Hornsea ONE Project

The Hornsea wind farm was built 75 miles off the coast of Grimsby, at an estimated cost to energy bill-payers of at least £4.2 billion.

The giant Hornsea Project One consist of 174 Siemens turbines , each 623ft tall - higher than the Gherkin building in London - and rated at 7MW each. The total site area is 407.32 km2 . At 1.2GW, the project is the world’s biggest offshore windfarm and the first to have more than 1GW of capacity. That would be capable of powering one million homes. The project has the world’s longest high-voltage AC offshore wind export cable system comprising more than 900km of cables, transferring the generated electricity to the shore and the national grid. The onshore substation for the HOW01 was constructed close to the existing NGET 400 kV Killingholme Substation. Generation capacity of HOW01 is 1200MW which is transferring from wind turbines by 34 kV array cables. The 34 kV array voltage is then stepped up to 220 kV at three offshore substations via 34/220 kV transformers (two 250 MVA transformers per each platform). Then three 220 kV subsea cables (export cables) transmit the generated power to the onshore substation. There are also 220 kV interlink cables between OSS11 and OSS12 and also between OSS12 and OSS13. For grid connection of the wind farm, the onshore substation steps up the voltage to 400 kV for connection to the NGET network.

In order to regulate the voltages along the full length of the cable as well as are able to transfer 1200MW through three export cables, a Reactive Compensation Substation (RCS) is required to compensate the capacitive reactive power generated by the cables. The optimal location of platform was chosen to be approximately 60 km from shore which is also approximately mid-way for the longest cable to offshore platforms. There are three 220 kV reactors on this platform (one for each export cable).