GB329048A - Electrical apparatus and means for protecting the same against transients, surges, and the like - Google Patents

Abstract

329,048. Smith, F. S. Feb. 21, 1929. Protective arrangements. - Electrical apparatus is protected against excess voltage by being connected in shunt with a fast discharge gap, the apparatus and the gap being housed in a casing which, with the gap, is filled with gaseous dielectric under pressure. The fast discharge gap is constructed to avoid corona preceding the breakdown and the gaseous dielectric has a low dielectric time lag. The dielectric may be a single gas such as nitrogen or carbon dioxide or a mixture of gases such as helium and nitrogen in such proportions and at such a density or pressure, for example, sixteen atmospheres, as will give the required insulation characteristic combined with adequate thermal conductivity. The transformer has a primary winding 4 on an insulating cylinder, and a spaced sectionalized high tension secondary winding on a cylindrical insulating support 5. The casing 2 is sealed and filled with the gaseous dielectric under pressure so that the windings have solid and gaseous insulations in series between them. The low tension terminals are housed in a bushing 24 in the base; one end of the secondary is earthed on the casing and the other connected to a terminal 8. A fast discharge gap is constituted by a conducting tube 10 surrounding and in connection with the terminal lead and a conducting bushing 11, welded into the transformer casing, which supports an insulating housing 9 for the terminal. The gaseous dielectric fills this gap and bushing. Breakdown of the gap is designed to occur at a voltage less than that which would harm the apparatus or rupture or overstress the solid dielectric.