Wind energy plays an important role in the establishment of an sustainable and low carbon environment

Wind turbines generate electricity by using wind energy to drive an electrical generator.

Wind turbines include critical mechanical components such as turbine blades and rotors, drive train and generators.
All turbine blades convert the motion of air across the air foils to torque and then regulate that torque in an attempt to capture as much energy as possible.

When the wind passes over the blades, it exerts a force on the blades making them to rotate.The rotating blades make a shaft turn inside the nacelle, which goes into a gearbox.
The gearbox speeds up the rotation to an appropriate level for the generator, which uses magnetic fields to convert the rotational energy into electricity.


TYPES OF WIND GENERATORS:

1.Direct Current (DC) Generators:

A Direct Current (DC) wind generator system consists of a wind turbine,an insulated IGBT inverter,transformer,controller,power grid and DC generator.

In shunt-wound DC generator,the current is directly proportional to operational speed of rotation of turbine blades.

Actual speed of wind turbine is determined by balance betwen the wind turbine torque and load torque.

Electricity is extracted from the brushes that connect the commutators that convert generated AC power into DC

Use of DC generator is not much efficient for large power applications and it needs regular maintenance and is costlier than other types.

2.Alternating Current (AC) Synchronous Generators :

AC synchronous WTGs  take DC excitations from either permanent magnets or electromagnets and hence are also called as PM synchronous   generators (PMSGs) and electrically excited synchronous generators (EESGs), respectively.
 When 3-phase power supply is connected to the stator,a rotating magnetic field is produced.If the rotor speed varies in case of fixed-synchronous then synchronization is lost.
 Synchronous generators have low damping effect and do not allow drive train transients to be absorb electrically
 These generators are more complex,costly are prone to failure than induction generators.
 During the past decades, PM generators are used extensively in wind turbines due to high-power density and low mass.
 The PM generator is installed on rotor to produce constant magnetic field and generated electricity via use of commutator,slip rings and brushes.
 PM generators are same in operation as that of synchronous generators but it can be operated asynchronously.
 A potential variant of synchronous generators is the high-temperature superconducting generator.It consists of stator iron,copper winding,HTS field coils, rotor core, rotor support structure, rotor cooling system, and others.
 Superconducting coils may carry 10 times the current than conventional copper wires with negligible resistance and conductor losses.
Synchronous generators may pose several technical challenges, especially for the long-life, low-maintenance wind turbine systems.

3.AC Asynchronous Generators:
Modern wind turbine power systems use induction machines on a large scale.

Induction generators are of two types:fixed-speed induction generator and squirrel-cage induction generator.
Induction generators have high level of damping and can absorb rotor fluctuations and drive train transients(fault tolerance).Uptil 1998,mostly fixed-speed induction of 1.5MW were manufactured.They are operated at 1500 rpm for 50Hz utility grid
Squirrel cage induction generators (SCIGs) can be used in variable speed wind turbines, as in controlling synchronous machines.

Induction generators are prone to voltage instability and result in power losses.
   

4.Switched Reluctance Generators:

Switched Reluctance Generators have strong stator and rotor components.With rotations of the rotor,the reluctance of magnetic lines linking stator and rotor changes and in turn induces current in the winding.
Reluctance generator is simple,easy to assemble since the rotor is made of laminated sheets without permanent magnet or any other electric field windings.

Why Wind mills are used........

Wind energy is one of the abundant natural resource available and can be used effectively to produce electricity.
Wind turbines work on principle that electricity should be generated using wind energy with help of generators.
Wind turbines can be located at offshores of sea or oceans.