Conditions challenge cable laying
Wind turbine cables are seen being layed in the Solway Firth.
As senior project manager Peter Mckenzie-Midlane told MJ , CTC Marine Projects is operating in some ‘ challenging’ conditions on the Robin Rigg Offshore Wind Farm in the Solway Firth of Cumbria UK.
‘By their very nature, wind farms are built in demanding locations, so we are very much affected by the ambient conditions, including strong winds, strong currents, waves and swell, said Mckenzie-Midlane. ‘The working conditions are made worse by the large tidal variation of 9m, which could mean the support barge sits on the seabed at times. However, the ‘Union Beaver’ is designed for this purpose and she can just sit down on her bottom without damage.’
The URS Union Beaver is a 1990 built, 600 ton self-propelled barge, which has been converted from a four point anchor handler to an eight point anchor handler with a proprietary aquatic reel system on board. Because of the conditions, which are very different to being in open water, it was necessary to find a barge that was exceptionally stable, but which could also, in an emergency, drop its anchors to wet storage and get itself out from amongst the towers to safety.
The barge is supported by the Odin, a chartered Shoalbuster anchor handler, and the dive support vessel Terramare. Ambient conditions affect the dive support operations as well and it is a demanding job to try and orchestrate the various vessels to maximise the work window, which can be small. ‘It is immensely frustrating having to stop operations due to the weather and sea conditions, but safety remains paramount,’ added Mr Mckenzie-Midlane.
CTC is contracted to connect seventeen turbines with 33kV inter-array cable and conduct the pull-ins at both ends, including testing prior to tie-back. The cable in question is 93mm diameter with link lengths of between 600m and 800m.
The company will carry out the work in two phases, installation and burial. The lay will be done using an aquatic reel drive system and tensioner and the burial will be carried out by CTC’s impressive CMR4 cable burial remotely operated vehicle.
Although this is its first major windfarm project, in the last 11 years CTC has successfully completed over 87 trenching and cable installation projects, which gives the company a good background in the necessary technology and engineering. With luck as well as skill, this particularly demanding project will be completed within the three month schedule.
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