US3364389A - Low loss conductor - Google Patents

Description

Jan. 16, 1968 G. N. J. MEAD LOW LOSS CONDUCTOR 2 Sheets-Sheet 1 Filed April 16, 1964 CURRENT FLOW F G. l

DIELECTRIC CONDUCTOR F I 7 INVENTOR GEORGE N.J. MEAD ATTORN EYS' Jan. 16, 1968 G. N. J. MEAD 3,364,339

LOW LOSS CONDUCTOR Filed April 16, 1964 2 Sheets-Sheet 2 INVENTOR GEORGE N. J. MEAD F166 WMWWAV ATTORNEYS United States Patent 3,364,389 LOW LOSS CONDUCTOR George N. J. Mead, Robin Lane, Exeter, NH. 63833 Filed Apr. '16, 1964, Ser. No. 369,277 13 Claims. (Cl. 315-168) This invention is generally related to low loss electrical conducting devices and more particularly is directed to wards a new and improved device for conducting electrical current with very low resistance at normal temperatures. This invention also contemplates a novel arrangement for controlling the flow of electrical current through a low loss electrical conducting device.

As is well known, conventional electrical conductors display inherent resistance to the how of current. For example, in electrically conductive solids, such as metals and semi-conductors, electrons moving from hole to hole through the crystal lattice collide with the atoms of the conductor producing vibrations which further impede the movement of the current carrying electrons. These collisions and the vibrations imparted to the atoms of the conductor are forms of electrical resistance and are usually considered as losses since a portion of the available electrical energy is converted into heat energy.

In devices such as gas filled tubes, for example, that employ a plasma as a medium for conducting a flow of electrical current, the IR drop is a function of the ionization potential of the gas. Not only is the ionization potential not recovered during deionization but there is a constant deionization and reionization that takes place within the plasma caused by collisions between the electrons and positively charged ions both in the conducting space and at the walls of the tube. These losses increase if the path of the electrical arc is made to curve.

In both of the above devices there is no problem of increased resistivity from an electron space charge by reason of the fact that neutralizing positive ions are distributed along the path of the electrical current. However, in a vacuum tube no such neutralizing effect is available to overcome the space charge and, as a result, the electrical conductivity of a vacuum tube is limited by the presence of a space charge which normally develops in front of the emitting surface of the cathode.

Various means have been proposed to reduce the internal resistance in electrically conductive devices to provide what is termed a superconductor. In general, the means taken to achieve a superconductive state is to lower the temperature of the device to an extremely low point, in some instances approaching absolute zero, so that current carrying electrons only are made to flow without hindrance from thermally excited atoms. This technique requires rather elaborate and expensive equipment to achieve the low temperature conditions in which the superconductive phenomenon appears.

It is an object of the present invention, therefore, to provide improvements in electrical conductors.

Another object of this invention is to provide a new and improved low loss electrical conductive device.

Still another object of this invention is to provide a low loss electrically conductive device adapted to function at normal or high temperatures.

A still further object of this invention is to provide an improved arrangement for controlling the flow of current through an electrical conducting system.

And yet another object of this invention is to provide a novel means for eliminating the effect of a space charge Within a vacuum conducting device.

More particularly this invention features a low loss conductor comprising an evacuated or gas-filled enclosure and having a pair of spaced electrodes connected to a suitable power source and of opposing polarity. Disposed between the two electrodes and extending substantially the full distance therebetween is a core having a plurality of parallel passages which extend from end to end thereof. The ends of the core terminate in closely spaced opposition to the electrodes. The core body is fabricated from electrically conductive material while the walls of the passages are coated with a dielectric stratum to prevent short circuiting of the current. In the vacuum mode of the invention, the core is given a positive static charge to provide a distributed positive charge along the current path which neutralizes the negative field of the space charge. The positively charged walls of the passages provide a field which extends into the passageways to neutralize the fields of the electrons in the electron cloud, thereby eliminating this source of electrical resistance for improved conductivity characteristics.

In the case of a gas filled device, the body would be given a negative charge so as to hold the positively charged ions within the gas and to reduce their transverse mobility to the point where collisions and recombinations are minimized. In this embodiment, the positively charged ions provide the distributed positive charge to neutralize the electron space charge.

However these and other features of the invention, along with further objects and advantages thereof, will become more fully apparent from the following detailed description of preferred embodiments of the invention, with reference being made to the accompanying drawings in which:

FIG. 1 is a cross-sectional view in side elevation, somewhat schematic, of a low loss conductive device made according to the invention,

FIG. 2 is a cross-sectional view taken along the line 22 of FIG. 1,

FIG. 3 is a fragmentary view of FIG. 2 on an enlarged scale to show details of construction,

FIG. 4 is a somewhat schematic view showing the relationship between the space charge and the charged passage walls,

FIG. 5 is a view in perspective of a modified core for the low loss conductor,

FIG. 6 is a view in perspective, somewhat schematic, of a modification of the invention,

FIG. 7 is a cross-sectional view in side elevation, somewhat schematic, of a modification of the FIG. 1 device and showing a device having a uni-directional current flow,

FIG. 8 is a view in side elevation, partly broken away, showing a low loss conductive device suitable for AC operation,

FIG. 9 is a view in side elevation partly broken away and partly schematic showing the low conductive device employed as a coil, and

FIG. 10 is a schematic arrangement showing the low loss conductor as applied to a power transmission line system.

Referring now to FIGS. 1 through 3,, the reference character 10 indicates a low loss conductor generally organized about a tubular jacket 12 having its inner surface coated with a dielectric stratum 14. Mounted at either end of the jacket 12 and insulated therefrom are electrodes 16 and 18 being the cathode and anode respectively.

Disposed within the jacket 12 is a conductive core 20 made up of a bundle of insulated electrical filaments 22 extending substantially the full length of the jacket with their ends terminating in close spaced relation to the electrodes 16 and 18 as best shown in FIG. 1. Each filament 22 is sheathed in a dielectric sleeve 24 and preferably both are circular in cross-section. With this arrangement, the insulated filaments 22 when grouped together into a bundle define a series of longitudinal passages 26 of small cross-section with each filament 22 being equally spaced from the center of an adjacent passage 26.

In practice, the device It) is fully sealed and in a preferred form the jacket is evacuated. Each of the filaments is connected to the positive side of a suitable power source 28 by means of a lead 30 which passes through the walls of the jacket and connects to each of the filaments. The lead 30 is insulated and at points of connection with the conductors 22, the joints are also insulated for reasons that will presently appear.

When the electrodes 16 and 18' are energized a current flows through the passages 26. Initially, the space charge 32, as shown in FIG. 4, will develop adjacent the cathode 16. The space charge will consist of a cloud of relatively immobile electrons which inhibit the flow of current carrying electrons between the electrodes. This cloud, in effect, increases the internal resistance of the device as in any vacuum tube. However, according to the present invention, this space charge can be eliminated by the filaments 22 providing a positive charge along the walls of the passages. The charged walls, it will be understood, are insulated from the flow of electrons to prevent current leakage.

The charged filaments develop positive fields which extend towards the center of each passage and have the effect of neutralizing the negative fields of the free electrons in the space charge. In practice, a few electrons may accumulate along the walls of the passage as suggested in FIG. 4. However, this sheath of electrons will be relatively inconsequential since the primary effect of the static positive field will be to neutralize the fields of the electrons.

By provinding a distributed positive charge along the walls of the passages, the space charge of the electron cloud traveling therethrough will be neutralized. In practice, it is desirable that the passages be quite narrow to provide a strong field which will be close to the electrons moving through the passages. By reason of the fact that the effect of the space charge is substantially eliminated, the device is characterized by very low resistance and high current density. This high conductivity permits high current density without overheating and thus makes the device particularly useful for generating magnetic fields of high intensities.

The resistance of the conductor may be controlled by varying the charge on the filaments 22. The device may then serve as an electrical valve useful in circuits of various types.

In practice, the individual filaments which make up the filaments 22 may be fabricated from various materials. For example, tungsten would be suitable for hightemperature applications and may be coated with a suitable dielectric such as a ceramic material, for example. Coated stainless steel may be employed to advantage. Also anodized aluminum wires would be useful insofar as the anodized coating would serve to insulate the filament from the flow of electrons through the passages. Where the device is used to conduct in one direction only, the cathode may be a thoriated tungsten element and the anode may be of some material such as graphite, for example. For two-way conduction, both electrodes may be of refractory material, either graphite or tungsten, for example, and for such applications, the coated electrodes would not normally be desirable. Refractory electrodes may require a cathode heater for efiicient electron emission. Other types of electron emitters obviously may be employed to advantage.

Various arrangements other than the bundle of insulated filaments may be employed as a core for use in establishing a positive field along the path of conduction and thereby neutralize the space charge within the device. For example, a one piece metallic core 33, such as shown in FIG. 5, may be employed in place of the bundle of filaments. This core is formed with a plurality of insulated internal longitudinal passages 35, each preferably circular in cross-section and coated with a dielectric Ii'latertal along the walls thereof to prevent electrical losses. In devices employing a statically charged core, there would be an automatic collection of positive charges within the metallic core along the passage walls to neutralize the negative fields of the free electrons and thereby neutralize the space charge effect. This automatic collection of positive charges will be produced by reason of the negatively charged electrons attracting a stratum of positive charges along the walls of the core passages; the effect is augmented if the core is connected to an infinite ground such as the earth. The action is analogous to the charging of a capacitor, but the effect is similar to the actively charged superconductor illustrated in FIGS. 1-3.

Another technique for forming a multiplicity of small passages between the electrodes would be to rule fine grooves on metal foil using a process similar to that used in the fabrication of diffraction gratings. Such a foil would be ruled along both sides with the grooves on one side being staggered with respect to those on the opposite side. If the grooves were all parallel to one another, the sheet of foil could be rolled into a cylinder with the grooves parallel to the axis of the cylinder so that the current flow would be axial. Alternatively, the grooves may be ruled as the radii of an annular disk and a plurality of these disks may be stacked together, as suggested in FIG. 6, to form an annular core 37 and in this embodiment, the current flow would be radial between a center cathode 39 and a surrounding anode 41 rather than axial as in the previous embodiments.

Another technique by which the passages may be formed through the core is to employ corrugated metal foil and join the layers together. This may be done by a sintering process or by utilizing extremely thin contact cement. The passages could be insulated by oxidizing the surface of the passages with a suitable oxidizing agent or by electrolytic action.

In this device, it is desirable to have the positive fields as close as possible to the electrons flowing through the vacuum along the passages. For this purpose, it is desirable that in the cae of the filament type core that the filaments be as thin as possible consistent with a reasonable strength factor. For example, filaments on the order of .0005 to .005 inch in diameter, may be employed. Thin filaments would be more efficient than thicker ones since the effect of the positive charge on the electron cloud is partly dependent on how close the filaments may be gathered together. Also, the effect of the positive field in the space charge is a function of the charge applied to the filament and the thickness of the insulation enclosing the filament. It will be appreciated that if the insulation of the filament is thick, the positively charged ions would be spaced further from the passage and its effect on the space charge would be diminished accordingly. The voltage which may be applied to the filaments, would have an effect on the current density up to a given level after which any increas in voltage would add nothing to the operation of the device.

In the gas filled device, the slow moving ions which move in a transverse direction are immobilized to improve current flow. The positive ions within the plasma would tend to move along the walls of the passages whereas the fast moving electrons would, by reason of the negaive charge on the core, move unimpeded along the center of the passages. The effect would be to eliminate the random movement of gas particles which normally limit the conductivity of the device by reason of collisions with the current carrying electrons.

Referring now more particularly to FIGS. 5, 6 and 7, there are illustrated flexible superconducting devices embodying features of the invention and constituting modifications of the invention. In FIG. 7, there is shown a flexible bellows type metal tube 34 covered on its outer surface by a woven wire protective sheath 36 and having its inner surface covered with a flexible dielectric material 38. Disposed within the tube 34 is a core 40 made up of filaments 42 similar to those described in conjunction with the embodiment of FIGS. 1 through 3. Each filament is circular in cross-section so that when gathered into a bundle the filaments nest to define a plurality of longitudinal passages 44. As before, each of the filaments is covered with a dielectric insulating layer 46.

Each end of the tube 34 is sealed by means of a cap 48 and 50 with the cap 48 carrying a concave electrode 52 which, in the illustrated embodiment, constitutes the cathode of the superconducting device. The cap 50 also carries an electrode of concave configuration and this electrode serves as the anode in the circuit. Both electrodes are spaced from the ends of the core 40 so as not to be in electrical contact therewith. The anode 54 is formed with a multiplicity of perforations 56 which accommodate the filaments 42 which are drawn therethrough for contact with a concave plate 58. The plate 58 serves as a common conductor whereby a positive charge may be applied to all of the filaments which make up the core 40. The plate 58 will be seen to be connected to the positive side of a suitable power source 60. It will be understood that the filaments 42 are insulated from the anode 54 to prevent short circuiting between filaments and the anode.

The system is similar in operation to the FIG. 1 device. That is to say, a positive charge applied to the filaments 42 through the plate 58 will cause positive charges to be formed along the walls of the passages which will serve to neutralize the field of the space charge. However, in the FIG. 5 device, the entire assembly is flexible so that it may be employed in the same fashion as any flexible lead. The device as shown in FIG. 7 is adapted to conduct current in one direction only and as such may be used as a rectifier. If conduction in two directions is desired, it is necessary to modify the device in the manner shown in FIG. 8.

In the FIG. 8 embodiment, the construction is generally the same as that of the FIG. 7 embodiment with the exception that the electrodes are connected to an AC power source 62. In the rectifier mode of FIG. 7 it is desirable that the ends of the filaments 42 terminate just short of the cathode in order to aid in drawing out the electrons from the emitting surface of the cathode. In the two-way mode of FIG. 8, this same arrangement could be used.

The flexible superconductor such as shown in FIG. 8 has particular utility for use as a coil 64 as illustrated in FIG. 9. A superconductor coil 64 of this type may be used in a wide variety of applications. For example, such a coil may be employed to advantage in an electro-rnagnet, or for any similar applications requiring the development of high-flux fields without a high heat release. Furthermore, the conductance of this device would not be impaired by either high magnetic flux density or by high ambient temperatures.

Referring now more particularly to FIG. there is shown a further modification of the invention. In this embodiment a pair of superconductors 66 and 68 of the flexible type described above are employed in a long-range power transmission line system. The reference character 90 indicates a generating station in FIG. 10 and a substation is indicated by reference character 72 With a load indicated by resistance 73. Connected to each filament core in the superconductors is a battery or generator 74 for applying a positive charge. The superconductive performance of these transmission lines permits the use of lower transmission voltages without reducing the amount of power that can be carried by a given line. This is because of lower line losses and higher current densities. For both A.C. and DC. power transission, lower transmision voltage oifers may advantages; e.g. it reduces the costof switch gear etc; furthermore, low voltages can eliminate the corona losses associated with high voltage lines. For A.C. power transmission, the lower transmission voltages 6 and the resulting close spacing permitted, reduces the losses from both the inductive and capacitive reactance of the lines.

While the invention has been described with particular reference to the illustrated embodiment, it will be understood that numerous modifications thereto will appear to those skilled in the art. Also, it will be understood that the above description and accompanying drawings should be taken as illustrative of the invention and not in a limiting sense.

Having thus described the invention, What I claim and desire to obtain by Letters Patent of the United States is:

1. A low loss conductor of electrical current, comprising (a) walls defining an enclosure,

(b) a pair of spaced electrodes disposed within said enclosure,

(c) means for energizing said electrodes thereby producing charged particles having an associated field within said enclosure,

(d) a core of electrically conductive material disposed between said electrodes and said core having at least one passage for electrons to flow between said electrodes, said core being electrically insulated from said electrodes and the inner volume of said enclosure,

(e) means to apply a charge to said core thereby inducing a distributed charge along the walls of said core passage, said charge being adapted to neutralize the fields of the particles within said volume and thereby reducing the resistance to current flow along said passage.

2. A low loss conductor of electrical current according the claim 1 wherein said core is grounded.

3. A low loss conductor of electrical current according to claim 1 wherein said core is formed with a plurality of spaced passages.

4. A low loss conductor according to claim 1 wherein said core comprises a plurality of electrically conductive filaments electrically insulated from one another and nested together into a bundle extending lengthwise between said electrodes.

5. A low loss conductor according to claim 1 wherein said walls and said core are flexible.

6. A low loss conductor according to claim 1 including means for varying the charge on said core.

7. A low loss conductor according to claim 1 wherein said enclosure is evacuated and said charge is positive.

8. A low loss conductor according to claim 1 wherein said enclosure is gas-filled and said charge is negative.

9. A low loss conductor of electrical current, comprising (a) a flexible tube,

(b) an electrode disposed at each end of said tube,

(c) means for energizing said electrodes, thereby producing charged particles having an associated field within said tube,

(d) a bundle of electrically conductive flexible filaments disposed within said tube and extending sub stantially the full length thereof,

(e) said filaments being electrically insulated from said electrodes and from the interior of said tube,

(f) said filaments nesting with one another to define a plurality of passages between said electrodes, and,

(g) means for applying a static charge to said filaments, said charge being adapted to neutralize the fields of the particles Within said tube and thereby reduce the resistance to current flow along said passages.

10. A low loss conductor according to claim 9 including means for Varying said static charge.

11. A low loss conductor according to claim 9 wherein said tube is evacuated and said charge is positive.

12. A low loss conductor according to claim 9 wherein said tube is gas-filled and said charge is negative.

7 8 13. A low loss conductor power transmission system References Cited mchdmg UNITED STATES PATENTS (a) at least a pair of superconductive lines,

(b) each of said lines being of tubular sealed con- 2,584,758 2/1952 siiutsman 313193 Struction, 5 2,765,975 10/1956 Lrndenbald 230 69 (c) electrodes disposed at each end of each of said 2,873,399 2/1959 Gamson lines, 2,899,588 8/1959 Mueller 313-209 (d) means for energizing said electrodes thereby pro- 2,926,677 2/1960 Whlte 135:1 ducing charged particles having an associated field 2,927,240 3/1960 vfilldershce Within Said lines, m 2,687,485 8/1954 Tlrlco 313-492 (e) an electrically conductive insulated core disposed 28692135 1 10/1954 Morton 315-35 within each of said lines and extending substantially 2,725,499 11/1955 Fleld the full length thereof, 3,128,408 4/1964 G O0drlch et al 31313O (f) said core being formed with at least one passage 3,162,716 12/1964 sllvel' lengthwise thereof and McFae (g) means for applying alternating static charges to said cores for neutralizing the fields of charged par- CRIS RADER Pnmary Exammer' ticles within said passages. T. B. JOIKE, Assistant Examiner.

Claims (1)

1. LOW LOSS CONDUCTOR OF ELECTRICAL CURRENT, COMPRISING (A) WALLS DEFINING AN ENCLOSURE, (B) A PAIR OF SPACED ELECTRODES DISPOSED WITHIN SAID ENCLOSURE, (C) MEANS FOR ENERGIZING SAID ELECTRODES THEREBY PRODUCING CHARGED PARTICLES HAVING AN ASSOCIATED FIELD WITHIN SAID ENCLOSURE, (D) A CORE OF ELECTRICALLY CONDUCTIVE MATERIAL DISPOSED BETWEEN SAID ELECTRODES AND SAID CORE HAVING AT LEAST ONE PASSAGE FOR ELECTRONS TO FLOW BETWEEN SAID ELECTRODES, SAID CORE BEING ELECTRICALLY INSULATED FROM SAID ELECTRODES AND THE INNER VOLUME OF SAID ENCLOSURE, (E) MEANS TO APPLY A CHARGE TO SAID CORE THEREBY INDUCING A DISTRIBUTED CHARGE ALONG THE WALLS OF SAID CORE PASSAGE, SAID CHARGE BEING ADAPTED TO NEUTRALIZE THE FIELDS OF THE PARTICLES WITHIN SAID VOLUME AND THEREBY REDUCING THE RESISTANCE TO CURRENT FLOW ALONG SAID PASSAGE.

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