Cylindrical Insulator Research Articles

AT present there is a great demand for insulators for high voltage outdoor isolating switchgear. With a pressure of 132,000 volts and a high mechanical stress, the greatest care has to be used in thei»design, as any breakdown in the continuity of supply of a large amount of electric power may disorganise many factories. In the usual design of high pressure insulators, cement is used inside the porcelain to join the shells and the metal parts together. Any expansion of the cement imposes bursting stresses on the porcelain, which often cracks. Some manufacturers, with this danger in view, sacrifice some of the mechanical strength of the joint by inserting elastic layers of bitumastic paint and, in addition, dilute the cement with sand to reduce the percentage expansion. Continental engineers have recently been using insulators in which internal cement layers have been entirely eliminated. They consist of porcelain cylinders carrying suitable projections called rain-sheds and containing no cement layers. The elasticity of the flanges takes up the expansion of the cement. This cylindrical construction has been developed in Great Britain by Messrs. Steatite and Porcelain Products, Ltd., who export them abroad. They now supply 132 kv. cylindrical type switchgear insulators for the substations of the latest section of the British grid. The disadvantage of the wide base customary with this type of insulator has been overcome by the introduction of ah ingenious series of flanged castings, so made that all the standard methods of fixing now in use can be applied to the cylindrical insulators. They are so designed that the greatest possible amount of surface is exposed to natural cleaning. The use of these new insulators on the grid will, during the next few years, give an opportunity of comparing them with the older type under working conditions. Then1 increasing use on lower voltages should help towards the electrician's ideal of complete continuity of service.

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