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Variable speed generators - help!

Variable speed generators - help!

Variable speed generators - help!

(OP)
Hello all, Chris here
I was wondering if there is anyone out there who could explain to me how a variable speed generator is contructed (if it is different to a synchronous or asynchronous generator, or can it be both) Also is anyone aware of any hydro plant which uses this technology?

Thanks alot for your time, would really appreciate it if you could give me your view

C

RE: Variable speed generators - help!

I have seen wind units with something like what you are talking about. However what they really were is a 3 phase syncronious generator, and an electronic conversion box (sort of the reverse of a VFD).

You might be talking about something different, maybe in the neiborhood of the new large wind generators.

The Hydros that I deal with are all pelton wheels, with the latest, being the smallest, using an induction generator.

RE: Variable speed generators - help!

I heard them described as varible frequency AC generators that clip the AC to DC with diodes, the you run an inverter to get the fixed frequency you need.

RE: Variable speed generators - help!

I assume by your alias that your interest is in hydroelectric power production.

The choices are pretty different depending on the scale of power plant you want.  1kW, 10kW, 100kW, 1Meg?

For very small systems, the budget doesn't usually allow for much more than an induction motor, with some "tweaking" to operate as a generator.  Above 10kW somebody wants some serious power so they will probably spend the money on purpose-built generators and regulate the water flow on top of regulating the power.

The answer is similar if you're asking about wind power: small wind is either DC output (brushed generators, yuck) or wild AC output from a PM alternator (needing rectifiers and inverters to make the AC 60Hz sine).  At larger scales >10kW or so it becomes economical to regulate the blade pitch too.  With proper blade control and yaw motors you can get back to induction generators but a certain amount of control circuitry is needed for safety and acceptable performance.

Steven Fahey, CET

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