Build a 48 VDC Generator with a 50 hp electric motor

[deckart]

again you're skimpy on detail.Are you locked into a single machine?
Does hydraulic imply low RPM ?
An alternator would relieve the need for an inverter, simplifying maintenance.

Searching for "low RPM alternator"
turns up whoever's bribed google
here's a 10 kw 50 RPM permanent magnet three phase unit
http://www.xindaenergy.com/10Kw-50r...Generator-for-vertical-wind-turbine-p205.html

here's an old line manufacturer that makes generators for industry
http://www.emersonindustrial.com/en...ernators/power-alternators/Pages/default.aspx
number of poles you'd want is
(3600/RPM of your torque supply ) X 2 and it has to be an even integer
ie
3600 rpm = 2 pole
1800 rpm = 4 pole
900 rpm= 8 pole
720 rpm = 10 pole

I used a 150 kw Kato machine for our simulator, found it well made and reliable
how 'bout that - Emerson bought them.
http://www.emersonindustrial.com/en...s/katoengineering/Pages/Kato-Engineering.aspx

good luckIf this is a "Red Green" project, a dozen truck alternators could make your 800 amps DC

View attachment 93706
check your PBS listings...

Jim, help me out on the details that are needed. I know I'm not asking the question correctly. I'm not sure how to ask it other than I want to convert up to 50 mechanical horsepower to grid ready 37.3 kW. This is a bridge I don't know how to build. What I don't understand is the kind of loading I will need to design to. When working with mechanical rotary applications I'm used to designing to loads and RPM/velocities that are predefined.

<101 electrical theory
What I've come to believe is that an electric motor is a generator when rotated in the opposite direction. So my vastly limited electrical brain thinks I should design to a 50HP, 1750 RPM, "off-the-shelf" electric motor and have the "sparky's" wire it up and make it work. That gives me a fixed torque (assuming there is a fixed load?) and from there a fixed hydraulic motor displacement. I could design the hydraulics to do that but it would be in intervals as the hydraulic energy was accumulated and then delivered to the hydraulic motor. So far, I've read that wind generators do this but don't store any of the energy when the wind velocities aren't there. Shutting down when the wind velocities where too low and then coming on line when they pick up. But they are able to work with varying wind velocities/rotor rpm after a minimum is reached.

So, a couple of my questions are, "will there be a constant load?", and "what is the RPM range?". I'm still confused on where the load comes from. In order to get a load from the grid, don't we need a higher voltage? This is where I'm in the weeds.

The hydraulic associations I have are:
voltage = pressure
current = flow
In order to get flow you need a pressure differential.

(What's required to get the AC sine waves synced up to the grid is a whole nuther topic.)

I see that my inquiries are all over the place, and that's why I'm here. I really appreciate your input.

 

[jim hardy]

wow you're starting from scratch on electric machinery? Brave man.

You need a mental image before jumping into formulas.
Here's a primer on alternators that'll show how one works, and what are the major pieces

the "Alternator" is also known as "Synchronous Machine"
it has a rotating field made of electromagnets as in that video, or of permanent magnets and is easy to understand.

What I've come to believe is that an electric motor is a generator when rotated in the opposite direction.

Actually direction stays the same, it's torque that reverses - hence direction of energy flow.

That gives me a fixed torque (assuming there is a fixed load?)

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

and from there a fixed hydraulic motor displacement.

Displacement ? I'm ignorant on hydraulics - volumetric fluid flow rate? I'd think that'd be f(rpm) not f(torque)

I could design the hydraulics to do that but it would be in intervals as the hydraulic energy was accumulated and then delivered to the hydraulic motor.

overriding clutch perhaps? I learned about them from my '53 Ford overdrive.

So far, I've read that wind generators do this but don't store any of the energy when the wind velocities aren't there.

Wind generators extract wind energy only when it's there. Somebody else has to store it.
A friend of mine in Colorado is trying to build a windfarm adjacent a pumped hydro plant, that'd save a lot of coal late at night when they're using electricity to pump water uphill instead of heating bathwater and running clothes dryers.

Shutting down when the wind velocities where too low and then coming on line when they pick up. But they are able to work with varying wind velocities/rotor rpm after a minimum is reached.

Newer wind uses clever electrical tricks to allow variable mechanical speed at fixed frequency.
For now think of fixed speed generator and one-way torque device , like that overriding clutch.(or is it over-running? I'm no Mechanical engineer)

"will there be a constant load?",

If your generator is small compared to local grid then you can push power into it without changing speed, so load is determined by your driver..

I'm still confused on where the load comes from. In order to get a load from the grid, don't we need a higher voltage? This is where I'm in the weeds.

Have you and your kids ever played with magnets on a table? The one under the table will drag one on top of the table around, to their great amusement? It's not much of a stretch to think magnets could transmit rotary torque, hence power.
The power is transmitted through an electric machine by magnetics

so you need to adjust your thinking to torque and angular displacement at operating RPM, just as if that magnetic coupling inside the machine were a spring.
Cavaeat - that's for alternators like in the video...

Your thinking was derived from DC and your analogies are okay
but AC adds angular displacement to all the math

Anorlunda wrote an "Insights" on generator/grid interaction.
It's a "beautifully self regulating system". Old timers used Mother Nature's propensity for a balance in their designs.

whew

one step at a time
and we took several

Train your search engine - search on keywords from articles and check out wikipedia's references

old jim

 

[anorlunda]

I'm not sure how to ask it other than I want to convert up to 50 mechanical horsepower to grid ready 37.3 kW. This is a bridge I don't know how to build. What I don't understand is the kind of loading I will need to design to. When working with mechanical rotary applications I'm used to designing to loads and RPM/velocities that are predefined.

You are asking random questions without the educational background to understand the answers. You refuse to hire an engineer. I think you're a disaster waiting to happen. Even in remote Alaska, there are laws and codes designed to ensure safety of the public, that you stubbornly ignore. I think that we on PF should refuse to participate in a project that could kill people, until you follow the advice already given, "Hire an electrical engineer."

 

[deckart]

You are asking random questions without the educational background to understand the answers. You refuse to hire an engineer. I think you're a disaster waiting to happen. Even in remote Alaska, there are laws and codes designed to ensure safety of the public, that you stubbornly ignore. I think that we on PF should refuse to participate in a project that could kill people, until you follow the advice already given, "Hire an electrical engineer."

I assure you that only electrical professionals will be wiring this up. No laws will be circumvented during installation and operation. No humans will be harmed by designing this system. My inquiries are aimed at specifying the generator so that I can design around it on the platform. Once the generator is in place, the electrical engineers will have a known entity to work with when interfacing the grid. I'll have a known entity to size the hydraulic interface. And, I'll be able to provide an accurate costing of the entire platform, less the electrical grid interface costs. No need to insult me or beat me up for not having the educational background.

 

[jim hardy]

"Hire an electrical engineer."

@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

 

[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.