GB329669A - Electric transformers - Google Patents

Abstract

329,669. Smith, F. S. Feb. 21, 1929. Transformers.-The insulation of transformers is so arranged that conducting parts at different potentials are separated by layers of solid and compressed gaseous dielectric in series, the arrangement being such that dielectric stress is divided between the two layers inversely as their permittivities. In a transformer having a shelltype core 4, the low voltage winding 10 is placed around a cylinder 11 of solid insulation and is separated from the high voltage winding 20 by an insulating cylinder 15 and a layer of the gaseous dielectric with which the casing 50 is filled. The high voltage winding 20 is divided into sections spaced apart by insulating spacing washers 16 which are of corrugated form in order that in the path of steepest voltage gradient between coil sections a layer of gaseous dielectric is interposed, whilst an extended leakage path along the surface of the solid dielectric is provided. For the same reasons, a series of holes 21 are provided in the cylinder 15. The sections of the high voltage winding may be further sub-divided as shown in Fig. 4 into two concentric parts separated by a solid insulator having longitudinal corrugations to permit circulation of the gaseous dielectric. The winding is supported between end discs 25, 26 which abut against X-shaped insulators 30, 31 secured to the upper and lower frame members 2, 3 supporting the core structure. The gas employed is preferably nitrogen, or, where a large amount of heat is to be dissipated, a mixture of nitrogen and helium, the pressure being of the order of fifteen atmospheres.