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Turbine efficiency

  1. Sep 10, 2011 #1
    1. The problem statement, all variables and given/known data
    I have attached the question. I'm not really sure how to do this one

    2. Relevant equations
    power = work done/time

    3. The attempt at a solution
    Is the turbine efficiency simply the power generation (750kW) divided by the mechanical output (800kW) which is so 750/800 x 100 = 93.75% efficiency?

    and then there's the combined turbine generator efficiency. How do you do that?

    Attached Files:

  2. jcsd
  3. Sep 10, 2011 #2
    Re: efficiency

    No it's not what you think.
  4. Sep 10, 2011 #3
    Re: efficiency

    You have been given rate of mass flow, height of water(70m). Calculate gravitational energy being converted (mgh).It gives potential energy converted per second.
  5. Sep 10, 2011 #4
    Re: efficiency

    so i simply do 1500(9.81)(70) = 1030050 J/s ? then what
  6. Sep 10, 2011 #5
    Re: efficiency

    Then you know the mechanical power output of turbine.Remember the power from potential energy can only be used by turbine and not by generator.
    Is efficiency of turbine.
  7. Sep 10, 2011 #6
    Re: efficiency

    I think answer's coming out to be 77.66% for turbine efficiency if you do the calculations.
  8. Sep 10, 2011 #7
    Re: efficiency

    ohh I get it, because j/s is watts - power. okay so then what is the electric power generation and the combined turbine-generator efficiency. is it simply (750000/1030050) x 100?
  9. Sep 10, 2011 #8
    Re: efficiency

    No.Just apply unitary method.
    800kW of mechanical output gives 750kW of electrical output.
    1W of mechanical output gives (750/800)W. ---equation (1)
    (kW get cancelled.You can Multiply 1W to both sides)
    We know efficiency of turbine as 77.66%.
    This means that when 100W of energy is inputted to turbine 77.66W of energy is it's mechanical output.
    Now multiply 77.6 to equation (1). answer is on right hand side-((750/800)*77.6).It comes around 72.81%
  10. Sep 10, 2011 #9
    Re: efficiency

    Ahh okkay thank you i get it now
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