Sub-Sea Cables
The cables at the wave site at Billia Croo and the tidal site at the Fall of Warness are broadly similar, with an 11kv cable running from an on-shore substation out to each open-sea berth.
The cables are wet-type composite cables consisting of three 120mm2 EPR-insulated stranded copper power cores designed for alternating current, three 2.5mm2 copper signal/pilot trip cables and a 12-core single-mode fibre-optic bundle. The cable is then armoured with two layers of galvanised steel wire. The subsea cables were built to specification for EMEC by Pirelli.
In 2010 a UK Department for Energy and Climate Change (DECC) funded project enabled EMEC to increase its berth capacity by installing new cables. The cables, built by Draka in Norway, are of a similar specification to the first cables described above with the inclusion of an additional 4 core 4mm2 auxiliary power cable. Two additional cables were installed at the tidal site and one at the wave site using a total of 12Km of newly procured cable.
The conductors on the Billia Croo cables are 50mm˛, giving a nominal rating of 2.2MW, while the conductors for the Fall of Warness cables are 120mm˛, giving a 5MW rating.
The cables were laid as standard sub-sea cables on the sea bed. As the cables approached the shore, in 15m of water, ductile iron cable protectors were attached. At the low water spring-tide mark, each passes into a trench dug 1200mm into the seabed and beach. On shore, the cables are fed into a manhole and then into the substation.
In the substation, each cable terminates at an 11kV circuit breaker, along with the tripping cable. The fibres are terminated in the communications area of the substation.
At the seaward end, each cable is terminated using a specially designed connector provided by J+S Ltd which allows EMEC to carry out planned condition monitoring of any cables not in use by developers. These terminators can, if required, be converted into splices to enable developers to use umbilical cables to attach their devices to the EMEC cables.