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Does torque reduce/increase through gears?

  1. Apr 25, 2010 #1
    Hi guys,

    Great forum. I'm a frequent reader and first time poster.

    I'm having a great deal of difficulty getting my head around something I have been researching.

    If you have a wind turbine that is powered by wind (obviously) and causes the rotor with blades to spin at a constant 16.7rpm (which in turn turns the shaft), which is directly connected to a gear.

    The gear is then connected to another gear and they have a 1:100.5 ratio. The power output is then 2MW (with the final shaft spinning at around 1680rpm).

    How would you calculate the torque at the main shaft where the rotor is?

    I came to this value, but I have no idea whether it's correct or not. It just seems like a lot for something that's only initially turning at 16.7rpm (by virtue of around 18m/s of wind).

    Code (Text):
    Torque [Nm] = ( 9549 * Power [kW] ) / rpm

    T = ( 9549 * 2000 ) / 1680 = 11367.86Nm

    Then I multiplied 11367.86 * 100.5 (gear ratio) = 1.142MN
    Any help would be appreciate to preserve my sanity!
  2. jcsd
  3. Apr 25, 2010 #2
    Dear PaulMa

    The key is to remember that power is constant throughout the drive train. Keeping this in mind together with the formula:

    P = T * omega

    shows you that when the power remains constant and the speed decreases, as is the case with the rotor of the wind turbine, then torque will increase.

    As for your calculation, everything is correct. I checked from the point of view that the two gears are in equilibrium and this is where you can see that the torque increases through gear sets.

    Janik Bessinger
  4. Apr 25, 2010 #3

    jack action

    User Avatar
    Science Advisor
    Gold Member

    Like janik.mech said, power is constant throughout the drivetrain, so it is much simpler to do:

    T = ( 9549 * 2000 ) / 16.7 = 1.14 X 106 Nm = 1.14 MNm
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