So a HVDC Converter Platform

One of the largest wind farms in Europe, So a O shore Wind Farm, will be realised 195 km o the coast of North East England, in the area known as Doggersbank. With 100 wind turbines covering a total area of 593 km2, totaling a capacity of 1.4 GW and an innovative High Voltage Direct Current (HVDC) converter platform, this wind farm will supply approximately 1.2 million British homes with sustainable energy in the future. The So a HVDC converter platform, to be installed at the heart of the wind farm, will be one of the largest and most powerful o shore HVDC converter platforms currently in existence or under construction.

A 25-metre-high telecom mast will be placed on the top deck of the topside. This telecom mast will provide a direct connection to the satellite dish on land. However, the challenge here is that when the platform is ready, it will be transported by ship through the Suez Canal. The platform will convert electricity from 66 kV alternating current (AC) to 320 kV direct current (DC). Two export cables of approximately 220 km in length, which together form a single high voltage direct current circuit, will transport the power from the wind farm to the onshore substation in Lackenby.

When converting alternating current to direct current heat is produced, which must be cooled. The HVAC system (i.e. heating, ventilation and air condition), that is required for cooling of the HV system demands a lot of space.

Iv-O shore & Energy has therefore applied a new cooling concept for the So a HVDC converter platform. Conventionally, the cooling system is subcontracted to an HVAC contractor who designs the system and supplies the components.

For this project, Iv-O shore & Energy is responsible for this HVAC system, including creating the design, purchasing of the necessary components and the integration with the process systems.

For the So a HVDC converter platform, it has been chosen to use a HVAC system, whereby the condenser is cooled with cold water instead of with air. Cooling with cold water has the advantage that the highest design temperature of the seawater used is lower than the temperature of the outside air. Furthermore, the heat transfer of water is better than that of air, which allows the system to be designed more compact. With the water-cooling system, lower temperatures can be achieved in the air conditioning system, and smaller ducts can be designed, which in turn also require less space.

The cutting of the rst steel for the fabrication of the platform has taken place in August 2021. The construction of the wind farm has started early 2021, beginning with the construction of the onshore substation in Lackenby. The o shore installation is expected to commence in 2023.

Neart na Gaoithe HVAC Substation

Client

EDF Energy Renewables (EDF-ER)

Technical data

Dimensions

OSS Topside (lxwxh): 36 x 26 x 20 m

Jacket height 41 m + height of the buckets 12 m

Weight

OSS Topside: 1200 mT

Jacket: 1261 mT

Water Depth variation between (-)28.6m and (-)29.8m

Field Power capacity: 450 MW

No of Offshore Substations: 2

No of WTG’s: 54 x 8.4 MW

Accommodation: 12 POB

Iv-Offshore & Energy was awarded a contract for the detailed engineering and procurement services for the two (2) Neart na Gaoithe (NnG) alternating current (AC) offshore substations. NnG is a 50:50 JV owned by EDF Renewables UK and ESB. As a subcontractor of HSM, Iv-Offshore & Energy performed the detailed design and procurement of all Piping, Auxiliary-, and HVAC equipment, as well as the integration of the high voltage equipment. Iv-Consult, a sister company of Iv-Offshore & Energy, produced the required structural shop drawing for both platforms. HSM has lined up with General Electric Grid System (GE-GS) in consortium for the Engineering, Fabrication, load-out and commissioning of this Wind Park Development in the North Sea near the Scottish coast.

The Neart na Gaoithe (“strength of the wind” in Gaelic) Wind development consists of a total of 54 Wind Turbine Generator (WTG) platforms located approximately 15.5 km from Fife Ness and 29 km from the East Lothian coastline. It covers an area of 105 km2 Each WTG has a capacity of 8.4 MW, which leads to a generating total of 450 MW being tied back to the offshore substation platforms by subsea array cables. Both offshore substation platforms are connected by an interconnector. The offshore substation platforms are connected to the onshore support station by an export cable. The onshore support station is connected to the Scottish grid system. The project will supply renewable energy to around 375,000 Scottish homes and will offset over 400,000 tonnes of CO2 emission each year.

The offshore substation platform configuration consists of a receiving end connected to the GIS of 66kV. The main transformer (MT) will transfer the power to the export cable in 220kV.

The offshore substation platform consists of two deck levels. The cellar deck houses the auxiliary systems for control, platform power requirements, communication and operation of the platform with a dedicated area (cable deck part of substructure) for the pull-in of the array cables and the export cable. The main deck has the MT installed at the center of the deck with GIS built on both sides. To improve the overall schedule and as such allow the full completion, installation and commissioning of the HV Equipment, prior to being lifted on the main structure, the GIS modules are built separately from the main structure.

The platform will normally be unmanned. However, for emergency reasons a shelter (12 POB) is provided. Furthermore, the platforms are equipped with lifting trunnions, a pedestal crane, laydown areas, W2W platforms, a heli-hoist area and other facilities to accommodate the installation works as well as future maintenance services.

The engineering phase started in June 2019. On the 15th of January 2020, the first steel was cut. The anticipated load out of the first offshore substation platform is scheduled in June 2022. The platforms are planned to be fully commissioned and handed over to EFD in Q1 of 2022.