Displacement and diffusion in fluid-flow arc extinction

The displacement and diffusion theories of arc extinction in flowing fluids are defined and contrasted. The question as to the possibility according to hydro-dynamical principles of the formation of the wedge required by the displacement theory is considered and decided in the negative. Photographic evidence is also found to contradict the displacement theory. How turbulence will multiply diffusive effects is considered, and an estimate of 100 fold multiplication is given for conditions existing in gas blast breakers. This enhancement of diffusion by turbulence is found to make the diffusion theory adequate for accounting for the circuit interrupting capacities of arcs in gas blast circuit breakers. I. Introduction The important large effect which motion of the circumambient fluid has upon the circuit interrupting ability of an a-c arc has long been known, but there are still widely diverging theories as to how this effect comes about. Slepian,¹ in discussing the influence of gas motion in self-generating gas blast devices such as oil circuit breakers and expulsion fuses stressed the effect of turbulence in causing a more rapid mixing of hot and cold gas volumes, thus speeding the spread of heat, and a more rapid mixing of highly ionized with unionized gas volumes, thus speeding the dilution of the ions into larger volumes. The theory here, then seems to have been that the function of the gas motion is to intensify or enhance diffusive effects, and more particularly, thermal conduction and ion diffusion. This type of theory which makes the powerful arc extinguishing effect of the fluid flow depend entirely upon its creating conditions where diffusive effects are greatly enhanced shall be called in this paper the “diffusion theory”.