Assessment of air-density correction for practical electrode systems

A survey is given of available data on the effects of air density upon pre‐discharges and sparkover for nonuniform field geometries under a variety of voltage waveshapes of both polarities. Semi‐empirical relationships describing the trends of the experimental data are presented. The correction methods set up by the IEC are reviewed and some emphasis has been given to the need to distinguish between the separate influences of pressure and temperature in the overall air‐density correction factors. The limits of applicability for density correction are also discussed. Finally, a generalised semi‐empirical equation taking into account the main atmospheric variations is proposed. This is shown to offer a good accuracy for the calculation of sparkover voltages over a wider density range than has been hitherto been possible.