An Experimental Method of Obtaining the Solution of Electrostatic Problems with Notes on High-Voltage Bushing Design

The electrodynamic method for obtaining the solution of electrostatic and allied problems is developed to a high degree of accuracy. The method is then applied to the study of high-voltage bushings. An experimental high-air-efficiency bushing was built and tested with the result that the arc-over was very materially lower than had been anticipated. A study was then made to ascertain the reason for this large discrepancy, which was found to be due to an unexpectedly large surface effect which varied greatly with different materials. After obtaining the numerical value for the surface effect a reasonably accurate predetermination of the arc-over of structures, in which the stress distribution is known, can be made. In order to determine the desirabilitv of using artificial equipotential surfaces to increase the efficiency of the use of the supporting dielectric, diagrams were taken and a small bushing of this type constructed and tested. A study was then made to find out whether the reduction in diameter of condenser bushings is principally due to equalization of potential or due the greater strength of insulation when barriers are used. As a result of this work, it is believed that the barrier effect greatly predominates. A short discussion follows which shows the difficulties of obtaining a sufficiently exact theory of bushing design to enable us to predetermine the most efficient shape for a practical bushing.