Study of the Electrical Resistance under Varying Conditions of some Glasses and Porcelains of Possible Utility for Commercial Insulators

JSGT 1939 V23 T197-T238

On twenty different glasses and nine porcelains (glazed and unglazed), in the form of short rods, systematic measurements were made of the volume resistivity in vacuo and of the surface resistivity under varying conditions, including temperature and humidity variation, and exposure, for varying periods of time extending to twelve months, to weathering in the atmosphere of a heavily industrialised neighbourhood. Measurements on the weathered specimens were also made after the application to them of mechanical and chemical cleaning processes. The degree of reproducibility of results was studied in detail. Wide variations in the surface resistivity of different specimens was the general experience whether after exposure to the ordinary atmosphere or to pure water vapour in a closed chamber. The volume resistivity values of different specimens of any one material examined in vacuo were in close agreement and remained practically constant with time; and the very varying resistivities of individual specimens were brought much closer together when treated in a closed space which could be evacuated, thus showing the dominating effect of the film of moisture or dissolved electrolyte, the various forms of deposit losing potency in the absence of moisture. It was shown that a wide range of suitable glasses is available to meet the electrical requirements of telephone and telegraph insulators.

 Eric Seddon, B.Sc., Ph.D., W. J. Mitchell, B.Sc., and Professor W. E. S. Turner