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Re: Flygen:how much loss within electrical cable?

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  • Joe Faust
    This keeps arriving in my notes about an aloft generator of special type: Type: Shade generator The flown system generates a blocking of sunlight. Such
    Message 1 of 17 , Mar 16, 2011

      This keeps arriving in my notes about an aloft generator of special type:

      Type: Shade generator

      The flown system generates a blocking of sunlight.

      Such blocking of sunlight might be used simply for generating shade for ground operations in special circumstances. Perhaps one wants shade for special agricultural reasons. Maybe for moviemaking reasons. Maybe for the comfort of spectators. Maybe for keeping animals comforted in specially hot days.

      While the shade is being generator, pehaps the same surface could be converting the impinging sunlight to electricity and heat for aloft uses.  Flagging of the shading surfaces might involve piezoelectric elements, messaging, advertising, active video, etc.      Flown shade generators might save the lives of refugees.

      Other uses of flown shade generators may be found.

      JoeF

    • Robert Copcutt
      Hi, Discussions such as these (about what to make tethers from) need hard figures before accurate conclusions can be drawn. The tether will experience numerous
      Message 2 of 17 , Mar 17, 2011
        Hi,

        Discussions such as these (about what to make tethers from) need hard
        figures before accurate conclusions can be drawn.

        The tether will experience numerous stress strain cycles in its life so
        close attention must be paid to fatigue resistance. For some materials
        there are published Wohler's curves (or S-N curves) to help decide how
        thick to make the tether. These are plots of the stress that broke the
        test specimen against the number of times the stress was applied. The
        trouble is that measuring this data takes time on sophisticated test
        apparatus so it is not as easy to find as tensile strength data which
        requires a single pull.

        I have prepared an Open Office spreadsheet to look at the tether
        material issue (and others to come). This is just the beginning and some
        of the data is just an estimate, but it is in the right ball-park and it
        allows some early conclusions. I will make an Excel version later when
        it is a bit more developed.
        http://www.copcutt.me.uk/Kite_design.ods

        High tensile steel (not stainless) is the clear winner partly because it
        is readily available and far cheaper than the alternatives.

        Using pure copper, that has been cold worked, as the only material in
        the tether is a surprisingly viable option. Better alloys are of
        interest for many applications so there has been a lot of work on
        developing them. eg. Hitachi Cable report developing a strong fatigue
        resistant copper alloy but I could not find the S-N curve so it is not
        included on the spreadsheet.

        If the tether resistance is too high it will be heated and this will
        decrease its strength.

        Although kevlar and dyneema are strong and light their resistance to
        frictional wear is poor, and they are expensive.

        All known insulating materials would not last long if used to encase
        metal cables under high tension on a drum (reel or winch). That means
        the kite needs to be tethered by 2 or 3 bare wires that are kept
        separate to prevent short circuits.

        Robert.




        On Wed, 2011-03-16 at 08:57 +0100, Pierre Benhaiem wrote:
        >
        > For example:wind speed is 10 m/s;a Makani's prototype is measured
        > about 4 and 8 kw.Losses into electrical cable are lower for high
        > voltage and little current than the inverse.
        >
        > For FlygenKite voltage is about 8-15V (average 10V);so for 100 W,10A
        > are needed.FlygenKite charges batteries but if we put an electrical
        > cable copper section is about 2,5 mm²,the weight of such a cable which
        > length is 20 m is too much,and loss is high (about 60%).I see also a
        > possibility with an extension for a 200 m cable (but not more) and a
        > higher voltage (about 100 V for example).
        >
        > So my opinion is for Makani the search of a high voltage to limit
        > losses within electrical cable.But the length of the cable is by far
        > higher.
        >
        > I do not think nanotube-tethered technology is superior in rapport to
        > conductivity (in rapport to copper),but only in rapport to mecanic
        > resistance.
        >
        > What is your point of view?
        >
        > Pierre B http://flygenkite.com
        >
      • Bob Stuart
        I m surprised that aluminum, as the third-best conductor, is not being considered. It can be plated onto glass fibers, and presumably others, which might
        Message 3 of 17 , Mar 17, 2011
          I'm surprised that aluminum, as the third-best conductor, is not being considered.  It can be "plated" onto 'glass fibers, and presumably others, which might improve fiber fatigue life, and it might even benefit from the hollow section of the conductor, as some bus bars do.  Does anyone know how the electrical resistance of the high-strength alloys compares to pure metal?

          Bob

          On 17-Mar-11, at 4:29 PM, Robert Copcutt wrote:

          Hi,

          Discussions such as these (about what to make tethers from) need hard
          figures before accurate conclusions can be drawn. 

          The tether will experience numerous stress strain cycles in its life so
          close attention must be paid to fatigue resistance. For some materials
          there are published Wohler's curves (or S-N curves) to help decide how
          thick to make the tether. These are plots of the stress that broke the
          test specimen against the number of times the stress was applied. The
          trouble is that measuring this data takes time on sophisticated test
          apparatus so it is not as easy to find as tensile strength data which
          requires a single pull.

          I have prepared an Open Office spreadsheet to look at the tether
          material issue (and others to come). This is just the beginning and some
          of the data is just an estimate, but it is in the right ball-park and it
          allows some early conclusions. I will make an Excel version later when
          it is a bit more developed.
          http://www.copcutt.me.uk/Kite_design.ods

          High tensile steel (not stainless) is the clear winner partly because it
          is readily available and far cheaper than the alternatives.

          Using pure copper, that has been cold worked, as the only material in
          the tether is a surprisingly viable option. Better alloys are of
          interest for many applications so there has been a lot of work on
          developing them. eg. Hitachi Cable report developing a strong fatigue
          resistant copper alloy but I could not find the S-N curve so it is not
          included on the spreadsheet. 

          If the tether resistance is too high it will be heated and this will
          decrease its strength.

          Although kevlar and dyneema are strong and light their resistance to
          frictional wear is poor, and they are expensive.

          All known insulating materials would not last long if used to encase
          metal cables under high tension on a drum (reel or winch). That means
          the kite needs to be tethered by 2 or 3 bare wires that are kept
          separate to prevent short circuits. 

          Robert.

          On Wed, 2011-03-16 at 08:57 +0100, Pierre Benhaiem wrote:
          > 
          > For example:wind speed is 10 m/s;a Makani's prototype is measured
          > about 4 and 8 kw.Losses into electrical cable are lower for high
          > voltage and little current than the inverse.
          > 
          > For FlygenKite voltage is about 8-15V (average 10V);so for 100 W,10A
          > are needed.FlygenKite charges batteries but if we put an electrical
          > cable copper section is about 2,5 mm²,the weight of such a cable which
          > length is 20 m is too much,and loss is high (about 60%).I see also a
          > possibility with an extension for a 200 m cable (but not more) and a
          > higher voltage (about 100 V for example).
          > 
          > So my opinion is for Makani the search of a high voltage to limit
          > losses within electrical cable.But the length of the cable is by far
          > higher.
          > 
          > I do not think nanotube-tethered technology is superior in rapport to
          > conductivity (in rapport to copper),but only in rapport to mecanic
          > resistance.
          > 
          > What is your point of view?
          > 
          > Pierre B http://flygenkite.com 
          > 


        • Robert Copcutt
          Adding anything to the metals that conduct well makes them more resistive. This has been studied in detail and things like copper, silver, gold, iron and
          Message 4 of 17 , Mar 17, 2011
            Adding anything to the metals that conduct well makes them more
            resistive. This has been studied in detail and things like copper,
            silver, gold, iron and aluminium all conduct best when very pure.

            Pure aluminium is soft and would soon rub off if plated onto a stronger
            material. I have discovered that copper alloys were extensively studied
            to find the best materials to use in CERN. Hence the list of copper
            alloys in my spreadsheet. I have not found such work for aluminium
            alloys. Maybe aluminium tether materials will be developed in the
            future, but for now steel wins by a large margin, particularly when you
            consider cost.

            Robert.



            On Thu, 2011-03-17 at 18:05 -0600, Bob Stuart wrote:
            >
            > I'm surprised that aluminum, as the third-best conductor, is not being
            > considered. It can be "plated" onto 'glass fibers, and presumably
            > others, which might improve fiber fatigue life, and it might even
            > benefit from the hollow section of the conductor, as some bus bars
            > do. Does anyone know how the electrical resistance of the
            > high-strength alloys compares to pure metal?
            >
            >
            >
            > Bob
            >
          • Pierre BENHAIEM
            DaveS, Indeed according to some informations the value of conductivity for both carbon nanotube and copper should be the same for a weight of 1/6 for
            Message 5 of 17 , Mar 17, 2011
              DaveS,

              Indeed according to some informations the value of conductivity for both carbon nanotube and copper should be the same for a weight of 1/6 for nanotube.Nethertheless the weight of the protection should be also identical,so quite high.For a common cable the weight of the protection is 2 times (one protection for each wire) or 5 times (add the global protection of the two wires for an usual cable) the weight of copper.However furthering for FlygenKite nanotube could be interesting for some configurations.

              PierreB
              http://flygenkite.com  
               




              > Message du 16/03/11 17:32
              > De : "dave santos"
              > A : "AirborneWindEnergy@yahoogroups.com"
              > Copie à :
              > Objet : Re: [AWECS] Flygen:how much loss within electrical cable?
              >
              >  

              >

              Pierre,

              The comparison you are seeking is very hard to properly define. Nanotubes are far too primitive still to presume any set value for conductivity, although in theory they will someday far surpass copper in performance. Its very risky to design with expensive unavailable materials. Even presuming copper, comparing your Flygen with Makani's prototypes is impractical because so many other critical factors are different.

              In my opinion the biggest obstacle Makani faces in "competing" with small-scale flygens is to meet airworthyness standards for a far larger mass traveling far faster. They must show greater reliability & margin-of-safety for all components than a small system with far less inherent risk. Higher voltage operation hardly makes safety easier for them. Safety drives cost.

              The two systems don't even share the same market. Makani is aimed at utility-scale & your system is at the personal scale. Your biggest advantage is to be first-to-market. Build revenue & in a few years you can buy-out Makani as they languish in engineering & regulatory uncertainty,

              daveS



              >


              >
            • Joe Faust
              Flying generator aloft: Not to forget Dave Santos early mention of bare wires in arch systems where shroud would not be needed, as the left line and right
              Message 6 of 17 , Mar 17, 2011
                Flying generator aloft: Not to forget Dave Santos' early mention of
                bare wires in arch systems where shroud would not be needed, as the
                left line and right line would be far separated.
              • Dave Lang
                Lest we forget, running a bare wire up into the atmosphere in the presence of extremely high electric potentials might be a bit sporty. It s bad enough even
                Message 7 of 17 , Mar 17, 2011
                  Re: [AWECS] Flygen:how much loss within electrical cable?
                  Lest we forget, running a bare wire up into the atmosphere in the presence of extremely high electric potentials might be a bit sporty. It's bad enough even with "insulation" on the wire, since the full voltage potential difference between a conductor (connected to ground), and the cloud charge, when separated by only the thickness of the insulation presents an electric E-field strength of extreme magnitude challenging the best dielectric materials.

                  DaveL


                  At 4:20 AM +0000 3/18/11, Joe Faust wrote:
                   
                  Flying generator aloft: Not to forget Dave Santos' early mention of
                  bare wires in arch systems where shroud would not be needed, as the
                  left line and right line would be far separated.

                • Robert Copcutt
                  Reasonably priced insulating materials of a realistic thickness are only good for a few thousand volts. Air is not much worse (maybe 10 to 100 times, depending
                  Message 8 of 17 , Mar 18, 2011
                    Reasonably priced insulating materials of a realistic thickness are only
                    good for a few thousand volts. Air is not much worse (maybe 10 to 100
                    times, depending upon what you are comparing with). Again, some real
                    figures will help. The spark gap voltage for 2 needle points 0.85 cm
                    apart is 10 000 volts (10 kV). For 100 kV the gap is 15.5 cm.

                    Lightning is not going to care if your tether is a conductor or not or
                    whether it is insulated or not. The fact is kites needs to be out of the
                    sky when lightning is around - end of story. However, that in no way
                    limits AWE. The approach of lightning can be measured by monitoring
                    certain radio frequencies. Someone needs to investigate this in more
                    detail.

                    Robert.



                    On Thu, 2011-03-17 at 21:45 -0700, Dave Lang wrote:
                    >
                    > Lest we forget, running a bare wire up into the atmosphere in the
                    > presence of extremely high electric potentials might be a bit sporty.
                    > It's bad enough even with "insulation" on the wire, since the full
                    > voltage potential difference between a conductor (connected to
                    > ground), and the cloud charge, when separated by only the thickness of
                    > the insulation presents an electric E-field strength of extreme
                    > magnitude challenging the best dielectric materials.
                    >
                    >
                    > DaveL
                    >
                    >
                    >
                    >
                    > At 4:20 AM +0000 3/18/11, Joe Faust wrote:
                    > >
                    > > Flying generator aloft: Not to forget Dave Santos' early mention of
                    > > bare wires in arch systems where shroud would not be needed, as the
                    > > left line and right line would be far separated.
                    >
                    >
                    >
                  • Dave Lang
                    ... Hmmm, if I have a non-conducting tether whose dielectric strength is greater than that of the surrounding air. Why would lightning choose that as a path
                    Message 9 of 17 , Mar 18, 2011
                      Re: [AWECS] Flygen:how much loss within electrical cable?
                      At 2:11 PM +0000 3/18/11, Robert Copcutt wrote:

                      Lightning is not going to care if your tether is a conductor or not or
                      whether it is insulated or not. The fact is kites needs to be out of the
                      sky when lightning is around - end of story. However, that in no way
                      limits AWE. The approach of lightning can be measured by monitoring
                      certain radio frequencies. Someone needs to investigate this in more
                      detail.

                      Hmmm, if I have a non-conducting tether whose dielectric strength is greater than that of the surrounding air.  Why would lightning choose that as a path to ground as opposed to the more conductive surrounding air?

                      DaveL







                      On Thu, 2011-03-17 at 21:45 -0700, Dave Lang wrote:
                      >
                      > Lest we forget, running a bare wire up into the atmosphere in the
                      > presence of extremely high electric potentials might be a bit sporty.
                      > It's bad enough even with "insulation" on the wire, since the full
                      > voltage potential difference between a conductor (connected to
                      > ground), and the cloud charge, when separated by only the thickness of
                      > the insulation presents an electric E-field strength of extreme
                      > magnitude challenging the best dielectric materials.
                      >
                      >
                      > DaveL
                      >
                      >
                      >
                      >
                      > At 4:20 AM +0000 3/18/11, Joe Faust wrote:
                      > >
                      > > Flying generator aloft: Not to forget Dave Santos' early mention of
                      > > bare wires in arch systems where shroud would not be needed, as the
                      > > left line and right line would be far separated.
                      >
                      >
                      >

                    • Robert Copcutt
                      ... Firstly, all surfaces attract dirt and water. Although the bulk material of the tether might have a higher resistance than air its surface would inevitably
                      Message 10 of 17 , Mar 18, 2011
                        On Fri, 2011-03-18 at 11:16 -0700, Dave Lang wrote:

                        > Hmmm, if I have a non-conducting tether whose dielectric strength is
                        > greater than that of the surrounding air. Why would lightning choose
                        > that as a path to ground as opposed to the more conductive surrounding
                        > air?
                        >
                        >
                        > DaveL
                        >
                        >

                        Firstly, all surfaces attract dirt and water. Although the bulk material
                        of the tether might have a higher resistance than air its surface would
                        inevitably be lower, even without rain.

                        Secondly, what makes lightning choose the path it does? Could tiny
                        eddies in the air caused by the tether create a favoured path? Probably.
                        I would not want to take the chance even if I had installed a fancy
                        tether cleaning device.

                        Lightning rarely lasts long and a special radio receiver could provide
                        automatic guidance about when to pull the kites down. In fact that is
                        probably something for the coolIP section. A device to work out the
                        chances of a lightning strike based on the strength of radio waves at
                        particular frequencies, or maybe based on the potential gradient in the
                        atmosphere. This device then sends a signal to tell the human or
                        computer that controls the kite what the strike likelihood is. Once
                        developed such a device need not be expensive and one would probably
                        suffice for a whole farm of AWEs.

                        Robert.
                      • Bob Stuart
                        We can pull down kites if an electrical storm is approaching, but what if it starts up right on our site? Bob
                        Message 11 of 17 , Mar 18, 2011
                          We can pull down kites if an electrical storm is approaching, but what if it starts up right on our site?

                          Bob

                          On 18-Mar-11, at 1:15 PM, Robert Copcutt wrote:

                          On Fri, 2011-03-18 at 11:16 -0700, Dave Lang wrote:

                          > Hmmm, if I have a non-conducting tether whose dielectric strength is
                          > greater than that of the surrounding air. Why would lightning choose
                          > that as a path to ground as opposed to the more conductive surrounding
                          > air?
                          > 
                          > 
                          > DaveL
                          > 
                          > 

                          Firstly, all surfaces attract dirt and water. Although the bulk material
                          of the tether might have a higher resistance than air its surface would
                          inevitably be lower, even without rain.

                          Secondly, what makes lightning choose the path it does? Could tiny
                          eddies in the air caused by the tether create a favoured path? Probably.
                          I would not want to take the chance even if I had installed a fancy
                          tether cleaning device.

                          Lightning rarely lasts long and a special radio receiver could provide
                          automatic guidance about when to pull the kites down. In fact that is
                          probably something for the coolIP section. A device to work out the
                          chances of a lightning strike based on the strength of radio waves at
                          particular frequencies, or maybe based on the potential gradient in the
                          atmosphere. This device then sends a signal to tell the human or
                          computer that controls the kite what the strike likelihood is. Once
                          developed such a device need not be expensive and one would probably
                          suffice for a whole farm of AWEs.

                          Robert.


                        • Robert Copcutt
                          ... The techniques I mentioned work independently of the history of nearby strikes. The potential in the clouds that causes lightning builds up over time. If
                          Message 12 of 17 , Mar 18, 2011
                            On Fri, 2011-03-18 at 13:40 -0600, Bob Stuart wrote:
                            >
                            > We can pull down kites if an electrical storm is approaching, but what
                            > if it starts up right on our site?
                            >
                            >
                            >
                            > Bob
                            >

                            The techniques I mentioned work independently of the history of nearby
                            strikes. The potential in the clouds that causes lightning builds up
                            over time. If the potential gradient near the ground can be monitored it
                            will give warning of strikes. The radio frequency emissions also warn of
                            developing strikes. I am not talking about the wide spectrum
                            interference heard on ordinary a.m. radios from actual strikes.
                            Apparently there is a pre-strike signal.

                            Robert.
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