The original electricity link between England (Dungeness) and France (Equihen) was formed by a pair of d c. cables laid on the sea bed. The link was very unreliable due to the large number of anchors and trawl boards that damaged either or both of the cables Repairs were continually being carried out using a specially fitted-out vessel, the Dame Caroline Haslett, previously a collier vessel A typical repair is shown in Fig 1 Once the faulty section of cable is removed a new length held m store on the repair vessel is joined to one end of the original cable
The new length of cable IS then re-laid on the sea bed until the second end of the original cable is reached. This cable is then recovered to the repair vessel and joined to the new cable, the end of which is retained on the vessel. A loop of cable approximately equal to twice the water depth is finally laid on the sea bed in the form of a bight or loop Any cable laid on the sea bed is vulnerable to anchor and trawl damage, and repair loops as described above add to the risk Such repairs are, however, relatively easy to carry out, but subject to adverse weather
Fig 1 A typical repair(Available in full paper)
Fig 2 Electricity connections between England and France(Available in full paper)
The new electricity connection between England (Folkestone) and France (Sangatte) (Fig 2) has the submarine cables buried 1 5 m into the sea bed Whilst this affords protection against trawl boards and the majority of anchors, it does present difficulties in repairing the cables when faults occur If the previous method of repairs were adopted it is considered extremely difficult to bury a repair loop, and if surface protection were used the cable would be at risk where it leaves the top of a "hard" walled trench Surface protection in many cases, i e concrete mattresses, is not considered a satisfactory method, although this has been accepted in certain circumstances
To overcome the above problems of repairing submarine cables the CEGB and EdF had a feasibility study carried out. This study was to examine all the problems and determine whether it was possible to produce a suitable environment on the sea bed in which a cable joint could be made on a high-voltage cable The prime requirement was for trained and experienced cable jointers to be able to operate in their normal environment, as it was not considered practical to tram divers to carry out this work With the age of such cable jointers being 30/35+ years it was considered necessary to have the habitat working at normal atmospheric conditions A further reason for such conditions was that with a relative-humidity requirement of 20% with a temperature of 20°C it was not considered possible to achieve this under hyperbaric conditions
