General questions

[mazen]

Hi
Recently, I have read a general research about "Wind Turbines" and I have some questions. I will quote specific parts of this research then put my question after.

1)Many low-power wind turbines built to-date were constructed according to the “Danish concept” , in which wind energy is transformed into electrical energy using a simple squirrel-cage induction machine directly connected to a three-phase power grid. The rotor of the wind turbine is coupled to the generator shaft with a fixed-ratio gearbox. Some induction generators use pole-adjustable winding configurations to enable operation at different synchronous speeds. However, at any given operating point, this Danish turbine basically has to operate at constant speed.

My question is : How to keep the generator speed constant for any wind speed ?? Is that done using the gearbox only??


2)"Modern high-power wind turbines are capable of adjustable speed operation. Key advantages of adjustable speed generators (ASGs) compared to fixed-speed generators (FSGs) are:
they provide simple pitch control; the controlling speed of the generator (frequency) allows the pitch control time constants to become longer"

My question: What does he mean by controlling the speed of the genrator?? or how to control the speed of the generator??
Also,What is the pitch angle??

[myocardia]

Hello, mazen. Welcome to Nature2Energy. The answer to your first question is that it isn't possible to keep a wind turbine's speed constant. The wind blows different speeds, and all wind turbine blades, no matter the design, can only be variable speed. The first paragraph that you quoted was saying that some of the turbines of the past used variable speed motors (different windings, a lot like gears in a transmission), to better take advantage of the variable speed of the blades in varying wind speeds.

The second paragraph you quoted is talking about how the new, large turbines use variable pitch blades. They keep them at their most efficient angle the majority of the time, but can turn the blades if they need to do so, to slow down the generator, so it won't be ruined by spinning too fast if the wind speed is too high. Pitch angle is the angle of the blades. Turbine blades are not flat. If they were, they would provide no lift, making them worthless, at least as far as being able to harvest wind. Haven't you ever seen a fan blade? They aren't flat for exactly the same reason.

[mazen]

Ok let me ask another question..
What is the main difference between adjustable speed generators (ASGs) and fixed-speed generators (FSGs) ??

[myocardia]

Adjustable speed generators have adjustable blades. Fixed speed don't. These should actually be called adjustable blade generators, and fixed blade generators, but my phone never rang while they were deciding on those names.

[mazen]

So, the main difference between them is taht one of them has a pitch angle control system and the other don't. right??

[myocardia]

Yeah, that's correct. Are you doing a research paper, or something?

[mazen]

yah something...it realy does matter??