Effects of temperature and pressure change on positive corona and sparkover under direct voltage in short airgaps

Measurements are reported of breakdown voltage values and pre-breakdown voltage-current characteristics as a function of air density in a simple rod-plane electrode gap 50mm in length. Pressure has been reduced and temperature raised from normal atmospheric values, independently of each other, to give the relative air densities in a common range less than unity. The effects of different diameters of rod have been studied. The results allow a comparison of the characteristics at equal relative air densities attained by either pressure or temperature adjustment. It is shown that at common relative air densities, breakdown is temperature- and geometry-dependent and that there is a temperature dependence of the pre-breakdown glow currents. The density-dependent relationship between the pre-breakdown glow discharge currents and breakdown voltages is discussed. © The Institution of Engineering and Technology 2007.