Performance of Sphere and Rod-Rod Gaps Under Direct Voltages

Up to now there is no detailed study dealing with the problems concerning the measurements of the highest d. c. voltages. The sphere gap is the only device recognized and normally used, but there are many doubts on its behaviour expecially as far as the accuracy is concerned. Additional causes of uncertainty are related to correction factors for atmospheric conditions and to the exact knowledge of the characteristics of very high ohmic voltage dividers, for which a precise and therefore difficult calibration must be required. This paper reports the results of a research on the behaviour of the sphere-gaps. The performance of the rod-rod gap is also examined with a view to the possibility of using it as measuring device. Finally the problem of defining a withstand test voltage is briefly discussed.