As I understand it, its very much like a TIG welder, except that the OCV can be over 200V, and there's also usually continuous HF overlay.
With that kind of voltage output, a welding transformer can't be used though.
The real secret to a plasma cutter is in the torch design. You've got crazy metals in the electrode, like hafnium, because while tungsten could take the heat, it can't take the air going past it (although I've heard that some older plasma cutters required separate argon and nitrogen inputs before the modern electrodes were designed), and a special part that ensures that the high speed flow of air is swirling, to keep it in a stable, narrow, jet.
By OBEWAN
Date 03-07-2008 19:28
Edited 03-07-2008 19:31
The older plasma units had special electronics too. There was a pilot arc that got the plasma column started. The main welding or cutting arc was delayed until an ionized plasma column was formed. The pilot arcs used to be pure argon. Then the relay kicked in, and boom the main higher powered plasma column jumped across. Then there is the transferred and non-transferred arc stuff. Somtimes the actual arc is only inside the torch, but the plasma column shoots out like a flame through the torch orifice. I went to plasma school at Linde (now ESAB) in 1981. I am sure a lot has changed since then.