Marx generator with electrical insulation devices

Abstract

The invention relates to a Marx generator (1), each capacitor stage (4.1, …, 4.n) of which comprises a first electrical insulation device (31), arranged in the interior space defined by the capacitor of the capacitor stage and extending over the length of the internal face of the capacitor (7), and a second electrical insulation device (32), arranged inside the first electrical insulation device (31), coaxially with the common axis (X-X) and extending along the length of the internal face of the capacitor (7), the generator (1) comprising a first impedance element (41), arranged between the first electrical insulation device (31) and the second electrical insulation device (32), and a second impedance element (42), arranged inside the second electrical insulation device (32).

Description

Marx generator with electrical insulation devices

[0001] The present invention relates to the field of high-voltage power tools and more particularly concerns a Marx generator.

[0002] As is known, a Marx generator has several capacitor stages which are charged in parallel and discharged in series via pairs of spark gaps arranged between two consecutive capacitor stages.

[0003] Each capacitor stage can be charged under voltages exceeding several hundred kilovolts, so that the voltage and energy available at the output of said generator can respectively reach a few megavolts and a few tens of kilojoules.

[0004] Initially, the capacitors connected in parallel are charged simultaneously to a given voltage. Subsequently, the spark gaps are triggered, connecting the capacitors in series so that the generator's output voltage is equal to the sum of the voltages across each capacitor.

[0005] French patent FR2637134B1 discloses a Marx generator architecture adapted for a cylindrical environment. In this document, the capacitor stages are electrically connected to each other via resistors placed between two consecutive stages.

[0006] However, these resistors, due to their proximity to the capacitors, can cause surface breakdowns ("crawl") and / or bulk breakdowns of surrounding materials, particularly electrically conductive or charged materials such as capacitors or spark gaps, which reduces the power, reliability and efficiency of the generator, or may even damage the generator.

[0007] An obvious solution is to move the resistors away from the surrounding components, but such an arrangement significantly increases the generator's dimensions. Documents CN201550347U and XP6093996A are background technology documents.

[0008] Therefore, there is a need for a simple and effective solution to remedy at least some of these drawbacks.

[0009] To this end, the invention initially aims at a Marx generator, comprising:

[0010] - a plurality of successive capacitor stages, in the shape of a torus, mounted coaxially to a common axis and juxtaposed along said axis from upstream to downstream between a first capacitor stage and a last capacitor stage;

[0011] - each capacitor stage having a crown-shaped capacitor, connected to two terminals, one being an upstream input terminal of the capacitor stage and the other being a downstream output terminal of the capacitor stage, the upstream terminal of the first capacitor stage forming the input terminal of the Marx generator and the downstream terminal of the last capacitor stage forming the output terminal of the Marx generator,

[0012] - for each pair of consecutive capacitor stages, the upstream capacitor stage includes a downstream spark gap head electrically connected to the downstream terminal of said capacitor stage and the downstream capacitor stage includes an upstream spark gap head electrically connected to the upstream terminal of said capacitor stage, said downstream spark gap head cooperating with said upstream spark gap head to form a pair of associated spark gap heads, the spark gap heads of each of said pairs of associated spark gap heads being housed between the two consecutive capacitors defining a breakdown gap.

[0013] The generator is remarkable in that:

[0014] - each capacitor stage comprises a first electrically insulating and hollow device, disposed in the internal space defined by the crown-shaped capacitor of said capacitor stage and extending along the length of the inner face of the capacitor, and a second electrically insulating and hollow device, disposed inside the first electrically insulating device, coaxially with the common axis and extending along the length of the inner face of the capacitor,

[0015] - said generator comprises a first impedance element, disposed between the first electrical isolation device and the second electrical isolation device and electrically connecting the input terminal of the generator and the downstream spark gap heads of the capacitor stages, and a second impedance element, disposed inside the second electrical isolation device and electrically connecting the upstream spark gap heads of the capacitor stages to the output terminal of the generator.

[0016] Thanks to the first and second electrical isolation devices, the high-field areas between the current return, capacitors, and spark gaps are free of other conductors. This allows them to be placed closer together while preventing breakdowns and ultimately reducing impedance. Reducing impedance minimizes the voltage rise time, which is related to the overall impedance, to a few nanoseconds, maximizes the discharge current, increases the frequency, and thus increases the system's efficiency, particularly for increasing the power generated at the application level, especially when its electrical impedance is low. For example, this increases the efficiency of an electric arc for generating pressure.

[0017] Preferably, the first electrical insulation device has a tubular shape, which makes it easy to manufacture and mount in the capacitor.

[0018] Preferably, the second electrical isolation device has a tubular shape, which makes it easy to manufacture and mount in the capacitor.

[0019] In one embodiment, the second electrical isolation device delimits an internal space devoid of material such that the spark gaps of a capacitor stage are directly visible (i.e., facing each other). This internal space devoid of material can, for example, be cylindrical when the second electrical isolation device is tubular. Since the internal spaces between the spark gaps are all aligned, the first spark gap to close generates a flash which, through photoionization, triggers the other pairs of spark gaps, which then close in a cascade.

[0020] In another embodiment, the generator includes a third, electrically insulating, hollow electrical isolation device that partially fills the internal space of the second electrical isolation device, creating an internal space free of material such that the spark gap heads of a capacitor stage are directly visible (i.e., face to face). This internal space free of material can, for example, be cylindrical when the second electrical isolation device is tubular. The third electrical isolation device serves as a support to maintain the impedance between the first and second electrical isolation devices.

[0021] Preferably, the third electrical isolation device has a tubular shape, which makes it easy to manufacture and mount in the capacitor.

[0022] Advantageously, the first impedance element comprises an electrically conductive wire, for example metallic (iron, copper, or any other suitable metal or metallic alloy). Such a wire allows the first impedance element to be given resistive and / or inductive properties.

[0023] This wire can preferably extend along the length of the inner face of the capacitor parallel to the common axis of the capacitors or be wrapped around the second electrical isolation device.

[0024] Advantageously still, the first impedance element comprises an electrically conductive rod or bar extending between the first electrical isolation device and the second electrical isolation device, along the length of the inner face of the capacitor and parallel to the common axis of the capacitors.

[0025] Such a rod or bar is preferably metallic, for example made of iron, or copper, or any other suitable metal or metallic alloy.

[0026] In one embodiment, the first impedance element comprises an electrically conductive rod or bar and an electrically conductive wire wound around said rod or bar to enhance both the resistive and inductive properties of said first impedance element.

[0027] Advantageously, the second impedance element comprises an electrically conductive wire, for example metallic (iron, copper, or any other suitable metal or metallic alloy). Such a wire allows the second impedance element to be given resistive and / or inductive properties.

[0028] This wire can preferably extend along the length of the inner face of the capacitor parallel to the common axis of the capacitors inside the second electrical isolation device or, where the capacitor includes a third electrical isolation device placed inside the second electrical isolation device, be wound around said third electrical isolation device.

[0029] Advantageously still, the second impedance element comprises an electrically conductive rod or bar extending inside the second electrical isolation device, along the length of the inner face of the capacitor and parallel to the common axis of the capacitors.

[0030] When the capacitor includes a third electrical isolation device placed inside the second electrical isolation device, the rod or bar may be arranged between said third electrical isolation device and the second electrical isolation device.

[0031] Such a rod or bar is preferably metallic, for example made of iron, or copper, or any other suitable metal or metallic alloy.

[0032] In one embodiment, the second impedance element comprises an electrically conductive rod or bar and an electrically conductive wire wound around said rod or bar to enhance both the resistive and inductive properties of said second impedance element.

[0033] In one embodiment, a space is formed between the inner surface of the first electrically insulating device and the outer surface of the second electrically insulating device, and the first impedance element is disposed in this space. This space accommodates the impedance 41, the first electrically insulating device 31, and the second electrically insulating device 32, which retains the impedance 41.

[0034] In one embodiment, the generator includes an enclosure, preferably sealed, for example cylindrical, in which the plurality of capacitor stages is mounted.

[0035] Preferably, an atmosphere of a dielectric gas prevails inside the envelope, for example air or nitrogen.

[0036] Advantageously, each capacitor is embedded in a dielectric coating, preferably a dielectric resin or oil.

[0037] In one embodiment, the upstream and downstream terminals of each capacitor are annular in shape and coaxial with the common axis.

[0038] Advantageously, the spark gap heads of each of the associated spark gap head pairs are housed between the two consecutive capacitors, defining a breakdown gap on the same insulating support so as to be mechanically linked to each other.

[0039] Other features and advantages of the invention will become apparent upon reading the following description. This description is purely illustrative and should be read in conjunction with the accompanying drawings, in which:

[0040] This is a cross-sectional view of a form of realization of Marx's generator according to the invention.

[0041] This is an enlarged view showing two consecutive capacitors of the generator.

[0042] This is a cross-sectional view of a capacitor from the generator in Figures 1 and 2.

[0043] Laillust schematically illustrates an example of Marx 1 generator according to the invention.

[0044] The Marx generator 1, shown schematically on the figure, comprises, in a conventional manner, a sealed casing 2, inside of which exists an atmosphere of a dielectric gas, for example air or nitrogen.

[0045] In enclosure 2, capacitor stages 4.1, 4.2, ..., 4.i, 4.j, ..., 4.n are arranged, which, as can be better seen in Figures 2 and 3, each have the shape of a torus with a rectangular cross-section. These capacitor stages are all mounted coaxially around a common axis XX and are juxtaposed along said axis from upstream to downstream between a first capacitor stage 4.1 and a last capacitor stage 4.n.

[0046] The capacitor stages 4.1, ..., 4.n are electrically connected to each other so that they can be charged in parallel and then discharged in series. In addition, electrical connections link these capacitor stages 4.1, ..., 4.n to external electrical control devices (not shown) located outside enclosure 2.

[0047] Furthermore, the capacitor stages 4.1, ..., 4.n are mechanically connected to each other and their assembly is mechanically supported by one or more supports 6, linking them to the casing 2. For example, the common axis XX is horizontal and the support 6 forms a base, which supports said capacitor stages and which is itself supported by said casing 2.

[0048] On the diagram, two consecutive capacitor stages 4.i, 4.j have been schematically represented in axial section.

[0049] As can be seen, each capacitor stage 4.i, 4.j comprises a ring-shaped capacitor 7, centered on the axis XX and embedded in a coating of dielectric resin 8 or oil. The coatings 8 themselves have the shape of a ring coaxial with the axis XX and have end faces 11, against which they can bear against each other.

[0050] Each capacitor 7 is connected, by a plurality of electrodes, to two terminals (annular, coaxial with said axis), one being an upstream terminal 17 at the input of the capacitor stage 4.i and the other being a downstream terminal 18 at the output of the capacitor stage 4.i, the upstream terminal of the first capacitor stage 4.1 of the plurality of capacitor stages 4.1, ..., 4.n forming the input terminal of the Marx generator 1 and the downstream terminal of the last capacitor stage 4.n of the plurality of capacitor stages 4.1, ..., 4.n forming the output terminal of the Marx generator 1.

[0051] On the diagram, terminals 17 and 18 of each capacitor stage are shown. Each terminal 17 and 18 has an annular shape and is located near the XX axis, to which it is coaxial.

[0052] With further reference to the above, for each pair of consecutive capacitor stages, the upstream capacitor stage 4.i comprises a downstream spark gap head 25 electrically connected to the downstream terminal 17 of said capacitor stage 4.i, for example by an electrode (not shown for clarity), and the downstream capacitor stage 4.j comprises an upstream spark gap head 26 electrically connected to the upstream terminal 18 of said capacitor stage, also for example by an electrode (not shown for clarity). Such electrodes are known to be made of thin metal strips (for example, a few tenths of a millimeter), generally referred to as foil.

[0053] Terminals 17 and 18 are respectively attached to spark gap heads 25 or 26 which are housed in an inter-capacitor space 27 formed between two successive capacitors 4.i, 4.j and arranged so that the downstream spark gap head 26 of a stage can cooperate with the upstream spark gap head 25 of the next stage, said spark gap heads 25 and 26 being aligned and arranged opposite each other to form a pair of associated spark gap heads 25, 26.

[0054] Preferably, the spark gap heads 25, 26 are mounted on the same insulating support so as to be mechanically linked to each other.

[0055] The arrangement of each pair of associated spark gap heads 25, 26 can advantageously be carried out in a unit block mechanically independent of the corresponding capacitor stages 4.i, 4.j.

[0056] With reference to Figures 2 and 3, each capacitor stage 4.1, ..., 4.n comprises a first electrical isolation device 31, a second electrical isolation device 32, a first impedance element 41 and a second impedance element 42.

[0057] The first electrical isolation device 31 is tubular in shape and is arranged in the internal space defined by the successive capacitor stages 4.1, …, 4n in the shape of a crown coaxially with the common axis XX and extends along the length of the inner face of the capacitor 7.

[0058] The second electrical isolation device 32 is also tubular in shape and has dimensions smaller than the dimensions of said first electrical isolation device 31 so as to be arranged inside the first electrical isolation device 31, coaxially with the common axis XX and extending along the length of the inner face of the capacitor 7.

[0059] A space can be formed between the inner surface of the first electrical insulation device 31 and the outer surface of the second electrical insulation device 32 to allow the placement of the first impedance element 41. Alternatively, the first impedance element can be held on the inner surface of the first electrical insulation device 31 and on the outer surface of the second electrical insulation device 32, which are then at least partly in contact.

[0060] In the example of Figures 2 and 3, the Marx generator 1 includes a third electrical isolation device 33, made of an insulating material and also tubular in shape, placed inside the second electrical isolation device 32. The third electrical isolation device 33 partially fills the internal space of the second electrical isolation device 32 while delimiting a cylindrical space 33A devoid of material around the axis XX allowing the spark gap heads of the capacitor stage to be opposite each other (i.e. in direct view) through said internal space in order to allow efficient cascade triggering of the spark gaps by photoionization.

[0061] The spark gap heads 25, 26 of each of the associated pairs of spark gap heads 25, 26 are arranged together by defining a breakdown space and are opposite the spark gap heads 25, 26 of the following and preceding stages through the internal space devoid of material delimited at the center of the third electrical isolation device 33.

[0062] The third electrical isolation device 33 serves as a support to allow the mechanical maintenance of the impedance 42 between the isolation device 32 and the isolation device 33.

[0063] The first impedance element 41 is arranged between the first electrical isolation device 31 and the second electrical isolation device 32 and electrically connects the input terminal of the Marx generator 1 and the downstream spark gap heads 25 of the capacitor stages.

[0064] The second impedance element 42 is arranged inside the second electrical isolation device 32 and electrically connects the upstream spark gap heads 26 of the capacitor stages to the output terminal of the Marx generator 1.

[0065] The first impedance element 41 has a purely resistive function, or a purely inductive function, or both resistive and inductive.

[0066] The first impedance element 41 can be an electrically conductive wire, for example wrapped around the second electrical insulation device.

[0067] Alternatively, the first impedance element 41 can be an electrically conductive rod or bar extending between the first electrical insulation device 31 and the second electrical insulation device 32 parallel to the common axis XX. This rod or bar can advantageously be made of metal, for example iron or copper.

[0068] Like the first impedance element 41, the second impedance element 42 has a purely resistive function or a purely inductive function or both resistive and inductive.

[0069] The second impedance element 42 can be an electrically conductive wire disposed inside the second electrical isolation device 32, for example wrapped around the third electrical isolation device 33 when present.

[0070] Alternatively, the second impedance element 42 can be an electrically conductive rod or bar extending inside the second electrical insulation device 32 parallel to the common axis XX. This rod or bar can advantageously be made of metal, for example iron or copper.

[0071] Grooves can advantageously be formed in the surface delimiting the material-free internal space of the third electrical insulation device 33 in order to eliminate electrical conduction by skin effect. When the Marx generator 1 lacks a third electrical insulation device 33, the grooves can be formed in the surface delimiting the material-free internal space of the second electrical insulation device 32.

Claims

Marx generator (1), comprising: - a plurality of successive toroidal capacitor stages (4.1, …, 4.n) mounted coaxially around a common axis (XX) and juxtaposed along said axis (XX) from upstream to downstream between a first capacitor stage (4.1) and a last capacitor stage (4.n); - each capacitor stage (4.1, …, 4.n) having a ring-shaped capacitor (7) connected to two terminals (17, 18), one being an upstream terminal (17) at the input of the capacitor stage (4.1, …, 4.n) and the other being a downstream terminal (18) at the output of the capacitor stage (4.1, …, 4.n), the upstream terminal (17) of the first capacitor stage (4.1) forming the input terminal of the Marx generator (1) and the downstream terminal (18) of the last capacitor stage (4.n) forming the output terminal of the Marx generator (1),- for each pair of consecutive capacitor stages (4.1, …, 4.n), the capacitor stage (4.1, …, 4.n-1) upstream includes a downstream spark gap head (25) electrically connected to the downstream terminal (18) of said capacitor stage (4.1, …, 4.n) and the downstream capacitor stage (4.1, …, 4.n) includes an upstream spark gap head (26) electrically connected to the upstream terminal (17) of said capacitor stage (4.1, …, 4.n), said downstream spark gap head (25) cooperating with said upstream spark gap head (26) to form a pair of associated spark gap heads (25, 26), the spark gap heads (25, 26) of each of said pairs of associated spark gap heads (25, 26) being housed between the two consecutive capacitors (4.1, …, 4.n) defining a breakdown gap, the generator (1) being characterized in that:- each capacitor stage (4.1, …, 4.n)n) includes a first electrically insulating and hollow electrical isolation device (31) disposed in the interior space defined by the crown-shaped capacitor of said capacitor stage and extending along the length of the inner face of the capacitor (7), and a second electrically insulating and hollow electrical isolation device (32) disposed inside the first electrical isolation device (31), coaxially to the common axis (XX) and extending along the length of the inner face of the capacitor (7),- said generator (1) includes a first impedance element (41), disposed between the first electrical isolation device (31) and the second electrical isolation device (32) and electrically connecting the input terminal of the generator (1) and the downstream spark gap heads (25) of the capacitor stages (4.1, …, 4.n), and a second impedance element (42), disposed inside the second electrical isolation device (32) and electrically connecting the upstream spark gap heads (26) of the capacitor stages (4.1, …, 4.n) to the output terminal of the generator (1). Generator (1) according to claim 1, wherein the second electrical isolation device (32) delimits an internal space devoid of material such that the spark gap heads (25, 26) of a capacitor stage (4.1, …, 4.n) are in direct view through said internal space. Generator (1) according to claim 1, wherein the generator (1) comprises a third electrically insulating and hollow electrical isolation device (33), partially filling the internal space of the second electrical isolation device (32) by delimiting an internal space devoid of material such that the spark gap heads (25, 26) of a capacitor stage are in direct view through said internal space. Generator (1) according to any one of the preceding claims, wherein the first impedance element (41) comprises a wire. Generator (1) according to any one of the preceding claims, wherein the first impedance element (41) comprises an electrically conductive rod or bar extending between the first electrical isolation device (31) and the second electrical isolation device (32). Generator (1) according to any one of the preceding claims, wherein the first impedance element (41) comprises an electrically conductive rod or bar and an electrically conductive wire wound around said rod or bar. Generator (1) according to any one of the preceding claims, wherein the second impedance element (42) comprises an electrically conductive wire. Generator (1) according to any one of the preceding claims, wherein the second impedance element (42) comprises an electrically conductive rod or bar extending between inside the second electrical isolation device (32). Generator (1) according to any one of the preceding claims, wherein the second impedance element (42) comprises an electrically conductive rod or bar and an electrically conductive wire wound around said rod or bar. Generator (1) according to any one of the preceding claims, wherein a space is formed between the internal surface of the first electrical insulation device (31) and the external surface of the second electrical insulation device (32).

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