RE: SSTC, Modes and soft switching

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

Original poster: "Steve Conner" <steve.conner-at-optosci-dot-com> 

 >Steve:
 >Are you certain the current grows in the primary or secondary with out
 >limit. I would expect it to level off as the input power equals the losses
 >i.e. only finite Q or do the input power grow too?

It will level off as the input power becomes equal to the losses. However
the losses are very low in a well-designed DRSSTC, so to a first
approximation the current is unlimited. It would certainly grow to a value
far in excess of the safe rating of the primary components, and blow the
apparatus to pieces.

In practice though, you design the coil so that it breaks out before the
primary current reaches an unsafe level. Once it has broken out the streamer
loading spoils the "Q" and stops the current from growing much further.

Streamer loading always seems to have this self-limiting effect* except in
the case of arcs to ground. These can practically short the secondary out,
and the primary then resonates alone with a high Q. This can cause
dangerously high currents during ground strikes. One approach for dealing
with this is to add a little extra resistance to the primary circuit.


*You can prove this by considering impedance matching. As the streamer
grows, its input impedance decreases, so the power delivered to it increases
and it continues to grow. However, once the streamer impedance gets equal to
the output impedance of the coil, any further growth would DECREASE the
power delivered to it. Hence no further growth is possible.

Steve C.