US3906270A

US3906270A - Bipolar crossed-field switch tube with uniform magnetic field

Info

Publication number: US3906270A
Application number: US507095A
Authority: US
Inventors: Hayden E Gallagher; Wolfgang Knauer
Original assignee: Hughes Aircraft Co
Current assignee: Raytheon Co
Priority date: 1974-09-18
Filing date: 1974-09-18
Publication date: 1975-09-16
Anticipated expiration: 1992-09-16

Abstract

Crossed-field switch tube has two electrodes to define an annular interelectrode gap. An annular magnetic field is produced in the gap with the field uniform along the length of the gap. Circuit connects electrodes so that, with alternating polarity, the gap alternately conducts with about the same voltage drop.

Description

Gallagher et al.

1 1 BIPOLAR CROSSED-FIELD SWITCH TUBE WITH UNIFORM MAGNETIC FIELD [75] Inventors: Hayden E. Gallagher; Wolfgang Knauer, both of Malibu, Calif.

[73] Assignee: Hughes Aircraft Company, Culver City, Calif.

22 Filed: Sept. 18, 1974 [21] Appl. No.: 507,095

[52] US. Cl. 313/157; 313/158; 313/161 1 l [58] Field of Search 313/157, 158, 161. 162

[56] References Cited UNITED STATES PATENTS 3,641.384 2/1972 Lund el al, 1. 313/161 [4 1 Sept. 16, 1975 Primary Examiner-Ri V. Rolinec Assistant ExaminerDarwin R. Hostetter Attorney, Agent, or FirmAllen A. Dicke, Jr.; W. H. MacAllister 9 Claims, 6 Drawing Figures [I Dr, I

PATENTED SEP 1 5 3975 SHKU 1 15 2 Fig. 2 PRlOR ART BIPOLAR CROSSED-FIELD SWITCH TUBE WITH UNIFORM MAGNETIC FIELD BACKGROUND OF THE INVENTION This invention is directed to a single gap bipolar crossed-field switch tube and circuit for particular use in circuits where conduction in either direction is desired.

Bipolar conduction capability in a crossed-field switch tube is essential for all AC applications of the switch tube. Furthermore, it is desirable also for DC breaker applications since, in multi-terminal transmission systems, reversal of power flow is achieved most conveniently by reversal of the current flow direction.

Crossed magnetic and electric field devices are known in the prior art. Perhaps the first disclosure of a crossed field device for switching is Penning US. Pat. No. 2,182,736. Boucher US. Pat. Nos. 3,215,893 and 3,215,939 are primarily directed to crossed-field rectifier type switching and are directed to an improvement where the shape of the magnetic field is asserted to improve rectifying action by providing a lower breakdown voltage in one direction than the other between the two electrodes which define the gas-filled space.

M. A. Lutz and R. C. Knechtli U.S. Pat. No. 3,838,061 is one of a series of patents which indicates modern developments for higher voltage off switching and higher current capability. Other patents of this nature include G. A. G. Hofmann US. Pat. No. 3,604,977 and G. A. G. Hofmann and R. C. Knechtli US. Pat. No. 3,558,960. There are also other patents directed to improvements in the crossed-field switching device.

One particular patent which is pertinent background for the present invention is G. A. G. Hofmann and R. E. Lund US. Pat. No. 3,641,384 which describes a crossed-field switching device which has three spaced electrodes and two gas-filled annular spaces therebetween. That patent represents a structure which was for the purpose of higher voltage hold-off in series connection and higher current capacity in parallel connection in DC applications. In other words, it was intended that both gaps would be conducting and off-switched at the same time.

SUMMARY OF THE INVENTION In order to aid in the understanding of this invention, it can be stated in essentially summary form that it is directed to a bipolar crossed-field switch which has two concentric electrodes to form an annular interelectrode gap and means for producing an annular magnetic field which extends substantially uniformly through the length of the interelectrode gap so, with opposite application of an electric field to the gap, opposite conduction takes place with about the same voltage drop.

It is thus an object of this invention to provide a bipolar crossed-field switch tube which is particularly arranged to conduct in either direction. It is a further ob ject to provide a crossed-field tube which is connectable into a circuit of such nature that conduction in either direction can be required by the circuit and can be achieved by the switch tube together with off-switching of such conduction. It is another object to provide a crossed-field switch tube with a single gap and having a magnetic field which is substantially uniform along the length of the gap to permit electric conduction in either direction at substantially the same voltage drop.

It is yet another object to provide a bipolar structure in a single envelope for economy of space, manufacture and maintenance.

Other objects and advantages of this invention will become apparent from a study of the following portion of this specification, the claims, and the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic circuit employing the bipolar crossed-field switch tube of this invention.

FIG. 2 is a longitudinal section through a schematic switch tube exemplifying the prior art.

FIG. 3 is a longitudinal section through a switch tube illustrating background for this invention for producing a uniform magnetic field in the interelectrode space.

FIG. 4 is a longitudinal section through a schematic switch tube exemplifying the second preferred embodiment.

FIG. 5 is a longitudinal section through a switch tube exemplifying another preferred embodiment.

FIG. 6 is a longitudinal section through a switch tube exemplifying another preferred embodiment of the switch tube of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 2 illustrates crossed-field switch tube 10 which shows the relationship of the parts and characteristics as known in the prior art. Switch tube 10 comprises an outer tubular cylindrical electrode I2 which is closed at the bottom and serves also as the enclosing tank of the device. Interelectrode I4 is positioned within outer electrode 12 and defines an annular interelectrode space or gap I6. Tubular insulator I8 engages around the upper reduced diameter neck 20 of outer electrode 12 and engages on disc 22 upon which interelectrode I4 is mounted. Thus they are physically secured with respect to each other to maintain gap 16 and to enclose the interior of the outer electrode so that the proper gas conditions can be maintained in the gap 16. The prior art discussed in the background discusses the gas conditions and other operating parameters of the switch device and that enumerated prior art is incorporated herein in its entirety by this reference. Electric connections are made to the two electrodes so that they can be connected into an appropriate circuit.

A magnetic field is supplied to the interelectrode gap. The field may be supplied by a permanent magnet and switched by means of an electromagnetic coil or the entire field may be supplied electromagnetically. In the present case, electromagnet 24 supplies a field 26 which is schematically illustrated in dashed lines.

Switch tube I0 is a crossed-field switch. When electric potential is applied, the potential is radial across the interelectrode space. The other field is the magnetic field provided by magnet 24. During conducton. both fields are on, and electrons spiral through the annular interelectrode space due to the magnetic field action to provide cascading breakdown, and thus conduction. For off-switching, the magnetic field is turned off so that the electron path is substantially radial, too short to cause cascading breakdown.

Prior art crossed-field switch tubes employed the outer electrode as the cathode, because the glow discharge is cathode area-limited rather than anode arealimited. With the outer electrode of larger area, this was the natural connection polarity. With the curved nature of the magnetic field 26, as illustrated in FIG. 2, there is axial concentration of the electrons during conduction so that the voltage drop is higher when the electrode 14 is connected as cathode than when electrode 12 is connected as cathode. This was originally thoL g. t to be a function of the cathode area-limiting factor, but it has now been discovered that the differ' ence in voltage drop in the two directions is a function of the magnetic field shape. This invention is directed to shaping the magnetic field in the gap so that there is substantially no axial shaping so that the voltage drop is substantially equal for conduction in each direction. With an axial magnetic field, voltage drop in either direction is about 500 volts for conduction of amperes per square centimeter. With the prior art magnetic field, the voltage drop with the outer electrode 12 connected as cathode was 300 volts for conduction of 10 amperes per square centimeter while with the interelectrode 14 connected as cathode was about 1,000 volts for conduction of 10 amperes per square centimeter. Current density figures are calculated using the cathode area.

The circuit of FIG. 1 is a schematic AC current limiter generally indicated at 30. Terminal 32 is connected to the line, and terminal 34 is connected to the load. Mechanical switch 36 is normally closed so that current normally flows therethrough. When a fault occurs and current rises, current limiter circuit is operated to hold the current down to tolerable levels until the fault is cleared or the circuit is opened by normal circuit breakers. When a fault is sensed, switch 36 is opened and switch tube 50 conducts the alternating current with the gap alternatly conducting so that the AC current is conducted until switch 36 is opened and deionized. Thereupon, the magnetic field is switched off of switch tube 50 so that it becomes non-conductive. This switches surge-limiting capacitor 38 and currentlimiting impedance 40 into the circuit to hold down the circuit current to tolerable levels, preferably substantially to full load levels. Current is thus limited until the fault is cleared or the main circuit breakers open the line.

Crossed-field switch device in FIG. 3 comprises inner electrode 52 and outer electrode 54 which define the interelectrode gap 56. The electrodes are supported as in the manner of FIG. 2 and are surfaces of revolution around the center axis 58 of switch 50. Magnet 60 provides a magnetic field in the gap.

Insulators

62 and 64 are positioned at the end of the gap and carry

auxillary electrodes

68 and 70 which cause trapping of the electrons between the axial ends of the gap. As electrically floating

electrodes

68 and 70 are negatively charged up by the first electrons leaking out of the trapped region, the electrode voltage repels or traps the remaining electrons in the interaction region. In this way, a uniform field is produced together with an axial electron trapping to result in conduction in either direction at a reasonable voltage drop, for example 500 volts for a conduction of 10 amperes per square centimeter of cathode area. The use of an electrically floating electrode to encourge axially electron trapping to aid in the initiation and maintainance of the plasma discharge is background to this invention.

FIG. 4 illustrates a preferred embodiment 72 of this invention. lt has inner electrode 74 and outer electrode 76 defining gap 78. Magnet 80 produces flux in the gap.

In crossed-field switch 72,

magnetic shims

82, 1, 86 and 88 are positioned to direct the magnetic flux along "m s 96. The magnetic shims are of magnetic material such as soft iron configured as annular rings positioned interiorly and exteriorly of the gap at its axial ends to direct the flux generally axially of the gap. With these magnetic shims, it appears that the flux passes from the center of the gap in an axial direction out through the shims so that the flux is concave in a direction toward both of the electrodes. This permits axial electron trapping while the switch tube is conducting to limit voltage drop. In this configuration, voltage drop in either direction of conduction is about 500 volts at a current of 10 amperes per square centimeter of cathode area. With the positioning of the pole pieces outside of the plasma gap, the voltage holdoff value is not compromised. Electron trapping by the curvatures of the magnetic field takes place only in a portion in the radial direction of the interaction gap. In the other radial portion of the interaction gap, the magnetic field curvature is in the wrong direction for electron trapping; however with proper dimensioning, the magnetic field curvature in the correct direction is adequate for adequate trapping. It is the simplest structure, because it leaves the interaction gap unencumbered by insulators or magnetic pole pieces which might interfere with the plasma or the interelectrode voltage breakdown value.

Crossed-field switch 92 of FIG. 5 has an inner electrode 94 and an outer electrode 96 which define the interelectrode gap 98. Magnet 100 provides a magnetic field to the gap, with the flux lines indicated at 102. In this embodiment of the crossed-field switch, soft iron pole pieces or

magnetic shims

104 and 106 are posi tioned at the axial ends of the annular gap.

Shims

104 and 106 are rings of soft iron or other magnetic material to direct the flux. When rings of the appropriate size and material are properly positioned, the magnetic flux lines 102 are substantially axial through gap 98.

Magnetic shims

104 and 106 are electrically separated from both of the electrodes and thus are electrically floating in the space to charge up and provide electron trapping. With this configuration, about the same voltage drop is achieved as with the configurations in FiGS. 3 and 4.

Crossed-field switch device 110 in FIG. 6 is also of the same general configuration. Inner electrode 112 faces outer electrode 1 14 to define annular gap 116. ln this case, two magnets (magnets 118 and 120) provide the magnetic field in the gap, as illustrated by flux lines 122. In each of the switch tubes in FIGS. 3 through 6, pressure is controlled in the gap, and magnetic field is supplied by an electromagnet or an electromagnet plus a permanent magnet. By switching the electromagnet, the magnetic field in the gap can be changed sufficiently to cause off-switching as described above. In this structure, electron trapping occurs in one polarity by curvature of the magnetic field by energization of one

solenoid

118 or 120 and occurs for the other polar ity by energization of the other solenoid.

There are two methods of operation of the crossedfield switch 110 of FIG. 6. in one method of operation, both

magnets

118 and 120 are on at the same time so that an adequate flux, as represented by line 122, is produced in the gap to permit conduction. Since there are two magnets, the flux lines are substantially symmetrical through the gap so that conduction in either direction has about the same characteristics. Thus,

voltage drop in the two directions is substantially equal. For off-switching, one or both of the magnets are turned off. The magnets can be sized so that both must be on for conduction so that. when one is turned off, off-switching occurs. For rapid off-switching, preferably both are provided with a bucking magnetic field for off-switching. As an alternate method of operation,

magnets

118 and 120 can be alternately energized for switching, depending upon the direction of desired conduction. When operated in this way, a lower voltage drop is achievable, but selective operation of the two magnetic fields is required, in response to the impressed polarity of the electric field.

This invention having been described in its preferred embodiment, it is clear that it is susceptible to numerous modifications and embodiments within the ability of those skilled in the art and without the exercise of the inventive faculty. Accordingly, the scope of this invention is defined by the scope of the following claims.

What is claimed is:

l. A crossed-field switch device comprising:

a cylindrical inner electrode, a hollow cylindrical outer electrode spaced around said inner electrode to define an annular gap in which a glow discharge cascading breakdown can be maintained, said gap having a lengthwise direction parallel to the axis of said electrodes, means for maintaining a subatmospheric gas pressure in said gap, the improvement comprising:

means for applying a potential at either polarity to said gap;

Magnetic field means for producing a magnetic field which is substantially axial of said gap in the breakdown region of said gap so that either electrode can act as cathode with substantially the same voltage drop because of substantially the same amount of electron trapping in the breakdown region of said gap with application of potential of either polarity.

2. The crossed-field switch device of claim 1 wherein said magnetic field means includes a magnet positioned exteriorly of said outer electrode adjacent said gap for inducing a magnetic field in said gap.

3. The crossed-field switch device of claim 2 wherein said gap has a line of symmetry therethrough along the length thereof and substantially equally spaced from said electrodes, said magnetic field being substantially symmetrical on opposite sides of said line of symmetry.

4. The crossed-field switch device of claim 3 wherein said magnetic field means includes a magnetic pole piece at each end of said gap positioned interiorly of said outer electrode and along the line of symmetry.

5. The crossed-field switch device of claim 2 wherein said magnetic field means also includes a magnet positioned within said inner electrode so that the net magnetic field resulting from said outer magnet and said inner magnet is symmetrical along the line of symmetry.

6. The crossed-field switch device of claim 4 wherein at least one of said pole pieces is electrically separated from both of said electrodes.

7. The crossedfield switch device of claim 6 wherein both of said pole pieces are electrically separated from both of said electrodes.

8. The crossed-field switch device of claim 4 wherein said magnetic pole piece is mounted on said inner electrode at each end of said gap for forming the magnetic field symmetry.

9. The crossed-field switch device of claim 8 wherein there is also a magnetic pole piece mounted on said outer electrode adjacent each end of said gap for shaping the magnetic field.

Claims

1. A crossed-field switch device comprising: a cylindrical inner electrode, a hollow cylindrical outer electrode spaced around said inner electrode to define an annular gap in which a glow discharge cascading breakdown can be maintained, said gap having a lengthwise direction parallEl to the axis of said electrodes, means for maintaining a subatmospheric gas pressure in said gap, the improvement comprising: means for applying a potential at either polarity to said gap; Magnetic field means for producing a magnetic field which is substantially axial of said gap in the breakdown region of said gap so that either electrode can act as cathode with substantially the same voltage drop because of substantially the same amount of electron trapping in the breakdown region of said gap with application of potential of either polarity.

7. The crossed-field switch device of claim 6 wherein both of said pole pieces are electrically separated from both of said electrodes.