The transfer of large amounts of, e.g., electrical energy, quickly may be desirable in a number of applications, for instance, as the technology for storage of large amounts of electrical energy improves. General non-limiting examples of applications may include, the transfer of electrical energy from one storage element (e.g., capacitor) to another, from a storage element to vehicle, from a storage element to a moving vehicle, from a storage element to a munition, from a storage element to a projectile launcher, from a storage element to a pulsed laser and from a storage element to other types of electromagnet, acoustic and mechanical transducers and actuators. Known devices, e.g., switches, such as high-current electrical switches, relays, contactors, circuit breakers and the like may be used, at least in part, to implement the above-noted applications. However, use of such devices may be problematic.
In at least one implementation, an apparatus comprises a first electrode and a second electrode. The first and second electrode are configured to support an arc that conducts electric current between the first and second electrode. A shape of at least one of the first and second electrode is configured to, after an arc is established between the first and second electrode, expand at least one of an arc footprint of the arc on at least one of the first and second electrode and an arc column of the arc between the first and second electrode as the electric current between the first and second electrode increases.
One or more of the following features may be included. The shape of at least one of the first and second electrode may be further configured to decrease a self-current magnetic constriction of the arc column. The shape of at least one of the first and second electrode may be further configured to change shape in one or more regions to modify a degree of the self-current magnetic constriction of the arc column. The shape of at least one of the first and second electrode may be further configured to contract the arc footprint of the arc and the arc column as the electric current between the first and second electrode decreases.
The shape of at least one of the first and second electrode, after the arc is established between the first and second electrode, may be further configured to provide a voltage between the first and second electrode of less than or equal to 50 volts, when time-averaged over a period of time. The voltage between the first and second electrode may be configured to decrease, at least in part, based upon a design parameter of at least one of the first and second electrode, wherein the design parameter of at least one of the first and second electrode may include an arc-enhancing material. The shape of least one of the first and second electrode may be further configured to define an arc gap, at least in part, as including a ratio of an area of at least one of the first and second electrode to an average arc gap distance.
The shape of at least one of the first and second electrode may be further configured to sustain continuously over a period of time, after the arc is established between the first and second electrode, the expansion of the arc footprint and arc column, wherein the expansion of the arc footprint and arc column may exclude at least one of pulsation to zero current, chopping, flicker to zero current, spark instability, plasma extinction and re-ignition, fluctuation to zero current and any time-domain instability of the arc involving the electrical current between the first and second electrode becoming zero. The shape of at least one of the first and second electrode may be further configured to sustain continuously over a period of time, after the arc is established between the first and second electrode, contraction of the arc footprint and arc column, wherein the contraction of the arc footprint and arc column may exclude at least one of pulsation to zero current, chopping, flicker to zero current, spark instability, plasma extinction and re-ignition, fluctuation to zero current and any time-domain instability of the arc involving the electrical current between the first and second electrode becoming zero.
The shape of at least one of the first and second electrode may be defined, at least in part, by an area of at least one of the first and second electrode upon which at least one of the first and second electrode supports the footprint of the arc column, wherein the area may determine a maximum arc current of the electric current between the first and second electrode that at least one of the first and second electrode supports, and wherein the maximum arc current may be determined, at least in part, by a ratio of the arc current to the area, wherein the ratio of the arc current to the area may include the arc current density Φarc. The value of Φarc may be adjusted by a design parameter of at least one of the first and second electrode, wherein the design parameter of at least one of the first and second electrode may include an arc-enhancing material.
The arc may include at least one of a non-thermionic cathode arc, a cold-cathode arc, a metal vapor arc, a cathodic arc, and an arc including at least 10% of atoms and ions originating from at least one of the first and second electrode. An arc gap between the first and second electrode may include a location at which a length of the arc gap is shortest. An arc gap between the first and second electrode may include the arc column, and the arc column may be at least one of completely-filled and densely-filled with plasma after the expansion of the arc footprint and the arc column. An arc gap between the first and second electrode may include the arc column, and the expanding arc footprint and arc column may move within the arc gap and may create one or more regions which formerly had plasma and then lack plasma, and within which the arc may no longer burn. The electric current between the first and second electrode may be configured to decrease towards zero in response to the moving arc column being expelled from the arc gap. An arc gap between the first and second electrode may be included, wherein a length of the arc gap may be shortest near a location of arc ignition and the length increases with lateral distance away from the location of arc ignition.
At least one of the first and second electrode may be further configured to move within a predetermined proximity relative to one another to conduct electric current. A position of at least one of the first and second electrode may be fixed. At least one of the first and second electrode may include an arc-enhancing material. The arc-enhancing material may be configured to burn one or more arc spots in one or more predetermined locations. The arc enhancing material may include at least one of Mg, Se, Zn, Cd, In, Sn, Sb, Sm, Yb, Pb, Bi, Li, Na, K, Rb, and Cs. The shape of at least one of the first and second electrode may be further configured to collect at least a first portion of the arc-enhancing material when vaporized, and may be further configured to re-apply at least a second portion of the arc-enhancing material back to at least one of the first and second electrode. At least one of an arc striker and an arc igniter may be included and configured to replenish the arc-enhancing material.
One or more structures may be included and configured to at least one of limit influence of atmospheric air upon the arc, capture an arc burning material when vaporized, retain heat from arc discharge, shield one or more surroundings of the arc from gases and radiation generated from the arc, reduce acoustic noise from the arc, and quench arc plasma in response to the expanding arc column when the expanding arc column expels from the arc gap. One or more design parameters may be included and configured to adjust a rate-of-rise of the electric current between the first and second electrode after the arc is established between the first and second electrode. The expansion may include at least one arc front of the arc column that propagates from a location of arc ignition in at least one direction into the arc gap and away from the location of arc ignition. The design parameter of at least one of the first and second electrode may include an arc-enhancing material.
The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features and advantages will become apparent from the description, the drawings, and the claims.
Like reference symbols in the various drawings indicate like elements.
As noted above, the transfer of large amounts of, e.g., electrical energy, quickly may be desirable in a number of applications, for instance, as the technology for storage of large amounts of electrical energy improves. Example quantities of electrical energy may range from, e.g., ˜0.1 Joule [J] to 10 gigajoules [GJ] and higher. Example time scales for electrical energy transfer may range from, e.g., 10 seconds [s] to sub-microseconds [μs]. Capacitors may be fabricated that can store, e.g., 1 MJ to 1 GJ and larger amounts of electrical potential energy at, e.g., 1000 to 10,000 volts and higher across the plates of the capacitor and contain charge separations of, e.g., 103, 106 and higher coulombs [C] within capacitors that are small and light enough to be carried on board heavy wheeled vehicles, ships, trains and the like and also may be located at terrestrial stations. This scale of stored electrical energy may be used for propulsion of the above-noted vehicles over a time period of hours or days and for operational work. For the above-noted applications, it may be beneficial to charge or re-charge such energy-storage capacitors in the shortest time possible, preferably seconds or less than 1 second.
In some implementations, the present disclosure may be directed to rapid charging of energy-storage capacitors (the “target” capacitors) in vehicles and devices that may use the energy from a “source” capacitor, magnetically charged inductor, inertial flywheel/generator or other form of electrical energy storage element. In those examples, the quantity of electrical energy to be sent from the source storage element and the quantity of energy that may be received by the target capacitor may be limited, but large (e.g., MJ, GJ or larger). Though the energy may be limited, rather large electrical currents on the order of, e.g., kilo-amperes (kA) to mega-amperes (MA) and higher may be necessary to transfer the energy in the desired time periods. In the above-noted example applications, temporary electric current conductors, switches, contactors, moving electrical couples and the like may be used that can safely and controllably conduct kA, MA and larger electrical currents for short periods of time, for example, less than 10 seconds. Repetitive use of these temporary electric current conductors, switches, contactors, moving electrical couples over a long life may be desired.
As noted above, known switches such as high-current electrical switches, relays, contactors, circuit breakers and the like may be problematic as concerns contact arcing may occur between the switch contacts or movable make/break terminals of the device. Additionally, contact-arcing between switch contacts may be troublesome upon opening (e.g., breaking) or closing (e.g., making) of the switch contacts. As is sometimes used when generally discussing switches, the terms “arc” and “contact arc” are ill-defined and may erroneously refer to a spark, a flash of light, an audible click or snap, a very hot region, an ionized gas, and various forms of metal vapor plasmas.
A family of devices related to switches may involve sliding contacts for electrical current, particularly ones in which the contacts may be brought into and out of touching, mechanical contact as part of routine use. Sliding contacts may have components such as brushes, slip rings, commutators, wipers, shoes, rails, tracks, fingers, sliders, electrodes (e.g., one or more anodes and/or one or more cathodes) and the like. For example, sliding contacts used with electric trains and trolleys may have catenary wire, pantograph slider and third rail/shoe type components. Another example family of devices related to switches may involve rolling contacts for electrical current. In addition to circuit make/break arcs, sliding and rolling electrical contacts may experience inter-contact arcs due to, e.g., contact bounce, vibration, surface imperfections (e.g., roughness), contamination, wear dust/debris and other causes. Sliding and rolling contacts may be included when the term “switch” is used herein, unless suggested otherwise by context.
Temporary surge or in-rush currents may occur when electrical switches make contact between, e.g., a high-energy, low-internal-impedance electrical source, such as a capacitor, and a low-impedance load that may draw current from the source. In-rush currents may also be encountered with source and load circuit elements other than capacitors, such as, e.g., large inductors during field build-up or collapse, filaments or glow bars before heating to high temperature (and thus high electrical resistance), motors starting up, dumping of energy from inertial storage devices and so forth. In-rush current may be desired or acceptable in the circuit served by the switch but may damage the switch. Damage to a switch may also occur due, e.g., to high voltage transients during or related to switching. A frequent cause of high voltage transients may be a rapid change of current I through an inductor of inductance L. A voltage Vinduct(t)=−L(dI/dt) may be superimposed upon any other voltage across the inductor and also be added to voltages at other nodes in the overall circuit. Thus, a switch in series with the inductor may experience a high reverse voltage when the switch is closing (dI/dt>0) or may experience a high forward voltage when the switch is opening (dI/dt<0). When the moving contacts of a switch are in partial contact but not fully engaged, as concerns mating surface area and/or contact force, a high resistance condition may exist while some or all of the current flowing across the contact junction is concentrated in a small cross-sectional area. This may cause localized heating on contact surfaces which may lead to evaporation or migration of contact material or coatings, plasma ignition, sparking, cold cathode arcing, high voltage arcing (arc flash), loss of temper of the contact metal and other damaging phenomena. Generally, contact arcs in switches and moving contacts may be considered detrimental and to be avoided or mitigated, if unavoidable. Contact arcs may be detrimental because, among other reasons, they may consume (waste) electrical energy, they may dump electrical energy as destructive heat, they may pit or roughen the surface of the contacts (e.g., leading to higher contact resistance), they may erode the contacts (e.g., shortening operational life), they may punch through a coating on the contacts, they may melt contact, rail or shoe surfaces, they may weld contacts together, they may generate contamination/debris, they may generate electromagnetic interference (EMI) or radio-frequency interference (RFI), and they may be a source of ignition. Contact arcs may more severe of a problem the higher the current to be forced through the switch or moving contact. Damage to the switch may be more severe if the circuit voltage across the open switch is high, such as, e.g., thousands or tens of thousands of volts or more. Such issues may go beyond the capability of practical, economical known switches in circuits allowing kilo-ampere (kA) to more than mega-ampere (MA) currents with high open-circuit voltages, such as thousands or tens of thousands of volts or more, where current surge or voltage spike conditions may persist for hundreds of microseconds to tens of seconds. In these cases, the total charge transferred in a pulse (=current×time duration) may range from, e.g., 0.1 to 1×107 coulombs [C], while the total energy available in a pulse (=voltage×current×time duration) may range from, e.g., 100 to 1×1011 joules [J]. While it may be beneficial to transfer this energy from source to load with as small as possible losses in the switch, even small fractions of such large magnitudes of energy dissipated in a switch may be destructive for most types of available, practical switches. Another issue, in addition to avoidance of destruction, may be providing for repetitive conduction of such pulses or surges over a long device or switch lifetime.
Some techniques may exist aimed at eliminating or mitigating contact-arcing in mechanical switchgear and in sliding/rolling contact couples. Some techniques may aim towards tolerating localized heating on contact surfaces and eliminating or mitigating contact arcs in mechanical switch gear. Switchgear with metallic contacts may be beneficial for high-current circuits having prolonged (e.g., >10 seconds) current-on durations, due to the low on-resistance achieved. Thus, previous techniques focus on the anti-arcing properties of metallic contacts. Contact materials may vary regarding their minimum voltage or current required to generate a contact arc, so choices may be made to keep circuit parameters below those values and avoid contact arcs altogether in some circumstances.
In some implementations, a snubber resistor-capacitor (R-C) network may be placed across the contacts of a switch. Upon opening the contacts, the capacitor may slow the voltage rise across separating contacts, thus limiting a rate of heating the contacts. Upon closing the switch, the charged-up capacitor may do only harm, increasing the current magnitude through the mating contacts, so a resistor may be added to limit this effect (which may also degrade the switch-opening benefit). While careful selection of contact material and snubber components may bring a marginal case within the non-arcing or mild-arcing range of available contact materials, thus giving a long-lifetime benefit, the present disclosure may in some implementations concern voltages and currents above such thresholds for known materials. Other fields may handle or prevent catastrophic, destructive electrical energy release, sometimes called “arcing” but actually a complex set of phenomena. Thus, arc-protection switches, vacuum interrupters, arc eliminators, shunts and so forth exist that may work in spite of such arcs inside the switches. Some techniques may use a high-speed moving slug or bullet to close the contacts of a shunt or crowbar switch. Most interrupter and shunt devices are intended for infrequent use (e.g., not for routine make/break cycling). Another known technique is to shunt a mechanical switch with a semiconductor device during making or breaking of the switch contacts. While such techniques may operate repetitively either making or breaking a circuit, typically a reasonably-sized semiconductor solid-state switch may not survive very high power switching, such as, e.g., MJ or GJ energy transfers, e.g., kilo-ampere (kA) to more than mega-ampere (MA) currents, depending upon the voltage at which the electrical energy is stored and the time duration of current flow.
For example, some of the above-noted devices may be designed for 350 volts or less. Higher voltage semiconductor switches may require higher on-resistance or forward-conducting voltage drop and may be undesirable for surge currents in the aforementioned range for all but the briefest pulses (e.g., <<1 s), so they may not transfer the quantities of energy desired. In the field of sliding contacts, some techniques may use a brush contact made of bundles of, e.g., 40 μm diameter cadmium bronze wires, the ends of which may rub along a solid ring or track counter-electrode. Such a device may eliminate contact arcs due to bounce, vibration or surface roughness during sliding, due to the multiplicity of small, spring-loaded points of contact, but may not provide sufficient current-carrying capacity upon gross making or breaking of an energized circuit. As another example, some techniques may use an electrically-conductive lubricant on sliding contacts. No contact arcs may be observed up to contact current densities of 200 A/cm2 (2×106 A/m2), but gross making/breaking of the energized circuit may not be attempted, and such current densities may imply large (e.g., ˜1 m×1 m) contact area for 1 MA currents. Other techniques may use liquid metals as the electrical contact medium in sliding contacts for, e.g., rail guns, but with keeping the liquid metal in place, it may give rise to repeatability and lifetime limitations.
Semiconductor and solid-state switching devices also may be damaged by high surge currents and high transient voltages during or related to connecting and disconnecting high-voltage, high-current sources to/from the types of loads mentioned above. In some implementations, the terms “switch”, “switch-gear” and similar may include semiconductor switching and regulating devices such as transistors, triacs, thyristors, solidtrons and the like, unless suggested otherwise by the context. Typically, a semiconductor junction may be in a state of partial conduction and with full circuit voltage across it during turn-on or turn-off, where large power may be dissipated transiently. Damage to semiconductor junctions may be due to, e.g., overheating, electromigration of dopants, breakdown of insulating layers and other mechanisms rather than contact arcs, but similar limitations to those encountered in mechanical switches may occur with semiconductor switching devices. Semiconductor junctions may not achieve as low values of on-resistance R as metallic contacts of mechanical switches, thereby exposing the semiconductor junction to damaging I2 R (Joule) heating during current surges. Moreover, some high-current semiconductor switch modules may include several semiconductor junctions connected in electrically parallel configuration, intending that the junctions share the current substantially equally. However, the junctions may not have the same on-resistance or the same turn-on time or rate-of-rise of current, and the junction conducting the most current may present the lowest electrical resistance to the external circuit, thereby tending to draw more current. Therefore, especially during turn-on and turn-off, one junction may conduct an excessive portion of the total current and become damaged.
Another field of switching may use electrical discharges to conduct current within switches. Some techniques may exist in the fields of vacuum switches, thyratrons, pseudo-spark switches, spark-gaps and similar devices. Generally, these devices may stand off voltages on the order of, e.g., 1,000 volts, 10,000 volts and higher when not conducting, and they may conduct currents of kA, MA and higher when conducting. The devices may provide extremely rapid rise-time of the switched current, often in, e.g., nanoseconds or picoseconds to give current rise times of 1012 A/s or higher. Thus, large, high-voltage versions of these devices may produce gigawatt or terawatt pulses, since the energy transferred may be delivered in a very short time period. However, such high-power pulses may be also typically of rather short duration, e.g., microseconds. A relatively robust spark gap switch, with intensive air and water cooling and an electromagnetically swept “arc”, may transfer only, e.g., ˜1 C of charge over a few tens of microseconds. For circuit voltages of, e.g., 1000 to 10,000 volts, the total amount of energy transferred (e.g., 1 to 10 kJ) may not be on the same order of magnitude as those listed above for, e.g., energy storage applications, though such a switch may provide multiple pulses per second. Trigger timing accuracy and jitter in pulse onset time may be important with these devices, however, such parameters may be of little concern for energy storage and energy transfer applications. A modern pseudo-spark device, for which the total amount of charge transferred in a lifetime of pulses might be on the order of 106 coulombs, while by contrast, a switch required for the proposed energy storage and energy transfer applications (discussed in greater detail below) may transfer 106 coulombs in a single switch conduction event, though the duration of such events may be usefully up to seconds rather than microseconds as in, e.g., vacuum switches, thyratrons, pseudo-spark switches, spark-gaps and similar devices. The above-noted techniques may not provide long conduction duration for large energy transfer as defined above.
Some techniques may involve replacing sliding or rolling contacts with an electrical discharge conduction medium. For example, use of cold cathode field emission mode atmospheric-gas plasmas to conduct electrical current between non-mechanically-contacting electrodes, which may be stationary or moving one with respect to the other. The moving electrode is generally associated with a train, trolley or similar vehicle, and may be intended to avoid more intense erosive “arcs”, which might involve vaporization and/or ionization of the electrode material. The technique may avoid arcs by, e.g., laterally dithering the electrodes to prevent hot spots, regulating the distance of separation of the electrodes and limiting the current drawn. Other similar techniques may add low-ionization-potential materials to one or both electrodes and to pump special gases into the plasma discharge region, to enhance the current-carrying capability of the plasma. These techniques may include a two-mode operation, with sliding solid-solid contact at zero or low vehicle speeds and plasma conduction taking over at higher speeds. The solid contact mode may be useful for high start-up currents drawn by the vehicle. The plasma conduction mode may be inadequate to conduct the large currents needed for rapid transfer of large amounts of stored energy as defined above. This may be seen with reference to
Further, with regard at least to glow discharge modes, especially at atmospheric pressure, there is a disadvantage of a substantial voltage drop (e.g., >350 v) that the
With other example techniques, the design of high-current and/or high-voltage switchgear may be dominated by considerations of, e.g., surge currents, transient high voltages, and contact arcs. In many applications, the normal running conditions may be much less severe and less potentially damaging than these surge or contact arc conditions. The practical result may be that switchgear is often sized much heavier, larger, costlier and inefficient than it could be if designed only for the normal running loads and conditions. For example, voltage drop and heating at contacts may be reduced if gold plating or other high quality contact material could be used, as may be possible if, e.g., only nominal running conditions are encountered, but these contact materials may not endure switch closing and opening arcs for long lifetimes. Therefore, if current surges, voltage spikes and contact arcs may be avoided or mitigated, especially during vulnerable periods of switch closing and opening, then smaller, cheaper, more efficient and longer-lasting switchgear may be deployed resulting in significant economic benefit.
Thus, some example issues may include the non-availability of simple, practical high-energy electrical transfer devices and of damage to known types of switchgear during making and breaking of high-voltage, high-current live circuits. While some techniques may include partial solutions, such as over-sizing the switchgear or frequently replacing switch components, they are inefficient, expensive, bulky, complex and/or labor-intensive. In some implementations, at least some of these issues may be addressed using an electrical current coupling device to connect, conduct and disconnect, e.g., kilo-ampere, mega-ampere or larger currents in circuits for transferring megajoule to gigajoule or larger quantities of electrical energy within a timescale of, e.g., seconds to sub-seconds. As will be discussed in greater detail below, in some implementations, the device may be configured to transfer this electric energy during relative motion of the objects sending and receiving the transferred energy. As will also be discussed in greater detail below, in some implementations, the device may include, e.g., substantial non-contact of electrical terminals, absence of impact forces, momentum transfer, rubbing friction and the like associated with mechanical contact during making/breaking of circuits and relative motion of the terminals of the device. As will also be discussed in greater detail below, in some implementations, the device may be configured to exhibit good operation without need of, e.g., intentionally added lubricants, conductive fluids, special gaseous media or shielding gases and the like. As will also be discussed in greater detail below, in some implementations, the device may be configured to operate at approximately, e.g., one atmosphere pressure. As will be discussed in greater detail below, in some implementations, the device may be configured to exhibit good operation in spite of the presence of unintentional environmental contaminants such as, e.g., dust, humid air, moving air (wind), incidental debris, oil mist and thin grease films. As will also be discussed in greater detail below, in some implementations, the device may be configured to exhibit good operation in spite of the presence of, e.g., unintentional environmental contaminants such as fog, rain, snow, ice, minor insect presence and the like encountered in outdoor use. As will also be discussed in greater detail below, in some implementations, the device may be configured to allow effective electrical energy transfer while tolerating relatively imprecise alignment and control of the relative position and distance between the electrodes, such as variations of, e.g., 1 to 10 mm.
In some implementations, the above-noted example issues of, e.g., a lack of high-energy electrical transfer devices and of switchgear being too easily damaged by contact arcs and energy dissipation during switching of electrical sources and loads that may engender high-energy surge currents at high voltages may be addressed, at least in part, by, e.g., providing switchgear in which a true arc is the switchable conducting element. Arc conductors provided by the disclosure may satisfy the object of transferring large amounts of electrical energy quickly and may absorb, with little or no damage, byproduct or wasted energy from circuits being switched.
In some implementations, the above-noted example issues of, e.g., switches, such as vacuum switches, thyratrons, pseudo-spark switches, spark-gaps, ignitrons and the like, which rely upon electrical discharges as the conductor, providing only low total energy transfer and brief pulses may be addressed, at least in part, by using unique arcing geometries, arcing materials and arc propagation principles to provide a low-voltage arc as an electrical conductor or switch.
In some implementations, the above-noted example issues of, e.g., high-energy, high-power true arcs that cannot be controlled and may be destructive, may be addressed, at least in part, by, e.g., the use of cold-cathode metal-vapor arcs, low-voltage arcs, broad area arcs and avoidance of self-current magnetic constriction of the arc, among others.
In some implementations, a mode of arcing between electrodes that are initially near room temperature, 25° C., and up to at least 500° C., may be mediated by the phenomenon of, e.g., cathode spots upon the cathode or negatively-charged electrode. For non-refractory metal cathodes, cathode-spot-arcs and derivatives may be the most likely kind of arcs to occur, because, e.g., the metal may not reach efficient thermionic emission temperatures (typically >3000K) before boiling. Such arcs may be referred to as, e.g., non-thermionic cathode arcs, cold-cathode arcs, metal vapor arcs and cathodic arcs. In general, almost all of the atoms and ions that may make up the arc plasma column may originate from the electrodes, but in any case no less than, e.g., 10% so originate. For historical reasons, such arcs may sometimes be referred to as vacuum arcs, though this term is widely understood to be a misnomer and mainly assures that the arcing vapor originates from the arcing electrodes. Vacuum environments have been used to study and utilize cathodic arcs for a number of reasons. For example, partial vacua (10−5 to 10−2 atm) may enable study of the transition from a gas glow discharge mode to a metal arcing mode, as in
In some implementations, when at least the surface of arcing electrodes become hotter (than, e.g., ˜500° C.), various other atomic mechanisms and modes of metal vapor arcing, such as anodic arcing, may further feed a metal vapor arc plasma and hence further enable arc conduction. An arc voltage may also be reduced if the mode of vaporization of metal atoms substantially changes over from cold-cathode arcing to metal vapor arcing in which a temperature of the electrodes (for example, the temperature of an outer layer) thermally vaporizes solid atoms. An arc may broadly be described as, e.g., a dense plasma discharge in which electrons are the primary charge transport species, due to their low mass and high mobility, and in which positive ions provide at least a space charge neutralization function for electron transport, where the discharge voltage (e.g., arc burning voltage Varc) may be near the ionization potential of whatever atoms provide the positive ions, such as, e.g., 2 to 20 eV, which may result in a similar Varc=3 to 30 volts, without limitation. Such arc voltages near the ionization potential of the atoms that may include the vapor sustaining the arc may be near the theoretical minimum voltage for any discharge or arc. An arc may persist over time at a low discharge voltage, where by contrast, a spark or flash may be transient and at higher discharge voltage. Arcs typically require at least a minimum or threshold arc voltage Varc,min and arc current Iarc,min to sustain themselves burning and may further require somewhat higher parameters to start or initiate. In a metal vapor arc, the atoms that may become ionized to positive ions may originate from the metal of the arc electrodes. Dense metal vapor plasma arcs may burn in an ambient atmosphere or medium, such as in air or under water, with predictable effects but still substantially as metal plasmas.
In some implementations, the above-noted cathode arcs may be used intentionally as, e.g., conductors, switches and control elements in electrical circuits and may carry large currents, e.g., 10n amperes where n=1 to 9 or more, with relatively small losses and practically desirable device characteristics. Such a circuit may include an electric power source, an arc conductor in series with an electrical load and a return current path from a second terminal of the load back to a second terminal of the source. In some implementations, types of arcs for which the electrical resistance of the arc as a circuit element decreases as arc current increases may be used. There may exist the potential for these types of arcs to go opposite to the trend of most other electrical devices, which is to degrade their usable properties as conducted current increases. Rather, desirable arcs according to some implementations may scale up gracefully to extremely high conducted currents while consuming or liberating unexpectedly low I2R waste power. In some implementations, the disclosure may be used practically in scaling to high currents in desirable devices.
In some implementations, cold cathodic arcs may provide: the ability to burn in a variety of ambient media, nearly instantaneous (e.g., sub-microsecond) ignition, operation at both low and high electrode temperatures, the ability to burn on a wide variety of electrode materials and the general robustness regarding electrode spacing, contamination, external fields and means of ignition. Cold cathodic arcs may be configured to be substantially metal vapor arcs, where at least a portion of an inter-electrode arc plasma may either include or may be modified by metal atoms or ions originating from a cathode electrode. In some implementations, an electrode serving as an anode may be configured in the present disclosure to participate in an anodic arc, where at least a portion of an inter-electrode arc plasma may either include or may be modified by metal atoms or ions originating from an anode electrode. In some implementations, metal vapor for the arc may be supplied by a non-electrode body or source such as an arc ignition means. These and other aspects of the disclosure may dramatically increase an ability to initiate and sustain conduction of very large currents across high electric potential differences, and the ability to do so repeatedly and with repeatable parameters over long device lifetimes.
In some implementations using arcing mediated by cathode spots on the cathode, and referring to
In some implementations, neutral metal vapor and ions of metal atoms from the cathode material may normally depart the cathode and make a coating of cathode material on all surfaces near or within line of sight of the cathode. In some implementations, there may be no upper limit to the electrical current cathode arcs may conduct, since dozens, hundreds or more cathode spots may exist simultaneously on the cathode surface, but electrode melting or erosion may become limiting. The anode side of the arc discharge may exist in several modes (e.g., diffuse-attachment, diffuse-spot, etc.) depending upon, e.g., the current density and anode temperature.
In some implementations, an arc conductor, an arc switch or a moving arc couple may be closed or “made” by, e.g., moving two electrodes, an anode and a cathode in a direct-current (DC) circuit, into predetermined proximity to and orientation with each other and striking a cold cathode arc between them. The switch may be “broken” or opened by a self-extinguishing of the arc when the anode and cathode come to approximately the same electrical potential or when the anode and cathode are moved a sufficient distance away from each other. The arc may be struck or ignited by, e.g., transient mechanical touching of the anode and cathode. Other methods to ignite the arc may also be used, such as a spark plug, laser pulse, electron beam pulse, radionuclide emitter of α-particles or β-particles, chemical explosive detonation and the like without departing from the scope of the disclosure.
In some implementations using arc-striking, within the type of transient mechanical touching of the anode and cathode, a striker rod or wire fabricated of a conductive material may be placed so as to short-circuit the anode to cathode. At least one of the anode and cathode may be moving into or fixed in an arcing position and the striker rod or wire inserted or fed into the anode-cathode gap at any desired time by any suitable actuator or feed mechanism. When electrical contact is made from anode to cathode through the striker rod or wire, current may flow through the striker rod or wire. The diameter, cross-section and/or mass of the striker rod or wire may be selected so that the current flowing through it may cause it to melt or even vaporize. The breaking of electrical contact by the destruction of the rod or wire may cause a “drawn” arc, which may provide, e.g., atomic vapor, ions and electrons to “trigger” or initiate a larger, general arc between cathode and anode. The vapor, ions and any unmelted length of material of the striker rod or wire may remain in the anode-cathode gap, become further heated and vaporized and become part of the arc discharge.
In some implementations, an arc conductor may be configured to expand from an initial spark or localized drawn arc into a broader-area arc column or arc channel within at least two electrodes of an arc gap. At least two steps may be recognized, a first ignition of, or breakdown of, the arc gap followed by establishment of an arc comprising at least one arc column. A subsequent phase may involve expansion of the already-established arc column. In some implementations, it may be beneficial to provide large lateral area or width of the electrodes, lateral being generally defined as substantially perpendicular to the short direction of a mechanical gap in which the arc burns. The distance in this short direction of the gap is known as an arc length larc of the arc gap. A large arc gap aspect ratio may be defined as a width of an electrode(s) divided by a length of the arc gap which may be equal to the arc length larc. For example, a large arc gap aspect ratio of the disclosure may be, e.g., 1, 10, 100 or more. As implied above, here the term “width” may generally stand in for an electrode area having two lateral dimensions so that the electrode area is on the order of, e.g., (width)2.
In some implementations, the use of the physics of cathode spots may provide orderly expansion and contraction of the arc column and its footprint on the electrodes, a resistance (or impedance) of the arc that may decrease with increasing arc current and the distribution of heat generated by the arc. As arc current increases, a larger number of arc spots may be accommodated by a desired lateral expansion of the arc column. This may be used to estimate a resistance of the arc as a circuit element and the power or energy dissipated from an external circuit into the arc.
In some implementations, broad lateral expansion of an arc column, with its increased number of cathode arc spots, may create a multiplicity of electrically-parallel charged particle emitters and collectors conducting electrical current between anode and cathode, some or all which may be operative simultaneously. A resistance Rspot may be assigned to one or more (or each) arc spots and its conductive plasma column, for each spot 1, 2, 3, . . . i, . . . Nspot. Thus, the overall resistance of a broadly-attached arc column, Rarc,column=Rarc, may have a property of parallel additivity by inverses similar to that of commonplace resistors in an ordinary electric circuit, that is,
though such resistances may be due to a plasma conductivity, which may be unstable or stochastic due to the nature of arc spots creating the plasma. The greater the number of cathode arc spots, the lower may the overall resistance or impedance of the arc column be. By way of example only, for a typical arc spot, Vspot≈Varc may be 10 volts and Ispot may be 20 amperes, so by Ohm's Law, Rspot,i may be ˜0.5Ω. Making an approximation that, over a time and population average, all of the arc spots are identical and have the same resistance Rspot and the same contribution Ispot per spot to the overall current conducted by the broad arc plasma column, then Eqn. 1 reduces to
R
arc
−1
=N
spots
/R
spot. 2)
With the aforementioned discussion that arc spots each provide, on average, a characteristic current Ispot, a value for Nspots can be estimated as
N
spots
=I
arc
/I
spot 3)
In some implementations, if an arc gap is conducting 1 MA, then 50,000 spots may be required, so Nspot=50,000, and by Eqn. 2, Rarc,column=Rarc=10 μΩ (micro-ohms). This may be an extremely small contact resistance for, as an example, million-ampere metallic contacts pressed together. In some implementations, million-ampere metallic contacts may be bulky or complex, while a million-ampere arc conductor couple may be, e.g., ˜0.1 m2, about 1 square foot (for Φarc of 10 MA/m2, which is relatively low) and may include substantially planar, cylindrical or spherical-section plates, which are of desirably small size and simple form. A general approximate scaling rule, most valid at high arc currents over a time-average, for the decrease in arc resistance with increasing arc current is obtained if we invert Eqn. 2 and insert Eqn. 3 for Nspots:
R
arc
=R
spot
/N
spots
=R
spot
·I
spot
/I
arc
=k·I
arc
−1. 4)
Thus, arc resistance may be inversely proportional to arc current with a proportionality constant k=Rspot·Ispot, which may be assigned k=Vspot≈Varc,min, since k has the units and dimensions of a voltage. The assignment of Varc,min for the constant k may be based upon the experimental observation that Varc does not increase substantially as Iarc is driven higher, within certain limits. The constancy of a Varc value near Varc,min may hold when lateral expansion of the arc column footprint upon the arc electrodes is unimpeded. Both Vspot and Varc, for arcs containing only a few spots may be poorly defined, unstable over time and highly dependent upon the impedances of external circuits in communication with the arc (which may include current loops and magnetic fluxes not in galvanic contact with the arc). This behavior of Varc at low arc currents may be due to the stochastic or chaotic phenomena including arc spots. In some implementations, arc resistance may be inversely proportional to arc current for high-current arc conductors to allow, e.g., kA to MA or higher currents to be conducted efficiently. Ease of arc attachments at the electrodes expanding into one or more broad, lateral, large cross-section arc column(s) may be provided and broad-area attachment may be used for achieving an arc impedance inversely proportional to the arc current. Thus, at high arc currents,
Rarc≈Varc,min·Iarc−1, where Varc,min constant. 5)
As mentioned above, however, there is a certain minimum arc current Iarc,min below which the arc may not continue to burn, so Rarc may be treated as infinite below that threshold current. As a somewhat more general scaling rule than Eqn. 5, but still approximate:
R
arc
≈V
arc,min/(Iarc−Iarc,min), for Iarc>Iarc,min. 6)
Arc impedance as a function of arc current calculated from Eqn. 6 with Varc,min=10 v and Iarc,min=10 A is shown in
Power dissipated in or by an arc conductor of the disclosure is also shown in
P
arc
=I
arc
2
·R
arc. 7)
Eqn. 6 says Rarc decreases inversely with increase in Iarc at large Iarc, which is equivalent to inserting Eqn. 4 for Rarc into Eqn. 7 to give
P
arc
=I
arc
2
·k·I
arc
−1
=k·I
arc
=V
arc
·I
arc, (Iarc>>Iarc,min and Varc≈constant) 8)
where Varc is close to Varc,min and identified with constant “k” as discussed after Eqn. 4. Eqn. 8 shows that, for an arc burning in a particular mode, the disclosure may provide Parc∝Iarc, rather than Parc∝Iarc2, as Eqn. 7 may imply. By contrast, a normal metallic conductor and, presumably, a metallic solid-solid contact junction of a relay or contactor, may have a power dissipation as given in Eqn. 7 but with a fixed resistance Rfixed in place of Rarc. A fixed contact resistance may give Pcontact∝Icontact2, and two typical cases like this are also plotted in
In some implementations, a lower Varc may be seen as arc current increases, which may be indicative that the arc has expanded or moved to vaporize and ionize other materials that are more arc-enhancing than the materials upon which the arc was initially burning. Varc may increase with Iarc, as well, which may be due to arc ingress to more arc-limiting materials. Other interpretations are possible. For example, Varc may decrease with increased Iarc if, e.g., the arc also moves to cooler metal, which may have lower resistance due to the positive temperature coefficient of resistivity of most metals. This temperature effect may be operative as a means of urging expansion (e.g., broadening) of the arc footprint on the arc electrodes shortly after establishment of the arc. In some implementations, it may be desirable to use a tendency of an arc footprint to move to cooler metal, but not allow the arc to stop burning on the hotter metal from whence it came. Thus, a tendency for the arc to move becomes a tendency for the arc to expand. Among other ways, the arc may be prevented from extinguishing at or moving away from already-hot electrode areas by, e.g., providing a shorter arc gap length there, as described below.
In some implementations, if an external electrical power source may provide large current at high driving voltages, the mode of arc expansion by cathode spots described above and its consequent reduction in arc impedance as current increases may lead to “runaway conduction” or “runaway current draw”. Proper selection of arcing conditions may provide a low arc voltage, so relatively little energy may be dumped into the arc or electrodes, if there were a proper load in series with the arc across which the dominant fraction of circuit voltage may appear (and into which the majority of energy may be dumped). Runaway increase of arc current may be desirable when arc ignition and establishment is used as the closing of a switch or to transfer energy quickly. It may be acceptable and beneficial to allow arc current to increase rapidly and without arc-self-limit, so long as an electrical source or load of an external circuit may limit the current at some value, and this current value and its attendant energy dissipated in the arc was within the capacity of the arc apparatus to absorb.
In some implementations, there may be a “feed-forward” increase of arc current based upon, at least in part, a principle of expansion of a width or a cross-sectional area of an arc column to conduct rapidly increasing arc current while always maintaining low arc voltage. In one or more implementations, a type of arc that includes cathode spots may provide feed-forward increase of arc current while allowing a voltage across the arc electrodes to remain low, such as, e.g., 2 to 10 volts but usually (and not always) less than 50 volts. At such arc voltages Varc, an acceptably low amount of energy (as generally defined below) may be dissipated in the arc apparatus. By “feed-forward” it is meant positive reinforcement, and a mode of arc expansion may be provided where an initial increment of energy may be taken from the external circuit to vaporize and ionize material in the arc gap, which in turn may allow more current and energy to be drawn from the external circuit, which in turn vaporizes and ionizes more material in the arc gap, which in turn may allow more energy to be drawn from the external circuit, and so forth on and on. In one or more implementations, cathode arc spots may facilitate the expansion. The runaway feed-forward increase of arc current may be conducted by, e.g., an arc plasma column or channel characterized by at least one “arc front” or arc ignition front propagating in an orderly pattern from a first arc ignition location throughout a broad-area electrode gap.
Generally, arcs are avoided because a) runaway current conduction at b) modest or high circuit voltages is thought to cause c) great release of electrical energy and consequent destruction of apparatus. However, in some implementations, arcs may be used as switches or temporary conductors, with no current limit and no ballast, to quickly transfer as much electric charge (e.g., current) to a load as the electrical source could deliver or the load could accept. Such loads may be, e.g., rail guns, high-voltage capacitors, pulsed lasers, plasma-chemical propellants, electromagnetic beacons and others. In some implementations, there may be beneficially rapid, unfettered, free-propagating feed-forward increase of arc current and of the size of an arc. In some implementations, a rate-of-rise of conducted current of such free-propagating arcs may be modified over a wide range (e.g., 0.1 to 100 kA/μs), which is beneficial for control in some of the above-noted applications. Those skilled in the art will appreciate that principles of the disclosure may also give scaling rules for arc conductor apparatus, such that not only extremely large energy and power may be transferred but also smaller energy and power in the neighborhood of, e.g., 100 joules and 100 watts may be beneficially transferred, thereby enabling use for replacing, augmenting and protecting more conventional switchgear.
In some implementations, in a low-voltage, runaway mode of arc expansion, it may be advantageous in one or more implementations that the arc electrode area not be over-filled with plasma before the source-to-load circuit current increases to a peak value and begins to decrease. According to one or more implementations, a quantity of heat energy released as electrical power in the arc plasma multiplied by the duration of the conduction event may be less than or equal to an amount that can be safely absorbed by the arc apparatus.
In some implementations, using rate of pressure rise and other parameters, arc expansion may be controlled for rate of arc front propagation, rate of plasma density growth and other parameters. A rate-of-rise of current through an arc conductor may be tailored via control of arc front propagation speed, electrode shape, arc column expansion rate, properties of the arcing materials and other principles and aspects of the disclosure. In one or more implementations, a rate-of-rise of arc current may be determined as a fixed design parameter, varied from one conduction event to another and/or varied within one conduction event.
In some implementations, the impedance of the arc column and of the arc gap as a circuit element may start relatively high immediately after first arc ignition, decreases to values in the 10, 1 to fractional ohms level as a first metal-vapor arcing mode is established and further decreases to milli-ohms (mΩ) to micro-ohms (μΩ) as lateral expansion of the arc column creates a multiplicity of electrically-parallel charged particle emitters and collectors operative simultaneously. See Eqn. 1 above. Because of this plurality of substantially independent charged particle emitters and collectors, a laterally spread-out, broadened or expanded arc channel or column may include multiple smaller-width arc channels or columns connecting cathode to anode, but these may be desirably merged together into one column and may be referred to in the singular herein. The speed at which the breadth of the arc column can expand may depend at least upon a mobility of cathode arc spots, a speed of sound in the ambient medium of the arc gap or a speed of sound in the arc plasma within the arc gap, each of which may be on the order of tens to hundreds of meters per second. Because the impedance of the arc plasma column may decrease with increasing current conducted by the arc, due to the broadening and mass-parallel emitter effect of the arc column with increasing current, the voltage across the arc gap in a desired conducting mode may stay near 10 volts, but usually between 2 to 50 volts, at all conducted currents from less than ˜100 A to greater than ˜107 A or more. The remaining voltage of an external circuit not appearing across the arc gap appears across the load. Thus, an arc conductor may be provided that can increase its conducted current rapidly (sub-μs to ms) and controllably from near zero to extremely high currents (MA and higher) while achieving on the order of μΩ “contact” resistances at the higher currents without damage to the arc gap.
Saturable inductors may be employed to control a rate-of-rise of current and prevent erosion damage to vacuum switch electrodes, but such inductors may be undesirably heavy when sized for the higher current and energy transfers of the present disclosure and may be unnecessary. Design parameters of the arc conductor or switch may adjust a rate of expansion of a width or a cross-sectional area of the arc plasma column(s), which in turn may adjust a rate-of-rise of current increase upon switch closure and also control the lateral area on the electrodes into which an amount of waste heat due to the arc resistance is deposited into the electrodes. When a current flow through the arc conductor or switch decreases due to circumstances in the external circuitry served by the arc conductor or switch, a width or a cross-sectional area of the arc plasma column may contract in an orderly fashion to maintain a voltage near, e.g., 10 volts, but usually between 2 to 50 volts, across the arc gap, which in turn maintains proper burning conditions for the arc until the arc current reaches a low value such as <100 A, <50 A, <20 A or lower at which time the arc may self-extinguish. The switch may then be in an open state.
In some implementations, an arc gap for the expanding plasma may include one or more arc electrodes providing a shorter arc gap length larc at a location of first arc ignition and smoothly increasing gap length in regions of the gap into which the broadening arc plasma subsequently expands. For example purposes only, a set of scaling laws or principles are disclosed whereby a pattern or rate of increase of gap length larc(r) with respect to lateral distance “r” from a location of first arc ignition may be selected or configured. In one or more implementations, the passing arc front leaves behind a time-sustained, low-voltage-burning arc plasma column conducting 1, 10 to 100 or more mega-amperes per square meter (MA/m2) of electrode area arc current density Φarc. Values of Φarc up to 1000 MA/m2 are provided within the disclosure. In one or more implementations, the arc column is substantially spatially continuous, i.e., laterally space-filling with arc plasma within the arc gap behind the arc front. In this sense, “behind” means opposite the direction of motion of the expanding arc front and back towards the location of first arc ignition.
In some implementations, an arc conductor or switch may be sized or configured for a circuit and its maximum surge current pulse parameters, such as peak current and duration. Scaling laws may concern a mass and a heat capacity of the arc apparatus materials sized to heat dissipated in the arc apparatus by arc conduction. In another aspect, the scaling laws concern an area of the arc electrodes available to sustain an arc in the arc gap sized to a current to be conducted by the arc apparatus (e.g., the maximum current) and a current density Φarc [A/m2] that may be conducted by the arc plasma. The scaling laws may concern a material of the arc electrodes, an arc striker and/or an arcing additive, where the material(s) may configure an arc gap to conduct at a certain current density Φarc, which may be used in another scaling law for electrode area. Using additional aspects of the disclosure including arc-enhancing materials, a lower power and energy end of a useful range for arc conductors may be extended to approximately, e.g., 100 watts and 100 joules. There appear to be no upper limits. According to the aforesaid scaling laws, many implementations of the arc conductors may be beneficially small, lightweight, inexpensive and rugged. Increasing a mass of the arc conductor apparatus or adding explicit cooling for the electrodes and/or arc gap components may permit higher duty cycle of repetitive switch use.
In some implementations, using other aspects of the disclosure may achieve arcs with a desired degree of electrical energy absorption out of the circuit it is serving by optionally choosing or varying one or more of: a shape of arc electrodes (which may, without limitation, give a non-uniform arc gap length), an area of the arcing surface of an electrode, selected arcing electrode materials, spacing of arc electrodes, selected arcing media between the arcing electrodes, chemical reactions between arcing electrodes and species within the arcing medium (for example, air), a thermal mass of one or more arc electrodes (which may affect a temperature rise during a conduction event) and arc-induced transfer of material from one electrode to another electrode, among others.
In some implementations, an arc conductor, arc switch and moving arc couple may use cathodic arcs to conduct electric current between non-mechanically-contacting cathode and anode electrodes. The anode and cathode portions of the switch may be moved relative to each other along an approximate expected path during desired portions of a switch closing, conduction and/or opening event. In some implementations, the path may be linear or circular though not limited to such.
In some implementations, the cathode may be fabricated from a metal with relatively difficult arcing properties and may be provided with a coating or surface layer comprising of at least one arc-enhancing material. The arc-enhancing material may be chosen to promote good arcing given the pressure of the environment and the quantity of energy to be transferred. The cathode's arc-enhancing material also serves as a means of promoting cathode arc spots to burn preferentially at desired locations within the switch. The cathode's arc-enhancing material may be sacrificial, in the sense of being vaporized and eroded by the arc, but means are provided to replenish the arc-enhancing material. For example, the anode may be fabricated of selected materials with a shape to not only efficiently collect electrons but also to collect vaporized cathode arc-enhancing material and re-vaporize it back to the cathode. A wire-feed or rod-feed arc striker or trigger may be provided, the vaporized material from which replenishes the cathode arc-enhancing material. The switch and moving electrical contact may be used repetitively. A set of baffles or shield structures may be provided to limit the influence of atmospheric air upon the burning arc, to capture cathode arc-enhancing material vapor for recovery and re-use, to retain heat from the arc discharge, to shield the surroundings from hot gases and radiation from the arc and to reduce acoustic noise from the arc escaping to the surroundings.
In some implementations, arc switches and conductors may produce quantities of waste heat lower than current technologies for pulsing or switching equivalent amounts of electrical energy. Arc conductors may be matched to and selected for a circuit they serve at least according to a thermal limit of the arc conductor apparatus. A thermal limit, or maximum temperature rise, may exist for any particular arc conductor apparatus, and the energy (heat) dissipated in the apparatus by a conduction event ought not cause this temperature to be exceeded. As mentioned, arc conductors may be used for short duration conduction of high currents. Referring again to
E
loss,arc
=P
arc
·Δt
pulse, 9)
where Δtpulse is the time duration of the arc conduction event or current pulse. Substituting the alternate formula besides Eqn. 7 for electric power loss, Parc−Iarc·Varc, into Eqn. 9 gives
E
loss,arc
=V
arc
·I
arc
·Δt
pulse
=V
arc
·Q
xfr, 10)
where Qxfr is the total charge in Coulombs transferred, since the integral over the interval Δtpulse of Iarc(t)dt=Qxfr. This form from Eqn. 10 is appropriate because the current value during a surge or in-rush event may rarely be constant over time. Eloss,arc may normally end up as heat Eheat dissipated in the arc apparatus. With arc conductors of the disclosure, such heat may simply and advantageously be dissipated in the mass of the arc electrodes or other structures of the arc gap apparatus. The arc apparatus may be designed to absorb the heat dissipated by any given circuit conduction event. The formula ΔTapparatus=Eheat/(Cp·m), where Cp is the heat capacity and m is the mass of the electrode material or arc gap apparatus, gives the temperature rise ΔT for any given energy Eheat dissipated. From
P
load
=V
load
·I
load=(Vcircuit−Varc)·Iload=(1000 v−10 v)·1×106 A=990 MW, 11)
and the energy=power×time provided to the load during the 0.1 s may be 99 MJ. The current transferred by the arc through the load may, however, vary during the conduction event as Iarc(t)=Iload(t) due to the nature of a load or source (for example, a capacitor becoming charged or discharged) or due to a change of arc conduction. Vload(t) may change for similar reasons. Therefore, the equation for energy transferred to the load is more generally written
E
load(t)=∫t=0tVload(t)Iarc(t)dt 12)
Within the approximation of a simple square-wave pulse of current at constant voltage, the arc conductor may consume, divert or dissipate ˜10 MW power for 0.1 second and generates ˜1 MJ of heat, which is only ˜1% of the energy and power prospectively transferred to the load. Eqns. 11 and 12 indicate that the higher Vcircuit, the smaller the percentage losses may be to an arc conductor of the present disclosure. (See Eqn. 13 below.)
In some implementations, a switch or arc conductor of the disclosure may be constrained by design details of its particular implementation to a certain maximum energy (heat) dissipated, beyond which, damage, such as melting, may occur to the arc conductor apparatus. This maximum quantity of energy may typically be expressed as an electrical current over a certain time duration or a power multiplied by the time during which that power is dissipated. For example,
% Loss in Switch Device≈100·Vfwd-drop/Vcircuit=100·Varc,min/Vcircuit. 13)
Thus, at Varc,min=10 v and in a Vcircuit=250 v circuit, an arc conductor may have ˜4% losses. At Vcircuit=1667 v, an arc conductor may have the same ˜0.6% losses as the cited semiconductor switch has at Vcircuit=250 v, assuming Varc,min=10 v. It may be explained below that Varc,min=10 v is merely a typical value and that both lower and higher values are readily accessible within the disclosure. Generally, the minimum arc voltage Varc,min may not be as low as the one or two “diode drops” Vfwd-drop typical of a simple semiconductor junction, because of the different physics involved, so it may seem advantageous to always use semiconductor junctions over arc conductors, to minimize wasted power. Some types of semiconductor junctions may even exhibit an apparent reduction in junction resistance as junction current increases, analogous to Eqns. 5 and 6 for arcs, albeit due to different underlying physics. However, arc conductors scale up very easily in both circuit current and voltage as is made clear herein, whereas solid-state semiconductors may be troublesome to scale up in either circuit current or voltage, much less both simultaneously. To scale up in current, multiple parallel semiconductor junctions are often necessary, but these must be carefully trimmed or elaborately controlled to share current equally especially during turn-on and turn-off. Otherwise one of the junctions may “hoard” circuit current due to its apparent reduction in junction resistance as current increases. To scale up in voltage, special thick semiconductor junctions must be grown, and these have both higher Vfwd-drop and reduced ability to conduct away dissipated heat. By contrast, a single arc gap configured according to the disclosure easily scales up in current, both within a single arc conductor device during a single current pulse and within separate arc conductor devices intended for different magnitudes of conducted currents. To scale an arc conductor up to higher voltage may be as simple as increasing the length of the arc gap. Therefore, considering ease of scale-up to high circuit current and voltage combined with relatively low losses at high circuit current and voltage, arc-conductor-based switching devices prove very desirable, especially during turn-on, turn-off and surge current conduction.
In some implementations, the arc conductor may be configured to operate in a pressurized medium, such as atmospheric-pressure air, initially residing in the arc gap. This is desirable for ease of deployment and cost, but may also play a beneficial role as fluid-mechanical resistance to arc front propagation, thereby urging the arc front into a more dense, unified, well-ordered structure. The medium may play little to no role in sustaining a burning of the arc and is mostly forced out of the gap by the expanding arc plasma.
A combination of aspects of arcing geometry, electrode materials and arc energy are provided to enable reliable, stable burning of an arc at near atmospheric pressure. An arc of the present disclosure may be a metal vapor arc derived from cathode-spot-like phenomena on non-refractory cathode materials. Such cathode materials may not sustain thermionic emission temperatures so as to emit electrons and thereby ionize the gaseous constituents of the atmosphere which anyway may be of insufficient number density and improper location to sustain the arc. Generally, the intense heat, electron flux and vapor pressure of the arc-volatilized cathode material displaces the air and maintains an ionized-metal-vapor plasma column through the high-pressure dielectric medium (air) through which a net electrical current may flow.
There exist several examples of high-pressure arcs, such as gas-tungsten arc welding (GTAW), underwater wet welding and thermal arc plasma spray coating. In these examples, which may rely on either thermionic or non-thermionic electron emission from the cathode, and where in the present disclosure, which may rely on non-thermionic emission, an ionized-metal-vapor column is a kind of inter-electrode plasma of the arc. In order for this plasma column to be stable, it may be necessary that the outward pressure Pchan is greater than or equal to the inward pressure of the atmosphere or dielectric environment, Penvir. This inter-electrode plasma column pressure is not to be confused with the arc plasma pressure close to the cathode spots, which is thought to range from 10 to 100 atmospheres even when the arc is operating in a vacuum. Also note that, in certain fields of atmospheric arcs, for example GTAW, certain practitioners in related fields may use the term “cathode spot” to indicate the region of plasma column attachment to the cathode even when the cathode is known to be operating in the high-temperature thermionic emission mode. This usage is opposite of the meaning predominant in all other fields involving vacuum arcs or cold-cathode arcs, wherein the term “cathode spot” is synonymous with non-thermionic emission from cathodes that cannot sustain thermionic temperatures without melting or vaporizing. This latter usage and meaning is used consistently herein.
Due to the stochastic nature of most arcing phenomena, the pressure exerted by the inter-electrode plasma in the ionized metal-vapor-column or channel is time-dependent, so
P
chan(t)avg≧Penvir, 14)
where the time-average is over a critical interval tcollapse which is related to the speed of sound c in the air (or other medium) and a characteristic width dchan of the arc column or channel, roughly the time after which the column may collapse in the absence of the arc. Thus
tcollapsedchan/c. 15)
In some implementations, for uninterrupted arc operation in the high-pressure medium, the time-scale of arc current fluctuation in the inter-electrode plasma (the ionized-metal-vapor column) may be much shorter than tcollapse or that the amplitude of the current fluctuations may be small relative to the arc current in the column or channel Ichan. Generally it may be the case that
dchan∝[Ichan]n, 16)
where the exponent n may vary with conditions and may not be an integer. The width of the ionized-metal-vapor column may increase with arc current, which may desirably increase tcollapse according to Eqn. 15. An example explanation for the relationship Eqn. 16 is that additional arc current may heat the arc plasma column and tend to increase the pressure inside it (Gay-Lussac's Law), but, when Penvir is approximately constant, the width of the arc column may tend to expand (Charle's Law) to render Eqn. 14 an equality. Of course, the ionized arc plasma column is not an ideal gas at all, and the fluctuating nature of cathode spots introduce a time dynamic. The cathode spot phenomena occur at 1 to 10 μs time-scales, the arc plasma column heating phenomena react more slowly and the environment or media reacts still more slowly. At any one location, the P-V-T responses may be out of phase (not at equilibrium, hence Charle's and Gay-Lussac's laws are not exact but still indicate trends), but the arc column as a whole may (or may not) be in an apparent steady-state condition with respect to its interaction with the environmental medium.
In some implementations, with broad, substantially flat cathode and anode electrodes, as in
In some implementations, the required electrode area needed to accommodate a certain maximum arc conductor or switch current may be estimated with the assistance of Eqn. 3. Cathode arc spots may tend to avoid each other and maintain a certain distance of closest approach, dspot,min. Thus [dspot,min]−2 gives an estimate of the maximum number of cathode spots per unit area of cathode surface achievable. From this and Eqn. 3 one can estimate the required cathode electrode size. However, at extremely high switch currents or longer conduction event durations (>10 ms, >100 ms, >1 s or longer), the near-surface heating of the cathode may achieve a temperature at which cathode arc attachment becomes dominated by physical phenomena other than cold-cathode spot attachment.
The arc length larc is of equal concern as the characteristic width dchan of the arc column, for stability of one or more ionized-metal-vapor plasma columns through a high-pressure (˜1 atm) dielectric medium. The arc length is generally identified as the cathode-anode electrode spacing. Defining a coordinate system with the z-direction pointing from cathode to anode, there may be cooling of the plasma in the arc column by losses to the dielectric medium and recombination of charged particles in the column plasma also assisted by contact with the medium. This may tend to reduce Pchan(z) as z increases but instead dchan(z) may decrease (Charle's Law) to keep Eqn. 14 an approximate equality. If dchan(z) decreases too much before z=larc, that is, before attachment of the arc plasma column to the anode, a high-voltage spark instability may develop. The “tendril” of highly conductive metal plasma, if truncated close to the anode but not electrically attached to it, may behave like a needle or sharp point and may enable a spark between it and the anode by a combination of field-emission and dielectric breakdown of the medium at high field. This assumes that the electric potential between cathode and anode can rise to high voltage (100s or 1000s of volts or more) in the absence of a low-impedance arc nearly short-circuiting the cathode and anode. This may be the case in one or more applications of the present disclosure, since there may be a transfer of large quantities of electrical energy between high-voltage capacitors. An effect of such a spark may be to re-heat the arc plasma column and re-establish a low-impedance arc column between anode and cathode. A spark may also have the effect of blowing apart the metal vapor plasma of the arc column thus destroying it permanently. A high-voltage spark may also vaporize and ionize some electrode material and thus re-strike an arc. Note that this scenario of a low-impedance arc plasma column deteriorating into a spark may only happen if the cathode-to-anode voltage is not otherwise “clamped” to low voltages (the 2 to 50 volts considered advantageous in the present disclosure). The cathode-to-anode voltage may indeed be clamped if there are multiple arc plasma columns connecting the cathode and anode, as was mentioned above. In that case, if one arc column develops too small a dchan size, it may simply die out rather than give rise to a spark. If there is only one metal vapor plasma column forming the arc contact between cathode and anode, there may exist a set of criteria for stability of that column. Whether one or many arc columns exist, an arc length larc may be selected according to the above criteria, and others such as may become recognized, in order to desirably avoid spark instabilities and to promote a continuously-burning, low-voltage and low-impedance arc discharge.
There may be a certain ratio flow of an arc plasma column characteristic width dchan to an arc length larc above which the arc column may be stable in a high-pressure medium (˜1 atm) and may have high conductivity and low impedance.
d
chan
/l
arc
≧f
low 17)
From Eqn. 16, whether for a single arc column or in the aggregate for multiple arc columns, the total time-averaged cross-sectional area Achan of arc column, where approximately Achan∝[dchan]2, may increase as total arc current increases. A similar expression as Eqn. 17 for arc column stability could be developed substituting Achan in place of dchan. Therefore another condition for arc stability at low electrical impedance in a high-pressure medium is
l
arc,maximum
∝[I
arc]n, 18)
in view of Eqn. 16, that is, the maximum stable arc length increases with arc current. There appears to be no loss of stability if arc length is shorter, provided that, e.g., the sheath, pre-sheath, plasma jets and initial arc column structures shown in
In some implementations, arc-enhancing materials may be used. An arc enhancing material may be favorable for sustaining, e.g., cold cathode arc spots. This means that cathode spots may exist with lower arc current per spot and at lower arc voltage overall. A material having these arc-enhancing properties has, among other characteristics, a low cohesive energy of the atoms in the solid, low ionization energy and large cross-section for electron-impact ionization of the free atoms in the vapor phase. The low cohesive energy may (or may not) be accompanied by a low melting temperature, low boiling temperature and a high vapor pressure of the arcing solid. The resulting arc plasma channel (or column) connecting cathode spots to an anode is characterized by high plasma density, low electron temperature, high current-conducting capacity and low plasma impedance. Together, arc spots burning on arc-enhancing materials and the plasma columns they produce tend to provide an arc conductor with low arc burning voltage, as presented to the external circuit being served by the arc conductor. This low arc burning voltage is a desired, though not limiting, mode of arcing for practicing the disclosure. For an example of the opposite, some aspects of some implementations of the disclosure make use of materials that cause a higher arc burning voltage, which may be called arc-limiting materials. An arc may preferentially burn on an electrode comprising arc-enhancing material rather than on a surface comprising arc-limiting material. As used herein, an arc-limiting material may either be a) a perfectly good electrical conductor that is readily able to sustain an arc, just at a few volts higher arc voltage than an arc-enhancing material, or b) an insulator or other surface unsuitable for arcing except under extreme conditions (undesirably high arc voltage of 100s or 1000s of volts). The tendency for an arc to preferentially burn on an arc enhancing material means that, unless otherwise prevented, an arc burning on an arc-limiting material may “jump” to burn on nearby arc-enhancing material(s). This arc jumping or “transfer” phenomenon may be mediated or influenced by an arc propensity contrast between arc-enhancing materials and arc-limiting materials and may be used in certain aspects and implementations of the disclosure.
Turning now to an explanation of arc-enhancing and arc-limiting materials, most of the pure elements have been surveyed and found that cohesive energy ECE of the solid correlates well with arc burning voltage Varc or Varc,min. By “solid” is meant generally a cathode electrode material upon which an arc is sustained at less than thermionic electron emission temperatures via cold-cathode arcing.
Arc-enhancing materials may promote efficient and rapid expansion or spreading of a width or area of an arc column during propagation of an arc to fill an arc gap. The low arc current per spot for arc-enhancing materials may lead to proliferation of many spots, which gives an opportunity for spot mobility and spreading out, since spots repel each other to a certain degree due to mutual interaction of their self-current magnetic fields. Also, arc jets from arc-enhancing materials may produce copious quantities of metal vapor having relatively low ionization potential and high ionization cross-section, at least for the higher-Z atoms. The large production of metal vapor helps displace air or other medium in the arc gap, which generally may not be as readily ionized as metal vapor.
In some implementations, Arc-limiting materials may include, e.g., Be, C, Si, Nb, Mo, Hf, Ta and W, their alloys and compounds. Many of the common structural metals, their alloys and many of the solid-solid contact metals, such as Al, Ti, Fe, Ni, Cu, Zr, Ag and Au, are also arc-limiting compared to the basic group of arc-enhancing materials: Mg, Se, Sr, Zn, Cd, In, Sn, Sb, Sm, Yb, Pb and Bi. The arc propensity contrast between these three groups is substantial. Approximately 5 volts difference in Varc and >2 eV/atom difference in ECE separates each group from its nearest other group. Since arcs comprise 102 to 109 or more amperes, a 5 volt difference in Varc translates into a 500 watt to 5 GW (giga-watt) difference in electrical power expended in the arc. At Iarc between 108 to 109 A, each second Iarc/e≈NAvogadro of vaporized atoms and ions may be involved in the arc, which at an ECE difference of 2 eV/atom translates into ≈0.2 MJ difference in electrical energy required merely to extract atoms from the arc electrodes. Here e is the electronic charge and NAvogadro is Avogadro's number. Some implementations of the disclosure may use this effect to transfer a spark between arc-limiting Ni, Ag, Au or other solid-solid contact metals into an arc in an arc gap comprised of arc-enhancing Zn, Sn, Bi or other materials.
In some implementations, arc-enhancing materials may play an additional role within the present disclosure. In a metal-vapor arc operating at near 1 atm pressure in air, chemical reactions of metal with oxygen in the air may be inevitable. These are of little concern during actual burning of intense arcs because most oxide reaction products may not be stable at arcing temperatures, and air is mostly excluded by the arc so such reactions are a minority process anyway. However, as an arc is extinguished, air may return and bring oxygen which may react with hot electrode surfaces and fresh metal-vapor deposits. Oxide layers may form which may make striking an arc difficult the next time the switch is used. A related concern is longer-term, ambient-temperature weathering and corrosion of the electrode materials. For both concerns, arc-enhancing materials may be selected that tend to form electrically conductive or semi-conductive oxide layers. These oxide layers may be self-limiting in thickness of their growth, also called “passivating”. Among the elements useful for arc-enhancing materials having low cohesive energy, Mg, Se, Zn, Cd, In, Sn, Sb, Sm, Yb, Pb and Bi, almost all may have modestly conducting or semi-conducting oxides, especially when a) the O-content is lower than in the stoichiometry of the most fully-oxidized compound, b) the atomic structure is amorphous or nanocrystalline, c) the morphology is thin-film or polycrystalline with significant grain boundary disorder or d) the electronic band structure is non-ideal due to impurities, alloying elements, dopants, vacancies, lone-pair electrons and the like. Exactly these sorts of non-ideal oxides do form under the circumstances prevalent in the switch of the present disclosure. Some oxides formed by these low cohesive energy arc-enhancing elements may be relatively unstable, that is, they themselves have one or more of the following properties: low heats of formation, low melting/decomposition temperatures or low cohesive energies. Low stability may mean that high temperatures, electron bombardment, ion sputtering, ultra-violet irradiation and/or other effects associated with exposure to arc plasma may easily decompose these oxides and render them ineffective in inhibiting plasma conduction. Table 1 data shows that indeed oxides of the low-cohesive-energy arc-enhancing elements (metals) have indicators of lower stability than the examples of refractory oxides included; in the cases of ZnO, MgO, In2O3, Sm2O3 and Yb2O3 the oxide melting points are quite high, but it is considered unlikely that any oxide may be fully-formed, so stability may still be low. Experience with two of these, Mg and Bi, has shown that striking of arcs after prior running of arcs and long exposure to air may be easier and these principles may hold not only for the elements listed above but other elements, alloys and compounds with identifiably similar oxidation and oxide characteristics. It is an aspect of the present disclosure that arc-enhancing material is constructed onto the cathode electrode surface but may be distributed to all arcing surfaces, especially including the anode, by plasma jet, thermal evaporation and other arc spot mechanisms, by the action of the arc itself, and thus provide environmental protection for the switch and ease of striking arcs.
In some implementations, another example role of arc-enhancing materials in the present disclosure may be as a striker material. The conductive striker material that short-circuits the anode and cathode to initiate the arc may become vaporized, incorporated into the general inter-electrode metal-vapor plasma and deposited as a metal film on various surfaces of the switch when the arc is extinguished. Initial vaporization of the striker material may be due to Joule heating from anode-to-cathode high current flowing through it. Subsequent heating of striker material may be due to contact with the intensely hot metal vapor of the arc column plasma. Even if unmelted pieces of striker material fall onto the anode or cathode surface, those may become melted, vaporized and incorporated into the general inter-electrode plasma. Even if unmelted pieces of striker material that fell onto the anode or cathode surface do not become fully vaporized during one operational cycle of the switch, they may fuse to the surface and form bumps or protrusions which may attract arc activity in subsequent operational cycles of the switch and may eventually be vaporized and distributed.
The mechanical form, size, diameter, length, mass, cross-section, material resistivity, material heat capacity and so forth of the striker material used to initially strike the arc may be chosen such that the striker may vaporize to a satisfactory degree given the open-circuit voltages, arc power levels, arc duration, arc energies and the like that a particular switch is designed to handle or conduct. It is a convenience feature that a relatively minor, consumable element of the switch, the striker wire or rod, may be swapped out to allow one electrode geometry to work successfully with a wide range of arc power and energy levels.
Vaporized striker material may be used to replenish arc-enhancing material within the switch that may likely be lost to the open sides or edges of the arc gap during repeated use of the switch. A variety of methods of the present disclosure may be used to assure that an adequate quantity of arc-enhancing material is provided to the interior of the switch. Without limitation, some of the methods are multiple strikers, continuous feed of striker material even after the gap arc is fully running and selection of a diameter and mass of the striker component.
In some implementations, an overall curvature of the arc electrodes and their corresponding gap may be provided, where a self-current magnetic constriction of the arc column decreases. This curvature may also include the increasing pattern of gap length larc(r) with respect to lateral distance r from a location of first arc ignition.
A possible limitation upon scaling up electric current carried by arc conductors and arc apparatus in general may be the self-current magnetic field of arcs. At large arc-conducted currents, e.g., above ˜1 to 10 kA, self-current magnetic constriction of the arc column may occur. Photographs of arc constriction are shown as
B=(μ0/4π)·(q/r2)·v×r, 19)
where μ0 is the permeability of vacuum (1.257×10−6 kg m C−2 or μ for a non-vacuum medium) and r=|r|, the distance from the charge. Because of the vector cross product, the resultant lines of flux form circles around the direction of motion v with the plane of the circles perpendicular to it. If a multiplicity of charged particles move in a time sequence along a path through a plasma, this is an electrical current, and lines of magnetic flux form similar circles around and perpendicular to that current path. One might say the successive flux circles around a current path form a flux tube, but the flux direction is perpendicular to the long-direction of the path. When two or more current paths lie near each other, neighboring flux circles sum-and-cancel according to their local direction at overlap. The resultant or net field is the origin of the self-current magnetic field of arcs, and it operates all the way from the individual arc spot scale up to the largest scales. In a typical flat, planar arc gap, most of these current paths are parallel to each other. The flux circles around these paths mostly cancel interior to the arc column, and the resultant field looks like a big flux circle (or flux tube) around the whole arc column, the plane of said circle being perpendicular to the direction of flow of charges in the arc gap. Because of this net self-current magnetic field, individual moving charges near the edge of the arc column experience an additional force F substantially equal to the magnetic term of the Lorentz force
F=q·v×B. 20)
This force accelerates electrons in the arc plasma much more strongly than heavy ions, and the average effect is to oppose electron motion laterally out of the arc column and urge motion laterally toward the center of the arc column. Because of space-charge effects, positive ions may not migrate where electrons cannot accompany them, so the arc plasma may not expand laterally. At still higher arc electric currents the arc column actually gets narrower, and this is the origin of the magnetic constriction of arcs at high arc current. As mentioned, such lateral constriction of an arc column may not be preferred for cases in which very rapid expansion of an arc column is desired, but it may be used to good effect in several ways, if due care is exercised to avoid excessive constriction of the arc with possible subsequent high-voltage arc instabilities. Arc constriction due to self-current magnetic fields may be counteracted within the disclosure by several methods. For example, segmented electrodes of opposite-polarity tiles may be used where these self-fields cancel laterally. Additionally/alternatively, the use of a bucking or counter-wound electromagnet coil(s) energized by the current through the arc conductor may be beneficial. In some implementations, at least one of the arc electrodes may be curved and thus curving the paths of charged particle motion and current flow between electrodes such that their magnetic fields do not sum-and-cancel to form resultant magnetic fields which are detrimental to broadening of arc column area or expansion of arc footprint on an electrode(s). Those skilled in the art will appreciate that other methods may also exist and are contemplated.
Another example role of arc-enhancing materials may be as damage-mitigating, anti-seize/weld and arc re-striking layers on the electrodes in case the electrodes touch each other while electrically energized or very hot. Some arc-enhancing materials listed above and in
Many known conventional, prior art means of initiating an arc and of extinguishing the arc may be used with an arc conductor of the disclosure. For example, a pair of parabolically-curved electrodes between which an arc is ignited (e.g., struck) by insertion of a conductive gap-breakdown material. As another example, a hollow cylindrical outer arc electrode and an off-center rotatable inner arc electrode having a spring-loaded lobe which strikes the inside of the outer electrode, thus drawing and initiating an arc. Regarding extinguishing arcs, an example application circuit may include either an electrical power source or an electrical load with an arc conductor in series between them with source or load configured such that the arc is self-extinguishing after circuit-making or breaking surge currents or high voltage transients subside. An arc conductor of the disclosure may self-extinguish if the circuit voltage across the arc gap decreases below about 10 volts or a current drawn by the external circuit decreases below about 10 A, by way of example and not limitation. A charged capacitor is an example of an electrical power source and a discharged capacitor is an example of an electrical load from/to which only a fixed amount of charge may be transferred, so that the arc is self-extinguishing. Further regarding extinguishing arcs, various implementations of the disclosure may be advantageously combined, such as electrode separation, arc chutes, magnetic deflection and quenching due to the arc medium. These are examples only and not meant to limit the scope of the disclosure.
Some implementations may be used as arc assistors, to protect switches known to be susceptible to high current surges, high voltage transients, high dissipated power or heat and other limitations described above. Surge or in-rush currents and high voltage transients in electrical circuits may be conducted or shunted by electric arcs. Switchgear embodying the principles of the disclosure use arc conductors which are substantially undamaged by arc-conduction of current surges and voltage transients associated with the making and breaking of a circuit. Arc conduction according to the disclosure may also be used to protect other circuit components besides switchgear, such as semiconductors, connectors, sliding contacts, batteries, lamps, resistors, and so forth, without limitation, by shunting high current around such components or clamping high voltage transients to substantially equal the arc burning voltage. Additionally, current surges or voltage transients may be conducted by arcs according to the disclosure whether the surges or transients originate from circuit switching or from another cause, such as, without limitation, change in the electrical supply, change in the electrical load, magnetic induction or electromagnetic pulses (EMP).
In some implementations, an arc conductor of the disclosure may serve as substantially the only conductor in a switch. In one or more other implementations, an arc conductor of the disclosure may serve as the principal conductor of a switch substantially during making and/or breaking of a circuit while other contact or conduction means serve as the conductor during long-term closure of the circuit. For this type of implementation, an example is given of an arc conductor of the disclosure residing in a separate device, a switch assistor, which serves a commercial off-the-shelf (COTS) switch by acting as the principal conductor substantially during making and/or breaking of a circuit while the COTS switch serves as the conductor during long-term closure of the circuit. In this implementation, an arc conductor of the disclosure shunts or bypasses, and thus protects, the switch from surge or in-rush currents and high voltage transients that may occur during or related to switching. Both mechanical-contact switches and semiconductor (solid-state) switches may used with an arc conductor (switch assistor) of the disclosure. In combination with known high-current semiconductor switches, which may often be parallel-connected gangs of semiconductor junctions, the shunt or bypass function of the disclosure may protect from unequal sharing of current among the several junctions during turn-on and turn-off. Runaway conduction by one of the parallel-connected junctions, which may result in its failure, formerly may have required careful matching of the junctions or elaborate control circuitry, which now may be eliminated in part or in whole because of arc shunting during turn-on and/or turn-off.
In some implementations where an arc gap is in electrical parallel relation to a closed and conducting prior art switch, and it is desired to protect the switch with an arc conductor while opening the switch, further aspects of the disclosure may include one ore more apparatus and/or methods to initiate an arc across an arc gap which is short-circuited to nearly zero voltage by the closed switch. One example implementation may employs a variable resistor to increase the voltage across an arc gap so that an arc can be struck (e.g., ignited) and established. A two-valued variable resistor that may include a helical spiral-wound sheet metal strip and/or accordion-folds of sheet metal may optionally form the resistor and be mechanically coupled to a drawn-arc ignition mechanism. In this way an arc may be already burning before beginning to open the switch. In another example implementation, the conventional switch may be a semiconductor device such as a transistor, where the voltage across the arc gap may be increased by putting the semiconductor junction into a state of partial conduction, after which an arc may be ignited in the arc gap, and after which the semiconductor switch may be opened.
In one or more implementations, the ruggedness, damage resistance, robust operational characteristics, simple construction and ease of scaling to large size of arc conductor components are advantageous and beneficial characteristics. The phenomena of arc spots on an arc cathode, ion bombardment, electron bombardment and intense heating, among others, are indeed “destructive” of at least an outer layer of material on arc electrodes. These lead to pitting of an electrode surface, ion sputtering, erosion of material, vaporization of material and thermal annealing or breakdown of material structures and chemistries, among other possible end effects. However, these are not substantially destructive of the function of arc electrodes or an arc gap. For example, pitting and roughening of arc electrodes are not a problem since a) locally flat electrode surfaces are not used for any function (such as solid-solid current conduction), b) the roughened surface may actually encourage arc activity and c) the roughening is self-limiting because the protruding asperities on electrode surfaces attract arc activity thus becoming eroded or melted flatter. As another example, erosion, vaporization, macroparticle ejection and “arc jetting” of material away from arc electrodes do ultimately restrict a usable lifetime of an electrode, but, according to optional aspects of the disclosure, this loss of material is drastically slowed by exchange of material back-and-forth between large-area, closely-spaced electrodes and may actually be used to disperse arc-enhancing materials over desired arcing surfaces. Also, eroded electrodes may be readily replenished by addition of material (which gets dispersed, as said) and by easy replacement of arc electrode inserts. In an open arc, that is, a vacuum arc in which the cathode and anode are far separated, cathode vaporization has been reported to be on the order of 10 μg/C, as measured by weight loss, but as mentioned this may be significantly reduced by “recycling” material within the relatively closed arc gaps of the disclosure. Generally, arc electrodes and their arcing surfaces comprise relatively simple bulk shapes of well-behaved, rugged solid materials. The function of arc gaps comprising such electrodes is not particularly sensitive to variations, distortions or other changes in the geometry or spacing of such electrodes; e.g., +/−1 mm changes of dimensions may normally be insignificant. Hence the operation of an arc gap is robust and tolerant of aging and wear of electrodes. For these reasons and because of the intense energies liberated in an arc gap, minor (e.g., <1 mm thick) contamination by dust, water, grease/oil and other incidental environmental debris may normally not permanently affect arc operation, but rather the foreign matter may be destroyed or burned away. Scaling up of an arc gap is often as simple as enlarging a plate or pipe section. Due attention may be paid to transport of electrical current and heat to/from an electrode and its mechanical support structure. Likewise, cooling of electrodes may be designed, and this may involve considerations of thermal conductivity and conductive cross-sections of electrodes and supports. Arc hardware may be robust and tolerant of modest under-design or operational overloads, even to the extent of partially melting or gravitational slumping of heat-softened electrodes; in such a case, the arc conductor may continue to work and even repair itself via redistribution of arcing material within the arc gap. As those skilled in the art of arcing may appreciate, the above list of characteristics of arcs and arc apparatus is not exhaustive but intended to be indicative of the relative ease by which arc conductors may be made rugged, damage resistant, operationally robust, simple and scaled to large size. By contrast, currently known switches in which arcing is an unwanted phenomenon on solid-solid conductor contacts, may have a very difficult effort to maintain good switch contact properties in the presence of arcs.
Arc conductors may include arcs burning over broad surface areas of arc electrodes (e.g., the arc attachment footprint) with concomitantly broad arc plasma columns. For non-thermionic cathodes, the terms broad arc attachment area and broad arc footprint area may be described generally to include the entire macroscopic region of the cathode surface having significant numbers of cathode spots persisting over many spot lifetimes, not the cathode attachment at a microscopic cathode spot nor even the sum of the areas of all such microscopic spots. Broad-burning arcs may conduct large circuit currents via mechanisms such as explained relative to Eqn. 1, among possibly other mechanisms. Broad-burning arcs may provide low arc burning voltage and hence low power loss or energy waste in the arc conductor. High arc current and low arc voltage is consistent with a low arc impedance or resistance.
In some implementations, the time-domain dynamics of arc conductors may be managed. The shape of the arc electrodes, at least in part, may promote both lateral spatial expansion of an area of an arc footprint on an electrode, along with the area of its associated arc plasma column, and time-domain stabilization of an arc in an arc gap. Both of these desirable, promoted properties may work within a single current pulse or conduction event of an arc gap. That is, an arc may be initiated at one or more small, localized positions on an arc electrode or in an arc gap, then grow or expand to more fully fill the arc gap. Also, once burning over a broad area, an arc is desirably time-stable with respect to low average arc voltage and high average current density conducting capability. Similarly, when the arc current driven by the external circuit is decreasing, the arc column and arc footprint may contract without time-instability, on-average, while maintaining low average arc voltage and high average current density. Note the term “average” is used to denote a time-average in explicit recognition of the often-observed phenomenon that many features of arcs may be relatively unstable on a short time scale, such as sub-microseconds to tens of milliseconds or more, without limitation. By “time-stable”, it is meant sustained properties substantially as described over periods of, e.g., 10 μs to 10 s. Thus, a provided voltage between the first and second electrode may be less than or equal to 50 volts, when time-averaged as described.
By contrast, the opposite case may be undesirable. If the external circuit being served by an arc conductor is capable of sustained high voltages and comprises large stored energy or high electrical generating power, then the absence of some or all of the attributes discussed above may result in very damaging conditions for the arc conductor and possibly surrounding areas. An absence of these attributes may imply, at least, a concentrated arc footprint area and/or arc column area and a high arcing voltage. The absence may also imply time-transient (shorter that time-sustained) impulses of current which do not, among other things, deposit sufficient heat into broad electrode surface areas to vaporize metal atoms or allow sufficient time for required arc plasma column structures (e.g., cathode spot jets, a cathode plasma sheath, a pre-sheath ionization zone and an anode plasma column) to become established and facilitate low-voltage arc burning. If under these undesirable conditions, high electrical currents are forced through the arc gap, then large electrical power and high quantities of electrical energy may be undesirably deposited in the arc conductor apparatus, as opposed to being desirably deposited in the circuit load or desirably cut off altogether (e.g., disconnected). Such undesirable and potentially destructive arcing modes may be of several types, but at least one likely mode is an “arc flash”.
In some implementations, the present disclosure may provide arc conductors which avoid any type of arc flash or destructive arcing mode, but possible occurrence of fault conditions or equipment misuse may suggest that arc conductor equipment implementations of the present disclosure may be evaluated therefore. Thus, after the arc is established between the first and second electrode, the arc conductor may sustain continuously over time, as long as the arc current is increasing, an expansion of the arc footprint and arc column, wherein the expansion of the arc footprint and arc column may exclude pulsation to zero current, chopping, flicker to zero current, spark instability, plasma extinction and re-ignition, fluctuation to zero current and any time-domain instability of the arc involving the arc current becoming zero. Likewise, after the arc is established between the first and second electrode, the arc conductor may sustain continuously over time, as long as the arc current is decreasing, a contraction of the arc footprint and arc column, wherein the contraction of the arc footprint and arc column may exclude pulsation to zero current, chopping, flicker to zero current, spark instability, plasma extinction and re-ignition, fluctuation to zero current and any time-domain instability of the arc involving the arc current becoming zero.
Broad-burning low-voltage arcs and desirable spatial and time-domain dynamics of an arc in an arc conductor may be promoted. However, not all aspects are and no single aspect is necessary in any one desirable implementation. One specific aspect is the already-explained action of arc-enhancing electrode materials concerning low arc voltage. The basic process of arc column broadening consists of energy from the external circuit deposited or absorbed at a localized first arc ignition location(s) in the arc gap being used to vaporize electrode material which is, in turn, ionized, heated and spread throughout the arc gap, thereby both expanding the burning arc and displacing or pushing out the former medium in the arc gap, usually air. The process is in some sense a feed-forward or positive-reinforcement process, because the newly ionized metal vapor and burning arc zones conduct even more current and absorb even more energy from the external circuit, thereby vaporizing increasingly more electrode material and creating yet more intra-gap plasma. This may happen very quickly (e.g., <<1 s), because, with cold-cathode arcs, there is no delay while waiting for bulk electrodes to heat up. This rapid feed-forward lateral expansion of the arc may be desired. Indeed, it cannot, or at least may not, be stopped, because there is risk of dielectric breakdown, sparks or high voltage flashes, if high circuit potentials could exist across the gap of the arc conductor. Such localized high voltage breakdowns are disfavored because they may be transient and/or may have mobile localized or filamentary electrode attachments. Arc modes such as these may not deposit enough sustained and broad-area power on the electrodes to vaporize sufficient electrode material to create or sustain a broad-area, quiescent, stable arc of arbitrarily-long time duration.
In some implementations, the arc may be anchored at a fixed location or region on the electrodes, as described below. This arc anchor location may also be the location of first ignition of the arc and ideally stays within the footprint of the arc column as it broadens. A number of example principles and aspects of the disclosure are enumerated below regarding rapid feed-forward lateral expansion of an arc in an arc conductor, along with means of controlling a rate of expansion. The feed-forward lateral expansion of the arc may stop when the external circuit can no longer provide more current, though in one or more implementations a rate of arc expansion may be controlled, modified or carefully limited. This means that an impedance of either the external circuit's source or load may limit the current through the arc conductor. In some implementations of the disclosure, the impedance of the arc conductor may be negligibly small compared to the impedances of the external circuit. However, during a surge of current after an arc is established between the electrodes, the arc gap may be the limiting impedance, and this impedance is adjustable according to principles of the disclosure. Principally, the impedance of the arc gap is determined by a lateral extent or a cross-sectional area (the already-achieved degree of expansion) of the arc column and/or arc footprint upon the electrodes within the gap. Examining Eqn. 1, an arc of smaller footprint may have a smaller value of Nspots which may result in a larger Rarc, and conversely an arc of larger footprint may have a larger value of Nspots and may present a smaller Rarc to the external circuit. Moreover, at any given footprint area, both the absolute arc resistance and also a rate of change of this arc resistance are adjustable, within a range. An absolute resistance of an arc in an arc gap may be adjustable by selecting a burning voltage of the arc, among possibly other means. This voltage may be influenced by parameters such as the length of the arc gap (e.g., arc length), several properties of the medium in the arc gap (e.g., such as electron affinity and heat capacity), external magnetic fields imposed in or near the arc gap, and, as described above, selection of electrode materials as arc-enhancing or arc-limiting. A rate of change of arc resistance may be adjustable by selecting a rate of expansion of the burning arc within the arc gap, among possibly other means. This rate of expansion may be influenced by the same parameters as affect arc resistance, plus others. This rate of expansion may also be influenced by surface chemical reactions and compounds at electrode surfaces, a variation in a length of the arc gap across an arc electrode, other properties of the medium in the arc gap (such as tendency to chemically react with electrode surfaces) and placement or injection of temporary modifiers to arc-enhancing or arc-limiting properties of the arc gap, among possibly other means. In general, these additional influences upon rate of expansion of the burning arc may have little or no effect on the absolute resistance of the arc after full expansion of the arc column has occurred. It may be desirable to extend a desired mode of arcing to a desired range of arc conductor operational parameters.
In some implementations, how cold-cathode arcs expand in intensity (e.g., arc column area) or increase in arc current over time may be envisioned as: 1) an arc gap completely filling its electrode area with arc plasma “instantly” at a low current density Φarc,low [MA/m2], then Φarc(t) increases everywhere over time; and 2) an arc gap starts with a small patch of its electrode area filled with arc plasma at a characteristic, nearly maximum current density Φarc,char, then the size of the patch expands over time to fill all the electrode area. Regarding 2) above, this mode of expansion may be urged by providing an arc gap having broad-area electrodes, varying arc gap lengths as a function of lateral location within that broad gap area, a location of minimum gap length, smoothly increasing gap length as a function of lateral position away from the location of minimum gap length and an first arc ignition location substantially the same as the location of minimum gap. An impedance of an arc may be lower when gap length is shorter, and an arc may burn preferentially at this location of shorter gap. If there is adequate driving potential and supply of electric charge, the arc may increase in plasma density or charge carrier mobility until Φarc reaches some value, Φarc,expand, at which it may be energetically “cheaper” (that is, provides a lower impedance current path) to expand a breadth or area of the patch of burning arc rather than increasing Φarc still higher.
A direction of lateral expansion of a patch of burning arc may be controlled, or at least urged, by gap lengths. The arc patch may first expand in a direction of least slope of increase in gap length. As an example of an arc propagation or expansion calculation by which an arc conductor may be matched to a given external circuit in its rate-of-rise of conducted current after arc establishment, consider a case in which the slope of increase of gap length is the same for 360° around the first arc ignition location; that is, the arc patch may expand as a circle. Assuming for example purposes only the arc is driven by a high-energy (high-voltage) circuit that could supply current with unlimitedly high dIsource/dt, then a dIarc/dt may be limited by some arc propagation speed, carc-prop. A speed of arc propagation may be modulated or controlled as, or at least likened to, a plasma “front” moving into the un-ionized medium that filled the arc gap before arc ignition. The speed of movement of such plasma front, carc-prop, may be limited by a speed of sound, by a cathode spot migration speed or by other parameters, such as ambipolar electron and ion diffusion constants, De and Di. Given the likely violent and energetic nature of an initial dielectric breakdown of a high-voltage arc gap, a diffusive model is considered unlikely, and models for fluid or material transport from detonation or explosion theory may give more relevant speeds. As a benchmark or reference datum, the speed of sound in air, carc-prop=303 m/s may be used. A cold-cathode arc's footprint on the cathode may be envisioned to be an expanding circle whose radius is expanding at a rate of carc-prop. The expanding-radius circle may have an area Aarc(t) giving an arc current of Iarc(t)=Achan(t)·Φarc,expand, where Φarc,expand, is a characteristic current density [MA/m2] conducted through the arc plasma. Note that Φarc,expand may not be a maximum current density sustainable in the arc gap but rather the density at which it is more energetically favorable to expand the area of the arc column rather than increase Φarc further, as explained above. Starting at t=0 with a current of Iarc,min, which implies a radius r0=SQRT(Iarc,min/(π·Φarc,expand)) and an arc column area of A0=π·r02, an exact expression, given the physics assumptions, is:
I
arc(t)=Iarc,min+Φarc,expand·[2π·SQRT(Iarc,min/(π·Φarc,expand))·carc-prop·t+π·carc-prop2·t2]. 21)
Eqn. 21 is dominated by the t2 term and the two constants Φarc,expand and carc-prop. Neglecting the term linear in t, using Iarc,min=10 A, carc-prop=303 m/s (speed of sound in air) and Φarc,expand=10 MA/m2 (which is believed to be easily attainable even without arc-enhancing materials), a representative rate-of-rise of Iarc(t) is given in
From TABLE 2 it can be seen that after 1 millisecond, the arc plasma may be conducting 2.8 MA and filling an electrode area of ˜0.5 meter×0.5 meter, if square. This electrode size may be undesirably large for some applications, but expansion of plasma column area may be stopped at any size, if the external circuit's source and/or load provide/require less peak current. The above calculation assumed an unlimited source and load. Also, as pointed out, Φarc,expand may be much less than any maximum limit of Φarc. This means that, if the arc plasma fills the electrode gap with plasma at Φarc,expand current density and the external circuit forces still more current, Φarc can then increase further to accommodate the higher Iarc without further increase in Aarc, albeit probably at slightly higher Varc. Arc-enhancing materials may provide higher Φarc in the range of, e.g., 50 to 1000 MA/m2, without limitation, which may dramatically reduce the electrode area required, and concomitantly may produce a faster rate-of-rise for Iarc(t).
Arc propagation speed, carc-prop, may be directly manipulated by factors under the designers or end-user's control. Different arc-enhancing (or limiting) materials, different surface chemical reactions and other factors may strongly affect arc propagation and burning behavior through properties such as arc spot migration speed, change of local work function, charge trapping or polarization, change of a surface energy, modification of a sputtering yield, modification of a secondary electron coefficient and other effects.
The apparatus of
A first arc ignition location may be provided at a location of minimum gap length between the electrodes. The location of minimum gap length and first arc ignition location coincides with the nested apexes of parabolic arcing surfaces 221 and 231 in
In some implementations, the gap length may be minimized so as to maximize a ratio of arc channel or column width dchan or area Achan divided by an arc length larc. Arc length may be generally the same as arc gap length and measured in the same direction, but variants of the disclosure allow an arcing plasma column, or portions of it, to be tilted in the gap and thereby allow larc to t exceed lgap. Generally, a high value of this ratio is favored so as to conduct large arc currents or high arc current densities at low arc voltage while simultaneously reducing a tendency for high-voltage plasma instabilities to form.
For operation, the arc conductor apparatus 200 detailed in
In some implementations, an orderly expansion of a cross-sectional area or a broadening of the arc column may be provided, and an orderly contracting of the area of the arc column, as arc current increases and decreases, respectively. By orderly it is meant, among other aspects, that the arc patch on the electrode(s) stays unitary and does not split or fragment into hot spots or tendrils of plasma. In other aspects, the arc front retraces its expansion path during recession and the arc footprint always includes, and may be centered upon, the first arc ignition location, though these aspects are optional. In yet other aspects, arc attachment at electrode surfaces is mobile, facile and exhibits current density which is substantially uniform or smoothly-varying with distance along the surface of an electrode, except near front 245. Orderly management of the arc footprint may discourage high-voltage plasma instabilities of the arc and thus extends an operational range of switch 200. As an example of desirable order of arc expansion and contraction in the apparatus of
In another aspect of orderly and free expansion of arc cross-section and footprint, the switch or arc conductor of
The shape of at least one of the first and second electrode may be configured in one or more regions to modify a degree of the self-current magnetic constriction of the arc column. In one or more implementations, the disclosure provides controlled self-current magnetic constriction of the arc column, or, more precisely, provides for controlled “urging” or forces on the arc column using the self-current magnetic fields. A degree of self-current magnetic field urging may be designed for and implemented to provide containment forces upon the expanding arc column, even if said forces do not entirely cease or reverse the expansion of the arc column. Moderate anti-expansion forces on the expanding arc column may be desirable for keeping the arc column or its plasma continuous, dense, well-defined and/or localized, as the column expands in cross-sectional area. When the current conducted between the arc electrodes decreases, the presence of moderate self-current magnetic forces may urge and assist the arc column and the arc foot print to contract in an orderly fashion, as defined above, and its plasma remain continuous and dense. The preference in the disclosure for a continuous, dense plasma column hinges on the principle that formation of new arc spots requires both a certain minimum level of energy input to the cathode surface [J/m2] and a dense plasma and plasma sheath close to the cathode surface; unstable gaps in plasma column risk losing one or both of these. These same forces may also be used to conform or confine the arc footprint to a certain shape of arc electrodes, to which the arc may not otherwise or naturally conform. In general, the strength of the magnetic urging forces is controlled by varying the shape of the electrodes, such as by varying the parameter “a” in r=a·z2+b for the electrodes of
The shape of at least one of the first and second electrode may be configured to change shape in one or more regions to modify (e.g., increase) strongly the degree of the self-current magnetic constriction of the arc column. In one or more implementations, an example of which is depicted in
The arc switch 200 implementation of
An appropriate baffle or trap (not shown) to capture such escaped vapor is disclosed elsewhere herein. Such baffle may also serve other functions, such as adjusting a back-pressure of medium 205, reducing acoustic emissions from switch 200 or filtering dust or other contaminants, among others. Notwithstanding the possibility of using electrodes made of thick-section arc-enhancing material, the implementation of
Arc ignition substance 710 may have other than the rod form depicted in
Electrical switching performance of a switch of substantially the size, design pattern and material content as the
As depicted in
An approximate heat-absorbing mass of the implementation of
Referring now to the results of TABLE 3 for electrical performance of the arc switch of
In some implementations, the conducted electric current between the first and second electrode may be configured to decrease towards zero in response to the moving arc column being expelled from the arc gap. For example,
In some implementations, it may be desirable to assure that substantially all of the plasma footprint and the plasma column are expelled from the arc gap between the first and second electrode, as the plasma expands and moves away from the location of first arc ignition 730 toward the open end or edge of the gap (depicted on the left of
The arc column in arc gap 210 may be configured to be compact, continuous and dense as provided in many implementations disclosed herein, but further configured to not fully fill the parabolic, cylindrically-symmetric gap 210 but rather to form a circular band-shaped footprint on each of first and second electrode and form an annular “dough-nut”-shaped plasma column. This plasma column is still continuous and dense but departs the location 730 of first arc ignition and leaves behind a void of plasma and a region in which the arc no longer burns. This expansion and shape of the arc plasma column is depicted in 2-dimensions in a time-progression in
In one or more implementations, this desired form and motion of the arc column may be accomplished by choosing arc igniter material 710 to be a relatively volatile arc enhancing material while constructing arc electrodes 220 and 230 out of relatively arc limiting materials. In this way, the volatile arc enhancing material gets driven by the heat and expanding motion of the arc away from first arc ignition location 730 out towards open ends of gap 210; the arc footprint follows the migrating arc enhancing material because the lowest impedance arc may exist wherever the arc enhancing material dwells on the surfaces of electrodes 220 and 230. As drawn in
While at least one of the above-noted implementations of
For some types of semiconductor devices, the voltage across the arc gap may be increased (to 20, 30, 50 volts or thereabouts) by putting the semiconductor junction into a state of partial conduction, after which an arc can be ignited and established in the arc gap and after which the semiconductor switch may be fully opened. In some implementations, in its various optional configurations, may solve those possible end-use needs for almost any type of switch and additionally employs an alternate first arc ignition means which may be more suitable for some end uses. In some implementations, selectable variability of the arc gap length may be offered.
These combine (along with other features and aspects) to provide both a broad arc plasma column or footprint and an orderly expansion (defined above) of an area or width of the arc plasma column as Iarc increases as well as an orderly contraction of the arc plasma column as Iarc decreases. All of these features and others promote broad, low-impedance, high-current, low arc voltage plasma columns, which in turn reduce power and energy dissipation in the arc switch and avoid high-voltage arc instabilities, all according to principles of the disclosure. As depicted in
However, as a design option, the off-parallel angle of the apex lines may be made larger, so that apex-to-apex gap length becomes larger than the off-apex transverse gap length, which may urge plasma to expand laterally before a plasma front in the plane of the apexes reaches the longitudinal end of electrodes 220 and 230 away from the location of ignition 705. Moreover, a degree of transverse curvature or generalized “radius” of curvature of electrode 220 or 230 (or both) may be varied along the length of these electrodes, not shown, which can further control a transverse-to-longitudinal gap length and thus control a longitudinal and transverse arc front propagation pattern in gap 210. Varying such arc propagation patterns may again at least affect a rate-of-rise of Iarc. Desirable variability of longitudinal versus transverse gap length may be implemented in many other ways without departing from the spirit of the disclosure. For example, elongated electrodes 220 and 230 need not be generally or grossly straight “bars” but may be curved in various circle-sections or crescent shapes, which may include curvature along the elongated direction of an electrode and in planes that change gap length at the apexes as a function of length along the electrode(s). For example, alternate arcing surface profile 222 of electrode 220 in the device of
Magnetic constriction of arc columns may also be mitigated in the implementation of
Some implementations may be advantageously configured with mechanically movable arc gap structures.
When inner electrode assembly 420 is stopped at an angular position near that depicted in
Functional and operational characteristics of an arc switch of type depicted in
In some implementations incorporating elongated arc electrodes as in
Electrically, an external circuit may be connected to apparatus 400 as shown in
Breaking or disrupting an arc that may be driven by a high open-circuit-voltage power source may be difficult, and this must be done with stringent attention to all possible stray arc conduction paths. In the implementation of
Construction details of elongated-electrode cylindrical arc switch 400 of
Grooves 411 are depicted only on one quadrant of cylinder 410 but may be provided everywhere on the interior. Likewise, similar structures to break up surface conduction paths may be provided on most surfaces of rotating electrode support 427 and on cylinder end closures 418, suitable shapes and placement of which may be known to those familiar with the art. Inner electrode 220, its rotating support 427 and its rotational drive shaft 425 may be considered a single assembly (420) and may be designed for easy replacement and low cost. Electrode body 220 may entirely comprise arc-enhancing material such as Sn, Pb or Bi, which are soft, low-melting metals. They may be hammered, pressed, forged, injected, cast or formed by other known operation into a mold to produce a desired shape. The shape may comprise an arcing surface profile similar to that depicted in
A rotary cylindrical implementation 400 of an arc switch 200 can also be configured as a switch assistor. As mentioned, an arc conductor switch 200 can solve the problem of surge currents and voltage transients causing damage to commercial-off-the-shelf (COTS) conventional, prior art metallic-contact or semiconductor-junction switchgear, in which case the arc switch may be termed a “switch assistor”.
A switch-closing operation utilizing switch assistor 400/500 starts from the state depicted in
A switch-opening operation utilizing switch assistor 400/500 of the present disclosure provides arc conduction in parallel with COTS switch 100 before opening 100, which may protect switch 100 from, by way of example and not limitation, inductive forward voltage spikes when a large motor or transformer is cut off.
Construction features and operation of variable resistor 500 may be explained with respect to
In operation, variable resistor 500 may change state from a low resistance (˜zero) state to a high resistance state in coordination with arc switch 400 to create switch-assistor 400/500. Generally, resistor 500 need be in a high resistance state only shortly before, during and shortly after ignition of an arc in 400 during a switch-100 opening operation; during a switch-100 closing operation, resistor 500 may stay in a low resistance state. Generally, resistor 500 may be in a low resistance state as a default, since especially if switch 100 is closed and load current is flowing, current may be flowing through 500 and power dissipated as Iload2·R500 in resistor 500 may normally be unwanted waste heat. Variable resistor 500 could be configured as a separate, stand-alone device, but a preferred implementation couples resistor actuator shaft 550 with arc switch shaft 415 to effect the aforementioned coordination of resistance state changes of resistor 500. Referring now to
In some implementations, much more adaptable and capable drive systems can be implemented. For example, rotary coupler 470 may also comprise a clutch, so that shaft 550 of resistor 500 may be rotated without moving rotatable electrode assembly 420, and friction ring/slip clutch 560 may allow rotatable electrode assembly 420 to move even though shaft 550 is at end-of-travel. Motive may mean completely different from motor-driven lead-screw or ball-screw may be used, such as pneumatic cylinder stroke, electromagnetic linear solenoid and numerous others. Since default or at-rest positions can be defined for both resistor 500 and rotatable electrode assembly 420, spring-loaded return to a standard position may be implemented, or a detent or latch can be provided to retain the moving component in an expected position. Such design may be beneficial in case of loss of information of the state of switch assistor 400/500.
A controller or operational/step sequencer means may be interfaced to switch assistor 400/500 and any appropriate sensors. Sensors for electrical current, temperature of resistive element 510 or electrodes 220/230, certain mechanical positions and other data may be useful for rapid operation and safe response in exception conditions. Though some step sequences can be mechanically, internally programmed as described above, an operation with several states and steps, such as the switch-opening operation of
An example implementation, e.g., of the metal-arc-based switch and moving electrical contact, may be used for charging and discharging high-energy (MJ, GJ and higher) capacitors capable of high power. Capacitor power refers to the speed of charging or discharging, which if taken as 0.1 second through a low-impedance load, may mean a power level of 10 MW, 10 GW and higher. A practical example of this preferred implementation is transfer of electrical energy quickly to capacitors in a locomotive of a moving electric train. The disclosure resides in apparatus components located both in the charging station and in the locomotive, as well as methods of their interaction to transfer motive energy to the locomotive. This implementation is by no means limiting, since many other types of vehicles other than trains, as well as many other devices and systems, may use the present disclosure for transfer of electric energy.
The general idea and nomenclature of rapid capacitor charging may be defined in the situation in which one energy storage capacitor charges another energy storage capacitor.
Further elements and functional aspects of switches 300 of the preferred implementation are depicted in
More detail of preferred striker assembly 700 is shown in
An issue for dual-switch 300 charging of one capacitor by another capacitor, as depicted in
A preferred variant of electrode shapes within switches of the present disclosure may be desirable to transfer large amounts of energy to loads such as locomotives, and such shapes are shown in
In some implementations, the present disclosure may be applied to other types of vehicles in addition to trains, such as automobiles and utility vehicles, as well as to portable, electric-cable-tethered and battery-operated appliances and tools. The case of the automobile benefits from an alternate implementation that combines anode and cathode runners or rails together and likewise combines anode and cathode shoes or sliders together. Such an arrangement is preferred for compactness and safety, and is feasible since the quantity of energy is considerably smaller than for a locomotive, for example.
Section A-A′ of
Additional aspects of the disclosure may include apparatus and methods advantageous for alternating current (AC) circuits. These aspects can be added to or combined with other implementations or instantiations of the disclosure disclosed elsewhere herein. Each phase of an AC circuit has periodic-in-time “zero-crossings” of both the current and voltage signals, whereat each of these signals reverse direction or polarity. Circuits having non-unity power factor may exhibit a (variable) phase angle difference between voltage and current zeroes at an arc gap. During zero-crossings, an arc may extinguish. If the arc remains extinguished, the current shunt and voltage clamping function of an arc conductor may be lost. Even if the arc reignited after the circuit comes out of zero-crossing, potentially severe arc pulsation may occur related to arc extinguishing (“chopping”) and re-ignition, and this may cause conducted, radiated or induced electrical noise, if not direct damage, in other circuit elements. These problems are solved according to AC aspects of the disclosure described below. Another concern is arc ignition when there may be zero-crossing, whereby no arc may strike or establish into a full arc. An arc may be struck when there is at least about 20 volts across an arc gap, not at a zero-crossing. While it may be possible to practice the disclosure by detecting a zero-crossing and igniting the arc at a desired phase angle away from the zero-crossing time, this is not considered necessary. A first example reason it is not necessary is that a byproduct of using arc-enhancing materials, as identified above, is ease of, and wide parameter latitude (range) for, arc ignition and propagation. A second example reason it is not necessary pertains to the preferred mechanical striking of arcs in one or more previously discussed implementations. The mechanical striking means may be used for re-supply of arc-enhancing material or because mechanical motion may be required anyway to break an arc once burning. These mechanical striking means are also able to linger through a zero-crossing of even the slowest standard AC frequency, 50 Hz→10 ms between zero-crossings, and draw power from the external circuit to get an arc started.
Referring now to
Arc transfer between arc gaps 210 and 250 is arranged, according to principles of the disclosure, by placing active arc electrodes 230 and 270 close together at gap 640. By active arc electrodes are meant the two electrodes not shorted together, 230 and 270 in
Some implementations, without limitation, may be used by taking either electrode in
In operation, some implementations, with either parabolic or elongated electrode configuration, or other electrode shape, as constructed using the prescription above, may be energized in a single-phase AC circuit similar to that depicted in
The terminology used herein is for the purpose of describing particular implementations only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps (not necessarily in a particular order), operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps (not necessarily in a particular order), operations, elements, components, and/or groups thereof.
The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present disclosure has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the disclosure in the form disclosed. Many modifications, variations, and any combinations thereof will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the disclosure. The implementation(s) were chosen and described in order to best explain the principles of the disclosure and the practical application, and to enable others of ordinary skill in the art to understand the disclosure for various implementation(s) with various modifications and/or any combinations of implementation(s) as are suited to the particular use contemplated.
Having thus described the disclosure of the present application in detail and by reference to implementation(s) thereof, it will be apparent that modifications, variations, and any combinations of implementation(s) (including any modifications, variations, and combinations thereof) are possible without departing from the scope of the disclosure defined in the appended claims.
This application claims the benefit of U.S. Provisional Application No. 61/548,455, filed on 18 Oct. 2011, by Baldwin et al., entitled Metal Vapor Arc Switch and Moving Electrical Contact for Electrical Energy Transfer, and U.S. Provisional Application No. 61/577,977, filed on 20 Dec. 2011, by Baldwin et al., entitled Arc Conductors, Arc-Assisted and Arc-Mediated Switches and Switching, the contents of which are all incorporated by reference.
Number | Date | Country | |
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61548455 | Oct 2011 | US | |
61577977 | Dec 2011 | US |