An Efficiency Analysis of the Aston Plasma Torch

Abstract

Earlier work on the efficiency analysis of a recently developed mains frequency plasma torch indicated the need for two main fields to be investigated. Firstly, an overall efficiency balance had to be obtained in order to assess the suitability of the device for industrial applications. Previously, the efficiency was only considered relative to the torch itself, but an overall efficiency analysis will include the external auxiliary apparatus without which the torch cannot be operated. Secondly, it became apparent that the validity of results obtainable from certain electrical measuring instruments in estimating the non-sinusoidal power input to the arc was questionable. This, of course, affected the accuracy of the energy balance, and therefore the most suitable method for obtaining these measurements had to be estimated. An electronic multiplier was found to be most suitable, especially if used in conjunction with an integrator to average the results over a reasonable time. The thermal wattmeter was found to be nearly as accurate, and would be easier to handle in less favourable environments than the laboratory. In accounting for the power converted into heating the gas, investigations showed the need for calorimetric methods to be used. Final results proved the torch to be competitive economically, since an efficiency figure exceeding 60% was obtainable. The overall efficiency analysis indicated a total output/input conversion capability of more than 30%. These figures were well above the reported efficiencies of other a.c. plasma torches.