The performance of glass insulators, and comparisons with porcelain

The present paper summarizes a number of separate investigations which, owing to their diverse nature, are described in self-contained sections. Nevertheless, they are complementary in that they serve to show the reaction of insulators to various hazards as represented by controlled test conditions and, in particular, indicate the relative behaviour of porcelain and glass insulators. Part 1 deals with the effect of power arcs which may develop as a result of a flashover, and is confined to suspension insulators. Part 2 indicates the differential heating which may occur under the sun´s radiation and which in turn leads to mechanical stresses and the possibility of fracture. Part 3 examines the hazards from stone-throwing and determines the impact resistance of insulators from this point of view. Part 4 provides impulse electric strengths of porcelain and glass from which the possibility of puncture due to surges can be estimated. Lastly, Part 5 notes some service experience on the behaviour of glass insulators in humid and polluted atmospheres. In general, the paper aims to estimate the security of insulators with respect to conditions of service which are not directly related to the standard tests. The various sections of the paper were contributed by the following organizations and individuals, to whom the Electrical Research Association wishes to make due acknowledgment:- The work on power arcs was carried out at the E.R.A. Laboratory by Messrs. A.E. Helden and C.E.R. Bruce. The work on the effect of radiation and impact tests was carried out at the E.R.A. Laboratory by Mr. A.M. Thomas, Miss M.V. Griffith and Dr. S. Whitehead. The impulse electric-strength tests were carried out at the High-Voltage Laboratory of the N.P.L. by Messrs. A.H. Davis and W.G. Standring. The observations on exposure to humid and polluted atmospheres were communicated by Mr. J.S. Forrest from the Central Electricity Board.