The Automatic Start Up and Shut Down of a Mains Frequency Plasma Torch and its Instrumentation

This paper describes an automatic control system for the start up and shut down of a 415V., 100kW. mains frequency plasma torch which has been developed [1] at the University of Aston in Birmingham. Instrumentation of the main input and output parameters is provided from a centrally-located panel. In view of the large power to be controlled, it is essential that the cooling water and electrical supplies are switched in the correct order both when starting up and shutting down, and the protection requirements necessitate ``fail-safe´´ operation of the control gear under fault conditions. This automatic operation represents a significant improvement upon the original control system, which was manually operated. A closed-loop control of the outlet temperature by regulating the air flow is described elsewhere [2]. Measurements of the efficiency of the torch in converting electrical energy to heat have also been published [3].