Effect of discharge products upon corona discharge and spark breakdown voltage

An investigation is described of the variations, with gas composition, of d.c. sparkover voltage between uniform-field and wire-cylinder electrodes. Measurements were made in flowing two-component mixtures of nitrogen, oxygen, carbon dioxide and argon. Substantial differences in behaviour were found between uniform and nonuniform field conditions, and between mixtures in which chemical combination was, or was not, possible. The results are generally explicable on the assumption that chemical compounds, formed in corona discharges that precede sparkover, often affect the sparkover voltage decisively. The term `electric strength¿ for gases requires careful definition; oxygen had a lower sparkover voltage than nitrogen in a uniform field and vice versa in a nonuniform field. Measurements of sparkover voltage in closed vessels, on mixtures of nitrogen and water vapour, showed the large effects of discharge products, including ammonium compounds and oxides of nitrogen, and the small effect of water vapour itself.