Sub-Sea Cables

The cables at the wave site at Billia Croo and the tidal site at Fall of Warness are broadly similar, with an 11kv cable runing from an on-shore sub station 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.

The conductors on the Billia Croo cables are 50mm², giving a nominal rating of 2.2MW, while the conductors for the Warness cables are 135mm², 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 capped using heatshrink caps and is fitted with a cable sock and buoy to allow retrieval to the surface. Developers use umbilical cables to attach their devices to the cables.