Horizontal axis machines have emerged as the most successful type of
turbines. These are being used for commercial energy generation in many parts of the
world. They have low cut-in wind speed, easy furling and, in general, show high power
coefficient. However, their design is more complex and expensive as the generator and gearbox are
to be placed at the top of the tower. Also, a tail or yaw drive to be installed to orient
them in the wind direction.
(1) The main component of horizontal axis wind turbine:
1. Turbine blade:
2. Hub:
3. Nacelle:
4. Power transmission system:
5. Generator:
6. Yaw control:
7. Brakes:
8. Tower:
The constructional details of the most common, three-blade rotor, the horizontal axis wind turbine are shown in Fig. The main components are as follows:
(a) Turbine blade:
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Horizontal axis wind turbine |
(a) Turbine blade:
Wind turbine blades need to be lightweight and possess adequate
strength and hence require to be fabricated with aircraft industry techniques. The blades
are made of glass fibre Reinforced plastic (F.R.P). They have an aerofoil type of cross-section
to create lift as the air flows over them. The blades are slightly twisted the outer tip to the
root to reduce the tendency to stall. In addition to centrifugal force and fatigue due to
continuous vibration, there are many extraneous forces arising from wind turbulence,
just gravitational force and directional changes in the wind. All these factors
have to be considered at the designing stage. The diameter of a typical, MW
range, the modern rotor may be of the order of 100m.
Modern wind turbines have two or three blades. Two or three blade rotor
HAWT is also known as propeller type Wind turbine. Three blades are
more common in Europe and other developing countries including India. The
American practice, however, is in favour of two blades.
The advantages and disadvantages of two and three-blade rotor are as
follows:
(l) The three-black machine has smoother power output and balanced
gyroscopic force compared to the two-black machine.
(2) The three-blade rotor allows the use of a simple rigid hub. The
blades may be cross-linked for greater rigidity.
(3) Adding a third blade increases output by about 5% only, while the
weight and cost of a rotor increases by 50%, thus giving a diminished rate of
return for an additional 50% weight and cost.
(4) The two-blade rotor is also simpler to erect since it can be
assembled on the ground.
(b) Hub:
A hub is the central solid portion of the rotor wheel. All blades are attached to the hub. The pitch angle control mechanism is also provided inside the hub.
A hub is the central solid portion of the rotor wheel. All blades are attached to the hub. The pitch angle control mechanism is also provided inside the hub.
(c) Nacelle:
It houses the generator, the gearbox, brakes, hydraulic system, and the
yawing mechanism. The nacelle is placed at the top of the tower and is linked with
the rotor.
(d) Power transmission system:
Mechanical power generated by rotor blades is transmitted to the
generator through a gearbox. From the gearbox, the transmission shaft rotates the
generator with a built-in friction clutch. The gearbox is provided to increase
the speed to suit the generator. The generated electrical power is conducted to ground terminals through
a cable.
(e) Generator:
Generally, the grid-connected large wind turbines have induction
generators. They use reactive power from grids and feed the generated power to boost the grid
supply. Medium capacity wind turbines use synchronous generators installed to electrify
villages and remote places. Small capacity wind turbines use permanent magnet DC generators
which supply power to microwave stations and illuminating lighthouse.
(f) Yaw control:
Yaw control continuously tracks and keeps the rotor axis in the wind
direction. Yawing is done by two yawing motors, which mesh with a big-toothed wheel
mounted on top of the tower. Wind direction sensor used to maintain the orientation. During
high-speed wind, i.e. more than the cut-out speed, the machine is stopped by turning the rotor
axis at right angles to the wind direction. In small wind turbines, a tail vane
is used for passive yaw control.
(g) Brakes:
Brakes are used to stop the motor when power generation is not desired.
An emergency stop activates the hydraulic disc brakes fitted to the high-speed shaft
of the gearbox.
(h) Tower:
The tower supports the nacelle and rotor. Modem wind turbine generators
are installed on tubular towers. Large turbines use lattice towers designed to
withstand gravity loads and wind loads. For medium and large-sized turbines, the tower is slightly
taller than the rotor diameter. In case of a small-sized turbine, the tower is
much larger than the rotor diameter as the air is erratic at lower heights.
Both steel and concrete towers are being used.
- Difference between Horizontal and Vertical axis wind turbine as follows:
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Comparison of Horizontal and vertical axis wind turbine |
Horizontal axis wind turbine
Reviewed by Harish
on
May 06, 2020
Rating:

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