Bidirectional gas discharge tube

Abstract

A two-way gas discharge tube (GDT) (100) includes a discharge chamber (110), a first cathode (104) and a second cathode (106), a gas (116) disposed within the discharge chamber, and a control grid (108). The first and second cathodes are disposed within the discharge chamber and include first and second faces, respectively. The first face and the second face are plane parallel. The gas is configured to insulate the first cathode from the second cathode. The control grid is disposed within the discharge chamber between the first and second cathodes. The control grid is configured to generate an electric field to establish a conductive plasma between the first and second cathodes to close a conduction path extending between the first and second cathodes.

Description

Technical Field

[0001] The present disclosure generally relates to high-voltage switching and, more particularly, to a bidirectional gas discharge tube. Background Art

[0002] Typical electrical systems include a direct current (DC) or alternating current (AC) power source, such as a battery, fuel cell, power supply, photovoltaic system, generator, or electrical grid, and an electrical load, device unit, or system. These electrical systems may also include one or more switches or disconnects disposed between the power source and the electrical load for purposes such as power conversion, fault current interruption, or overcurrent protection, such as a circuit breaker. At least some of these switches may be implemented using gas discharge tubes.

[0003] DC and AC power grids and distribution networks, particularly high-voltage DC grids, require bidirectional current control to enable isolation of various components of the DC grid. Conventional gas discharge tubes, while capable of withstanding high-voltage standoff of either polarity, can only conduct current in one direction, e.g., from anode to cathode, without other destructive breakdowns occurring in the gas discharge tube itself. Therefore, two conventionally gas discharge tubes arranged in anti-parallel are required to provide bidirectional current control. Summary of the Invention

[0004] In one aspect, a bidirectional gas discharge tube is provided. The bidirectional gas discharge tube includes a discharge chamber, first and second cathodes, a gas disposed within the discharge chamber, and a control grid. The first and second cathodes are disposed within the discharge chamber and include first and second faces, respectively. The first face and the second face are plane-parallel. The gas is configured to insulate the first cathode from the second cathode. The control grid is disposed within the discharge chamber between the first and second cathodes. The control grid is configured to generate an electric field to initiate the establishment of a conductive plasma between the first and second cathodes to close a conduction path extending between the first and second cathodes.

[0005] In yet another aspect, a bidirectional gas discharge tube is provided. The bidirectional gas discharge tube includes a discharge chamber, first and second cathodes, a gas disposed within the discharge chamber, and first and second control grids. The first and second cathodes are disposed within the discharge chamber. The gas is configured to insulate the first cathode from the second cathode. The first control grid is disposed within the discharge chamber near the first cathode and between the first cathode and the second cathode. The first control grid is configured to generate a first electric field to initiate the establishment of a conductive plasma to close a conduction path extending between the first cathode and the second cathode. The second control grid is disposed within the discharge chamber near the second cathode and between the first cathode and the second cathode. The second control grid is configured to generate a second electric field to initiate the establishment of a conductive plasma and close the conduction path. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] These and other features, aspects, and advantages of the present disclosure will become better understood when the following detailed description is read with reference to the accompanying drawings, in which like reference numerals throughout the drawings indicate like components, where:

[0007] Figure 1 is a cross-sectional view of one embodiment of a bidirectional gas discharge tube; and

[0008] Figure 2 is a cross-sectional view of another embodiment of a bidirectional gas discharge tube.

[0009] Unless otherwise indicated, the drawings provided herein are intended to illustrate features of embodiments of the present disclosure. These features are considered to be applicable to a variety of systems including one or more embodiments of the present disclosure. As such, the drawings are not intended to include all conventional features known to those of ordinary skill in the art that are necessary to practice the embodiments disclosed herein. DETAILED DESCRIPTION

[0010] In the following specification and claims, many terms are used with the following meanings.

[0011] The singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.

[0012] "Optional" or "optionally" means that the subsequent described event or circumstance may or may not occur, and the description includes instances where the event occurs and instances where it does not.

[0013] As used throughout the specification and claims herein, approximate language may be applied to modify any quantitative representation that can vary without resulting in a change in the basic function to which it is related. Accordingly, values modified by one or more terms, such as “about,” “approximately,” and “substantially,” will not be limited to the exact values specified. In at least some instances, the approximate language may correspond to the precision of the instrument used to measure the value. Here and throughout the specification and claims, range limitations may be combined and / or interchanged; such ranges are noted and include all the sub-ranges contained therein, unless the context or language indicates otherwise.

[0014] Some embodiments relate to the use of one or more electronic processing or computing devices. As used herein, the terms “processor” and “computer” and related terms (e.g., “processing device,” “computing device,” and “controller”) are not limited solely to those integrated circuits referred to in the art as computers, but rather generally refer to processors, processing devices, controllers, general-purpose central processing units (CPUs), graphics processing units (GPUs), microcontrollers, microcomputers, programmable logic controllers (PLCs), reduced instruction set computers (RISC) processors, field-programmable gate arrays (FPGAs), digital signal processing (DSP) devices, application-specific integrated circuits (ASICs), and other programmable circuits or processing devices capable of performing the functions described herein, and these terms may be used interchangeably herein. The foregoing embodiments are merely examples and are not intended to limit in any way the definition or meaning of the terms processor, processing device, and related terms.

[0015] In the embodiments described herein, the memory may include, but is not limited to, non-transitory computer-readable media such as flash memory, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), and non-volatile RAM (NVRAM). As used herein, the term "non-transitory computer-readable media" is intended to represent any tangible computer-readable media, including but not limited to non-transitory computer storage devices, including but not limited to volatile and non-volatile media, and removable and non-removable media such as firmware, physical and virtual storage devices, CD-ROMs, DVDs, and any other digital source such as a network or the Internet, and digital devices yet to be developed, with the sole exception being transient propagated signals. Alternatively, floppy disks, compact disc read-only memory (CD-ROM), magneto-optical disk (MOD), digital versatile disc (DVD), or any other computer-based device implemented by any method or technology may also be used for short-term and long-term storage of information such as computer-readable instructions, data structures, program modules and sub-modules, or other data. Thus, the methods described herein may be encoded as executable instructions, e.g., "software" and "firmware" implemented in non-transitory computer-readable media. Further, as used herein, the terms "software" and "firmware" are interchangeable and include any computer program stored in memory for execution by a personal computer, workstation, client, and server. When executed by a processor, such instructions cause the processor to perform at least a portion of the methods described herein. Additionally, as used herein, the term "real-time" refers to at least one of the time at which an associated event occurs, the time at which predetermined data is measured and collected, the time at which data is processed, and the time at which the system responds to the event and the environment. In the embodiments described herein, these activities and events occur substantially instantaneously.

[0016] Embodiments of the present disclosure relate to bidirectional gas discharge tubes. The bidirectional gas discharge tubes described herein provide a single hermetic electrical insulation enclosure that provides voltage cancellation, current conduction, and current interruption in two directions, i.e., regardless of current polarity. Thus, embodiments of the bidirectional gas discharge tubes described herein provide bidirectional current control for a DC power grid without adding a second gas discharge tube in an anti-parallel arrangement, resulting in reduced cost, reduced size, and reduced complexity of the power switch. For example, including a second gas discharge tube anti-parallel to the first gas discharge tube results in using twice the space, doubling the cost of the gas discharge tube, and requiring twice the support equipment, such as oil insulation and power electronics for operating the control grid. A single bidirectional gas discharge tube also improves reliability by reducing the number of parts and joints that can fail. The bidirectional gas discharge tubes described herein include two cathodes and one or more control grids. During operation, for a given direction of current flow, one cathode acts as a cathode while the other cathode and potential control grids act as anodes or "anodic cathodes". Further, each cathode operates at a low forward voltage and with an extended lifespan.

[0017] In some embodiments of the bidirectional gas discharge tubes described herein, a single control grid is positioned between the two cathodes to create two high-voltage cancellation regions. In at least some embodiments, the cathode planes are parallel to each other and to the control grid to maintain the correct orientation of the electric field relative to the electrode surfaces, resulting in improved high-voltage cancellation performance and reduced gas breakdown. In at least some embodiments, the cathodes include rounded edges to control the electric field magnitude around the electrode edges. In such embodiments of the bidirectional gas discharge tube, the high-voltage cancellation for the device varies at least with the distance between the control grid and each of the electrodes for the two cathodes, as well as with the gas type and pressure. For example, this spacing should be small enough to prevent electrical breakdown of the intervening gas and also large enough to prevent unwanted electron emission from the negative electrode. Additionally, the spacing of the conductors as they leave the outer surface of the bidirectional gas discharge tube should be large enough to prevent unwanted electrical breakdown or "flashover" in the dielectric or fluid surrounding the device.

[0018] In certain other embodiments of the bidirectional gas discharge tube described herein, two control grids are positioned between two cathodes to create a high-voltage cancellation region between the two control grids. In at least some embodiments, the control grids include rounded edges to control the magnitude of the electric field around the electrode edges. In such embodiments of the bidirectional gas discharge tube, the high-voltage cancellation for the device varies at least with the distance between the two control grids and the gas type and pressure. Additionally, when conductors exit the outer surface, the spacing of the conductors should be at least sufficient to prevent electrical breakdown in the medium or fluid surrounding the device on the outer surface of the bidirectional gas discharge tube.

[0019] Figure 1 is a cross-sectional view of an exemplary bidirectional gas discharge tube 100. The bidirectional gas discharge tube 100 includes a housing 102, a first cathode 104, a second cathode 106, and a control grid 108. The first cathode 104, the second cathode 106, and the control grid 108 are disposed within a discharge chamber 110 that is at least partially defined by the first cathode 104, the second cathode 106, and insulating barriers 112 and 114. In certain embodiments, the insulating barriers 112 and 114 are different regions of a single integral cylindrical insulator. Although this exemplary embodiment includes a single control grid 108, other embodiments may include more than one control grid 108. Generally, current conducts from the first cathode 104 to the second cathode 106, or from the second cathode 106 to the first cathode 104, through an ionized plasma contained within the discharge chamber 110. The discharge chamber 110 is filled with a gas 116 and has a pressure in the range of about 0.01 to 100 pascals, depending at least on the types of the first cathode 104 and the second cathode 106 and the type of the gas 116. For example, for a cold cathode, the pressure in the discharge chamber 110 may be in the range of about 1 to 10 pascals. For example, for a hot cathode in hydrogen or a hydrogen isotope such as deuterium, the pressure may be about 0.1 to 1.0 pascals. In one embodiment, the gas 116 is hydrogen. Alternatively, the gas 116 may be any other suitable gas or combination of gases capable of enabling the operation of the bidirectional gas discharge tube 100 as described herein, such as an inert gas or an inert gas mixture. For example, in an alternative embodiment, the gas 116 includes the inert gas xenon.

[0020] In some embodiments, the first cathode 104 and the second cathode 106 are cold cathodes. The first cathode 104 and the second cathode 106 can conduct a high total current with low forward operating losses over a long operating life. In alternative embodiments, the first cathode 104 and the second cathode 106 can be field emission cathodes, thermionic emission cathodes, or any other suitable type of cathode for establishing a conductive plasma within the bidirectional gas discharge tube 100. For example, a thermionic cathode has a relatively low forward voltage and thus has low losses during normal operation (i.e., during normal current conduction through the bidirectional gas discharge tube 100). For example, in some embodiments, the first cathode 104 and the second cathode 106 can be composed of lanthanum hexaboride (LaB6), or can be a composite structure that sets an effective work function for barium (Ba), or any other thermionic emitter material with a low work function, such as rare earth oxides, metal carbides, or metal borides. For example, the first cathode 104 and the second cathode 106 can include a tungsten sponge embedded with barium oxide, where the barium oxide decomposes into metallic barium and migrates to the outer surface during operation, where it affects the electron emission characteristics of the surface.

[0021] Generally, cathodes emit electrons through secondary emission, field emission, or through thermionic emission. Secondary emission is in response to incident particles (such as ions, electron-excited atoms, or photons) carrying some amount of kinetic or potential energy in electron volts (e.g., energy of thermal energy above 0.025 eV at room temperature). Field emission is in response to a strong electric field at the surface that pulls electrons out of their trapping potential wells (e.g., generally requires an electric field of more than about 1 GV / m). Thermionic emission occurs when the cathode metal is heated until electrons "evaporate" through their trapping potential wells. The potential wells are defined by the work function of the material, which varies from 1 to 5 eV for most materials. Generally, electron emission can occur simultaneously through all three mechanisms, and in some cases, these mechanisms cooperate. For example, thermionic emission and field emission can cooperate to produce field-enhanced thermionic emission. However, one emission mechanism typically dominates the other emission mechanisms, and the cathode is associated with the dominant emission mechanism.

[0022] The control grid 108 is used to selectively control the electrodes of the gas discharge tube 100 by applying, removing, and / or varying an electric field. In some embodiments, the control grid 108 is a thin shell (e.g., about 0.5 mm thick) having apertures that permit the flow of plasma current. The apertures may be circular holes arranged in an array, each having a diameter such that the control grid 108 can block the flow of plasma current of a given current density when desired. For example, in some embodiments, the diameter may range from about 0.5 mm to about 2 mm. In one exemplary embodiment, the diameter is about 1 mm. Also, the spacing between the apertures can be as close as possible to maximize the area of the plasma current channels without sacrificing the mechanical integrity of the control grid 108. For example, in some embodiments, the edge-to-edge spacing is about 15 microns. In alternative embodiments, the aperture diameter and spacing may be larger or smaller for a given application of the control grid 108 and the gas discharge tube 100.

[0023] In Figure 1 embodiments, depending on the polarity of the current conducted through the bidirectional gas discharge tube 100, electrons are emitted from the first cathode 104 or the second cathode 106. The electrons pass through the gas 116 within the discharge chamber 110 and are collected at the opposite cathode (i.e., the second cathode 106 or the first cathode 104, depending on the polarity of the current). The control grid 108 is used to selectively control one or more electrodes of the bidirectional gas discharge tube 100 by applying, removing, and / or varying an electric field. For example, to close the circuit, the control grid 108 is energized to create an electric field that draws conducting plasma from the region between the first cathode 104 and the control grid 108 or from the region between the second cathode 106 and the control grid 108 and enables the formation of an ionized gas 116 within the discharge chamber 110. When the bidirectional gas discharge tube 100 is closed (e.g., turned on, conducting, etc.), the gas 116 within the discharge chamber 110 is ionized (i.e., some portions of the molecules are dissociated into free electrons and ions), resulting in a conducting plasma that connects the first cathode 104 and the second cathode 106. In the case where the gas 116 is a molecular gas such as hydrogen, then the plasma may also contain molecular ions and neutral fragments of the molecules.

[0024] When the first cathode 104 and the second cathode 106 are cold cathodes, electrical continuity is maintained between the first cathode 104 or the second cathode 106 and the gas 116 through secondary electron emission due to ion collisions. High-energy (e.g., 50 to 500 electron volts (eV)) ions from the plasma are attracted to the surface of the first cathode 104 or the second cathode 106 by a strong electric field. The collisions of the ions on the first cathode 104 or the second cathode 106 release secondary electrons from the surface of the first cathode 104 or the second cathode 106 into the gas phase. The released secondary electrons contribute to maintaining the plasma. Magnets are typically used to generate a magnetic field of about 100 to 1000 gauss near the cathode surface to increase the current density at the cathode surface to a useful level, such as greater than 1.0 A / cm 2 . Thus, in such an embodiment, the control grid 108 does not need to be continuously energized to maintain the plasma for normal forward conduction operation. In an alternative embodiment where the first cathode 104 and the second cathode 106 are thermionic cathodes, the first cathode 104 and the second cathode 106 release electrons in response to heat externally applied, for example, by a heating element. In some embodiments, the first cathode 104 and the second cathode 106 are heated due to the recombination of incident ions at the surface of the first cathode 104 or the second cathode 106 and the kinetic energy they carry.

[0025] Generally, in embodiments of the bidirectional gas discharge tube such as Figure 1 the bidirectional gas discharge tube 100 described herein, the materials of the first cathode 104 and the second cathode 106 do not evaporate to an extent that significantly changes the properties of the gas 116, whether in its insulating state or in its conductive state. In contrast, for example, a mercury cathode can emit mercury vapor during operation, potentially degrading the cathode and shortening its service life, and making it necessary to carefully control the mercury vapor pressure and the cathode temperature. Alternatively, there is some interaction between the gas 116 and the evaporative material from the first cathode 104 or the second cathode 106. When the bidirectional gas discharge tube 100 is turned off (e.g., switched off, non-conductive, etc.), the gas 116 insulates the first cathode 104 from the second cathode 106.

[0026] The first cathode 104 and the second cathode 106 each include planar parallel faces 118 and 120. Notably, the planar parallel faces 118 and 120 are also planar parallel to the control grid 108. Generally, vacuum breakdown and gas breakdown in a gas discharge tube occur where the electric field strength is the strongest or where the gas insulation is the weakest. The planar parallel faces 118 and 120 generate electric field lines approximately perpendicular to the planar parallel faces 118 and 120. The planar parallel faces 118 and 120 result in good high-voltage cancellation performance and resistance to electrical breakdown of the gas 116. The planar parallel faces 118 and 120 can achieve as uniform an electric field as possible on the surface of the first cathode 104 or the second cathode 106 or on the control grid 108 at a negative potential, and achieve a field strength close to the field emission limit of the materials of the first cathode 104 and the second cathode 106 and the gas 116. For example, a good high-voltage material such as stainless steel or molybdenum can sustain an electric field strength of approximately 100 kV / cm. The uniform electric field near the material limit ensures that there are no local regions with a higher electric field that can cause field emission to start. Similarly, gas breakdown or runaway ionization in a bulk gas can occur at any local volume where the voltage between the electrodes exceeds the Paschen breakdown criterion (e.g., due to pressure and electrode spacing). The planar parallel faces 118 and 120 can achieve both a uniform field strength and a uniform electrode spacing, for example, between the first cathode 104 or the second cathode 106 and the control grid 108.

[0027] In some embodiments, the first cathode 104 and the second cathode 106 include rounded edges 122 to reduce the extent to which the electric field becomes greater at the edges of the first cathode 104 and the second cathode 106 and prevent deterioration of the high-voltage cancellation performance (e.g., resistance to electrical breakdown of the gas or field emission that causes vacuum breakdown).

[0028] In some embodiments, the first cathode 104, the control grid 108, and the second cathode 106 are implemented as concentric cylinders. In such embodiments, conduction occurs between the concentric walls or "nested" walls of the cylinders forming the first cathode 104 and the second cathode 106, rather than between the planar parallel faces 118 and 120 of the first cathode 104 and the second cathode 106 respectively. As in Figure 1In the planar geometry shown, the insulating barriers 114 and 112 can be implemented as a single insulating cylinder disposed within the housing 102. Similarly, the insulating barriers 112 and 114 themselves can be integrated with the housing 102. Further, in such an embodiment, the dimensions of the insulating cylinder, the first cathode 104, and the second cathode 106 are all designed to define an annular-shaped space between the insulating cylinder and each of the first cathode 104 and the second cathode 106, and are designed to define a spacing between each successive cylinder forming the first cathode 104, the control grid 108, and the second cathode 106. For example, the radius of curvature must be large enough to prevent excessive field concentration on the inner cylinder, which could lead to an undesired vacuum breakdown, and the annulus should be small enough to prevent Paschen or gas breakdown.

[0029] In at least some embodiments, the first cathode 104 and the second cathode 106 are positioned such that the space 124 between the first cathode 104 or the second cathode 106 and the insulating barrier 112 or the insulating barrier 114 is small to inhibit triple-point emission. A triple point exists where a metal, an insulator, and a volume of gas or in a vacuum meet. When such a location is at a negative potential (e.g., negative) relative to some facing structure, a strong electric field can form nearby, which can lead to an undesired electron emission that initiates an electrical breakdown. In a gas discharge tube, a triple point exists where a metal electrode meets an insulator, e.g., where the first cathode 104 or the second cathode 106 meets the insulating barrier 112 or the insulating barrier 114. In the gas discharge tube 100, triple-point emission is mitigated by positioning the triple points in deep, narrow recesses 136 between each of the insulating barriers 112 and 114 and each of the first cathode 104 and the second cathode 106. The recesses 136 inhibit triple-point emission as well as flashover and gas breakdown (if there is still some small amount of triple-point emission).

[0030] For example, in certain embodiments, the space 124 is approximately 1 millimeter, or in the range of about 0.5 to 1 millimeter. In certain embodiments, the space 124 can be larger or smaller based on a particular application (e.g., offset voltage requirements). In an embodiment where the two-way gas discharge tube 100 is cylindrical, as opposed to Figure 1 the planar geometry shown, the spacing 124 is the distance between the insulating barriers 112 and 114 and the first cathode 104 and between the insulating barriers 112 and 114 and the second cathode 106. The two-way gas discharge tube 100 has a spacing 124 that is less than, for example, the spacing 128 between the feedthrough 132 for the first cathode 104 and the face 118 of the first cathode 104. The spacing 128 is the depth of the annular recess 136. In certain embodiments, the spacing 128 is at least three times the spacing 124. Further, in certain embodiments, the spacing 128 is at least ten times the spacing 124.

[0031] The voltage cancellation performance of the bidirectional gas discharge tube 100 also depends on the cancellation ability outside the discharge chamber 110. For example, the voltage cancellation also varies with the space 134 between the feedthrough 132 for the first cathode 104 and the control grid 108. The space 134 should be large enough to prevent electrical breakdown or flashover on the outer surface of the volume of the housing 102, which housing 102 may be disposed in a medium such as, for example, air or electrical insulating oil. For example, in certain embodiments, the space 134 is in the range of about 2 cm to 20 cm. Further, to mitigate triple point emission from the triple point where the control grid 108 meets the insulating barriers 112 and 114, the triple point is located in a recess 138 having a depth 140 and a radius 142. The recess 138 extends radially with a radius 142 (in certain embodiments, the radius 142 is about 0.5 to 1 mm) and a depth 140 (the depth 140 is at least three times the radius 142). In certain embodiments, the depth 140 is at least ten times the radius 142.

[0032] In certain embodiments, the bidirectional gas discharge tube 100 further includes a seal 144 disposed around each feedthrough for the control grid 108. The seal 144 is disposed in the recess 138 where the control grid 108 meets the insulating barriers 112 and 114. The seal 144 can be formed, for example, by hard soldering or be composed of a sealing glass. Similar seals can be implemented at any point where an electrode such as the first cathode 104, the second cathode 106, or the control grid 108 exits through the insulating barriers 112 and 114.

[0033] Generally, the voltage cancellation varies with the space 126 between the control grid 108 and each of the first cathode 104 and the second cathode 106. The Paschen gas breakdown criterion sets an upper limit on the electrode spacing for a given voltage, gas type, and gas pressure. In particular, for the bidirectional gas discharge tube 100, the cancellation voltage performance varies to a large extent with the space 126 between the planar parallel faces 118 or 120 of the first cathode 104 or the second cathode 106 and the control grid 108. For example, in certain embodiments, the space 126 can be about 1 cm per 100 kV rated voltage (where the rated voltage is the higher of the nominal system voltage and the transient interruption voltage of the electrical system). For example, for a voltage rating of 50 - 300 kV, the spacing 126 should be about 0.5 - 3 cm. In alternative embodiments, the spacing 126 in such embodiments can be in the range of about 0.25 to 10 cm. Thus, the first cathode 104 and the second cathode 106 can be spaced apart sufficiently, i.e., the spacing 126 is large enough to enable the insertion of the control grid 108 between the first cathode 104 and the second cathode 106.

[0034] The offset voltage performance also varies with the type of gas 116 and the pressure within the discharge chamber 110. In an embodiment of the bidirectional gas discharge tube 100, a conductive plasma will form and current will conduct through the discharge chamber 110 having a relatively low internal gas pressure and a relatively large electrode spacing.

[0035] Figure 2 is a cross-sectional view of an exemplary bidirectional gas discharge tube 200. The bidirectional gas discharge tube 200 includes a housing 202, a first cathode 204, a second cathode 206, a first control grid 208, and a second control grid 210. The first cathode 204, the second cathode 206, the first control grid 208, and the second control grid 210 are disposed within a discharge chamber 212 that is at least partially defined by insulating barriers 214 and 216. Generally, as in the bidirectional gas discharge tube 100 ( Figure 1 as shown), current conducts from the first cathode 204 to the second cathode 206, or from the second cathode 206 to the first cathode 204, through an ionized plasma contained within the discharge chamber 212. The discharge chamber 212 is filled with a gas 218 and has a pressure in the range of about 0.01 to 100 pascals, depending at least on the types of the first cathode 204 and the second cathode 206 and the type of the gas 218. For example, for a cold cathode, the pressure in the discharge chamber 212 can be in the range of about 1 to 10 pascals. For example, for a hot cathode in hydrogen, the pressure can be about 0.1 to 1 pascal. In one embodiment, the gas 218 is hydrogen. Alternatively, the gas 218 can be any other suitable gas or combination of gases, such as tritium or an inert gas or a mixture of inert gases, that enables operation of the bidirectional gas discharge tube 200 as described herein. For example, in an alternative embodiment, the gas 218 includes the inert gas xenon.

[0036] The first cathode 204 and the second cathode 206 can be cold cathodes, field emission cathodes, thermionic emission cathodes, or any other suitable type of cathode for establishing a conductive plasma within the bidirectional gas discharge tube 200. In certain embodiments, the first cathode 204 and the second cathode 206 are thermionic cathodes that have a relatively low forward voltage to reduce losses during normal operation (i.e., normal current conduction through the bidirectional gas discharge tube 200). For example, in certain embodiments, the first cathode 204 and the second cathode 206 can be composed of lanthanum hexaboride (LaB6), a barium-containing structure, or any other thermionic emitter material having a low work function, such as rare earth oxides, metal carbides, or metal borides. A LaB6 cathode as described herein exhibits a forward voltage drop of approximately 20 V when the gas 218 is deuterium, or a forward voltage drop of approximately 5 V when the gas 218 is xenon. In contrast, solid metal cold cathodes composed of materials such as stainless steel or molybdenum exhibit a forward voltage drop in the range of approximately 150 - 500 V. Certain other cold cathodes can exhibit a lower forward voltage in the range of approximately 50 to 150 V.

[0037] The first cathode 204 and the second cathode 206 conduct a high total current with low forward operating losses over a long operating life. During operation, depending on the polarity of the current conducted through the bidirectional gas discharge tube 200, electrons are emitted from the first cathode 204 or the second cathode 206. The electrons cross the gas 218 within the discharge chamber 212 and are collected at the opposite cathode (i.e., the cathode acting as an anode, which is the second cathode 206 or the first cathode 204, depending on the polarity of the current). The first control grid 208 and the second control grid 210 each include one or more electrodes that are used to selectively control the bidirectional gas discharge tube 200 by applying, removing, and / or varying one or more electric fields. For example, to close the circuit in one direction, the first control grid 208 is energized to create an electric field that pumps conductive plasma from the region between the first cathode 204 and the first control grid 208 so that the gas 218 within the discharge chamber 212 can be ionized. Conversely, to close in the opposite direction, the second control grid 210 is energized to create an electric field that pumps conductive plasma from the region between the second cathode 206 and the second control grid 210 so that the gas 218 within the discharge chamber 212 can be ionized. When the bidirectional gas discharge tube 200 is closed (e.g., turned on, conducting, etc.), the gas 218 within the discharge chamber 212 is ionized (i.e., some portions of the molecules (e.g., hydrogen molecules) are dissociated into free electrons, hydrogen molecular ions, hydrogen atoms, hydrogen atomic ions, etc.), resulting in a conductive plasma that electrically connects the first cathode 204 and the second cathode 206. The cathode acting as an anode collects electrons along its entire surface and on any connected structures (such as fins or shields, for example). In some cases, the control grid closest to the cathode acting as an anode can be electrically connected to the cathode to collect electrons during normal conduction. Such electron collection enables efficient thermal management and reduces the voltage drop in the gas 218 near the cathode.

[0038] When the bidirectional gas discharge tube 200 conducts current in one direction, for example by electron emission from the first cathode 204, and the gas discharge tube 200 is to be turned off, the first control grid 208 is pulled to a potential lower than that of the first cathode 204 to repel electrons from the vicinity of the first control grid 208. The potential applied to the control grid 208 is typically about 1 to 5 kV relative to the first cathode 204. Then, the control grid 208 temporarily acts as a negative electrode with respect to both the first cathode 204 and the second cathode 206. The control grid 208 acts as a cold cathode and is not able to supply a sufficient electron current to maintain current continuity with the first cathode 204 or the second cathode 206, and the intervening plasma density is reduced to zero. Similarly, when the bidirectional gas discharge tube 200 conducts current in the opposite direction by electron emission current from the second cathode 206 to the first cathode 204, and when the gas discharge tube 200 is to be turned off, then the potential of the second control grid 210 is pulled to a potential lower than that of the second cathode 206. Then, the second control grid 210 temporarily acts as a negative electrode, and the plasma is interrupted in the same manner as described above for the control grid 208.

[0039] In the case where the first cathode 204 and the second cathode 206 are cold cathodes, electrical continuity is maintained between the first cathode 204 or the second cathode 206 and the gas 218 by secondary electron emission generated by ion collisions. High-energy (e.g., 50 to 500 electron volts (eV)) ions from the plasma are attracted to the surface of the first cathode 204 or the second cathode 206 by a strong electric field. The collisions of the ions on the first cathode 204 or the second cathode 206 release secondary electrons from the surface of the first cathode 204 or the second cathode 206 into the gas phase.

[0040] Therefore, neither the first control grid 208 nor the second control grid 210 requires continuous external excitation to maintain the plasma for normal forward conduction operation in either direction. Instead, once the conductive plasma is maintained and allowed to float, the first control grid 208 and the second control grid 210 can be electrically disconnected from the external excitation. When normal forward conduction is interrupted in either direction, the control grid closest to the negative electrode (i.e., the first electrode 204 or the second electrode 206) acts as a conventional control grid and intercepts the current for a sufficient duration (e.g., about 1 microsecond) to allow the high-voltage cancellation region defined between the first control grid 208 and the second control grid 210 to deionize. For example, in the case where the electron flow is from the first cathode 204 towards the second cathode 206, the first control grid 208 acts as the control grid, and the second control grid 210 defines the opposite pole of the high-voltage region. Thus, the second cathode 206 will collect electrons and is part of the normal electron current path through the bidirectional gas discharge tube 200.

[0041] In an exemplary embodiment, the materials of the first cathode 204 and the second cathode 206 do not evaporate to an extent that significantly changes the characteristics of the gas 218, whether in its insulating state or in its conductive state. Alternatively, there is some interaction between the gas 218 and the evaporative materials from the first cathode 204 or the second cathode 206. When the bidirectional gas discharge tube 200 is off (e.g., turned off, non-conductive, etc.), the gas 218 insulates the first cathode 204 from the second cathode 206.

[0042] The first control grid 208 and the second control grid 210 form a high voltage cancellation region between the first control grid 208 and the second control grid 210 rather than between a single control grid and each cathode in the Figure 1 embodiment. The first control grid 208 is disposed within the discharge chamber 212, adjacent to the first cathode 204 and between the first cathode 204 and the second cathode 206. Similarly, the second control grid 210 is disposed within the discharge chamber 212, adjacent to the second cathode 206 and between the first cathode 204 and the second cathode 206. In some embodiments, the first control grid 208 and the second control grid 210 include rounded edges 224 to reduce the extent to which the electric field at the surfaces of the first control grid 208 and the second control grid 210 becomes stronger at the edges of the first control grid 208 and the second control grid 210 (e.g., in the high voltage region) and to prevent degradation of the high voltage cancellation performance (e.g., resistance to electrical breakdown of the gas or field emission that causes vacuum breakdown).

[0043] In at least some embodiments, the first control grid 208 and the second control grid 210 are positioned such that the space 226 between each of the control grids 208 and 210 and the insulating barrier 214 or the insulating barrier 216 is small relative to the length 232 from the high voltage region to the feedthroughs for the first control grid 208 and the second control grid 210. For example, in some embodiments, the space 226 is about 0.5 to 1 millimeter. In some embodiments, the space 226 can be larger or smaller based on a particular application (e.g., cancellation voltage requirements). Generally, the length 232 is at least three times the space 226. In some embodiments, the length 232 is at least ten times the space 226.

[0044] In some embodiments, the bidirectional gas discharge tube 200 is cylindrical rather than Figure 2 the planar geometry shown in Figure 2In the embodiments shown, the insulating barriers 214 and 216 can be implemented as a single insulating column disposed within the housing 202. Further, in such embodiments, the sizes of the insulating column, the first control grid 208, and the second control grid 210 are all designed to define a space between the insulating column and each of the first control grid 208 and the second control grid 210.

[0045] Generally, for the bidirectional gas discharge tube 200, the cancellation voltage performance varies to a large extent with the space 228 between the faces of the first control grid 208 and the second control grid 210 and varies with the control grid material. For example, a control grid made of molybdenum can maintain an electric field of about 15% stronger without vacuum breakdown compared to, for example, stainless steel. The cancellation voltage performance also varies with the type of gas 218 and the pressure within the discharge chamber 212.

[0046] The voltage cancellation performance of the bidirectional gas discharge tube 200 also depends on the cancellation ability outside the discharge chamber 212. In particular, the voltage cancellation varies with the space 230 between the external electrodes for the first control grid 208 and the second control grid 210. The space 230 should be large enough to prevent electrical breakdown or flashover on the outer surface of the volume of the housing 202, which can be disposed in a medium such as, for example, air or electrical insulating oil.

[0047] The above-described embodiments of the present disclosure relate to bidirectional gas discharge tubes. The bidirectional gas discharge tubes described herein provide a single hermetic electrically insulating enclosure that provides voltage cancellation, current conduction, and current interruption in two directions, i.e., regardless of the current polarity. Thus, the embodiments of the bidirectional gas discharge tubes described herein provide bidirectional current control for DC and AC power grids without adding a second gas discharge tube in an anti-parallel arrangement, resulting in a reduced cost, reduced size, and reduced complexity of the power switch. The bidirectional gas discharge tubes described herein include two cathodes and one or more control grids.

[0048] Exemplary technical effects of the methods, systems, and devices described herein include at least one of the following: (a) providing a single hermetic electrically insulating enclosure that has voltage cancellation, current conduction, and current interruption in either direction, i.e., regardless of the current polarity; (b) reducing the size of the bidirectional gas discharge tube implementation by eliminating the second anti-parallel gas discharge tube; (c) reducing the cost by eliminating the second anti-parallel gas discharge tube; and (d) improving the reliability of bidirectional switching by having two unidirectional gas discharge tubes arranged in anti-parallel.

[0049] Exemplary embodiments of methods, systems, and devices for switching circuits are not limited to the specific embodiments described herein, and moreover, the components of the system and / or steps of the method can be used independently of other components and / or steps described herein. For example, the method can also be used in combination with other non-conventional gas discharge tubes and is not limited to being practiced only with the systems and methods described herein. Instead, the exemplary embodiments can be implemented and utilized in conjunction with many other applications, devices, and systems that can benefit from reduced cost, reduced complexity, commercial availability, improved manufacturability, and reduced time to market.

[0050] Although specific features of various embodiments of the present disclosure may be shown in some of the figures and not in others, this is merely for convenience. In accordance with the principles of the present disclosure, any feature of a figure can be referenced and / or claimed in combination with any feature of any other figure.

[0051] This written description uses examples to disclose the embodiments, including the best mode, and also enables any person skilled in the art to practice the embodiments, including making and using any device or system and performing any incorporated method. The patentable scope of the present disclosure is defined by the claims and may include other examples that occur to those skilled in the art. If these other examples have structural elements that are not different from the literal language of the claims, or if they include equivalent structural elements that have no substantial difference from the literal language of the claims, then these other examples are intended to be within the scope of the claims.

Claims

1. A bidirectional gas discharge tube (GDT) (100), comprising: A discharge chamber (110); A first cathode (104), which is disposed in the discharge chamber and includes a first surface (118); A second cathode (106), which is disposed in the discharge chamber and includes a second surface (120), wherein the first surface and the second surface are parallel planes; A gas (116), which is disposed in the discharge chamber and is configured to insulate the first cathode from the second cathode; and A control grid (108), which is disposed between the first cathode and the second cathode in the discharge chamber, the control grid being configured to generate an electric field to initiate the establishment of a conductive plasma between the first cathode and the second cathode to close a conduction path extending between the first cathode and the second cathode, Wherein the bidirectional GDT (100) further includes at least one insulating barrier (112, 114) that at least partially defines the discharge chamber (110), wherein the at least one insulating barrier (112, 114) and each of the first cathode (104) and the second cathode (106) are spaced apart by a distance (124) of about 0.5 to 1 millimeter, and Wherein the at least one insulating barrier (112, 114) defines a recess (138), and the control grid (108) extends radially outwardly through the recess (138), the recess having a depth dimension (140) that is at least three times the width dimension (142), wherein the depth dimension is parallel to the control grid.

2. The bidirectional GDT (100) according to claim 1, characterized in that, At least one of the first cathode (104) or the second cathode (106) is a cold cathode.

3. The bidirectional GDT (100) according to claim 1, characterized in that, The control grid (108) forms a first high-voltage cancellation region between the first cathode (104) and the control grid, and a second high-voltage cancellation region between the second cathode (106) and the control grid.

4. The bidirectional GDT (100) according to claim 1, characterized in that, The first cathode (104) and the second cathode (106) have rounded edges (122).

5. The bidirectional GDT (100) according to claim 1, wherein The first surface (118) and the second surface (120) are spaced apart by a distance in the range of about 5 to 20 centimeters.

6. The bidirectional GDT (100) according to claim 1, wherein, The bidirectional GDT (100) further includes: An electrode for the control grid (108), which extends from the discharge chamber (110) to the outside; and Corresponding electrodes (132) for the first cathode (104) and the second cathode (106), the corresponding electrodes (132) extending from the discharge chamber to the outside, wherein the electrode for the control grid is spaced apart from each of the corresponding electrodes for the first cathode and the second cathode by a distance (126) in the range of about 4 centimeters to 20 centimeters.

7. The bidirectional GDT (100) according to claim 1, wherein, The bidirectional GDT (100) further includes a seal (144) disposed in a recess (138) defined by the at least one insulating barrier (112, 114), the seal being formed around the control grid (108).

8. A bidirectional gas discharge tube (GDT) (200), comprising: A discharge chamber (212); A first cathode (204), which is disposed in the discharge chamber; A second cathode (206), which is disposed in the discharge chamber; A gas (218), which is disposed in the discharge chamber and is configured to insulate the first cathode from the second cathode; A first control grid (208), which is disposed in the discharge chamber near the first cathode and between the first cathode and the second cathode, and the first control grid is configured to generate a first electric field to initiate the establishment of a conductive plasma between the first cathode and the second cathode to close a conduction path extending between the first cathode and the second cathode; And A second control grid (210), which is disposed in the discharge chamber near the second cathode and between the first cathode and the second cathode, and the second control grid is configured to generate a second electric field to initiate the establishment of the conductive plasma and close the conduction path, Wherein the bidirectional GDT (200) further includes at least one insulating barrier (214, 216) that at least partially defines the discharge chamber (212), and wherein each of the at least one insulating barrier (214, 216) and the first cathode (204) and the second cathode (206) is spaced apart by a distance (226) of about 0.5 to 1 millimeter, and Wherein the at least one insulating barrier defines a first space between the first control grid and the at least one insulating barrier, and a second space between the second control grid and the at least one insulating barrier, and the first space and the second space are in the range of about 0.5 to 1 millimeter.

9. The bidirectional GDT (200) according to claim 8, characterized in that, The first control grid (208) and the second control grid (210) form a single high-voltage cancellation region between the first control grid and the second control grid.

10. The bidirectional GDT (200) according to claim 9, characterized in that, The control grid adjacent to the cathode that emits electrons in the first cathode (204) or the second cathode (206) in the first control grid (208) or the second control grid (210) is energized so as to interrupt the normal forward current for a sufficient duration to deionize the gas in the single high-voltage cancellation region between the first control grid and the second control grid.

11. The bidirectional GDT (200) according to claim 8, characterized in that, At least one of the first cathode (204) or the second cathode (206) is a thermionic cathode.

12. The bidirectional GDT (200) according to claim 11, characterized in that, The thermionic cathode includes lanthanum hexaboride (LaB6).

13. The bidirectional GDT (200) according to claim 8, characterized in that, The first control grid (208) and the second control grid (210) have rounded edges (224).

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