Abstract
SOME progress is being made with the unifying of the electric supply undertakings in Great Britain, and electricians are beginning to look forward to larger generating stations and higher electric pressures of distribution. This is reflected by the activity of research in connexion with the dielectrics of cables for use with very high pressures. Both the Institution of Electrical Engineers and the Junior Institution of Engineers have discussed papers on this subject this year. In both these papers the progressive nature of a breakdown when it occurs is emphasised. There seems, however, to be some confusion as to what physicists mean by the electric strength of a homogeneous dielectric. This electric strength varies with temperature and mechanical pressure. The so-called “time lag” before the insulating material breaks down is due to the fact that its temperature is gradually rising and its electric strength is therefore diminishing. A spark or a brush discharge occurs when the electric strength becomes less than the maximum applied electric stress. To attempt to express “time lag” by a formula seems to us to be waste of time. There are many miles of 33,ooo-volt cable in use in Great Britain and some of them have been in uninterrupted operation for more than six years. Mr. Emanueli of the Pirelli Cable Company said that a cable had been in successful operation in Italy for eighteen months at 130,000 volts. He attributed its successful operation to the fact that air and gas bubbles had been entirely eliminated from the insulation. The manufacture of cables which will withstand these enormous pressures is a very considerable step in advance, and, provided that the price is reasonable, it will affect very appreciably the trend of the development of electrical supply all over the world. The cost of the transmission cables in any large scheme of electricity supply is always the major part of the capital cost. As raising the pressure largely reduces this cost, it will cheapen the supply to the public.
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Current Topics and Events. Nature 116, 826–829 (1925). https://doi.org/10.1038/116826a0
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DOI: https://doi.org/10.1038/116826a0