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Homework Help: Significance of number of magnetic poles in ac generator

  1. May 30, 2012 #1
    I am supposed to discuss the benefits of having high number of magnetic poles in ac generators with constant frequency.

    From formula it is obvious that the higher number of poles the lower the speed of rotation.
    But is there anything else, or what is the benefit of lower speed?
    The only thing I can think of is less friction losses.
  2. jcsd
  3. May 31, 2012 #2
    It is much easier to construct a rotor running at 1500 RPM (4 pole 50 Hz) then 3000 RPM 2 pole, start to think about centripetal reactions (centrifugal force) and out of balance forces.
  4. May 31, 2012 #3
    Thanks for that. Thats very good answer. I understand the effect of rotor speed on centrifugal forces, but I can not see why it is easier to construct 4 pole motor than 2 pole.
    Any other benefits of having lower speed?
  5. Jun 1, 2012 #4


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    Staff: Mentor

    I'm thinking of hydro power. The speed of falling water is probably better matched to turning a slower water turbine, rather than a rapidly spinning one.

    If there are sliding contacts, they probably perform better at slower rotational speeds.
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