Very Small 3-Phase Synchronous Generator with Field Winding

[dmorrish]

My apologies if my terminology is not exactly correct, my background is more in embedded programming.

My colleague and I are in the feasibility stage of a project to build a scale model of a hydro-electric dam as a teaching aid for our students. We need two small three phase generators with field windings for voltage regulation. Something in the range of 30W. The idea is to have the students install and commission all the protection and control for the "dam" including synchronizing the voltage/frequency/phase of the generators by controlling the "wicket gates" (some type of control valve).

We tried searching for pico generators, but they all seem to be tailored for charging battery banks and have DC output. We've thought about brushless DC motors, but they use permanent magnets for the field. We discussed using an automotive alternator, but we're not sure if it will produce a nice sine wave and the RPM would have to be quite high. We will have about 3m of head and perhaps 750L of water.

Is there an option that we're missing?

Thanks for any help you may be able to provide!

 

[djs]

An auto alternator should fir the bill. It can turn rather slow and still produce electricity.

 

[benta]

A possibility could be browsing magazines about model steam engines, specially the "classifieds" section.
A lot of projects involve a steam engine and a generator, and there are companies supplying the small generators ready-made.
Another place could be here:

http://www.chaski.org/homemachinist/

I like your project, good luck.

Benta.

 

[waross]

Auto alternators have multiple field poles so they will be turning less than 3600 RPM. I'd guess about 1200 RPM or less. You may have to find some way to supply extra cooling to the field coils if you push it to 120 Volts at low speed.
An auto alternator will produce about 1000 Watts more or less. If you push the voltage up to 120 Volts, your may be looking at the range of 10 kW.
Pretty big for your application.
Self Synchronous (SelSyn) motors may work, They will be about the right size.
The construction is the same as an alternator. Three phase stator windings and a wound field on the rotor.
Apply DC instead of AC to the field. You will have to spin them at 3600RPM.

http://www.fsplanet.com/store/Ge-Selsyn-Motor_251718846649.html

http://www.ebay.com/itm/Set-2-pcs-S...727777?hash=item3d12f01061:g:qcgAAOSwKrhVaGQP

Search Ebay
Good luck

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[waross]

Alternators seldom generate a perfect sine wave. As long as your two generators are similar, they should develop similar waveforms and should run well in parallel.
Auto alternators:
Six pole pair claws are common. That would develop 60 Hz at 600 RPM. However the voltage is proportional to both the field strenght and to the speed. Although automotive alternators are easily capable of generating over 100 Volt, it is doubtful if you can get enough field strength to generate 120 volts at 600 RPM. You will probably be limited by both heat and saturation. I doubt that you will get more than 13 or 15 Volts output at 600 RPM.
The Selsyns are commonly designed for 115 Volts AC on the rotor and develop around 60 Volts on the stator. However Selsyns will develop full voltage on the stator at zero RPM. Selsyns will probably develop 120 Volts easily at 3600 RPM with a moderate DC voltage on the rotor. Selsyns are probably close to your target capacity.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[dmorrish]

Thank you all so much for the quick replies! We sourced an alternator to start experimenting with and if that fails, we'll look into SelSyn motors.

 

[waross]

Can you share the details of your alternator with us?
Thanks.

Bill
--------------------
"Why not the best?"
Jimmy Carter