Moisture control of cable environment with particular reference to surface troughs

The rate of dissipation of heat from buried cables is dependent on the thermal resistivity of the surrounding backfill. It is well known that, for granular materials, e.g. sands, the thermal resistivities vary markedly with the moisture contents, and high resistivities can be reached because of drying. The paper discusses the factors that lead to moisture migration, and gives practical information on methods of controlling the moisture content in cable backfills. Information on mean wind speeds, hours of daylight and average rainfall are collated to support the theory of establishing a `moisture-control season¿ that is suitable for UK installations. Results of field trials are analysed, and indicate the major effect of rainfall and the smaller effect of solar radiation on the performances of cables laid at different depths. Difficulties associated with calculating water losses are outlined, and the results of experiments to establish a rate of loss from surface troughs are recorded. Recent cable circuits with automatic-moisture-control facilities are described. These have been confined to surface-trough in stallations employing cement-bound-sand backfills, but the possibility of extending the technique to cable reserves and other types of installation is suggested. The economic advantages of moisture control and future trends resulting from savings in cost and space are also discussed.