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Re: [microhydro] Grid connected IMAG

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  • ericnoharet@netcourrier.com
    Hello, If you have a constant production. Put a contactor to reverse the current on a resistive load and capacitor when the grid disepear. Very simple and
    Message 1 of 9 , Nov 29, 2012
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      Hello,

       

      If you have a constant production.

      Put a contactor to reverse the current on a resistive load and capacitor when the grid disepear.

       

      Very simple and reliable.

       

      Else, nothing, the imag need capacitive current to produce current. So the connection to the grid will not create a big over current. So no problem for me (at this level of power)

       

      Eric



      ----Message d'origine----
      A: microhydro@yahoogroups.com
      De: "beeperkid2003"
      Date: Wed, 28 Nov 2012 21:32:42 -0000
      Sujet: [microhydro] Grid connected IMAG
       

      I'm at a fairly advanced stage now with my Turgo based hydro and am just having the enclosure built to fire 4 jets at one of Joe's turbines.

      I'm having to run a step up pulley system as the head is only 7 metres.

      I am designing the control system myself being an electronics engineer.

      My question relates to getting the IMAG back under control after a temporary loss of grid power which happens every now and then here in Devon, UK.

      The motor will be single phase rated at ~1.5 kW and estimated maximum exported power is ~ 1 kW.

      When the grid is lost the IMAG will run up to twice its normal speed and will be disconnected from the grid of course.

      I need some automatic way of getting the speed back down to near its correct running speed before I reconnect to the grid because I assume that current surges will be excessive unless I do this.

      What is the best electrical way of doing this ? Could I temporarily connect a self excitation capacitor and then a resistive load to get it under control ?

      Any ideas please ?

      Perran Newman
      Devon, England

    • ian benson
      Hi. Assuming you are interested in the electronics and not valvegear (most Turgo s would have spear valve or at least some flow control to regulate
      Message 2 of 9 , Nov 29, 2012
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        Hi.
        Assuming you are interested in the electronics and not valvegear (most Turgo's would have spear valve or at least some flow control to regulate speed/output)...

        Agree head is low for a turgo, but still realistic for just 1kW (you must have a nice big runner!)

        Make sure you don't exceed the nameplate current in the motor windings, this is possible with overspeed and excitation capacitors alone. You can make a dump load and electronic load controller to maintain speed within close enough limits for G83 (th UK grid connect standard), but the other aspects of that standard are much harder to deal with.

        Any grid connected system in the UK should have type approved interface equipment to meet G83. If you wish to flout the regs, that's your risk, but i wouldn't as they are not too hard to meet.  Have you considered using a G38 inverter intended for PV? I can pretty much guarantee it'll work very well - Sunny Boy's have been used by us for low power (0.2 and 1.2 kW) G83, and at 10-40m head.

        Have fun..
        Ian.

        On 28 November 2012 22:27, Bill Sepmeier <bill@...> wrote:
         

        Thinking out loud ... not designing ...

        With just 7m of head, you probably should have used a different turbine altogether ... http://www.borderhydro.co.uk/water-turbines/francis---low-head/nautilus-t-type-scroll-case/

        If you're IMAG is excited by the grid and loses field excitation with loss of grid, consider a water shut off valve at the headrace (with appropriate vacuum preventer pipe/valve to let air into the penstock) - a valve held open by the AC presence, with a spring-controlled shutoff would work to stop the turbine when power failed.  Something along the line of a common "zone valve" used in hydronic heating systems, though sized for your penstock, would be easy to fabricate, if not available.  You might contact Miles at the above site ... he does a lot of grid intertied microhydro in the UK.



        From: beeperkid2003 <pvlnewman@...>
        To: microhydro@yahoogroups.com
        Sent: Wednesday, November 28, 2012 2:32 PM
        Subject: [microhydro] Grid connected IMAG

         
        I'm at a fairly advanced stage now with my Turgo based hydro and am just having the enclosure built to fire 4 jets at one of Joe's turbines.

        I'm having to run a step up pulley system as the head is only 7 metres.

        I am designing the control system myself being an electronics engineer.

        My question relates to getting the IMAG back under control after a temporary loss of grid power which happens every now and then here in Devon, UK.

        The motor will be single phase rated at ~1.5 kW and estimated maximum exported power is ~ 1 kW.

        When the grid is lost the IMAG will run up to twice its normal speed and will be disconnected from the grid of course.

        I need some automatic way of getting the speed back down to near its correct running speed before I reconnect to the grid because I assume that current surges will be excessive unless I do this.

        What is the best electrical way of doing this ? Could I temporarily connect a self excitation capacitor and then a resistive load to get it under control ?

        Any ideas please ?

        Perran Newman
        Devon, England




      • Tom
        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
        Message 3 of 9 , Nov 29, 2012
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          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
        • 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 4 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 5 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 6 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 7 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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