The design of an ellipsoid voltmeter for the precision measurement of high alternating voltages

This paper discusses the various factors that influence the design dimensions for an ellipsoid voltmeter to be used for the precision measurement of a specified range of high alternating voltages. Having selected the overall dimensions of the ellipsoid itself, methods for evaluating the constants of the instrument are discussed, and a method is given for determining the necessary constants for a given ellipsoid from a series of weighted measurements. The theory leading to the simple equation giving the field strength as a function of the period of the ellipsoid makes certain simplifying assumptions, and the magnitudes of the errors arising from these are considered. Where they are of the order of 0.01% or more, correction curves are given by means of which the necessary allowances can be made in any given case. The theoretical treatment is illustrated throughout by reference to a particular instrument, and it is concluded that, after its performance had been analysed on the above lines, it would give results having an estimated error of less than ±0.03%.