Wind Turbines

Classification of Wind Turbines

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Variable and Constant Speed Wind Turbines
Although known and exploited for a long time, wind energy was completely neglected during the industrial era, for the almost exclusive benefit, except hydroelectricity, of fossil fuels.


HAWT Turbines


The kinetic energy of the wind can be directly converted into mechanical energy and be usable for example in old windmills or to operate pumps. But nowadays we transform it into electrical energy by using wind turbines.


The new interest in wind energy since the mid-1970 s is the result of two concerns: first, the protection of the environment and the resulting saving in fossil fuels. On the other hand, the evolution of technologies makes the conversion of this energy more and more profitable and therefore its use becomes economically competitive compared to traditional sources of the same power.


Currently installed wind turbines can be classified into two categories:


1-Constant speed wind turbine


The speed of a wind turbine is relatively slow. constant speed wind turbine technology is based on synchronous rotating machines (rather with a wound rotor for connected wind turbines at medium voltage) at low speed, therefore comprising a large number of poles, and consequently having a large diameter.
Wind turbines based on variable reluctance machines also fall under this category of generators.

2-Variable speed wind turbine 

This technology is based on the use of an asynchronous machine. In a general way, the latter rotates at a much higher speed than the wind turbine. So It is necessary to adapt it to the speed of the turbine by inserting a mechanical multiplier.


The multiplier 


The multiplier transforms the power at slow speed and at a high torque produced by the rotor of the wind turbine, into power at high speed and at a low torque used by the generator.


These mechanical multipliers have the disadvantage of requiring increased maintenance and affect the reliability of the wind turbine. However, for the generation of high power, it is the technology that is used by manufacturers for connection to a medium voltage network.




Connection to the grid


The connection of these turbines to the electrical network requires controlling the frequency of the current generated by them. And you can use Power Electronics and have a set of electronic units that control the electric current to go out with the required frequency. It can also work properly with stand-alone units, i.e. it works as an independent power plant.


Wind turbines are considered as generators of variable power. Connected on an electrical network, wind generators do not impose the amplitude of the voltage and do not regulate not the power-frequency ratio, in other words, they do not participate in system services, and so disturb the stability of networks more than their penetration rate is important.  With the use of power electronics, new technologies have appeared to optimize this generation of energy.


The technology inherent in the first category of wind turbines is well mastered. Indeed, it is a technology that has demonstrated the simplicity of installation, reliability, and low cost, which allows the rapid installation of hundreds of kW of wind generation. However, with the very gradual implementation of wind turbine projects whose power is greater than MW, it is variable speed wind turbines that will develop in the future for this range of power generated.


Indeed the latter has several advantages, in particular, better exploitation of the wind energy, the reduction of the oscillations of the couple and the mechanical efforts, and great flexibility as for the connection to the network thanks to the use of total power converters controllable.



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