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Distributing Electricity to Country Districts


    DURING the last ten years, the distribution of electricity by means of overhead lines has made rapid progress; but there are still nearly 80 per cent of the occupied rural areas of England where electric supply is not available. There is a vast amount of development work to be done in these areas. Already the capital sunk for distributing power is considerably in excess of that used for generating power. The annual expense in distribution is at the present time three times greater than that for generation. The progress already made shows that there is plenty of scope for technical improvements which would increase the factor of safetv and lower the cost of supply. The rural schemes already installed prove that an overhead distribution at 11,000 volts (11 kv.) is economical when the loads are small. When heavier loads are anticipated, 33 kv. is generally adopted. In a paper by R. Dean read to the Institution of Electrical Engineers on May 15, the available data relating to rural design have been collected and the many numerical tables given will enable engineers to obviate many tedious calculations. Official regulations and a number of practical details in design are also given. For rural supply, it has been found that wood poles are the best. Both concrete and steel poles are about 12 per cent more expensive. The admissible factor of safety for wood poles has now been reduced to 3-5. At the time of constructing the 132 kv. grid, steel-cored aluminium was the most popular conductor to use, but the author's tables show that copper-cored steel or steel-cored copper provide rather cheaper lines. The requisite experience has not yet been obtained of the effects of electrochemical action on these lines after a number of years exposure to the weather. There are many subsidiary advantages in favour of steel-cored aluminium for high-voltage lines.

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