Re: SSTC Reliability

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

Original poster: "Steve Ward" <steve.ward-at-gmail-dot-com> 

Hi Steve,

With proper de-rating of the parts i believe 10kva is possible, but
not likely on most experimenters budgets.  One thing to keep in mind
is if your inverter was even 90% efficient you will have to dissipate
1000W in heat... thats not a trivial task.

Basically, if you rate the silicon for hard switching at the desired
voltages, currents and frequency, and keep them at say 40*C, and feed
them nice drive waveforms i think its entirely possible.

I would question, is it worth it?  In a standard SSTC (not DRSSTC)
system you are going to see very little spark length gain after about
20-30" of spark (usually 2-3kva input for 20-25" sparks).  There are
some issues that limit the achievable voltage with SSTCs.  First, you
need tight coupling to get a good impedance match, so this means you
must allow an easy breakout for the HV at the top of the coil.  Its
this low break out voltage that is somewhat to blame for the stunted
spark growth as you push up the power.

I think Justin or Aron from HVguy-dot-com built a SSTC that they managed
7kva input on and only achieved about 36" sparks.  I would still be
impressed to see such a machine, but that is an awful lot of power!

If you went the DRSSTC route, 10kva would be quite insane and would
probably be capable of 15' sparks (or more).  As of yet im not aware
of a highly reliable DRSSTC system on this scale.  Some may claim to
have a highly reliable DRSSTC, but even the best pop some IGBTs
unexpectedly... its the time period between these failures that makes
us happy.  There is still question over the best way to drive the
system, and its in the nature of DRSSTCs to overdrive the silicon to
get the maximum peak current of the devices used.  Soft switching is a
MUST.  So unless you were willing to use stacks of CM600 IGBTs, then
10kva might not be achievable with high reliability.  And one arc to
the primary or control circuitry and it may all be over in an instant
depending on how lucky you are that day ;-).

I would really like to see more high powered solid state systems out
there.  They are like no other and the rewards of having them *not*
explode is great :-).

Steve


On Mon, 08 Nov 2004 08:12:36 -0700, Tesla list <tesla-at-pupman-dot-com> wrote:
 > Original poster: "S&JY" <youngsters-at-konnections-dot-net>
 >
 > This is directed to those members that have experience with large SSTCs,
 > high powered induction heaters, particle accelerator Klystron drivers and
 > other applications using high power semiconductor arrays at RF.
 >
 > My question is, what is the likelyhood of being able to produce high powered
 > SSTCs (e.g. 10 KVA or more) with museum quality reliability?   That is,
 > coils that one can trust to run several times a day, day after day, year
 > after year, without exploded IGBT bricks and other failures?  Can reliable
 > "overload" monitoring, anti-shoot-through, shutdown and restart protective
 > circuitry be developed?  We know the challenges - highly variable secondary
 > loads and reflected impedance changes, severe RFI and EMI for the driver and
 > protection circuits, etc.  Quite an engineering challenge.
 >
 > Thanks,
 > --Steve Y.
 >
 >