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Turbine Efficiency with Generator load

  1. Nov 29, 2016 #1
    Hi, I have developed a 2KW hydro turbine prototype with a generator connected.

    Generator Type - Brushless DC Permanent Magnet (16Pol-18Slot) (2000Watts, 2000 RPM, 54VDC)

    Generator test report (by manufacturer) is given below;
    Code (Text):

    RPM                Volts             Current
    1000               29.8                34.7
    1500               44.65              35.2
    1900               56.5                35.3
    1930               57.5                34.8
    2000               59.5                36.2
    With the Generator connected to Turbine, I am able to achieve 1930 RPM with no Load connected. Since the generator test report shows 57.5 Volts * 34.8 Amp = 2001 Watts at 1930 RPM, Can i assume the same to be my system output efficiency ? or I will have to add dummy load to generator to find final system efficiency.
    Last edited by a moderator: Nov 30, 2016
  2. jcsd
  3. Nov 29, 2016 #2


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    You will certainly have to perform tests .Turbine rpm will drop considerably when generator is loaded .

    Do you have a performance characteristic plot for this turbine ? How did you arrive at the 2KW output figure ?
    Last edited: Nov 29, 2016
  4. Nov 29, 2016 #3
    A centrifugal pump is used to create hydrostatic head.

    Gauge Pressure: 2.5 kg/cm2 = 25 Meter of Water column
    Flow = 8lps
    Input Watts = Mass*Gravity*Head = 25*9.81*8 = 1962 Watts
  5. Nov 29, 2016 #4


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    Staff: Mentor

    Taking a step back here, you aren't comparing two different powers to each other (that I can see), so it isn't even clear what calculation you are doing to get efficiency. The only two powers implied there are "no load" (zero) and loaded at 2001 Watts. Since the power output at no load is zero, your effficiency must also be zero. Since your power output loaded is known, but your power input isn't known, your efficiency can't be calculated.

    So, what exactly are you calculating? Are you really just asking if loaded and unloaded rpm are the same? Then no (as indicated).
    Please tell me you aren't trying to create a perpetual motion machine!?! Whatever you are doing, since your input and output numbers are roughly the same, and since the output doesnt include inefficiency, your 2000W (output) pump can't possibly power your 2000W (output)generator at full load.
    Last edited: Nov 29, 2016
  6. Nov 29, 2016 #5
    I am using a 5HP (3728.5 Watts) pump to create hydrostatic head. Pump efficiency is 52.6% at duty head of 25 Meters with flow rate of 8LPS

    Hence, ignoring pump losses, I have taken Water Horse Power (WHP) 1962 Watts as input energy and trying to convert this energy to mechanical energy at turbine shaft.

    Turbine diameter is 8 inches and it rotates at constant speed of 2080 RPM with bare shaft (without generator connected)
    When the said generator is connected to Turbine, its RPM comes down to 1930 (compared to bare shaft RPM)

    Generator is rated for 2150 Watts at 2000 RPM, hence required generate torque is 10.266 N.m
    Torque required to prevent the turbine from rotating = 17.5 N.m (based on water mass discharged, velocity and turbine radius)

    Is there a way to calculate turbine efficiency without a generator ?

    Kindly advice
  7. Nov 30, 2016 #6


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    Staff: Mentor

    Not with the information provided. You will either need to provide a load (doesn't have to be electrical as long as you can measure the torque and rpm) or do a computational fluid dynamic modeling of the turbine. Every turbine performs differently and the rpm when unloaded just isn't a useful piece of information.
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