Figure 43 Gas-insulated switchgear, © ABB.
Function
The electrical system integrates AC power output from individual turbines and transforms to a higher voltage for export to onshore substation.
An HVAC system will increase output from individual turbines from for example 66 kV to 220 kV for transmission to shore via the export cable. An HVDC system will increase and convert the output from individual turbines from for example 66 kV to 320 kV DC for transmission to shore via the export cable.
What it costs*
About £80 million for a 1 GW wind farm.
Who supplies them
Hitachi Energy, GE Grid Solutions and Siemens Energy.
Key facts
Offshore substations located more than 80-100 km from the onshore substation may use HVDC to reduce transmission losses. Concerns about the reliability of offshore HVDC convertor stations, and the higher capital costs have led some developers to implement technology solutions to allow AC transmission to be used over longer distances. Some sites have used additional reactive power compensation equipment, located on offshore platforms part way along the offshore cable route, or in onshore substations close to the coast.
Key components include:
- HV switchgear sets to isolate and protect each array and export connection to the substation.
Transformers (if AC) in order to transform to higher voltage for onward transmission. A typical offshore substation will have two or more transformers to improve availability. Transformers are oil cooled, requiring the use of fire and blast protection. - Converters (if HVDC) in order to convert AC to DC for onward transmission.
Passive and active reactive power compensation, typically large coils and power electronics, to improve stability of the local grid system. - Earthing systems including lightning protection connecting electrical components and the substation structure.
- Cable trays, tracks, clamps and supports to protect electrical items.