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Voltage of DC Generator

  1. Apr 9, 2010 #1
    1. The problem statement, all variables and given/known data

    A dc generator is rated at 10 kW, 208 V, and 50 A when it rotates at 1000 rpm. The resistance of the armature windings is 0.56 . Assume that the magnitude of the magnetic field remains constant.
    (a) Calculate the "no-load" voltage at 1000 rpm (when there is no circuit hooked up to the generator).

    (b) Calculate the full-load voltage (i.e. at 50 A) when the generator is run at 800 rpm

    2. Relevant equations
    V-Vw - Vl = 0
    Vw = IRw
    Faraday's Law (where EMF = the magnetic flux with respect to time ->the derivative)

    3. The attempt at a solution

    I got part a because i know that the no load voltage supplied by the genrator is the voltage of the idealized generator. Thus 208V + (.56 x 50A) = 236 Volts = CORRECT

    Part B I can't seem to find! I know we're looking for the voltage load, and that the voltage is poportional to faradays law, where (BxA) x w = radians / sec..

    BAsically if V = 236 V at 1000rpm, vL = ? at 800 rpm? I even tried figuring that the rpm frequency is 20% less, so maybe the voltage would be 20% less? (188.8) = wrong
  2. jcsd
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