Prof. Vilas Shamrao Patil

1. Dr. Vilas Patil Nates/Renewable Energy/Wind Energy Page no-1
1.15 : SUB SYSTEM OF WIND-TURBINE-GENERATOR UNIT
A wind turbine-generator unit converts wind power into electrical
power. The ratings of such unit range between 15 kW to 14 MW. A
wind turbine-generator unit consists of the following subunits or
subassemblies.
1.A wind turbine with vertical or horizontal axis : The axis of a wind
turbine has a central shaft with a hub and a propeller (wheel). The
shaft is mounted on two bearings. The propeller has a few blades with
aero foil design. The blades are similar to a fan-blade. The planes of the
blades are perpendicular to the axis of the hub and designed on
aerodynamic principle such that the wind glides over the profile of the
blades and pushes the blades in proper direction. The axis of the turbine
may be horizontal or vertical. The wind passing through the propeller
produces a torque on the wheel and the shaft on the axis and makes it
rotate. It, thus, converts the wind energy into mechanical energy. [Fig.
(12.4)]
2.Gear chain : To control the speed of rotation, the shaft is connected
to the axle of the generator through the gear box and speed of
rotation is increased from the shaft to the axle.
3.An electric generator : It consists of a coil about the shaft axis and
with the shaft is rotated in the strong magnetic field. By
electromagnetic induction current is induced in the coil, thus
mechanical energy and hence the wind energy is finally converted into
electrical energy.
4.Installation unit : An assemblage of the wind-turbine, gears,
generator, control gears etc. are mounted in a housing called the
nacelle.
Associated civil work with the tower, electrical and mechanical
auxiliaries, control panels etc.
The wind-turbine with the gear chain, electric generator and other
installation sub units form a unit and is called a 'wind-turbine generator
unit. [Fig. (1.7)].
1.16. TYPES OF WIND TURBINE GENERATOR UNIT:

2. Dr. Vilas Patil Nates/Renewable Energy/Wind Energy Page no-2
The wind turbine, gears, generator together form a wind turbine
generator unit. A wind farm has several such units which operate in
parallel and feed electrical energy to an isolated load or the electrical
grid. The wind turbine generator units have different types. Based on
axis of turbine they are :
(i)Horizontal Axis Wind Turbine (HAWT) generator units.
(ii)Vertical Axis Wind Turbine (VAWT) generator units.
In HAWT generator unit, the axis of wind turbine is horizontal and the
blades of the rotor rotates in vertical plane. These units are
manufactured very widely and are commonly used. They have unit
rating from few kW to 3 MW.
The HAWT generator has different configurations as follows.
1. Propeller type horizontal axis : It has small, medium and large
ratings from 15 kW to 3 MW. Single blade design is for small ratings
and double and triple blade design is for medium and large ratings.
Wind turbine, gear and generator are with common axis mounted in
nacelle mounted on tall tower.
2. Space frame rotor man forth design : It is very large in size and
ratings (3 MW to 14 MW). It has large framed space structure like giant
wheel and supports the blades in two parallel vertical planes in
symmetrical radial fashion.
3. Windmill type multi-blade design : Here several blades with
increasing width and with a slant are arranged symmetrically around a
central rotatable hub. It is traditional design used for pumping sets and
not for power plants.
4. Bicycle wheel multiblade design : In this case several blades are
arranged radially like spokes of bicycle wheel, but with certain width
and slant. Similar to windmill type design above, it is also used for
pumping set and not for power plants.
The VAWT are built commercially by a few manufacturers with two
types of designs as :
1. Darrius wind turbine with (Φ) configuration : It has unit rating as
high as 4 MW.

3. Dr. Vilas Patil Nates/Renewable Energy/Wind Energy Page no-3
2.VAWT with H-configuration : The blades of rotor in HAWT and
VAWT are designed on aerodynamic principle. The root of each blade
is fixed on to the hub. The profile has a gradual inclination against the
plane of blades such that the wind glides over the profile and pushes
the blade in desired direction. Depending upon the number of blades
used on the hub, the wind turbines are divided into three types.
In the next article we have seen the design, construction and working
of a propeller type HAWT in general. There are three types of such
HAWT, namely mono blade (or single blade type), twin blade (two
blades type) and three blades type. Except for the number of blades,
every other thing in all types is the same. But every type has its own
advantages and limitations. The three types of HAWT are shown in the
Fig. (1.7).
1. Monoblade HAWT : It is simple, favourable, easy to install and
simple yaw positioning (orienting axis of wind turbine in the direction
of wind). It has disadvantages such as teeth-ring control (see-saw like
swinging motion with hesitation between two alternatives) required,
not useful for large power. It has applications in the field of irrigation,
sea-water desalination and small power farms in remote areas.
2. Two (twin) - blade HAWT : This has large unit ratings of 1, 2 or 3
MW. Cost of this is higher than monoblade HAWT and lower than 3
blade HAWT. It also needs teeth-ring control.

4. Dr. Vilas Patil Nates/Renewable Energy/Wind Energy Page no-4
3. Three-blade HAWT : This type has large unit rating, large weight,
more cost and more stability compared to monoblade and twin-blade
HAWT. It is discussed in detail in text section (1.16 and shown by Fig.
(1.7)).
1.17: Planning of Wind Farm
Several identical units of Wind-turbine generators installed in a large
area is said to form a wind farm. The accumulated power of the units
forms a high magnitude of electric power. A single wind farm may have
10 to 50 wind turbine units of small or medium size, each of capacity of
15 kW to 300 kW. Therefore, the electrical power output from a wind
farm with 50 units of medium size wind-turbine generators goes to 1.5
MW. The planning of wind farm requires following points to be paid
attention to :
•Wind farms are located in vast field open space away from thick
forests, cities and hilly areas. Such a vast open space field firstly must be
available and secondly it must also be at low price, because it should
not increase the total cost of production.
•At the site, there must be favourable wind available throughout
the year, with average speed of 7 m/s.
•The site must be safe. There should be no frequent storms, gusts,
lightning, floods. It should be earthquake free.
•The site, at the same time, should not be far away from the existing
load centre or distribution network, so that parallel combination or
standby arrangement with the conventional electric power network
can be managed.
1.18.HORIZONTAL AXIS PROPELLER TYPE WIND TURBINE
GENERATOR UNIT The HAWT generator unit is shown in Fig. 1.7. Let
us consider the different terms related to it. 1. Hub : It is central solid
part of the propeller (wheel).
2. Propeller : It is revolving shaft with blades. Propellers are two types.
One is upwind type in which wind approaches from front and drives
rotor and nacelle is on the rear side of the blades. The other is
downwind type. The wind approaches from nacelle side and moves
towards blades.

5. Dr. Vilas Patil Nates/Renewable Energy/Wind Energy Page no-5
3. Nacelle : It is an assembly consisting of wind turbine, gears,
generator, bearings, control gear, etc. mounted in a housing (casing)
and installed on tall tower. From Fig. 1.7, it is seen that when wind
strikes the blades of turbine, it rotates the blades in desired direction.
This gives conversion of wind energy into rotary mechanical energy.
This rotates the generated connected axis of rotation of hub through
gears.
The generator converts mechanical energy into electrical energy of
desired voltage, current, power and frequency. This electrical power is
produced in nacelle and is taken to the ground through power cable and
given to the grid for further distribution. All these actions are controlled
from ground with control cables going from nacelle to ground. The
Nacelle is installed on the top of tower to get sufficient wind velocity.
Good quality civil work is involved in the construction of tower. Higher
the tower, more is the cost of the wind turbine generator unit.
The propeller is a wheel with blade/s fitted to the hub. The propeller
is connected to a horizontal shaft as the axis. It is connected to a gear
box which connects the rotation of the shaft to the axle of the electric
power generator at the desired speed. The control and protection
panel takes care of the balance and position of the assembly. The
whole system is kept in a box called nacelle and the nacelle is
supported in horizontal plane by a high altitude vertical tower . The
output cables from the generator are taken out by power cables The
wind on passing through the propeller rotates the blades, thereby

6. Dr. Vilas Patil Nates/Renewable Energy/Wind Energy Page no-6
rotates the horizontal shaft, thus converting the wind energy into
mechanical energy. The gear box transfers this energy to the axle of
the generator at the required speed and the generator converts
mechanical energy into electrical power (energy). Generator rotor
speed is higher than the propeller speed. It is carried out through the
power cable through control cable unit. The ball bearings support the
horizontal shaft and help rotating it smoothly. The power drawn from
the wind by the propeller type wind turbine depends upon the most
important parameter called the specific speed which is the ratio of the
speed of the tip of a blade to the speed of the wind. To extract more
power this ratio must be high for which the length of the blades has to
be large. [Since by circular motion, v = wr, hence for a given w, r must
be large to have large speed v]. The propellers are of two types :
(1) Upwind type, and (2) Downwind type.
In the upwind type, the wind falls on the blades from the front., while
in the downwind type, the wind falls on the blades from the back side
i.e. nacelle side. The wind-turbine generator is provided with a yaw
control (not shown in the figure) which adjusts the plane of the blades
perpendicular to the wind direction, even if the wind direction changes
(and it does change frequently.) The tips of the blades are provided
with hydraulic pitch control. It helps to obtain desired speed of the
blades to draw maximum wind power.
Types of HAWT-Mono, Twin and Three Blade HAWT: In the previous
article we have seen the design, construction and working of a
propeller type HAWT in general. There are three types of such HAWT,
namely mono blade (or single blade type), twin blade (two blades type)
and three blades type. Except for the number of blades, every other
thing in all types is the same. But every type has its own advantages

7. Dr. Vilas Patil Nates/Renewable Energy/Wind Energy Page no-7
and limitations. The three types of HAWT are shown in the Fig. (1.8).
Types of HAWT 1. Mono-Blade HAWT : This type of generator can yield
usable electrical power of unit rate 15 kW to 50 kW. Advantages :
(i) It is simple and lighter in construction, hence
(ii) is can be done by simple mechanism. available at low price,
(iii) It is easy to install and maintain.
(iv) Yaw positioning
Disadvantages : (i) Teethering control is necessary. When the wind
speed is high it holds extra force on the blade in the upper position and
less force in the lower position. Due to this force difference the nacelle
experience a torque in the vertical plane and begins to vibrate severely
ad f. Therefore, tethering control is provided such that the blade
rotates i nn slanting positions at higher speeds and the force difference
is reduced to minimum.
(ii) It is not suitable for higher power ratings (above 50 kW)
Applications : (i) Field irrigation (for lifting and distributing water).
(ii) In places. sea-water desalination plants.
(iii) Electric power supply for farms and remote places.
2. Twin-Blade HAWT : Such a type of HAWT supplies electrical Power
at higher unit-rates of 1to 3 MW
Advantages :
(i) Higher electrical power rating.
(ii) Lower cost in comparison with three-blade type.

8. Dr. Vilas Patil Nates/Renewable Energy/Wind Energy Page no-8
(iii) Weight is less than that of equivalent three blade type. Hence
(iv) Installation and maintenance is comparatively easy.
Disadvantages :
(i) It needs tethering control.
(ii) Power rating is low in comparison to three-blade type.
Applications : (i) Electric power supply for moderate power
requirement plants.
(ii) Are installed singly and feed power into distribution network. Some
of the largest wind turbine generator units are twin-blade HAWT.
3. Three-Blade HAWT : This is a world-wide used type of HAWT. It can
supply electrical power of unit rate from any lower value to 14 MW.
Advantages : (i) Power supply of very wide range of unit-rate (from a
few kW to 14 MW).
(ii) No vibration problem as in mono-blade and twin-blade type HAWT.
(iii) This type gives most favorable design compromise between cost,
power rating and operational reliability.
(iv) Simpler design.
(v) Full electrical protection and control e.g. Earth fault protection,
over frequency protection, lightning protection.
(vi) Higher distribution of power to the grid.
Disadvantage : A little costly.
Because of the wide range of electrical power output and simple
design, several units of three-blade HAWT are installed and being
installed in India to exploit its wind energy potential to a maximum
extent.