Generator used in a power station

[davidcowling]

What sort of generator is used in a power station? (synchronous, asynchronous)... And what is the difference between.

- Asynchronous Generator
- Synchronous Generator
- Alternator
- Dynamo

Thanks!

 

[chaoseverlasting]

Synchronous Generator. Is this homework?

 

[davidcowling]

No its not. I am currently applying for a place on a graduate scheme and looking at some of the possible questions they will be asking.

Thanks for your help

 

[Okefenokee]

You got through an undergrad degree without learning this? My program required electro-mechanical studies.

Anyway, my probably too short answer:

Asynchronous - Induction motors basically. Speed varies with load when used as a motor. Frequency varies with load when used as a generator.

Synchronous - Constant speed motor or constant frequency generator regardless of load. This is why it's used in power systems. Too much load causes instant stall. It also has interesting impedance properties that can be used to tune power grids. Cannot self-start. Needs a kick-start motor.

Alternator - A catch-all term for anything that generates AC power. If there is some definition that is more formal then I don't know it.

dynamo - DC motor/generator. Unlike AC motors, the dynamo's speed can be electrically controlled over a wide range. AC motors tend to have target speed ranges (called a speed-torque curve) and they'll stall outside of their designed operating conditions. Dynamo's are good for variable speed applications. Generally less efficient than AC motors at high throughput but more efficient at very small powers.

 

[davidcowling]

Am i right in thinking that a synchronous machine used in a power station has to be spun past its synchronous frequency to generate electricity?

 

[Okefenokee]

No, but that's what you would have to do for an asynchronous generator depending on the load.

 

[JTE]

Both synchronous and async generators are used in power stations. Async tend to be smaller and must be in a network capable of supplying the extra reactive power. The largest async one I have worked on is 2MW, small.