Re: OLTC update

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

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

Hi Terry,

On 28 Aug 2002, at 12:34, Tesla list wrote:

> Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>
> 
> Hi All,
> 
> I ran various MicroSim models with K going from 0.05 to 0.25 with primary
> resistances of 0.5, 1.5, and 2.5 mOhms.  I found the resulting peak
> secondary voltages:
> 
> 	http://hot-streamer-dot-com/temp/OLTC08-28-01.gif
> 
> 	http://hot-streamer-dot-com/temp/OLTC08-28-02.gif
> 
> I think the dip in the yellow line at 13 is a mistake in my data.  In the
> low loss (r=0.0005) case you can see the effect of sweet spots above k=0.20.
> 
> It's sort of neat in that you can see the affects of primary resistance,
> self quenching, and "some" of the sweet spots Marco and Antonio speak of.
> I guess I have to disagree a little on the sweet spot thing since those
> analyses do not take into account Rs, Rp, or streamer loading.  If the coil
> is really efficient, the sweet spots become more important.  But for a coil
> with typical loss, other factors tend to overshadow the sweet spots.
> 
> Note that high coupling is not always the best as in this case.  But I have
> a great advantage in being able to quench at any time too.  That actually
> adds about 76% to the streamer power!  It also reduces the stress on the
> IGBTs which is getting to be an issue.
> 
> So it looks like a k of 0.115 is optimal with a dwell time of 102.5uS.
> 
> 	http://hot-streamer-dot-com/temp/OLTC08-28-03.gif
> 
> I will raise the secondary tonight for this.  Not that I am quenching while
> the voltage on the caps is negative to help "push" the resonant charging.
> This is also a zero current crossing which eases IGBT and TVS stresses from
> the primary coil kicking back.
> 
> The latest schematic is at:
> 
> 	http://hot-streamer-dot-com/temp/OLTC08-28-04.gif
> 
> I also have a chart showing the line voltage and current here:
> 
> 	http://hot-streamer-dot-com/temp/OLTC08-28-05.gif
> 
> The line noise and power factor are excellent.  The coil has an input power
> of 286 watts right now at 120VAC.  I'll pick up some 2.5 amp fuses today too.
> 
> One thing that is a little scarry is that the IGBTs will see a 3356 amp
> peak current.  Their rating is 2040 amps.  I am pretty sure I will be OK
> now at 120VAC but at 240VAC, the peak current will get near 4500 amps!  I
> will order up some more IGBTs today for my peak current testing.  I may
> need more IGBTs since 450 amps is over twice the rated peak current.  I'll
> just have to test some and see...

Each IGBT is discharging an individual cap isn't it? If that's the 
case, then the only ways of alleviating the stress on the devices is 
to start paralleling them with others or reduce the capacitance 
associated with each.

     Re the coupling, Eddie Burwell has it. Could you post a url for 
an oscillogram of the primary ringing alone please? I don;t have time 
to wade through all the urls you post unfortunately (my problem, not 
yours ;)

Regards,
Malcolm