Wind Energy using wind turbine generators is a key technology in renewable energy, providing a clean and sustainable source of electricity. Offshore wind energy is the energy taken from the force of the winds out at sea, transformed into electricity, and supplied to the network onshore.
It is so popular nowadays, as offshore wind power is a constantly renewable and infinite energy source, and the conversion of wind into power creates no harmful greenhouse gas emissions.
As many countries work to tackle climate change and reduce greenhouse gases, offshore wind power will play an essential role in our future electricity generation.
Electrical Layout of the Offshore Wind Power Plant:
The typical electrical layout of offshore wind Power plants consists of a High Voltage Alternative Current (HVAC) system, with strings of 6 to 8 turbines connected by an inter-array cable (IAC), ~up to 50 km, to the offshore substation.
The offshore substation steps up the power and transmits it to shore along an export cable. An onshore substation cleans, steps up the power, and connects it to the transmission network.
For smaller projects, closer to shore (~ <10 km) it may be possible to remove the offshore substation, using an array cable(s) to transmit the power directly to an onshore substation.
Offshore Wind Substation:
The major purpose of this plant is to step up the voltage from the array cable operating voltage to the export system operating voltage.
This plant includes transformers, reactors, switchgear, control, fire protection systems, and low-voltage auxiliary systems. All this equipment is contained in a large fabricated topside structure which usually includes two or more stories and is installed upon a support structure.
To mitigate damage and risks from the harsh offshore environment, equipment is typically housed inside multiple containers or the topside is fabricated as a single fully sealed unit.
Onshore substation:
The onshore substation receives power from the export cable(s), steps the power up to the transmission voltage, and connects the wind farm to the onshore transmission (high voltage) network. Switching devices allow connection or disconnection of equipment and protection equipment helps respond to faults.
Reactive power and other grid code issues are dealt with. Onshore substations for offshore wind farms are almost identical to substations for other power-generating technologies.
Wind Turbine Installation:
Offshore wind turbines can be installed in several different ways.
- Spar-buoy
- Semi-submersible
- Tension Leg Platform
- Spar-buoy
The floating platform shown in the figure is a spar-buoy concept where its center of mass is below sea level, which helps stabilize the wind turbine during operation. One can anticipate that the spar-buoy will exhibit large rotor motions for large amplitude wave forcing with high-frequency content.
- Semi-submersible
Finally, the right platform is a barge platform concept, which employs a wide base to balance the turbine. This barge platform operates much like an oil rig and is attached to a mooring-line system to keep the turbine 2 on station. This barge concept has recently been adapted into a semi-submersible platform concept.
- Tension Leg Platform
A tension-line FOWT, where taut lines embedded into the bedrock of the ocean keep the wind turbine stable. One can anticipate that this platform would provide the most stable configuration. However, considerable tension-line fatigue may occur during above-rated conditions that force periodic motion on the wind turbine.
Offshore Wind Turbine Generators:
The major components in the drive train of offshore wind turbines are the generator unit and (for non-direct drive models) the gearbox.
Rotor Blades: The turbine has several large blades (usually 2 or 3) attached to a hub. These blades are designed to capture the wind’s kinetic energy. As the wind blows, it causes the rotor blades to rotate. The design of the blades is crucial for efficiently capturing wind energy.
Shaft and Gearbox: The rotating blades turn a shaft connected to a gearbox. The gearbox increases the rotational speed of the generator.
Generator: The high-speed shaft connects to a generator, which converts the mechanical energy from the rotating shaft into electrical energy. This is typically done through electromagnetic induction, where the relative motion between magnets and coils of wire generates electricity.
Power Transmission: The electricity generated by the turbine is usually in the form of three-phase alternating current (AC). It is transmitted through cables within the turbine tower.
Control System: Modern turbines have sophisticated control systems that monitor wind speed, direction, and other factors. These systems optimize the turbine’s performance and protect it from damage in high winds.
Power Grid Connection: The electricity produced by the turbine is often fed into a power grid. Before connecting to the grid, the voltage and frequency of the electricity might need to be adjusted to match the grid’s requirements.
