The electrical system receives electrical energy from the generator and adjusts voltage and frequency for onward transfer to the wind farm distribution system.
What it costs
The electrical system cost is included in that of the nacelle.
Who supplies them
Cables: Nexans, NKT and Prysmian.
Electrical components: ABB, AVK SEG, Crompton Greaves, GE Power Conversion, Ingeteam, S&C, Schneider Group, SGB, Siemens Power Transmission and Distribution and The Switch.
All wind turbines have a control panel at the tower base to facilitate on-site control of the turbine by maintenance staff without climbing the turbine. For many turbines, the space near the base of the tower is used to mount various elements of the power take-off including convertor and cooling systems.
Most wind turbines have variable speed generators connected to the array cables via AC-DC-AC power converters. There is a range of different generator/converter architectures used. With high power density, insulated-gate bipolar transistor (IGBT)-based power converters frequently are water-cooled.
Critical in the design of power converters are the requirements imposed by grid operators for wind turbines to support and stabilise the grid during grid faults and to provide or consume reactive power on demand (see B.4 and B.5 for further information). Some convertors may be split between nacelle and lower tower section to reduce tower head mass.
Where the turbine voltage rating does not match that of the wind farm array, transformers are often placed in the nacelle, or sometimes at the base of the tower. Typically, they transform from low kV (0.69 kV to 3.3 kV) to 66 kV for distribution around the wind farm array and must meet detailed corrosion, environmental and combustion requirements.
Converters and transformers are expected to be located at the tower base when the floating market is larger, as there is a higher premium on tower-head mass than for fixed offshore wind turbines.
Switchgear is designed specifically for wind turbine applications, for example gas-insulated for compactness and safety at up to wind farm distribution voltage.
Down-tower cabling is routed to enable the cables to twist, allowing the nacelle two complete revolutions of movement by the yaw system before an untwisting operation is required.
The only access to the inside of the tower base is via the access door, so if the transformer is mounted in the tower base, it is essential to be able to replace it via the door in case of failure.
If sensitive electrical systems are placed at the tower base, then these are protected by a local air conditioning system.
Electrical components and cables are generally supplied by the turbine supplier to the tower manufacturer for fit-out.