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Re: [microhydro] Re: Grid connected IMAG

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  • Mark Drabick
    Might as well throw in my 2 cents as well.........i ve been running a 1.2 KW and a 4 KW Grid Tied IMAG since 1984..........and have gone through many many
    Message 1 of 9 , Nov 29, 2012
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      Might as well throw in my 2 cents as well.........i've been running a 1.2 KW and a 4 KW Grid Tied IMAG since 1984..........and have gone through many many "lost the grid" cycles...........my control panel is wired such that when the grid disappears, the main contactor drops out isolating the IMAG from the grid (of course) and simultaneously disconnects the Capacitors.....the IMAG which usually spins at 1830 rpm of course speeds up and approaches 3000 rpm..............and it just sits there happily spinning away unloaded until the grid voltage and freq returns whereby the contactor and caps are re-energized (after a two minute stability delay) and the generator slips back into its sync speed. Yes the power is just lost to windage but the current spike is nominal and not an issue (at least tor these low power units). No special controls/power dumping/electronic load dumping/solenoids/tach controllers etc etc..................m
       
      ----- Original Message -----
      From: Tom
      Sent: Thursday, November 29, 2012 3:23 PM
      Subject: [microhydro] Re: Grid connected IMAG

       

      Hi

      can't you put electric solenoid valves on a couple of the input water feed lines that control the speed?
      Just use a mag pick-up speed sensor ( or something separate from the HZ speed, since a generator going that fast won't have accurate HZ output)

      I'm just guessing here, but if the unloaded RPM is nearly double, then you're putting in double the H2O.... so my guess is throttle back on two of the inputs.

      even if it doesn't shut off the water, at least reduce it.

      My 2 cents

      Tom

    • Radu Babau
      For Tom, In impulse type turbines, the runaway regime (~1.8...2 x rated speed) means that the turbine goes to a blade tangent speed almost equal to the nozzle
      Message 2 of 9 , Nov 30, 2012
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        For Tom,
         
         
        In impulse type turbines, the runaway regime (~1.8...2 x rated speed) means that the turbine goes to a blade tangent speed almost equal to the nozzle jet speed (the water slips 100% by the blade surface, without transfering any energy). This means that is you close half of the nozzles (half flow) the turbine will not freely spin slower. Another feature of the runaway speed is that the turbine output shaft torque is zero, and it will remain there no matter how many of the nozzles are open (provided that there is pressure on the turbine inlet). The mechanical power is therefore null (almost twice the rated speed multiplied by zero torque).
         
        The torque will rise by applying an external breaking torque (the electric generator does that), while the speed will decrease, and that means you will start harvesting power (the water slips partially by the blade, partially "pushing" it = energy trasfer). You are going to the rated point where the you will have rated torque and speed, i.e. rated power, which corresponds to the max. harvestable power from that water source. The turbine is dimensioned (nozzles number & diameter, spoons number & dimensions, etc.) so that it will provide the max. power at the rated speed of the generator (imposed by the grid frequency). At this point, the blade tangent speed is roughly half of the nozzle jet speed.
         
        Compared to this point, if you apply even higher braking torque (not the case for fixed speed grid applications, but encountered in island operated applications), the turbine speed will go down, while the torque will go up. You will ultimately reach the standstill point (turbine stalling), where the blade is standing, the water hits them with the greatest force (torque around 2 x Tn). Again, the power is null (zero speed multiplied by twice the rated torque).
         
        Basically, while you go from zero to runaway speed, the torque decreases liniarly with the speed, from 2x Tn at zero speed, to zero torque at 2 x rated speed. If you multiply this torque characteristics with the speed, you will have the power vs. speed curve, which is a hill shaped graph, having it's maximum at the rated speed.
         
        Again, by closing some of the nozzles, you will only change the amplitude of these graphs, but not move them anywhere on the speed axis.
         
         
        For Perran: why can't you close all the nozzles of you looses the grid, and leave your gadget at rest for the times when the grid is not present ? Everybody does that in hydro, wind, thermal and nuclear power plants.
         
         
        Best regards,
         
         
         
        ----- Original Message -----
        From: Tom
        Sent: Thursday, November 29, 2012 10:23 PM
        Subject: [microhydro] Re: Grid connected IMAG

         

        Hi

        can't you put electric solenoid valves on a couple of the input water feed lines that control the speed?
        Just use a mag pick-up speed sensor ( or something separate from the HZ speed, since a generator going that fast won't have accurate HZ output)

        I'm just guessing here, but if the unloaded RPM is nearly double, then you're putting in double the H2O.... so my guess is throttle back on two of the inputs.

        even if it doesn't shut off the water, at least reduce it.

        My 2 cents

        Tom

      • Thor
        Hi Perran. When the grid goes off, the turbine will spin up to runaway speed very, very quickly and closing the jets fast enough is probably not an option
        Message 3 of 9 , Nov 30, 2012
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          Hi Perran.

          When the grid goes off, the turbine will spin up to runaway speed very, very quickly and closing the jets fast enough is probably not an option because of waterhammer effect in the penstock.

          A better solution is to have jet deflectors of some kind, but the conventional type might be a difficult problem to install here.

          I have another suggestion.

          Disclaimer: I have not actually tried this, but anyway here are my thoughts :-)

          I think it is possible to reduce runaway speed for a Turgo or Pelton with a jet aimed at the wheel in the reverse direction or a jet aimed at the side of the normal jet, changing its direction from the wheel.

          This brake-jet does probably not have to be very accurate or efficient
          as its purpose is to waste power, not produce it!

          The brake- or deflector-jet could be controlled with a simple ball valve, with a weight that drops and opens the valve if power goes off. The weight could be held up by a firedoor holding magnet or similar.

          When power returns one waits a minute for the grid to stabilize, then connects generator to grid and finally starts a small motor or other mechanism to lift the weight and close the braking valve.

          For the control system I would most likely look for some common "Control Relay" (Micro/nano PLC) like Schneider Zelio, Crouzet Millennium, Siemens Logo!, Moeller Easy, etc.

          Power it from the grid side and program the startup sequence into it.

          Somehow I suspect you already might have a microcontroller/computer to handle this.

          Best regards.

          Thorhallur Ragnarsson
          (electronics technician)


          --- In microhydro@yahoogroups.com, Tom <tommygator@...> wrote:
          >
          > Hi
          >
          > can't you put electric solenoid valves on a couple of the input water feed lines that control the speed?
          > Just use a mag pick-up speed sensor ( or something separate from the HZ speed, since a generator going that fast won't have accurate HZ output)
          >
          > I'm just guessing here, but if the unloaded RPM is nearly double, then you're putting in double the H2O.... so my guess is throttle back on two of the inputs.
          >
          > even if it doesn't shut off the water, at least reduce it.
          >
          > My 2 cents
          >
          > Tom
          >
        • Nando
          To All : I have been mentally away from the group because health reasons . The idea of leaving the IMAG s that are Grid tied to run feely when the Grid
          Message 4 of 9 , Nov 30, 2012
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            To All :
             
            I have been "mentally" away from the group because health reasons .
             
            The  idea of leaving the IMAG's  that are Grid tied to run feely when the Grid  Drops is common, specially when the RPM of the turbine is driving IMAGs of lower RPM this to avoid the human labor to put the system back in service once the Grid power is reconnected and in quite some cases this is done in places where the Grid  disconnection in is not often done.
             
            Though the idea of controlling the turbine Nozzles is not a problem, technically, often a lot  of those Grid tied systems are not installed by highly technical personnel that do not see the need to add those controlling apparatus to reduce the cost of the investment.
             
            1540 or 1840 RPM ( 50 or 60 HZ) when unloaded may work around twice the RPM and the design of the turbine or IMAGs are well within their RPM limits so many see it as not necessary to stop the turbine.
             
            With IMAGs it is easy to do an automatic stopping by just using the GRID power to open a small hydraulic valve to fill a container that opens a valve closing the jets, once the  power arrives again, the valve will close allowing the container to empty and the valve to open allowing turbine  operation again , this is  done if the GRID drops often, like in some countries.
             
            In addition the idea of islanding the turbine and generator for limited local power is another way that in some areas or countries such set up is allowed if the proper protection of personnel is implemented.
             
            All  those turbine & generator arrangements are really defined by the needs and desires of the installer/owner etc.
             
            Right or  wrong they are implemented often defined by needs or financial needs or limitations
             
            Nando
             
            ----- Original Message -----
            Sent: Friday, November 30, 2012 02:50
            Subject: Re: [microhydro] Re: Grid connected IMAG

             

            For Tom,
             
             
            In impulse type turbines, the runaway regime (~1.8...2 x rated speed) means that the turbine goes to a blade tangent speed almost equal to the nozzle jet speed (the water slips 100% by the blade surface, without transfering any energy). This means that is you close half of the nozzles (half flow) the turbine will not freely spin slower. Another feature of the runaway speed is that the turbine output shaft torque is zero, and it will remain there no matter how many of the nozzles are open (provided that there is pressure on the turbine inlet). The mechanical power is therefore null (almost twice the rated speed multiplied by zero torque).
             
            The torque will rise by applying an external breaking torque (the electric generator does that), while the speed will decrease, and that means you will start harvesting power (the water slips partially by the blade, partially "pushing" it = energy trasfer). You are going to the rated point where the you will have rated torque and speed, i.e. rated power, which corresponds to the max. harvestable power from that water source. The turbine is dimensioned (nozzles number & diameter, spoons number & dimensions, etc.) so that it will provide the max. power at the rated speed of the generator (imposed by the grid frequency). At this point, the blade tangent speed is roughly half of the nozzle jet speed.
             
            Compared to this point, if you apply even higher braking torque (not the case for fixed speed grid applications, but encountered in island operated applications), the turbine speed will go down, while the torque will go up. You will ultimately reach the standstill point (turbine stalling), where the blade is standing, the water hits them with the greatest force (torque around 2 x Tn). Again, the power is null (zero speed multiplied by twice the rated torque).
             
            Basically, while you go from zero to runaway speed, the torque decreases liniarly with the speed, from 2x Tn at zero speed, to zero torque at 2 x rated speed. If you multiply this torque characteristics with the speed, you will have the power vs. speed curve, which is a hill shaped graph, having it's maximum at the rated speed.
             
            Again, by closing some of the nozzles, you will only change the amplitude of these graphs, but not move them anywhere on the speed axis.
             
             
            For Perran: why can't you close all the nozzles of you looses the grid, and leave your gadget at rest for the times when the grid is not present ? Everybody does that in hydro, wind, thermal and nuclear power plants.
             
             
            Best regards,
             
             
             
            ----- Original Message -----
            From: Tom
            Sent: Thursday, November 29, 2012 10:23 PM
            Subject: [microhydro] Re: Grid connected IMAG

             

            Hi

            can't you put electric solenoid valves on a couple of the input water feed lines that control the speed?
            Just use a mag pick-up speed sensor ( or something separate from the HZ speed, since a generator going that fast won't have accurate HZ output)

            I'm just guessing here, but if the unloaded RPM is nearly double, then you're putting in double the H2O.... so my guess is throttle back on two of the inputs.

            even if it doesn't shut off the water, at least reduce it.

            My 2 cents

            Tom

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