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High voltage electromachinery - the key to absurdly high power to weight ratios?

  1. Nov 28, 2007 #1
    I've recently become very interested in designing efficient motors and alternators for use in a gas turbine hybrid electric vehicle. I feel that these designs may be able to achieve uniquely high power to weight ratios compared to the components in commercially available hybrid electric drivetrains due to the very high shaft speeds available from gas turbine engines. (thus compounding the advantages gas turbines may have over reciprocating engines in the next generation of hybrid vehicles)

    These fast shaft speeds may facilitate very high voltages, which in turn could reduce the amount of windings and material required in such devices. I feel that a move away from the standard enameled copper winding paradigm to polymer insulation or more exotic designs could be the key to unlocking high voltage electric machines.

    I am trying to source information and journals on the design of high voltage electric machines and dielectric breakdown mechanisms in such machines, but I haven't had much success.

    Does anyone know of any journals that address this topic? A good book on alternator and motor design would be pretty handy as well.

    Does this idea have any merit?

    Maybe this thread would be more suited to the engineering forum?
    Last edited: Nov 29, 2007
  2. jcsd
  3. Nov 28, 2007 #2


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    Shaft speed relates to output frequency.
    Shaft speed has no particular relation to voltage other than shaft speed must not be equal to 0.

    For some possible information sources try googleing -> alternator design textbook
  4. Nov 28, 2007 #3
    I would have thought that would depend on the alternator architecture/design. Shaft speed is proportional to frequency in synchronous machines.

    I've googled most permutations without much success.
  5. Nov 29, 2007 #4


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    We design our own PMGs for some of our engine applications. They operate around the 40 krpm range. I know that their voltage increases with shaft speed. I am not certain about the architecture of an alternator if something prevents that from happening though.

    The only reference item I can think of off the top of my head is a paper written by NASA for calculating windage losses in alternators. It is NASA TN D-4849.
  6. Nov 29, 2007 #5


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    Unless I'm misunderstanding this statement, the shaft speed will definitely affect the output voltage of a synchronous generator (alternator).

    The typical relation is given by,

    E = ns*phi*k


    E = excitation voltage (this is the source voltage when the alternator is providing power to the bus).
    ns = synchronous speed
    phi = flux
    k = constant

    ns = 120*f/P


    f = frequency
    P = number of poles

    Note with a constant bus frequency the machine speed (rotor speed) is equal to the synchronous speed.

    phi = N*I/R


    N = number of turns of wire/pole
    I = DC field current
    R = reluctance of magnetic circuit
  7. Nov 29, 2007 #6
    Have you seen this before?

    An old post of mine:
    HTS - The Future of Navy Motors - high temperature superconductor
  8. Nov 29, 2007 #7
    cool idea (pun not intended)

    its probably a bit impractical for a car though since (to my knowledge) the highest temperature superconductors are around the 70 kelvin mark, which would require a pretty beastly cooling plant.

    presumably they're using this motor to decouple the power generation from the drivetrain ?(much like what I'd like to accomplish in a gas turbine hybrid)
  9. Nov 29, 2007 #8
    From what I remember the "super-cooling" is used in the manafacturing process of the HTS wire, and not in the operation of the final product.

  10. Nov 29, 2007 #9
    if that's the case then calling it a superconductor is a misnomer. Either it's cooled to around liquid nitrogen temperatures and its a superconductor, or it's a good quality wire which offers better properties than copper wire and has a catchy name.

    The posts in the first link you sent suggest the motor is cooled with liquid nitrogen.
  11. Nov 29, 2007 #10


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    You are talking about peak voltage changes for shaft speed changes on a particular design.
    You can have a 230v alternator running at 500 rpm.
    Or a 12v altenator running a 3000 rpm.

    There is no reason to assume a high voltage or that the system would be more efficient.
  12. Nov 30, 2007 #11
    I'm sure you have the ability to look past the marketing slogans and concentrate on the scientific facts. I have faith.

    About Us
  13. Nov 30, 2007 #12
    "Superconducting materials known today, including both high temperature superconductor ("HTS") and low temperature superconductor ("LTS") materials, need to be cooled to cryogenic temperatures in order to exhibit the property of superconductivity." - taken from their about us page.

    as far as i know, no high temperature superconductor exists that doesn't need to be cooled to liquid nitrogen temperatures. there'd probably be some big party, outrageous news stories and wild share market movement if someone came up with one.
  14. Dec 3, 2007 #13
    yep, looks like you are right, been a while since I read the materials.

    They consider -300 degrees "high temperature" for a super conductor.:bugeye:
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