Re: Terry's DRSSTC - First light ;-))

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Malcolm Watts" <m.j.watts@xxxxxxxxxxxx>

On 6 Mar 2005, at 19:41, Tesla list wrote:

> Original poster: Terry Fritz <teslalist@xxxxxxxxxxxxxxxxxxxxxxx>
>
> At 10:41 AM 3/6/2005, you wrote:
> >............
> >
> >It still seems to be somewhat of a mystery as to why primary strikes
> >are so catastrophic to a DRSSTC.  Some of my coils have survived many
> >primary strikes, other times just a hint of a streamer forming on the
> >primary will kill the thing.  ...........
>
> I modeled a secondary strike to the primary.  It gave this messy
> event:
>
> http://drsstc.com/~terrell/pictures/PrimaryHitModel.gif
>
> I(Ct) is the secondary current that was at say 4 amps but it suddenly
> loops down to -70A!!  That is why the streamer had a bright flash to
> it.  That current runs back through the driver and causes the
> following messy things to happen:
>
> The antiparallel diode on IGBT3 goes in and out of conduction at 20
> and 35 amps in like 40 nS pulses.
>
> IGBT3 follows the reverse of that.
>
> IGBT2 follows a slower current crossing path.
>
> Not sure what IGBT1 is doing...
>
> But all this happens in less than 100nS!!  So something goofs up and
> it cross conducts and blows.  The high current pulse simply messes up
> the timing and cross conduction in the bridge and she blows...  Our
> little high speed IGBT high speed current dance just goes haywire...
> The model quickly crashes at this point...
>
> Depending on the coil and exactly when the streamer hits probably has
> all kinds of good and bad results...  If the primary current were say
> 300 amps, it would not reverse bias anything and all would be fine.
> But much of the time the current pulse will drive the silicon
> backwards and then it is all over...  So it looks like a high current
> pulse from the stored charge in the top load goes back and reverse
> biases the silicon at super high speed and it looses control.

Presumably, by the time a significantly long streamer is issuing from
the topload the primary current has dropped substantially so my bet
would be on that kind of event being fatal to the driver more often
than not.

?
Malcolm

>
> I just got my new strike rail installed ;-))
>
> http://drsstc.com/~terrell/pictures/StrikeRail.JPG
>
> Cheers,
>
>          Terry
>
>
>
>