Horizontal Axis Wind Turbine (HAWT) Generator
- Horizontal axis wind turbine generators are being used all over the world successfully. The main component of a propeller type wind generator is shown by a schematic diagram in Figure A.
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| Figure A |
- Usually it has two or three blades made of wood (for low power generation) or high density glass fibre reinforced plastic (F.R.P) of aerofoil section. Diameter of rotor is 2 m to 25 m in diameter. Modern rotors may be upto 100 m diameters. Rotor blades are assembled on hub The turbine shaft is mounted in the bearings.
- Whole system is mounted on tower top. It is designed to withstand the wind loads during gusts.
- Electromagnetic brakes are provided for automatic application of brakes if the wind speeds exceed the designed speed.
- The hub, brakes, gear box generator with electrical controls are housed in box called nacelle.
- A yaw control mechanism is provided to adjust the nacelle around vertical axis to keep it facing the wind.
- In small wind turbines, a flap or a tail vane is provided on the nacelle achieve the automatic positioning of the turbine axis in line with the wind direction. In larger wind mills, a servomechanism operated by a wind direction sensor controls the nacelle so that the turbine blades are always oriented in the direction perpendicular to wind to have the maximum wind stream area.
- It is provided with a generator which may be a 3-phase synchronous generator or a 3-phase induction generator. Former is used when it is operated in synchronism with the grid frequency having the constant speed.
- The later is used with a constant speed aero-turbine. The wind energy is converted into mechanical energy by aero-turbine.
- This mechanical power is transmitted through gears to the generator to increase its speed. Since rotor speeds are low, an overdrive is necessary to match the synchronous speed of the generator. The generator coverts the mechanical power into electrical power.
- The pitch of the blade (0 to 30%) is controlled automatically so as provide the feathering action. Thereby the power and speed of the wind turbine shaft is adjusted to match with the generator speed and its electrical output.
- The pitch control mechanism is shown in Figure B. The pitch control mechanism is provided through the hub of the rotor using hydraulic jack in the nacelle. The controller continuously adjusts the pitch to obtain the optimum performance.
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Figure B
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- A typical propeller type wind mill has its blade 25 m to 40 m in diameter to produce 120 kW power at a speed of 300 rpm to 400 rpm.
