US3046436A - Electrical switch - Google Patents

Description

July 24, 1962 c. c. CAVALCONTE ELECTRICAL SWITCH Filed sept. e, 1960 INVENTOR CHARLES C. CAVALCONTE A ToRA/EY.

United States Patent 3,046,436 ELECTRICAL SWITCH Charles C. Cavalconte, Mineola, N.Y., assigner to Republic Aviation Corporation, near Farmingdale, N.Y., a corporation of Delaware Filed Sept. 6, 1960, Ser. No. 54,029 Claims. (Cl. 313-146) This invention relates to electrical switches and, more particularly, to a high current, high voltage switch, i.e., one capable of passing megampere currents at kilovolt potentials.

The present invention contemplates an improved switch design predicated on a novel operating concept whereby large currents `and voltages are readily passed with an attendant low erosion and wear to its parts. At the same time, the instant high voltage, high current switch is capable of repeated operation with relatively no time delay between successive switching operations.

Moreover, the proposed switch ydesign allows for the handling of a relatively wide range of current and voltage values incorporating adjustable and contoured switch electrodes whereby the length and path of the arc thereacross during operation may be pre-established to the end .that predictable, conducting characteristics are obtainable. Such control of the arc finds particular utility in applications where pulse-shaping of currents, i.e., accurate control of the amplitude and phase of current discharges, is important.

In prior switches capable of passing substantial currents at high voltages, the designs have been such that reliability of operation is adversely affected with 'the increase in the value of the currents and voltages handled and the attendant heat generated thereby. Thus, several seconds elapsed time is required between switching operations in these earlier `designs and they fail to meet the requirements of many present day applications because of their repetition rate. For example, switches are currently available which adequately handle current and volt-age values approaching those `herein contemplated, but approximately one minute of elapsed time is prescribed between each switching operation. Such switches are obviously useless in applications, for example in thermonuclear and magnetohydrodynamic devices, requiring m-any distinct switching operations a second with currents in the order of, for example, 0.5 megampere and voltages of 30 kilovolts.

The present invention is, among other things, directed toward a switch that will meet the requirements set forth above and to this end proposes a switch design predicated on a novel concept by which a greater repetition rate is obtained at high current and voltage. Moreover, this proposed design lends itself to pulse-shaping of currents and `a long life expectancy of its components.

The switch lherein proposed is founded on a triggered gap principle depending for its operation on the ionization of a gas in the gap and the creation of magnetic fields which interact to control the current path through the switch. More specifically, the instant switch comprises coaxial conductors insulated lineally and interconnected adjacent corresponding ends. One of these conductors is interrupted in its length rto establish a space or gap preventing a completed circuit. The terminals of the interrupted conductor ydefini-ng this gap constitute the switch ICC electrodes which are adapted to operate in a controlled atmosphere, the switch being enclosed in a dielectric, gaslled envelope sealed at low pressure.

iIn the preferred form of the invention, a selected, constant potential is applied to the coaxial conductors, such potential being less than that required to bridge or arc lthe gap between the switch electrodes. The gap is normally maintained at a constant voltage breakdown value by adjustment of the space between the electrodes and the ygas or inert iluid pressure therein. However, electrical means, including means to control its operation, is provided to ionize the gas in the gap when desired to support a current and thereby complete the circuit.

In any case, the coaxial design is employed to produce when operative substantially coextensive currents of opposite directions, each with an individual, associated magnetic field. The interaction of these magnetic iields in the area of the gap produces a magnetic pressure on the current across the gap resulting in a phenomenon known as inverse pinch, i.e., lateral movement of the currents outwardly from the conductors, rst assuming an arc or bow in the current formation lacross the gap which eventually ruptures to break the circuit.

'Phe iadjacent surfaces of the switch electrodes are contoured in accordance with the particular application to establish a predetermined current formation across the gap and movement thereof outwardly rat a prescribed rate whereby its phase and amplitude are made to correspond to the requirements ofthe associated load. Additional control refinements are accomplished by means of and through adjustment means to locate the electrodes with reference to each other and thereby determine the length of the gap. Thus, by relating the plasma dynamics as determined by the particular gas employed tothe resulting magnetic forces established by the electrode shape and spacing, ythe conducting characteristics of the high current, high voltage switch can be tailored to a given application'.

With the above and other objects in view, as will be apparent, this invention consists in the construction, combination and arrangement of parts -all as hereinafter more fully described, claimed and illustrated in the raccompanying drawings, wherein:

FIG. l is a transverse section taken through a switch constructed in accordance with the teachings of this invention to show a preferred embodiment thereof, including associated electrical control means `for its operation, connected in an illustrative high voltage, high currentcarrying circuit;

FIG. 2 is a schematic exploded view of the inner and outer conductors of the coaxial design illustrating the current path of each and for purposes of analysis the individual magnetic fields established thereby; and

FIG. 3 is a ldiagram symbolizing the individual current direction of each conductor Iand Ithe summation forces of the resulting magnetic iield directions illustrated in FIG. 2.

With particular reference to the drawings, 10 designates the present switch 'assembly adapted to be connected to, and control the current passing through, a circuit 11 connecting a power supply 12 to a loadY 13 requiring a large current at high voltage. A battery of capacitors 14 is operatively connected to the power supply 12, being charged vthereby and upon operation off the switch to effect large current discharges satisfying the requirements of the load 13.

The switch assembly 10 comprises a pair of coaxial conductors and 16, the inner conductor 15 constituting a rod the outer end of which is adapted to form one terminal by which the switch 10 is connected to the power side of the circuit 11. The corresponding end of the outer conductor 16 is adapted to form the other terminal for connection of the switch y10 to the load side of the circuit 11. Medially of its length the outer conductor 16 is interrupted, creating a gap 19 with the adjacent ends of the conductor that define this gap constituting a pair of coacting electrodes 17 and 18.

The inner conductor 15 is electrically connected to the electrode 17, for example, being press fitted in a recess provided in the center thereof and electrically insulated from the electrode 18 by a wrapper 20 of dielectric material preferably one having good heat resistance properties which overlies and encloses that portion of the inner conductor 15 adjacent the electrode 18 and across the L gap 19.

The electrodes 17 and 18 are provided with coacting adjacent surfaces 17a and 18a, respectively, that are generally convex to locate the minimal distance point adjacent the axial center of the gap 19. Adjacent its center, surface 17a is additionally formed with a recess 17b adapted to surround and thereby separate the rod 15 and insulating wrapper 20 from the minimal distant point between the surfaces 17a and 18a. Thus, when a discharge of current is effected, by means to be described, across the electrodes 17 and 18, this current and accompanying heat is directed away from the wrapper 20 to prevent the deterioration thereof.

The end of the electrode 18 remote from the gap 19 terminates in a threaded concentric projection 21 adapted to receive a coacting nut 22, The nut 22 is pierced centrally by a hole through which the rod 15 passes and to which it is secured against lineal movement by suitable means such as a lock-ring and seal 23 of flexible material adapted to -be compressed against the end surface of the projection 21 and the surface of the wrapper 20 upon tightening of the nut 22. Thus, the position of the -rod 15 may be adjusted in the electrode 18 and maintained in the adjusted position, establishing the relative positions of the electrode surfaces 17a and 18a and the length of the gap 19 accordingly.

Adjacent the projection 21 the electrode 18 is provided with a lateral flange 24, the peripheral surface of which engages and is suitably secured, as by press fit, to the inner marginal surface of an envelope or casing 2S which encloses and houses the coaxial conductors 15 and 16. A removable and replaceable cover plate a closes this end of the envelope 25. The length of the ange 24 is such that the interior walls of the casing 25 are disposed in spaced relation to the conductors 15 and 16 and thereby Acreate a chamber 26 in which the conductors are concentrically mounted. The envelope 25 including cover 25a is fabricated of dielectric material and is provided with a port adapted to receive and connect an inlet duct and check valve 27 by `means of which an inert fluid such as nitrogen, argon, etc., is admitted into and fills the chamber 26 where it is maintained at a selected low pressure.

A pair of opposed conducting probes 28 are mounted within the envelope 25 and terminate inwardly thereof in ends disposed within the gap 19 in spaced relation. The outer end of each probe 28 is secured in a recessed bearing of dielectric material, preferably one having good heat resistance properties, forming a localized area of the wall of the envelope 25. The bearings 30 also serve as seals to prevent uid leakage from the chamber 26. O-rings 29 may be employed if desired for the same purpose adjacent each opening in the envelope 25 through which the duct 27 and conductors 15 and 16 are adapted to pass.

The outer end of each probe 28 is appropriately connected by a conductor 31 to the opposite ends of the high voltage side of a step-up transformer 32. The low voltage side of the transformer 32 is connected at its opposed ends in a circuit 33 comprising a power source such as, for example, battery 34 and a push button on-off switch 35.

The operation of the assembly as above described is as follows:

Constant power is available from the supply 12 and the capacitors 14 to the inner conductor 15 and electrode 17 of the outer conductor 16. However, the rod 15 is ad justed lineally and secured in the adjusted position by lock-nut 22 to establish the dimensions of gap 19 whereby the circuit 11 through the outer conductor 16 to the load `13 is interrupted. When it is desired to complete this circuit, switch 35 is closed momentarily whereby a -relatively small current from battery 34 passes through the circuit 33 including the primary of the transformer 32. When the primary is thus energized, a sufficient voltage is induced in the secondary of transformer 32 to produce a current arc across the probes 28. The gases in the gap 19 are thereby ionized, causing a breakdown of this gap whereby the voltage applied on electrode 17 of the outer conductor 16 results in a current across the gap, completr ing the circuit to the load 13.

Referring momentarily to FIG. 2, it is seen that a current passing through the inner conductor 15 takes a path in a direction I and establishes an associated magnetic field B. On the other hand, a current passing between the electrodes 17 and 18 has a direction I' and an associated magnetic field B. Since the current density appearing on the inner conductor 15 is greater than that of the outer conductor 16, the magnetic field B' is of less magnitude than the field B. Moreover, these fields B and f B due to the current direction in the conductors 15 and 16 are of opposite direction (FIG. 3). The natural interaction of these opposed fields results in a radially outward magnetic pressure that forces the current in the gap 19 from an initial position substantially parallel to the axis of the conductors 15 and 16 to an arcuate or bowed position.

Thus, the current l' passing between the surfaces 17a and 17b 0f the electrodes 17 and 18 of the outer conductor 16 is not concentrated in any loaclized area but distributed rapidly over the entire area of the electrode surfaces by successive lines of current moving from a point or points adjacent the axial center of the gap 19 outwardly. Normal electrode erosion is thereby held to a minimum during operation of the gap switch.

In addition, the frequency and amplitude of the current discharge across gap 19 and to the load 13 as determined by the current formation and bowing as described may be controlled by preselecting the areas and contours of the electrode surfaces which define the gap 19. Additional control is obtained by precise adjustment of the length of the gap 19, i.e., the spacing between the surfaces 17a and 18a, by locating the position of the electrode 17 relative to electrode 18 through means 22. The size of the envelope 25 is such that the width of the chamber 26 permits total bowing of the current across gap 19 and ultimate rupture of the current lines prior to contact with the walls of the envelope 25. It may, therefore, be said that the current discharge across the electrodes is unconfined and controlled solely by the magnetic pressure or blow out effect produced by interaction of the current fields as described.

From repeated operations of switches constructed as hereinabove described, it has been learned that current discharges across the electrodes 17 and 18 have had substantially no deleterious effect upon the probes 28. Presumably, this is explained by the fact that such discharges are of short duration, i.e., less than microseconds. Moreover, no backup effect has been experienced in the circuits 31 and 33 as a result of the current discharges across the electrodes 17 and 18, since the circuit 31 has a high impedance relative to the circuit 11.

What is claimed is:

l. An electrical switch comprising coaxial conductors insulated lineally from each other and electrically connected adjacent one of their ends and electrically unconnected adjacent their other ends, each being individually connected at said other ends to opposite sides of a circuit, a gap in the length of one of the conductors interrupting current continuity, and control means operative to bridge said gap whereby current continuity is established through the conductors.

2. A switch as recited in claim 1 including means to adjust said gap.

3. An electrical switch comprising a pair of coaxial conductors insulated lineally one from the other and electrically connected one to the other adjacent corresponding ends, individual -terminals adjacent the other corresponding ends of said conductors, a lead connecting each of said terminals to a power supply and load, respectively, a gap in the length of one of the conductors interrupting current continuity, and means operative to bridge said gap whereby said power supply is electrically connected to said load.

4. An electrical switch comprising a pair of coaxial, substantially coextensive conductors insulated one from the other and electrically connected adjacent corresponding ends, a gap in the length of One of the conductors interrupting current continuity, means maintaining inert fluid in said gap at low pressure, and means operative on said uid to ionize it whereby current continuity is established through said conductors.

5. A switch comprising a pair of coaxial conductors electrically connected adjacent one of their ends and insulated lineally, terminals at the other ends of said conductors, one said terminal ybeing connected to a power supply and the other said terminal being connected to a load, a gap in the length of one of the conductors interrupting current continuity, current discharging means operative in said gap to ionize iiuid therein, and control means for the operation of said current discharging means whereby current continuity is established through the conductors from the power supply to the load.

6. A switch comprising a pair of coaxial conductors electrically interconnected adjacent corresponding ends and insulated one from the other substantially throughout their length, a source of applied voltage connected to the free end of one of said conductors, a load connected to the free end of the other of said conductors, a gap in the length of one of the conductors interrupting current continuity therethrough, means maintaining inert fluid in said gap at pressure below that required to support a current across the gap, and means operative on said iiuid to ionize it whereby said applied voltage results in a current discharge across said gap to said lo-ad.

7. An electrical switch comprising a pair of electrodes, a gap between adjacent ends of said electrodes, means producing a discharge current between said electrode ends and across said gap outwardly of the axial centerline thereof, and a current of opposite direction to said discharge current adjacent said centerline, said current establishing a magnetic eld at right angles to said discharge current forcing it radially outward of the gap.

8. An electrical switch comprising a pair of axially aligned electrodes, a gap 'between said electrodes, lmeans producing a discharge current and an associated magnetic eld across said electrodes outwardly of their centerline, and a current of opposite direction to said discharge current adjacent said centerline establishing a magnetic iield in opposition to the iirst magnetic eld whereby said current discharge is forced radially outward orf the gap and eventually interrupted.

9. An electrical switch comprising coaxial conductors interconnected at one of their ends, a pair of electrodes in the length of one of said conductors, a gap between said electrodes, a power supply and a load, respectively, connected to the other ends of said conductors, and means operative to discharge said power supply producing a discharge current across said electrodes completing la circuit to said load whereby magnetic fields are created in said gap to force the current therein in a radial `direction and eventually breaking said circuit.

10. An electrical switch comprising a gas-filled envelope having individual, insulated terminals, a pair of insulated coaxial conductors within said envelope connected at one of their ends tto said terminals, respectively, means establishing opposite current directions through the con; ductors, means establishing a gap in one of said current directions, a source of applied voltage constantly connected to one of said terminals and normaly inoperative to pass a current across said gap, electrical means operative in the gap to ionize gas therein and support a current, and a control to render said electrical means 'operative whereby current passes bet-Ween said terminals.

11. An electrical switch comprising `a duid-tight envelope, a pair of coaxial conductrs interconnected at corresponding ends and disposed within said envelope, a gap in the length of `one of -said conductors norm-aly operative to interrupt current continuity therethrough, means connected to and forming a part of the envelope for iilling and maintaining it including said gap with gas at a selected pressure, and control means mounted in and opera-ble exter-nally of the envelope to ionize gas thereiniwhereby current Icontinuity is established 'across said gap and through the conductors.

12. An electrical switch comp-rising a pair of coaxial conductors electrically interconnected adjacent one of their ends and insulated lineally one Ifrom the other, a gap i-n the length of the outer of said conductors dened by adjacent, generally convex surfaces, means constantly connecting a source of electric power -to the free end of the inner conductor, means connecting a load to the free end of the outer conductor, the dimensions of the ygap being such as to normally interrupt current continuity -front the source to the load and establish a voltage diiferential across the gap, means to maintain a gas in the gap, and electrical means operative to ionize -said gas thereby establishing current continuity yacross the gap.

13. An electrical switch comprising la lfluid-tight envelope, a pair of coaxial conductors mounted within said envelope, the inner of said conductors including a central conductive rod disposed within and projecting externally from the envelope and connected to a source of electrical power, the end of said rod with-in the envelope being electrically connected to the corresponding end of the outer conductor, a pair of spaced coacting electrode elements in the length of the outer conductor overlying and surrounding the rod and creating a gap, electrical connection means between the outer conductor and a load, and means operable externally of the envelope to ionize fluid in the gap aforesaid whereby current continuity is established across the gap between the electrode elements aforesaid.

14. An electrical switch comprising a uid-tight envelope, a pair of insulated, coaxial conductors mounted within said envelope, the inner of said conductors cornprising a lineally adjustable, conductive rod disposed within and projecting externally from the envelope to connect a source of electrical power, the end of said rod within the envelope being electrically connected to the outer conductor, the outer of said conductors including a pair of spaced, axially aligned, concentric electrode elements establishing a variable gap therebetween as determined by the adjusted position of the rod, an insulator between the rod and said gap, an electrical connection between said outer conductor and a load, an inert gas in the gap, and means to ionize said gas whereby current from the source is discharged across said gap and applied to the load.

15. An electrical switch comprising a fluid-tight envelope, a pair of insulated coaxial conductors mounted within said envelope, the inner of said conductors comprising a central conductive rod disposed within and projecting externally from the envelope to connect a source of electrical power, the end of said rod within the envelope being electrically connected to the outer conductor, a pair of coacting electrode elements in the length of said outer conductor one connected to the rod and the other to the envelope in spaced relation to the rst to create a gap, adjustment means to regulate the length of the rod disposed within the envelope whereby the length of said gap is `established and current continuity through the conductors is interrupted, electrical-connecting means between said electrode element and a load, and means operable externally of -the envelope to ionize uid in the gap aforesaid whereby current continuity is established across the gap between the electrode elements whereby electrical power from the source is applied to the load.

References Cited in the fiile of this patent UNITED STATES PATENTS

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