Design and construction of the 400 kV cable system for the Severn Tunnel

The paper describes the reasons for the construction of a cable tunnel under the Rivers Severn and Wye, and the application of an integrally cooled pipe-type cable system to the crossing. Difficulties of applying, to the tunnel scheme, the results of a field trial involving a buried pipe/cable scheme are examined, and the solutions described. The final design of cable and cooling system is given which enables a 4 × 400 mm2 s.c.a. overhead line to be matched in current carrying capacity by a single cable per phase.