Stabilization of plasma arcs when feeding with rectangular alternating currents of medium frequency

H.-J. Scheibe, H.-D. Musikowski

Summary: Application of plasma discharges operated at higher frequencies is of increasing interest for a number of plasma arrangements and procedures. It is beneficial to use advanced power electronics for discharge feeding utilizing dynamic current stabilization on IGBT basis. Electric arcs and plasma arcs subjected to a gas flow can be operated at m.f. power supply.
The investigations made on the free-burning arc under various inert gases (Ar; N2; H2) with 10 to 50 mm spacing between graphite electrodes show a tendency of the r.m.s. values of the arc voltage under Ar to increase with increasing frequency.
The changed operating properties of m.f. arcs can be more clearly demonstrated in operating the plasma torch than the free-burning torch. Caused by the commutation process, short-time current interruptions occur between half periods. Compared with d.c. operation, this approach allows to obtain beneficial changes in operational performance.
Even at low gas flows rates, improved mobility of the discharge channel results in a more intensive motion behaviour of the root of the arc in hollow electrodes and a tendency to better arc performances.

Hans-Jürgen.Scheibe@et.uni-magdeburg.de