance but not the proximity
loss or other losses due to coupling with the surroundings.  Usually
these Q predictions are a factor 2 to 4 higher than obtained in 
practice because of all the extra un-accounted losses that affect the
real coil.  The actual figure of 45 seems pretty reasonable under the
circumstances.

I agree with your revised figures for the primary. 

The OLTC faces two challenges, one being the low impedance of the
primary (copper losses and Vds become significant) and the other being
the low frequency of the secondary (large Lsec leads to high copper and
proximity loss).  

Neither of these difficulties is at all surprising, since you're 
asking for an overall voltage transformation which is a factor 100
times what a normal TC achieves.  That's a tough proposition and it's 
great that it's working so well.

The question now is whether these low Q factors lead to low power-to-
streamer efficiency, which in turn depends on how quickly the streamers
form.  Do they take a quarter-cycle, or maybe a few cycles, or does
it require repeated bangs?

Those questions lead us to where the tssp project is right now. We need
to get that topvolts probe sorted out.

Can you use a fibre-optic current probe between topload and breakout
point?  That would give us the streamer current.  We could at least
see where in the RF cycle the streamers are taking current.  

I'm having trouble modeling your triple parallel turn primary - the
interaction between the three is not modeled by the tssp software and
they are too far apart to model as a single turn.  This is why I 
haven't sent any V/I profiles.
--
Paul Nicholson
--