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In order to study the degradation of insulating materials when subjected to high alternating voltages, two methods of test are usually used. In one method the solid dielectric in sheet form of a size large enough to prevent flashover is placed between two metal electrodes and the voltage is increased until surface ionization and sparking occurs at the edge of the high-potential electrode. The material is then usually left on test until failure by breakdown occurs. The other method is to place the dielectric in a corona discharge through a gas, terminated at both ends by an insulating layer of glass. This method lends itself to simpler interpretation because tests can be made in a closed system. The power consumed in the glass corona generator can be measured by either of two methods using equipment that is available in most laboratories. Agreement between the two methods is shown to be within a few per cent. It is also found that the corona power increases linearly with voltage and that certain organic insulations when subjected to ionization in a closed system with pure oxygen degrade at a rate proportional to the measured power.
Reynolds, S. I.
Research Associate, The Knolls, Schenectady, N. Y.