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The Protection of Telecommunication Lines and Equipment Against Lightning Discharges (Chapters 1 to 5)

image of The Protection of Telecommunication Lines and Equipment Against Lightning Discharges (Chapters 1 to 5)

This Handbook contains a general survey of atmospheric discharge phenomena and of the protection devices in use. It gives the explanations in the appendices to the various chapters are necessary for an understanding of the phenomena as well as for calculating the design of protection devices. For a wider study of theory and physical phenomena, reference should be made to the numerous specialized publications. It seems best to limit the field of application of this Handbook to telecommunication lines and associated equipment. The latter also include cable and overhead lines which lead to transmitting installations, radio relay stations, etc. at high altitude, which are thus more than normally exposed. The present Handbook does not deal with the protection of the stations themselves, since such problems concern the protection of buildings against lightning and this, for transmitting stations and radio relay stations, falls within the domain of radio technique. The protection of the buildings in which the telecommunication equipment is installed is governed by the national regulations on lightning protection.

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Atmospheric discharges and resultant physical phenomena

Thunderclouds usually develop either on a hot summer day (heat storm) or as the result of the impact of advancing cold air on a mass of warm air (frontal storm). To start the growth of such a cloud, the air must contain a certain amount of moisture and two adjacent air masses must exist at different temperatures. In these conditions, the warmer air rises and, in expanding, is cooled. At a height of 5 000 feet water vapour begins to condense from the moist air. The latent heat of condensation is then transmitted to the surrounding air so that the normal decrease in temperature with increasing height is reduced. The temperature of air with condensed water is thus higher than the surrounding unsaturated air at the same level. It is this comparative warmth which produces the strong upward air currents in a thundercloud.

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