High Current Arc Discharge Phenomena with Particular Reference to the Plasma Torch

Abstract

The purpose of this investigation was to study high current
arc discharge phenomena with particular reference to the plasma
torch, The principle object was to provide basic information where
required to enable the factors affecting the operation of a plasma
torch used for industrial process heating to be evaluated. This has
been achieved.

An extensive literature survey of
( i) Arc discharge processes relevant to the operation of a plasma torch, -
(ii) Existing arc devices used for heating gases
has been made. A plasma torch operated from both direct current and
alternating current has been used to establish the areas where further
research was required.

The preliminary investigations indicated that further fundamental
information on the behaviour of arcs rotated at high velocities
between co-axial electrodes in an axial magnetic field was necessary.
In particular the conditions required for the apparently diffuse nature
of the arc that had been observed at high rotational velocities and the
variation of the erosion rate of the arc electrodes with arc velocity
were required, These were investigated experimentally and the results
employed in an a.c. plasma torch operating at 410V 50 Hz at power
inputs up to 60 kW and with conversion efficiencies greater than 60%,
measured in terms of electrical power input to the arc and the useful
heat output.

The results from the literature survey, basic investigations
and the final version of the plasma torch have been used to establish
the design criteria for a d.c,. or a.c, plasma torch suitable for
industrial process heating.

In addition results of a wider application have been obtairad
including the development of a synchronous switch suitable for supplying
accurately controlled high current pulses, improved methods of
arc ignition and a new definition of arc stability that enables quantitative
measurements of arc stability to be made.

Date of Award	1968
Original language	English