Natural and forced-cooling of HV underground cables: UK practice

Abstract

The paper reviews the progress of the various forms of cable cooling systems that have been developed for the UK CEGB's major high-voltage transmission network. The generation and transmission system in the UK prior to the establishment of the 132kV grid is discussed, together with the reasons for building the higher-voltage network. The statutory duties of the CEGB and its transmission responsibilities are outlined, special reference being made to the undergrounding of part of the network for amenity reasons. The investigations of soil properties, their effect on cable ratings and the subsequent adoption of standardised thermal resistivity and temperature values are considered, together with the development of special backfill materials. The different types of forced cooling system are discussed: separate water-pipe, trough and weir, air, integrally and internally cooled methods being covered comprehensively. Rating limitations caused by cable joints, and the methods used to overcome them, are included. Cooling stations and the plant and control equipment installed therein are described, reference being made to the different sources of coolant, e.g. air, borehole water, river or lake water etc. A brief description of the computer methods of solving the complex equations derived for forced cooling installations, using thermal image, finite difference, finite element and analytical techniques, is given. The Appendix comprises three Tables, giving the essential design details of naturally cooled, separate-pipe water-cooled and tunnel systems installed on the CEGB's transmission system.

Mechanical and electrical engineering aspects of long-distance underground power transmission

“…Several designs of air-cooled systems in tunnels have been proposed such as those described by Williams [3] or the air/water system suggested by Kumai and Hashimoto [9], where water pipes positioned at the roof of the tunnel remove the heat from the hot air rising from solid conductors in the tunnel. The aforementioned tunnelling schemes though consider large diameter tunnels, i.e.…”

“…The most popular method of underground transmission has been cable burial and several studies concerning heat dissipation through soil, use of special backfill materials to optimize heat dissipation etc. have been carried out [3]. In general, technological development has concentrated on underground cable design and performance [4], with little work relating to alternative underground power transmission technologies such as cable ducting systems and tunnels.…”