During 2010, DONG Walney (UK) Limited, a wholly owned subsidiary of DONG Energy A/S, has been fabricating and building an offshore windfarm with a capacity of approximately 183 MW. The Walney Offshore Wind Farm is located in the eastern Irish Sea, approximately 15 km west of Walney Island, Cumbria, UK.
Phase 1 of the Walney Offshore Wind Farm consists of 51 wind turbines each of 3.6 MW, and 1 offshore substation. The turbines will be interconnected to an offshore substation by approximately 6.3 km of 33 kV inter array cable systems. The offshore transformer platform (substation) will be situated in the middle of the windfarm and will be connected to the 400 / 132 kV Heysham grid substation onshore. Approx. 45 km of 132 kV submarine armoured cable and approx. 2.7 km of underground cable is needed to connect these two substations.
Visser & Smit Hanab is handling the work at the intertidal area of the southern side of the Port of Heysham and is responsible for the coordination and cable pull ashore.
The scope of work consists of the following:
● Engineering of the landfall;
● Coordination between offshore and onshore;
● Prepare site and install site office compound;
● Mobilisation of land-based equipment;
● Pull-back of the plough towards the pre-installed duct;
● Positioning of our cable rollers on the beach;
● Pull-in of HV cable from "Stemat Spirit" into the joint bay;
● Burying HV cable between duct and grade-in of the plough to the required depth;
● Demobilisation of equipment.
The complicating factors on the project are the long flat beach area with a tidal difference of around 8 metres and the crossing of the Barrow export cable, which is in use.
The Barrow export cable is supported by a concrete tunnel installed underneath the cable, in which a PE duct of 560 metres is installed to the shore. Another challenge is the cable route with an almost 90˚ curve at the intertidal area.
The two Visser & Smit Hanab-owned 40 ton pulling winches are being used to pull in the HV cable to shore. Prior to the cable pulling, the VSMC-owned plough was pulled towards the end of the PE duct. During the cable pull, the friction of the cable was reduced using our specially designed heavy-duty cable rollers.
Although the schedule is tight, Visser & Smit Hanab was able to pull the cable with a minimum of delays to our cable laying vessel "Stemat Spirit".
Thanks to close co-operation between all inter-company parties (VSMC, VolkerInfra and Visser & Smit Hanab), the near-shore cable work has been completed to the satisfaction of all stakeholders.