When the turbines on Greater Gabbard offshore wind farm were erected, there was no mains connection available to power and complete the offshore project. Normally this would be supplied from the National Grid via subsea cables, but these were still to be laid and commissioned. A temporary power supply was required until each string of turbines received power direct from the grid.
The voltage requirements for the turbines varied between 415V and 690V. 690V was required for the heaters and dehumidifiers to protect the electrical components of the turbines, as well as the internal lifts and the hydraulic pumps. Whilst the anti-corrosion system was a “cathodic protection system” which required power at 415V to prevent the structures corroding in the sea.
A temporary power package was therefore needed to provide both 415V and 690V and this had to be located within a small area at the base of the transition piece (TP), which connected the foundation pile to the turbine. There was also a 1.5T weight limit on the lift.
Temporary power and climate control equipment was also needed during the build of the substation and while it was offshore, prior to mains connection. This was to prevent deterioration of the HV equipment and switchgear located within the substation and also to provide a domestic power supply for the offshore workforce.
Aggreko provided an offshore specification 415V generator connected to a step-up transformer. This meant that both 415V and 690V supplies could be maintained at the same time. Aggreko provided all cables and connections through 415V and 690V trailing sockets. All equipment was fitted with lifting slings. The machines were all lift-certified at the start of the project and every six months offshore thereafter.
Aggreko supplied a 125 kVA generator fitted with a fire protection panel and distribution board to provide power to the substation structure and for climate control equipment.
The maintenance and repair of this equipment was carried out by Aggreko’s service team. All engineers received offshore training specific to the offshore wind sector. Access to the TP for servicing was from a crew transfer vessel for which additional safety training was carried out. A full risk assessment was completed and procedures were agreed by Aggreko’s Health and Safety Officer, the customer and local service manager.
Result for the customer
The solution prevented deterioration of both the turbine structures and the electrical and electronic equipment. The rotors were turned regularly to prevent damage to the bearings and to enable static commissioning to be carried out.