On the record, what is the most efficient generator ever built?

  1. I have no idea of our current capability in designing generators, have we reached 90% efficiency or we're not even close? Could it ever be possible to reach values higher than that with our current technologies? Current generators have an average efficiency of what? And what might be the highest efficient generator ever recored?
    Last edited: Jul 8, 2014
  2. jcsd
  3. SteamKing

    SteamKing 8,343
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    It depends on the type of generator you are talking about.

    Automotive alternators are rather small, with limited output. Their efficiencies are in the 70%-80% range at medium speeds, with efficiency dropping at higher speeds.

    Large central station alternators can be up to 98% efficient, due to their carefully controlled speed.


    And, the word is 'record'. 'Recored' means something which has been 'cored' again.
  4. NascentOxygen

    Staff: Mentor

    Operating the rotor in a near-vacuum can minimize losses due to windage.

    I believe the mistyped word is "recorded".
    Last edited: Jul 8, 2014
  5. SteamKing

    SteamKing 8,343
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    Check the thread title.

    << Mentor note -- I fixed the thread title to "record" >>
    Last edited by a moderator: Jul 8, 2014
  6. gerbi

    gerbi 162
    Gold Member

    Power generators ? (hundrets of MVA) around 99%. Could be higher with superconducting materials.
  7. Now that's amazing.
    Thanks for sharing, and btw, sorry about that misspelling.
  8. Is the efficiency related to internal resistance btw? Of those power generators?
  9. losses of efficiency are usually more related to magnetics. Stray magnetic energy that doesn't get converted to electricity, magnetic energy that gets converted into eddy currents inside the magnetic material instead of the wires, stuff like that. When you have a known torque and known RPM, you can design the magnetics to perfectly suit those characteristics and have very high efficiency.
  10. I noticed, that the whole process for example of a coal power plant has quite a low efficiency, 30%-35% converting coal's stored energy into electrical energy. Such a system's efficiency seems low.

    Generators of 70% efficiency and more are what exactly? They convert mechanical energy to electrical energy with that rate? If so, why do power plants have such low efficiency?
    Last edited: Jul 9, 2014
  11. that is related to thermodynamics and the ideal gas law. If you want, study Carnot Theorem and the Rankine Cycle. Its also a question suited toward the mech engineers. long story short, the maximum efficiency depends on the difference between the temperature of combustion and the temperature of the outside air or water that the waste heat flows into. The outside temp is fixed by the environment, and there are real limitations to how hot you can burn the fuel.
  12. gerbi

    gerbi 162
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    Regarding power generators (like I said, hundrets of MVA, full load of machine): total losses are around 1%.
    1) Losses in magnetic materials (stator core mainly): 10-20% of losses,
    2) Losses in winding (total, stator + exciter): ~ 70%,
    3) Mechanical losses (mainly friction): ~10 %.

    This relations will vary (but not very much) with different designs etc.
    Проектирование турбогенераторов, Хуторецкий Г.М., Токов М.И., Толвинская Е.В.
    Turbogeneratory, W. Latek
    + own experience
  13. I'm confused, gerbi are there generators that consume an energy source(hydro,coal,gas,etc...) that have an efficiency over 80% Power plants based have much more less percentages.

    Check this link.
  14. Well, I'm just amazed as to the limits that power plants have, in terms of their efficiency(being 40% for gas powered plants, and 90% for hydro).
  15. gerbi

    gerbi 162
    Gold Member

    Hmm.. you confuse some terms here. I am talking here about generator efficiency (this is only one of elements in chain). Generator (electric machine which generates electric power) shaft is driven by a turbine (gas, steam). Steam is produced in water-steam loop heated by a boiler.

    Total efficiency depends on efficiency of each of elements. In this chain generator is (usually) the most efficient element.
  16. hydro doesn't have to create any water vapor. Coal and other fuels have to boil the water, then get energy out of the hot steam. Then, the old steam (now medium temperature) needs to be evacuated so that new hot steam can be created. This is unavoidable waste heat. In contrast to the water cycle, when motion is converted into magnetic energy, there isn't a hard limit on how much of that magnetic energy can be converted into electricity. hence you have efficiencies that are close to 100%
  17. sophiecentaur

    sophiecentaur 13,285
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    Hydro power is not a heat engine so it is not limited by a fundamental thermodynamic efficiency, given by the hot source and cold sink temperatures. The water cycle part of the process that raises the water up from the sea to the mountain top is very thermodynamically inefficient but that doesn't bother the power engineers.
  18. Baluncore

    Baluncore 2,428
    Science Advisor

    A near-vacuum does have lower windage but it has terrible thermal transfer characteristics.
    Large rotary electrical machines are filled with hydrogen gas as coolant because it has low viscosity.
  19. SteamKing

    SteamKing 8,343
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    When you calculate the thermal efficiency of any complex power cycle, you have to look at the efficiencies of the individual machines which make up the plant.

    For example, in a conventional coal-fired generating plant, you have a boiler, which burns coal to make steam for a steam turbine, and an alternator driven by the steam turbine which makes the electric power coming out of the plant.

    Now, the individual efficiency of each major machine in this process can be relatively high. For example, modern boilers can be designed to be about 88% efficient, that is, 88% of the total heating value of the coal consumed by the boiler is transmitted to the steam coming out of the boiler. Steam turbines are wonderfully simple machines, and it is hard to design one with less than 85% efficiency. Similarly, a properly designed alternator can be up to say 98% efficient.

    When you combine these individual efficiencies to estimate an overall thermal efficiency for converting a pile of coal into a bunch of megawatts coming out of the plant, you have to multiply all these efficiencies together, which brings the final value down a bit. Thus:

    Boiler: 88%
    Turbine: 85%
    Alternator: 98%
    Combined efficiency: 0.88 * 0.85 * 0.98 = 0.73 = 73%

    From this 73% efficiency is still to be deducted the losses for the various auxiliary machinery which is required to run the plant, like pumps and blowers, before you get to the largest amount of heat loss in the plant, the condenser, which turns the exhaust steam from the turbine back into liquid water, which is then pumped back into the boiler and turned into steam again.

    If, instead of a steam plant, you have a gas turbine or large diesel engine turning the alternator, you can eliminate the need to heat water to turn it into steam and condense it back to liquid again, plus all of the associated machinery and its losses. This helps to raise the theoretical efficiency of the generating plant, but you are no longer able to use relatively cheap coal as a fuel. You must use a liquid fuel or natural gas, which are a bit more expensive.
  20. I apologize if this is shifting more from electrical engineering to mechanical engineering :tongue:
    But thank you greatly for this information, greatly helpful.
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