Synchronous generator and full converter

[bluter]

Hi all,

The standar configuration of a Synchronous generator with salient poles has a squirrel cage in the pole shoe in order to damp the load oscilations.

In some wind aplications, generator is completely decoupled from the grid by a power electronic converter connected to the stator winding. (Generator side diode rectifier or voltage-source converter and grid side voltage-source converter).

I would like to know how the squirrel cage works in these aplications. Could be designed pole shoes without squirrel cages?

Thanks!

 

[Skogsgurra]

Since the normal "springy" connection between grid and the synchronous machine's rotor doesn't exist in an application like the one you describe, the damping effect of the amortisseur windings is not needed and the windings can be left out of the design.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[waross]

If the generator is used as a motor for starting, the amortisseur winding may be needed.

Bill
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"Why not the best?"
Jimmy Carter

 

[Skogsgurra]

That never happens in a wind turbine application. No power flow possible from grid to generator because of the rectifier between generator and inverter.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[bluter]

yes, in this case generator never works as a motor...

Although generator dosent need squirrel cage due it is not directly conected to the grid, what about the harmonics surged by the rectifier? does squirrel cage have any advantege about these harmonics in terms of shoe heating or losses?.

Another question related with this issue is the voltage shape wave. Synchronous generator conected to he grid have to get a sinusoidal shape (THD<5%), but in this case that the output power is rectified (AC/DC/AC), should the output voltage of generator have a sinusoidale shape?

 

[davidbeach]

The likelihood of it actually being a synchronous generator are pretty small. The only synchronous machines I'm aware of being used in wind applications are small PM machines that are allowed to run wild with rectifier/inverter taking care of the random output frequency. Anything larger that I've seen have all been induction machines, often wound rotor induction machines at the largest sizes.

 

[cswilson]

David:

Increasingly, the large (multi-megawatt) wind turbine generators feed the grid through rectifier/inverter stages. All of the new designs I have seen in the last several years do so. There is just so much advantage in efficiency and reliability in completely decoupling the generator frequency and phase from the grid that the cost and the losses of the power electronics are justified.

Many of the designs do use synchronous generators -- I have even seen permanent-magnet synchronous at over a megawatt!

Curt Wilson
Delta Tau Data Systems