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Are air resistance and weight of generator's rotor the only frictions or there is something else?

  1. Oct 10, 2014 #1
    What I know is there 2 friction; Air resistance and Weight of rotor?
    Is load of generator consider as friction?

    I noticed that when generator's load is half, fuel consumption is reduced (but RPM and frequency is still same). I tried to think how that, although weight of rotor is constant. does that mean it needs less power?
    Why that?

    Is there something affects or make it hard to spin? beside the friction of weight and air?
  2. jcsd
  3. Oct 10, 2014 #2
    There are several issues here.
    The major losses come from the cooling fans, (which drive air around the internals of the generator) and the bearing losses, (rotating friction) at constant speed these losses will remain the same whatever the load.
    The fuel consumption depends on several things, the amount of load, the losses and the driver fuel efficiency. At low loads a bigger proportion of your fuel consumption will be taken up with your losses so each kilo-watt hour of electricity produced will take more fuel than if running at full load. The prime mover will also have an efficiency curve which will get better towards higher loads. If there are no other concerns you should try to run a generator set close to maximum power.
  4. Oct 10, 2014 #3
    Prime mover only moves rotor.. if rotating friction and air resistance is the same at constant speed, how load affects on fuel consumption?
    and when we reduce the load, fuel consumption becomes reduced too. is it means that torque/power-needed become lower.
    when load is reduced, the magnetism in rotor's electromagnets become lower.

    Why that?
  5. Oct 10, 2014 #4


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    Staff: Mentor

    The primary -- 96% or so -- power drain is the generated electrical power itself. Generators are magnets: they produce a torque that opposes the prime mover when there is a high current. The "losses" due to inefficiencies are the tiny 4% or so of what is doesn't create electricity.
  6. Oct 10, 2014 #5
    Last edited: Oct 10, 2014
  7. Oct 10, 2014 #6
    Rotor weight is not a source of frictional loss a all. This seems to be a misconception here.
  8. Oct 11, 2014 #7
    It should be mentioned that while frictional loss in the bearings is undesirable, the loss due to air resistance isn't so bad. It participates in cooling down the machine.
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