Wind Turbines Flashcards
What is the typical size and rated performance of the largest commercially available available wind turbines?
Rotor diameters are usually 160-180m with rated power of up to 9.5MWe
Vestas 164 - 164m and 9.5MW
Siemens SWT 8.0-154 - 154m and 8.0MW
Adwen AD-180 - 180m and 8.0MW
What is the cut-in speed of a turbine?
The steady wind speed at which enough torque is being applied to the rotor to rotate it and produce electricity.
3-5m/s
What is the rated output speed of a turbine?
This is the wind speed at which the maximum power is being produced from the generator. The rotational speed of the turbine is kept constant by altering the demanded torque of the generator and/or the attack angle of the blades.
10-13m/s
What is the cut-out speed of a turbine?
This is the wind speed at which the turbine shuts down in order to protect itself from damage due to high structural loads.
25m/s
How is the power from a wind turbine synchronised with the national mains grid distribution irrespective of rotational speed?
Power generated is converted from AC to DC and then electronically synchronised to the mains through pulse width modulation (using an inverter). This is called in-line frequency control.
More sophisticated control allows for the rotor and stator windings to be controlled individually. The stator windings feed directly to the grid, but the rotor windings can either feed or take power so as to synchronise the output requirements to the grid. this is called doubly fed induction generation. Only the load from the rotor has to go through the electronics.
Why do modern turbines usually have 3 blades?
- It is the industry standard
- Fewer than 3 results in a yaw wobble
- Greater than 3 results in increased drag and therefore lower efficiency
What is Betz’s law?
No turbine can capture more than 16/27 (59.3%) of the kinetic energy in the wind.
How is electrical power generated from the wind?
A propeller (turbine) is placed in the wind. The wind turns the propeller which turns a dynamo that generates electricity.
Why is it only in the recent past that wind power has started to make a significant contribution to national power generation?
- Wind mills used to be used, but would only produce 2kW (compared to fossil power stations that produced 2GW)
- Technological development such as composite blades, aero performance, etc…
- Desire for society to become more sustainable
- Government incentives
Give the equation for thrust.
Thrust = Pressure Drop x Sweep Area
Give the equation for the pressure drop across a turbine.
DP = 0.5 x Density x (Uf^2 - Ud^2)
