Generator Design

[acamer14]

If you buy a generator (gas powered etc) there is only a certain amount of watts that the generator can put out. This is because the engine only has a certain power rating. However, if one were to put a higher power engine on the generator head and remove the safety breaker for amperage, you could get more power from the generator head. However, the generator head design would be underrated for this, surely can not handle it, and would malfunction.

What about the generator would malfunction in this scenario? In my opinion the system would overheat from the higher amperage. The cooling is not designed for this. However, is this the only problem you can think of?

My thoughts are could there be some way of expanding the cooling to get a higher output generator. Specifically, setting the generator head in a bath of mineral oil. People do this to computers for cooling all of the time.

 

[dicksewerrat]

Why would you try that? The motor/generator are a unit. Designed to SAFELY work. Who pays when your jury rigged machine zaps someone? If you want more amps, buy a bigger generator.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[acamer14]

dicksewerrat:

Yes this would be a good recommendation if your just a consumer trying to power your house. However, I am an engineer looking at the possibility of designing and building generators from the start this way. It could prove to be a huge cost advantage over the massive cost of larger generator heads.

Can anyone think of any other issues of operating a generator head under mineral oil in this manner?

 

[ZDR1985]

I believe that is waste of engine power which the head cannot produce.

 

[acamer14]

Why would the generator head not be able to produce the extra power. If the breaker on the generator head were replaced with a higher amperage breaker, then there would not be anything preventing the head from making that extra power. Except for the fact that the head was not designed for this and would over heat. Unless you can think of something else that would come into play with this small gen head putting out more amperage.

 

[davidbeach]

So you'd have an oil gap instead of an air gap? Your losses (not windage anymore, not sure what they'd be called) would be way higher. If that would really work it would already be being done. Heat has long been the size limitation. The worst of the heat isn't where you'd want oil.

Really big machines have H2 cooling in the air gap and water circulating in the windings, but small machines are optimally air cooled.

 

[electricpete]

I don't know exactly what a generator "head" is.

In general, the temperature is the biggest factor limiting generator power rating as you say. Efforts to cool generator are tricky - can you get the coolant where it's needed. If you apply coolant to a housing, will there be differential expansion where the rotating parts are much hotter than stationary parts resulting in bearing damage?

There is a torque level which will cause pole slip. If you increase steady state torque, your margin to pole slip is decreased (for a given field level).

Torque is applied to stationary and rotating components. Probably you have more margin in design of these components than you have margin to pole slip.

Higher current through sync reactance may tend to decrease terminal voltage, which your voltage regulation may or may not be able to compensate for. Probably could, but something to look at.


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(2B)+(2B)' ?

 

[acamer14]

electricpete:

Thank you for your response. I've always known it as a generator head. The part that actually doing the power generator. So its the engine and generator minus the engine.

Could you explain a little more on pole slip?

 

[acamer14]

davidbeach:

Yes there would be more losses on the system due to the viscosity of the oil over the air. Plug the cooling fan at the front of the generator head would be pumping heavy oil through the system instead of air. That fan component would need to be made smaller in diameter as to not pump so much oil through the inside of the head.

 

[VTer]

The term you are looking for is an alternator not generator head. You would have to consider the MMF drop across the oil gap vs air. I am not sure what the relative permeability of oil is and what your leakage flux would be. I did not think this all the way through but i believe that any potential gains will be offset or made worse due to electrical losses. You would also have to overcome fluid issues such as cavitation. I see the alternator becoming a a bad oil pump with very large losses. Good luck!

"Throughout space there is energy. Is this energy static or kinetic! If static our hopes are in vain; if kinetic ù and this we know it is, for certain ù then it is a mere question of time when men will succeed in attaching their machinery to the very wheelwork of nature". û Nikola Tesla

 

[iceworm]

... What about the generator would malfunction in this scenario? In my opinion the system would overheat from the higher amperage. The cooling is not designed for this. ...

Exactly what size systems are you thinking of. I'm asking because the issues don't scale. Here is a purely arbatrary division:
residential < 25kw
commercial < 500kw
industrial < 10MW
heavy > 20MW

Which one are you looking at? What is your goal? Using the same amount of copper and iron do you want an extra 10%? or 50%? And of course, there is the money. You need pumps, tanks, filters, plumbing, monitor equipment. Very little money at 10MW, probably 1000X negative at 25kw.

Consider most generators are KW limited by the driver, and KVA limited by the alternator heat rejection. So, if one could limit the pf to .99, one could crank up the driver output 20%

As for cooling the alternator - sure its possible. As noted H2 is used on utility grade to reduce windage. But I would not use a computer dunked into an oil tank as comaparable - no moving parts. Maybe look at submersible pumps where the motor is down in the fluid, or hermetic refrigerant motor-compressors. I've seen some 700hp motors that use pressurized water as bearing lubricant. Maybe you want to use de-ionized water. And then there are issues with shaft seals.

Of course you could always use a vertical shaft engine like a recip heliocopter, and drop the alternator below in a non-pressurized tank - still have to circulate the fluid and dump the heat..

Here is your chance to do original research and write your IEEE paper on freon cooled residential generation.

ice

Harmless flakes working together can unleash an avalanche of destruction

 

[DanEE]

Yes I can think of another problem.. the magnetic circuit... How are you going improve the magnetic circuit of the generator, unless you are starting from scratch...

Magnetic core materials are nonlinear; the reluctance in a magnetic circuit is not constant, as resistance is, but varies depending on the magnetic field. At high magnetic fluxes the ferromagnetic materials used for the cores of magnetic circuits saturate, limiting the magnetic flux, so above this level the reluctance increases rapidly. Just generates heat... and quick failure.. Saturation also drastically alters the waveforms generated.

A couple of advanced level courses in electromechanical energy conversion would serve you well....

 

[JohnMcNutt]

I agree that magnetic saturation would likely be a major issue.

If you were to design a liquid cooled alternator, it would be a floor-up design. All the materials and dimensions would be different from air cooled.

Additionally, if you were to design something that relied on liquid cooling for heat removal, you would be using smaller windings and thus have more resistive losses in the stator. Whether this would be a significant ongoing cost would need to be determined, but as wire size increases, heat dissipation and thus cooling requirement decreases and efficiency increases.

Also, besides the aforementioned additional complex systems that would be needed, imagine the additional expense required if a stator or rotor needed to be removed and large quantities of oil needed to be contained and/or disposed of.

 

[electricpete]

it was a reasonable question for op to ask. But I'm in full agreement with the spirit of comments about floor-up design. Op should appreciate that the generator he purchases has already been extensively engineered. It's very unlikely he can create some dramatic improvement in output per cost of power generating equipment by attempting to reengineer what has already been engineered (unless he has expertise comparable or better than the OEM)

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