Electrostatic field studies for busbars running in ducts

Various proposals are now being studied for running h.v. conductors supported by insulating spacers in cylindrical gas-filled ducts, in the paper, it is suggested that for economy and convenience a single cylindrical duct may be used to house more than one conductor. A 3-phase system is considered having each conductor separately housed in a duct with a cross-section which is a 120° sector of a circle. A conductor shape has been calculated that will make the potential gradient a minimum when placed within a given size of 120°-sector duct. Similar analyses are presented for duct cross-sections that are a semicircle, a 60° sector of a circle, a square and an equilateral triangle. The calculations have been made by relaxing the field between a slender skeleton conductor at unit potential and the duct wall. Variations in the gradient/potential ratio in several directions around the skeleton conductor have been examined, to find an equipotential line such that, if it were replaced by the profile of a conductor, the resulting surface potential gradient would have the minimum attainable value. By successive modifications to the position and shape of the skeleton conductor, it has been found possible to approach, by trial and error, the conductor profile that gives the minimum gradient. Gradients, cross-sectional areas enclosed by conductor and capacitances are determined for the duct shapes analysed. Comments are made on possible practical applications.