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What Generator for Hydropower Demonstration Setup?

  1. May 14, 2016 #1
    Ok, So I'm bulding a prototype of a hydropower plant, that will be used to teach kids.
    I have NO CLUE about what generator to use.

    So here's how it works (check the attached pic):
    - We have a water tank
    - A pump pulls the water from the tank
    - the water is used in a pelton wheel
    - a generator will use the turbine rotation to create eletricity
    - there will eletric loads after the generator

    Ok, so our teacher told us to keep the turbine rotation at 60Hz and H=2 bar. It's gonna be a self controlled system.
    The kids are gonna play with the loads -> let's say they increase the load, so the turbine will slow down
    the valve is gonna open to take the turbine rotation back to 60Hz (motor controlled valve)
    as the flow increases, H decreases
    then the frequency inverter is gonna increase the frequency of the 3 phase motor of the pump, so it goes back to the original pressure (H=2 bar)
    (check this http://bit.ly/1YsqKpr )

    With the turbine rotating at 60Hz, will the generator too?
    Well, I don't even know what to ask... Help me out please
    Thanks in advance

    Attached Files:

  2. jcsd
  3. May 14, 2016 #2
    << Mentor Note -- Two cross-posted threads merged >>

    Attached Files:

    Last edited by a moderator: May 15, 2016
  4. May 14, 2016 #3


    Staff: Mentor

    Neat project. On a previous thread there were some very helpful YouTube videos. I'll try to find them for you tomorrow.

    It is likely that you will want some pulleys and belts so that the generator shaft speed does not need to match the turbine shaft speed.

    How much vertical head (water height) do you have? I ask because Pelton wheels need higher pressures than other types of turbines. You say 2 bars, that is roughly 20 meters of head.

    Your narrative about 60 hertz and inverter and three phase motor sounds jumbled. What kind of generator will you have AC? DC? How much power must you generate? How much water flow do you have?
  5. May 14, 2016 #4
    Thanks a lot.

    Yes, probably pulleys and belts so I can work with smaller rotations on the turbine, right? 1:4

    Well, I'll be using a water pump to pull water from a water tank. I can work with the pressure. Btw, the pelton turbine I have is small (check attached pic).

    Yes, what I said about keeping the pelton wheel in 60 Hz doesn't make sense, because it's rotation depends on how much rotation I need on the generator.

    About the generator.. Well, I couldn't find a small generator/alternator so I'll probably use an inverted 3 phase motor as generator (not sure yet). I don't need much power, I think I'll be lighting a few light bulbs as a load.

    I'll work it with water pump as well. I have no clue about the volume of the water tank yet.

    Just to clarify what I said before about the inverter and the 3 phase motor of the water pump...
    Let's say we are working with a flow of 3.2l/s, pressure of 2 bar, and that this outputs 60Hz on the generator.
    Then someone lights more light bulbs.
    By doing so, the frequency on the generator is gonna go down a bit, let's say it goes down to 50Hz.
    Then I'll open the valve a bit to increase water flow (lets say it goes to 5l/s), making the turbine go faster, and thus making the generator output 60Hz again. Ok.
    But by increasing the flow, the pressure is gonna go down a bit. Let's say it goes down to 1 bar.
    The pressure must be kept at 2 bar (proper simulation of a waterfall (constant height, constant pressure)).
    To fix the pressure, I'll increase the frequency on the 3 phase motor of the pump, with the frequency inverter.
    Q: water flow , N: frequency of the 3 phase motor of the pump , H: pressure
    Q1= 3.2l/s , Q2= 5l/s , H1= 2 bar , H2= 1 bar
    Let's say we had N1= 100Hz
    By increasing N, we can change the point of operation of the pump.
    So by increasing N we can increase the pressure (taking it back to 2 bar), without changing the flow.
    Check the other picture :)

    Thanks a lot for your help!

    Attached Files:

  6. May 15, 2016 #5

    Simon Bridge

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    Science Advisor
    Homework Helper

    How fast the generator turns depends on how it is connected to the turbine ... if you connect it via gears, then it could turn faster or slower.
    If the connection is stiff, it could turn slower anyway.

    Your options are wide open.
    A stiffer generator will get you more power per rotation, but it may be to stiff for the water to turn.
    It is common to use an electric motor as a generator in these sorts of demonstrations... I've seen a waterwheel build from an old bike turn an electric drill to generate power.
  7. May 15, 2016 #6


    Staff: Mentor

    Here is the video I was thinking of. It uses a waterwheel instead of a pelton wheel. However the owner did an excellent engineering job of keeping is simple (KISS) and making it practical.

    I think that you should consider an automobile alternator for the generator.
    • You can get one at low cost at a junk yard.
    • 12DC is much safer than 120VAC, especially when you plan to have kids experimenting with loads.
    • An alternator is designed to give nearly constant output over a wide range of speeds, so a speed controller may not be necessary (KISS again)
    • As shown in the video, use pulleys and a belt to make both the turbine and the alternator run at their optimum RPM.
  8. May 15, 2016 #7
    Thanks a lot, you're so right about the connection.

    Yes, I've read I can use a 3 phase motor inverted as generator... Thing is... The university is gonna buy it for us, so why not pick a proper generator?
  9. May 15, 2016 #8
    Thanks a lot again!
    The thing is
    The university is gonna buy the stuff I need, so why not pick a proper generator? Instead of having to spend hours converting the motor
    The output must be AC, because we are simulating a hydropower plant

    Thanks a lot!
  10. May 15, 2016 #9


    Staff: Mentor

    OK, you have thousands of AC motors/generators to choose from.

    Regardless of who pays the bill, please keep three things in mind.
    1. Safety.
    2. The KISS principle. (KISS increases the chances that any project actually gets finished.)
    3. Requirements. (Clearly stating all requirements before beginning design is a sound engineering principle.)
  11. May 15, 2016 #10


    User Avatar
    Science Advisor
    Gold Member

    I would try to keep the voltage low and an automotive alternator would work for this. Simply remove the internal rectifier and regulator and take 3 phase AC from it. This is exactly how a power plant would be except you would have the safety of a lower voltage. After all, this is a simulation right? And not the real thing.
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