Build a 48 VDC Generator with a 50 hp electric motor

[deckart]

@deckart
You'll do that before the project gets into much detail.
I don't mind helping you become mildly conversant in the basics so you'll be better able to pick one.
Codes exist for good reason and you'll need knowledgeable help.I've seen from the ferryboat windmills in some small SE Alaska settlements and i wondered how they're kept running.
If as you said earlier maintenance is an issue - you need simplicity. Look for an engineer who appreciates that.
old jim

Thanks, Jim. I've got the design down to a single cylinder used as the pumping mechanism, a wire rope pulley system to reduce the travel and increase force to the cylinder, and a hydraulic motor (yet to be specified). That's the extent of the moving parts. Sheave bearings are probably going to be the biggest wear item. Simplicity is definitely key to making this a usable system.

I've already learned great deal from your posts. I'm not trying to become an electrical engineer, just understand the fundamentals. Now I understand the relationship between the number of poles and RPM!

 

[jim hardy]

That's fair. One needs vocabulary.

Have you accepted that in a constant speed system torque determines power?

When you run across the term induction generator don't throw up your arms...
In induction generator the rotor''s magnetic field is produced by a slight relative difference in speed between rotor and the grid. Like a very few percent .
Example - a 4 pole induction generator tied to a 60 hz system has a nominal speed of 1800 RPM. But - at exactly 1800 there is no relative speed difference to create a rotor field , so no torque can be transferred.
So an induction generator will be driven slightly off synchronous speed.
At 1801 RPM it will transfer some power into the grid
at 1799 it RPM will draw some power from the grid
That speed difference is called "slip" and is what creates the rotor's field.
Slip is typically less than 5%.

Just like a synchronous machine or a DC one, an induction machine is equally happy as a generator or a motor.
Induction machines have a speed-torque curve that looks like this

which came from here and you ought to digest the whole article
http://www.purduecal.edu/cpmi/NSF%20Courses/ECET-212/CLASSPRESENTATION/InductionMotors.pdf

The only useful range of speed is that steep part right around synchronous and that's where you'll operate

look at some induction motors around your house and note rated RPM
most of them will be four pole
difference between rated and synchronous is slip
1760 would be 40/1800 = 4.4% slip, typical
1650 would be 8.3%, which is a lot
1785 would be <1% which is tight

if you used them as generators those speeds would be 1840, 1950 and 1815

so your hydraulic motor will operate , after accelerating the machine, over the small range of slip speed 1800 to say 1840
which for first approximation purposes is constant speed. Again, torque determines load.

Work it in your head..

We had a recent thread about wiring a washing machine motor.
https://www.physicsforums.com/threads/trying-to-wire-a-washer-motor-to-power-a-grain-mill.833300/
I wired one for multispeed,
when i selected from high speed to low it visibly jumped on my bench as the rotor slowed down returning its inertia to the grid by generator action. But it wasn't big enough to make the power company's generators overspeed...Such tinkering though gives one that intuitive feel he needs in order to believe what the equations say.
We learn by doing - so keep plugging.

old jim

 

[deckart]

It's a triad - power, speed and torque
in utility work we always lock speed at 60 hz , so power and torque are in proportion
the electric machine is equally happy providing power to or extracting power from the electric grid to which it's connected
by convention positive power flows into the grid

old jim

From what I've learned so far (that video was very good), I'm going to size the hydraulic motor to a 120-400 RPM generator (alternator). I don't need to fully understand how it is loaded but from your statement I'm going to assume that most of the hydraulic energy will be converted to 60 Hz AC with the appropriately sized generator and the grid will readily accept it after it is conditioned to the correct phase and voltage. Knowing that much, I can let an electrical engineer specify that actual generator. Thanks for the help.

 

[jim hardy]

I'm going to assume that most of the hydraulic energy will be converted to 60 Hz AC with the appropriately sized generator and the grid will readily accept it after it is conditioned to the correct phase and voltage.

Generators in parallel are like pumps in parallel, you need some sort of governor or inherent torque-speed characteristic that tends toward stability.
Hopefully this thing is small compared to your whole grid.

old jim

 

[deckart]

Generators in parallel are like pumps in parallel, you need some sort of governor or inherent torque-speed characteristic that tends toward stability.
Hopefully this thing is small compared to your whole grid.

old jim

It will be smaller but in some of these villages it may not be by much. There are so many small grids out there.
http://www.iser.uaa.alaska.edu/Publications/2012_07-RS-EnergizingAlaska.pdf

 

[russ_watters]

Yes, I have the general schematic completed but the components aren't yet specified. See attached.

Good! I'm pleasantly surprised.

But, you see my point, you want to see details.

My advice from here is that you focus on the details of the cylinder. That's the unique part of this and the part who's performance drives everything else.

I'm debating whether I should just put this up as a PF group project or not. If there is actually something that's patentable in the system, I'd be killing that ability by publishing it in a public forum...

Probably nothing patentable here...

I disagree. People have been working on wave power for a very long time, trying to make it viable. If you have a unique way to collect it, it would certainly be patentable.

...you don't create a hydraulic system (or any system) and then try to make it work on an application. The application defines the system components. Then prime mover, the "input", is the ocean wave action, the application is the gen motor.

If the prime mover were a gas engine selected from a catalogue, sure. But because the wave power system is custom and its output is unpredictable, you may find you've selected components that don't match what it gives you. You're spending time/effort (here) on the easy/everyday parts and not on the key piece of your device.

 

[russ_watters]

Why don't you start on a smaller scale? You cannot expect to design and get this project working in one shot. Ever hear of proof of concept? It seems you don't understand the relationship between watts, volts, amps, horsepower, etc. If you started on a smaller scale I think you might learn enough so that you would not rely so heavily on the people here that are not giving you the answers you desire. This goes along with what one of my favorite members here on PF that says: "A question well stated is half answered." Likewise, start at an easier scale and answers to your questions will become obvious. Some answers you will like, some you may not.

I wholeheartedly agree. And in particular you will demonstrate whether the wave power harvesting piece actually works and what it can do. That's the toughest part of this. After that, scaling it up is not difficult.

You'll also save time/effort/money -- and risk. And you'll set yourself up with a system you can patent while working on scaling it up.

 

[deckart]

I wholeheartedly agree. And in particular you will demonstrate whether the wave power harvesting piece actually works and what it can do. That's the toughest part of this. After that, scaling it up is not difficult.

You'll also save time/effort/money -- and risk. And you'll set yourself up with a system you can patent while working on scaling it up.

Definitely. I can certainly make a micro version of it for proof-of-concept. Drive a small automotive alternator and battery. A 12V inverter and run a 1000W light bulb on the buoy indefinitely. Showing it working will definitely help get buy-in for the useful, larger, scale version that will actually pay for itself.