Patent Application
20120067854
The embodiments described herein relate generally to plasma guns and, more particularly, to ablative plasma guns for use in eliminating arc flashes.
Electric arc devices may be used in a variety of applications including, for example, series capacitor protection, high power switches, acoustic generators, shock wave generators, pulsed plasma thrusters, and arc mitigation devices. Such known devices generally include two or more main electrodes separated by a gap of air. A bias voltage is then applied to the main electrodes across the gap. However, at least some known electric arc devices require the main electrodes to be positioned closely together. Contaminants, or even the natural impedance of the air in the gap, can lead to arc formation between the main electrodes at undesirable times, which can lead to a circuit breaker being tripped when it would be otherwise unnecessary.
Accordingly, at least some known electric arc devices simply position the main electrodes further apart to avoid such false positive results. However, these devices are typically less reliable because of a less effective spread of plasma from a plasma gun. For example, at least some known plasma guns provide a plasma spread that does not effectively promote effective dielectric breakdown and reduction of impedance in the gap of air between the main electrodes. Such plasma guns can therefore show a lower level of reliability.
In one aspect, an ablative plasma gun includes a first portion having a first diameter and a second portion having a second diameter that is larger than the first diameter, wherein a chamber is defined by the first portion and the second portion.
In another aspect, an arc flash elimination system includes a plurality of main electrodes, wherein each of the plurality of main electrodes is coupled to a different portion of an electrical circuit. The arc flash elimination system also includes an ablative plasma gun positioned with respect to the plurality of main electrodes. The ablative plasma gun includes a first portion having a first diameter and a second portion having a second diameter that is larger than the first diameter, wherein a chamber is defined by the first portion and the second portion.
In another aspect, a method of assembling an arc flash elimination system includes coupling each of a plurality of main electrodes to a different portion of an electrical circuit, and positioning an ablative plasma gun with respect to the plurality of main electrodes. The ablative plasma gun includes a first portion having a first diameter and a second portion positioned above the first portion and having a second diameter that is larger than the first diameter, wherein a chamber defined by the first portion and the second portion.
Exemplary embodiments of systems, methods, and apparatus for use in arc flash elimination by initiation of an isolated arc within a self-contained device are described herein. These embodiments provide an ablative plasma gun that includes a chamber having a first portion, or lower portion, having a first diameter, and a second portion, or upper portion, having a second diameter that is larger than the first diameter. This plasma gun design facilitates an increased reliability and enhances plasma breakdown and arc creation between main electrodes of an arc elimination system. For example, the embodiments described herein provide a greater plasma spread after the arc is created between the main electrodes, which facilitates enhanced dielectric breakdown within a main gap between the main electrodes. The additional plasma spread and dielectric breakdown enable the arc elimination system to perform under a wider range of bias voltages between the main electrodes, including bias voltages as low as 200 volts, and at a wider range of impedances within the main gap.
Moreover, plasma gun 100 includes a cover 114 and a base 116. In the exemplary embodiment, cover 114 is mounted on base 116 and is sized to enclose cup 102. Specifically, cup 102 is positioned between base 116 and cover 114. In addition, a nozzle 118 is formed within cover 114. Nozzle 118 is positioned above an open end 120 of cup 102. In the exemplary embodiment, cover 114 and/or base 116 are formed from the same ablative material as cup 102. Alternatively, cover 114 and/or base 116 are formed from one or more different ablative materials than cup 102, such as a refractory material or a ceramic material.
Furthermore, in the exemplary embodiment, plasma gun 100 includes a plurality of gun electrodes, including a first gun electrode 122 and a second gun electrode 124. First gun electrode 122 includes a first end 126 and second gun electrode 124 includes a second end 128 that each extend into chamber 104. For example, first end 126 and second end 128 enter chamber 104 from radially opposite sides of chamber 104 about a central axis (not shown) of chamber 104. Moreover, first end 126 and second end 128 are diagonally opposed across chamber 104, to define a gap for formation of an arc 130. Electrodes 122 and 124, or at least first end 126 and second end 128, may be formed from, for example, tungsten steel, tungsten, other high temperature refractory metals or alloys, carbon or graphite, or any other suitable materials that enable formation of arc 130. A pulse of electrical potential that is applied between electrodes 122 and 124 creates arc 130 that heats and ablates a portion of the ablative material of cup 102 to create a highly conductive plasma 132 at high pressure. Plasma 132 exits nozzle 118 in a spreading pattern at supersonic speed. Characteristics of plasma 132, such as velocity, ion concentration, and an area of spread, may be controlled by dimensions of electrodes 122 and 124 and/or by a separation distance between first end 126 and second end 128. These characteristics of plasma 132 may also be controlled by the interior dimensions of chamber 104, the type of ablative material used to form cup 102, a trigger pulse shape, and/or a shape of nozzle 118.
Moreover, system 300 includes a logic circuit 322, such as a relay or processor. It should be understood that the terms “logic circuit” and “processor” refer generally to any programmable system including systems and microcontrollers, reduced instruction set circuits (RISC), application specific integrated circuits (ASIC), programmable logic circuits, and any other circuit or processor capable of executing the functions described herein. The above examples are exemplary only, and thus are not intended to limit in any way the definition and/or meaning of these terms. In the exemplary embodiment logic circuit 322 is communicatively coupled to one or more sensors 324, which may include light sensors, sound sensors, current sensors, voltage sensors, or any combination of these. Furthermore, system 300 includes one or more circuit breakers 326 that are communicatively coupled to logic circuit 322.
During operation, sensors 324 detect an event that is indicative of an arc flash is on the power circuit. For example, a current sensor can detect a rapid increase in current through a conductor of the power circuit, a voltage sensor can detect a rapid decrease in voltage across multiple conductors of the power circuit, or a light sensor can detect a light flash. In some embodiments, sensors 324 include a combination of current sensors, voltage sensors, and/or light sensors, such that multiple events may be detected within a specified time period to indicate the occurrence of an arc flash. In the exemplary embodiment, sensors 324 transmit a signal representative of the detection to logic circuit 322. In some embodiments, logic circuit 322 analyses the detection to determine whether the event is indicative of an arc flash or some other event, such as a trip of circuit breaker 326. When logic circuit 322 determines that the event is indicative of an arc flash, logic circuit 322 transmits an activation signal to trigger circuit 316. Main arc device 302 is then triggered by a voltage or current pulse to plasma gun 100 from trigger circuit 316. In response to the voltage or current pulse, plasma gun 100 injects ablative plasma 318 into main gap 308, which reduces the impedance of main gap 308 sufficiently to enable initiation of a protective arc 320 between main electrodes 304 and 306. Arc 320 absorbs energy from the arc flash and opens circuit breaker 326, which quickly stops the arc flash and protects the power circuit. As used herein, the term “main” refers generally to elements of a larger arc-based device to differentiate these elements from elements of plasma gun 100.
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Exemplary embodiments of systems, methods, and apparatus for use in arc flash elimination are described above in detail. The systems, methods, and apparatus are not limited to the specific embodiments described herein but, rather, operations of the methods and/or components of the system and/or apparatus may be utilized independently and separately from other operations and/or components described herein. Further, the described operations and/or components may also be defined in, or used in combination with, other systems, methods, and/or apparatus, and are not limited to practice with only the systems, methods, and storage media as described herein.
Although the present invention is described in connection with an exemplary power circuit environment, embodiments of the invention are operational with numerous other general purpose or special purpose electrical circuit environments or configurations. The power circuit environment is not intended to suggest any limitation as to the scope of use or functionality of any aspect of the invention. Moreover, the power circuit environment should not be interpreted as having any dependency or requirement relating to any one or combination of components illustrated in the exemplary operating environment.
The order of execution or performance of the operations in the embodiments of the invention illustrated and described herein is not essential, unless otherwise specified. That is, the operations may be performed in any order, unless otherwise specified, and embodiments of the invention may include additional or fewer operations than those disclosed herein. For example, it is contemplated that executing or performing a particular operation before, contemporaneously with, or after another operation is within the scope of aspects of the invention.
When introducing elements of aspects of the invention or embodiments thereof, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.
