EP1629577B1 - Spark-gap device, particularly high-voltage spark-gap device - Google Patents

Abstract

Spark-gap device comprising two discharge electrodes (2; 3) each having an elongated conductor portion (10; 5), called the active portion, with a connecting longitudinal end (11; 7) fixed to a connector. The electrodes are arranged in such a way that, when an electric arc is generated, said arc is formed between the active portions and the resulting electric current induces a magnetic field moving the electric arc along said active portions, preferably at an erosion-limiting high speed. At least a discharge electrode further comprises at least a second conductor portion (9, 16; 6), called the passive portion, electrically connected to the connector and/or the active portion and with a form adapted to prevent a spontaneous electric arc from being inopportunely generated in normal usage conditions of the device.

Description

The invention relates to a spark gap and is particularly advantageous in the case of a high voltage spark gap for transferring a large quantity of electric charges.

A spark gap is a device of the closing switch type comprising two remote electrodes, called discharge electrodes, separated by a dielectric (gas, vapor, vacuum, etc.), between which an electric arc is formed when the potential difference between the electrodes is greater than a threshold value. In a high voltage spark gap, this threshold value is greater than a few kV, and the operating voltage of the spark gap (voltage applied to the spark gap, that is to say the potential difference between its electrodes) can go up to 1 MV. Such a spark gap makes it possible to transfer a quantity of electrical charges ranging from a few hundred milli-Coulombs to several hundred Coulombs, corresponding to an electric current flowing through the spark gap between 1 kA and 1 MA.

Associated with a current generator, and in particular with a capacitor able to accumulate the aforementioned quantities of electrical charges, such a high-voltage spark gap is used in particular to power sequentially a test bench of materials under high pressure or any other device, says charge. Each operation of discharging the capacitor and transferring the charge, by the spark gap, of the electrical charges initially accumulated in the capacitor, is called a shot.

Among the known spark gaps, one of the most efficient is a spark gap which comprises two hollow cylindrical discharge electrodes, symmetrical of revolution, each having an inner radius of about 8 cm, an outer radius of the order 10 cm and a length of the order of 20 cm. The two cylindrical electrodes are aligned "end to end", that is to say arranged so that their axes of symmetry coincide and they have axial ends, called closure ends, 8 mm apart and opposite in the axial direction (direction of the axes of symmetry). It is between these axial ends of closure, whose facing annular end faces are substantially flat (in transverse planes), that forms the electric arc. The opposite axial ends of the electrodes, called connection ends, are each connected to a connector for integrating the spark gap into an electrical circuit. In particular, one of the connectors can be used to connect a current generator (capacitor) and the other to connect a load.

A shot is triggered by a third electrode, called trigger electrode, which initiates the formation of an electric arc between the two discharge electrodes. During a firing, the electrical charges, which the current generator transmits to the discharge electrode to which it is connected, propagate from the connection end of the electrode towards its closure end in the axial direction, then are deflected, by means of inclined slots in the closing end of the electrode, so as to move in a direction comprising a tangential component (following the circular periphery of the electrode in a transverse plane). The electrical charges then pass through the space between the electrodes in the axial direction, forming an axial electric arc, and are then again deflected tangentially in the closing end of the other discharge electrode, by means of inclined slits (in the opposite direction). contrary), to then find a substantially axial propagation to the connection end of the electrode.

This tangential displacement of the electrical charges in the closing ends of the discharge electrodes induces a radial magnetic field, which displaces the electric arc in a circular manner along the annular faces of said closing ends. Depending on the amount of charge transferred, the electric arc can perform several turns (usually two turns). It is noted that the speed of the arc in the second lap is higher than its speed in the first lap despite a lower current intensity.

Despite this displacement, for a quantity of conducted charges greater than 140 ° C., the electric arc generates a large and rapid wear of the closing ends of the electrodes by erosion, forcing to provide closing ends made of a special alloy of copper and tungsten. . This alloy, particularly expensive, strike the cost of the spark gap. It is only at this price that the known sparkler cited above can now claim a lifespan of 18,000 shots.

Document is also known US 3,450,922 a vacuum spark gap, comprising two parallel electrodes in the form of cylindrical plates, mounted fixed and distant from each other, each electrode being connected by its respective connecting rod to an electric circuit. A third insulating ceramic sheathed trigger electrode passes through one of the trays and is flush with the surface thereof at a point away from the tray axis. During a shot, the electric arc triggered to the right of the third electrode is removed under the effect of a magnetic field generated by the arc current. However, such a spark gap is difficult to achieve due to the necessary alignment and sealing of the third electrode through the casing and the discharge electrode plate. In addition it requires special and expensive materials, not releasing gas during firing stresses, so as not to reduce the life of the interior vacuum.

The invention aims to overcome these disadvantages by providing a simple and inexpensive spark gap, having similar performance or greater than known spark gaps.

In particular, the invention aims to provide a high-voltage spark gap, which can operate at voltages similar to or greater than the usual operating voltages of the aforementioned spark gap, which can switch currents of similar or greater intensity to the switched currents. by the aforementioned known spark gap, having a similar or greater service life than the known spark gap mentioned above, for a negligible undesirable failure and trip rate, and a lower cost price than the known spark gaps (and in particular to the known spark gap mentioned above).

• deux électrodes de déchargement rigides, montées fixes et distantes l'une de l'autre, et
• au moins deux connecteurs, chaque électrode étant reliée à l'un des connecteurs en vue de la connexion desdites électrodes à un circuit électrique comprenant un générateur de courant,

dans lequel :

• chaque électrode de déchargement présente une portion conductrice allongée, dite portion active, présentant une extrémité longitudinale, dite extrémité longitudinale de connexion, reliée au connecteur, et une extrémité longitudinale opposée dite extrémité aval,
• des moyens de déclenchement sont adaptés pour initier la formation d'un arc électrique entre les portions actives des électrodes, dans une zone, dite zone de déclenchement d'arc électrique,
• les portions actives des électrodes de déchargement sont agencées pour pouvoir canaliser un courant électrique et pour pouvoir former une portée allongée de déplacement de l'arc électrique sous l'effet d'un champ magnétique induit par ledit courant,
• au moins une électrode de déchargement présente au moins une autre portion conductrice, dite portion passive, électriquement reliée au connecteur et/ou à la portion active, ladite portion passive présentant une surface, dite surface utile, définie comme la partie de surface de la portion passive qui s'étend en vis-à-vis de l'autre électrode, ayant un rayon de courbure minimal qui est supérieur à un rayon seuil en dessous duquel l'intensité du champ électrique entre les électrodes de déchargement est supérieure à une valeur minimale d'auto-amorçage dans des conditions normales d'utilisation de l'éclateur, ladite portion passive étant adaptée pour empêcher toute formation spontanée intempestive d'un arc électrique (dite auto-amorçage) dans lesdites conditions normales d'utilisation de l'éclateur.

The invention relates to a spark gap comprising:

• two rigid discharge electrodes, mounted fixed and distant from each other, and
• at least two connectors, each electrode being connected to one of the connectors for the purpose of connecting said electrodes to an electrical circuit comprising a current generator,

in which :

• each discharge electrode has an elongated conductive portion, said active portion, having a longitudinal end, called the longitudinal end of connection, connected to the connector, and an opposite longitudinal end called the downstream end,
• triggering means are adapted to initiate the formation of an electric arc between the active portions of the electrodes, in an area called an electric arc trip zone,
• the active portions of the discharge electrodes are arranged to be able to channel an electric current and to be able to form an elongated range of displacement of the electric arc under the effect of a magnetic field induced by said current,
• at least one discharge electrode has at least one other conductive portion, said passive portion, electrically connected to the connector and / or the active portion, said passive portion having a surface, called the useful surface, defined as the surface portion of the portion passive which extends opposite the other electrode, having a minimum radius of curvature which is greater than a threshold radius below which the intensity of the electric field between the discharge electrodes is greater than a minimum value self-priming under normal conditions of use of the spark gap, said passive portion being adapted to prevent inadvertent spontaneous formation of an electric arc (so-called self-priming) in said normal conditions of use of the spark gap .

Note that the term "elongated", used to describe the active portion of the discharge electrodes according to the invention, means that said active portion extends mainly along a line, called the guideline. In other words, it has a dimension along this guideline, called length, much higher than its other dimensions. Said guideline may be straight or curved. Moreover, the terms "transverse direction" of the active portion at a point designate a direction orthogonal, at this point, to the guideline (that is, orthogonal to a direction tangent to said line) of the active portion. ; and "transverse plane" at a point means a plane orthogonal at this point to the guideline of the active portion. Similarly, the cross section of the active portion at a point is the section of said portion in the transverse plane passing through this point.

According to the invention, each discharge electrode of the spark gap therefore comprises an elongated active portion. By their shape and their relative arrangement, the active portions of the two electrodes are adapted to, when a current is established, channel the current and induce between them a magnetic field that moves the electric arc along said portions. The active portions provide an elongated range of displacement of the arc, which is advantageously free of slits.

Furthermore, at least one discharge electrode according to the invention also comprises at least one passive portion, specifically designed to prevent any closure of the spark gap by spontaneous and inadvertent breakdown under normal conditions of use of the spark gap, and the shape and arrangement are adapted to fulfill this function. Each passive portion is especially designed and arranged to reduce the intensity of the electric field between the two discharge electrodes.

The presence of the passive portion (s) according to the invention makes it possible to choose and adjust the shape of the active portions so as to increase the performance of the spark gap. In particular, it allows to choose and adjust the shape of the active portions so as to limit the risk of erosion of said portions by the arc. This shape is chosen in particular so as to obtain (when an arc is formed) a high current density along said active portions, which induces a stronger magnetic field giving the arc a greater speed of displacement. A rapid displacement of the arc limits the risk of erosion of the active portions.

Note that the terms "use conditions of the spark gap" used above designate all the external parameters of use having an influence on the proper operation of the spark gap. Among these parameters of use, mention may be made of the voltage applied to the spark gap and the pressure of the gas (or vapor) contained in the spark gap, which gas electrically isolates the electrodes from each other in the absence of 'electric arc. These conditions are said to be "normal" when the values taken by these parameters fall within the usual predefined ranges of use of the spark gap, for which the spark gap has been specifically designed. In particular, under normal conditions of use, the voltage applied to the spark gap must be within a given operating range, and must in particular, be less than a maximum operating value, which can be from 1 kV to 1 MV depending on the spark gap and according to its use. Outside these normal conditions of use, and especially if a voltage greater than a maximum expected operating voltage is applied to the spark gap, breakdown of the spark gap is not excluded despite the presence of the passive portion (s) according to the invention. Note that, if such a breakdown occurs, the formed arc will also appear between the active portions of the electrodes.

According to the normal conditions of use of the spark gap, the two discharge electrodes or only one of them has (s) a passive portion.

In all the following, the terms "upstream" and "downstream" are used, for each of the discharge electrodes, with reference to the guideline of the active portion of the electrode and to the direction of movement of the electric arc along of this active portion.

Advantageously and according to the invention, the active and passive portions of at least one of the discharge electrodes are separated at least for a fraction of the length of the active portion downstream of the electric arc trip zone. This feature facilitates the channeling of electrical charges into the active portion when a current is established. In a first version of the invention, the active and passive portions are distant on this fraction of length and only separated by the gas present inside the spark gap. In a second version, an insulating solid element (of synthetic material for example) extends between said active and passive portions over this fraction of length.

Advantageously and according to the invention, the spark gap comprises a trigger device, such as a trip electrode, capable of initiating the formation of an electric arc in the electric arc trip zone.

As a variant, the voluntary formation of an electric arc is triggered either by applying to the spark gap a voltage greater than a minimum self-priming voltage, or by modifying the pressure of the gas contained in the spark gap, in order to cause a self-priming of the spark gap. In this variant, the shape and arrangement of the active portions of the discharge electrodes are adapted so that the self-priming electric arc is formed in the electric arc trip zone.

Advantageously and according to the invention, the active portion of at least one of the discharge electrodes has a guideline, said longitudinal direction, substantially straight at least downstream of the electric arc trip zone. Alternatively or in combination, the active portion of at least one of the discharge electrodes has a curved guideline.

In a preferred version of the invention, the active portions of the discharge electrodes extend substantially facing each other, at least downstream of the electric arc release zone, it being specified that one This means that any transverse plane (downstream of the tripping zone) of the active portion of at least one of the electrodes intersects the active portion of the other electrode. The transverse direction in which the active portions are facing is said unloading direction, given that the electric arc that is formed between the active portions extends substantially in this direction.

Advantageously and according to the invention, the active portions of the discharge electrodes have longitudinal connection ends located on the same side of the spark gap, and preferably arranged substantially facing one another.

Advantageously and according to the invention, the active portions of the discharge electrodes have similar overall shapes. In particular, the active portions of the discharge electrodes both have substantially straight elongated shapes and substantially straight lines (longitudinal directions). Alternatively, they both have curved guidelines substantially following the (the) same (s) curvature (s). In particular, the active portions may have substantially circular guidelines and open crown shapes.

Whether straight or curved, the guidelines of the active portions are preferably substantially parallel, at least downstream of the electric arc trip zone. The active portions are then facing each other at least downstream of the trigger zone, and the spacing of said portions is substantially constant over the entire length of the active portions. The electric arc moving along these active portions therefore also has a substantially constant length. This preferred version of the invention does not exclude the possibility of providing unloading electrodes whose active portions have guide lines forming, at a point or at any point, a non-zero angle and / or active portions of which the spacing is not constant. In particular, the spacing of the active portions may increase downstream (in the direction of movement of the arc).

Advantageously and according to the invention, the active portion of each discharge electrode has a shape adapted for the induced magnetic field to move the electric arc at a speed sufficient to avoid erosion of said active portions by melting and / or local vaporization (s). ) (at the point of impact of the electric arc). Such a speed makes it possible to dispense with the use of expensive alloys (example: copper and tungsten alloys) for the production of these electrodes. Thus, advantageously and according to the invention, the active portions - as well as the passive portion (s) - of the discharge electrodes are made of a basic conductive material chosen from among steels, stainless steels, brasses, aluminum, copper, some copper-based alloys ... (this list is not exhaustive).

In particular, each active portion has a surface, called a useful surface, of suitable dimensions for the induced magnetic field to move the electric arc at a speed sufficient to prevent erosion of the active portions by local melting and / or vaporization (s), the effective area of the active portion being defined (geometrically) as the surface portion of the active portion extending opposite the other electrode downstream of the electric arc trip zone.

This useful surface of the active portion may have, for at least one of the discharge electrodes, a substantially constant width, the term "width" denoting a dimension in a transverse direction orthogonal to the transverse direction of unloading.

As a variant or in combination, the active portion of at least one unloading electrode has a useful surface of increasing width downstream (in the direction of movement of the arc, towards the downstream end of the active portion). This feature is advantageous for the following reasons. The triggering of an electric arc establishes an electric current through the spark gap, the intensity of which is increasing in an initial phase, before reaching a maximum value and to decrease towards zero (aperiodic regime) or to oscillate in s damping (oscillating speed) until the energy initially stored in the capacitor (s) is completely dissipated. This initial phase is critical given the low intensity of the current and the low kinetic energy of the electric arc. During this initial phase, the arc is displaced along an upstream fraction of the active portion of the electrode, from its point of formation in the electric arc trip zone. On this upstream fraction, to move the arc at a high speed, it is therefore necessary to have a strong magnetic field between the electrodes, in particular capable of compensating for the low intensity of the current in the arc. The use, for each electrode, of an active portion having a useful surface of small width on such an upstream fraction makes it possible to increase the density of the current flowing in this fraction and to have a strong magnetic field opposite it. On the other hand, the width of the usable area may be greater on a downstream fraction of the active portion along which the displaced electric arc has a high current intensity and / or a certain kinetic energy. In this downstream fraction, the induced magnetic field is indeed sufficient to move the arc at the desired speeds without it being necessary to increase it using a small width active portion.

It is therefore possible to provide an active portion whose useful area widens downstream. Note that this enlargement can be progressive along the active portion or abrupt portion punctually (the effective area having a constant width over fractions of length of the active portion). This widening also makes it possible to limit the presence of a possible passive portion to an upstream fraction of the active portion, if however the useful surface of the active portion is designed so as to have, in its enlarged downstream fraction, a radius minimal bending so that any risk of self-priming in this area is eliminated.

By way of example, in the case of a high-voltage spark gap capable of transmitting an electric current of intensity of between 1 kA and 1 MA, and transferring a quantity of charges of between 0.1 and 200 ° C., the surface the active portion of each discharge electrode preferably has a length of between 5 and 200 cm, and a width less than 50 cm over this length and less than 7 cm at least on an upstream fraction of this length. The width of the useful surface may advantageously be less than 2 cm at least on an upstream fraction of this length if the spark gap is intended to transfer quantities of charges lower than 20 C. In all cases, the speed of displacement of Arc obtained allows the use of electrodes of a basic and inexpensive material such as copper or stainless steel.

• au moins une des électrodes de déchargement présente une portion active ayant une forme de tige cylindrique (une telle tige possède une ligne directrice droite), au moins entre la zone de déclenchement d'arc électrique et son extrémité aval,
• au moins une des électrodes de déchargement présente une portion active ayant une forme de tige (de ligne directrice droite ou courbe) de section transversale circulaire, au moins entre la zone de déclenchement d'arc électrique et son extrémité aval. A noter que la largeur de la surface utile d'une telle portion active correspond au diamètre de la tige. Ladite tige présente une section transversale de diamètre sensiblement constant, de préférence inférieur à 2 cm si les quantités de charges à transférer sont inférieures à 20 C. En variante, ladite tige présente une section transversale de diamètre croissant (de façon progressive ou non) vers l'aval, ledit diamètre étant inférieur à 2 cm dans la zone de déclenchement d'arc électrique si les quantités de charges à transférer sont inférieures à 20 C,
• la portion active d'au moins une électrode de déchargement présente une extrémité longitudinale aval électriquement isolée.

Advantageously and according to the invention, the spark gap also has one or more of the following characteristics:

• at least one of the discharge electrodes has an active portion having a cylindrical rod shape (such a rod has a straight guideline), at least between the arcing trip zone and its downstream end,
• at least one of the discharge electrodes has an active portion having a stem shape (of straight or curved guideline) of circular cross section, at least between the electric arc trip zone and its downstream end. Note that the width of the useful surface of such an active portion corresponds to the diameter of the rod. Said rod has a cross section of substantially constant diameter, preferably less than 2 cm if the quantities of charges to be transferred are less than 20 C. In a variant, said rod has a cross-section of increasing diameter (progressively or non-progressively) downstream, said diameter being less than 2 cm in the arc trip zone if the quantities of charges to be transferred are less than 20 C,
• the active portion of at least one discharge electrode has an electrically isolated downstream longitudinal end.

Furthermore, according to the invention, at least one discharge electrode has a passive portion. Each passive portion preferably extends substantially opposite the active portion of the electrode in the transverse direction of unloading. Advantageously and according to the invention, each passive portion extends along at least an upstream fraction of the active portion of the electrode; said passive portion protrudes from a longitudinal edge of the active portion and so as not to pass through an intermediate space extending between the active portions of the two electrodes.

The passive portion must in particular extend along at least an upstream fraction of the active portion in which the shape of said active portion (small width and / or small radius of curvature of the active portion surface which is oriented towards the other electrode ...), thus chosen to induce in this zone a high magnetic field, also generates a strengthening of the electric field capable of triggering the unexpected formation of an electric arc (self-priming) under normal conditions of use of the spark gap. Depending on the shape chosen for the active portion, the passive portion may also extend over the entire length of the active portion.

Advantageously and according to the invention, each passive portion has a surface, called a useful surface, having a minimum radius of curvature which is greater than a threshold radius below which, under the normal conditions of use of the spark gap, the intensity the electric field between the discharge electrodes is greater than a minimum spark gap self-priming value (defined as the minimum electric field strength causing spontaneous arcing). The useful area of the passive portion is defined as the surface portion of the passive portion extending opposite the other electrode. Note that according to this definition, the useful area of the passive portion may possibly extend upstream of the electric arc trip zone (unlike the useful surface of the active portion as defined above).

Advantageously and according to the invention, the passive portion of at least one discharge electrode has a plane useful surface (that is to say of infinite radius of curvature).

• une portion active qui présente, au moins en aval de la zone de déclenchement d'arc électrique, la forme d'une tige cylindrique de section circulaire, dite tige active,
• une portion passive présentant la forme d'un tube cylindrique creux, dit tube passif, de section supérieure à celle de la tige active, ledit tube présentant une fente longitudinale en regard de laquelle s'étend la tige active, ledit tube passif et ladite tige active étant agencés de sorte que la tige s'étende entre le tube et l'autre électrode de déchargement. L'extrémité longitudinale aval de la tige active est avantageusement portée par une extrémité longitudinale aval du tube, à laquelle elle est reliée par des moyens de fixation de préférence électriquement isolants.

In one version of the invention, at least one of the discharge electrodes comprises:

• an active portion which has, at least downstream of the electric arc trip zone, the shape of a cylindrical rod of circular section, called an active rod,
• a passive portion having the shape of a hollow cylindrical tube, said passive tube, of greater cross section than that of the active rod, said tube having a longitudinal slot opposite which extends the active rod, said passive tube and said rod active being arranged so that the rod extends between the tube and the other discharge electrode. The downstream longitudinal end of the active rod is advantageously carried by a downstream longitudinal end of the tube, to which it is connected by preferably electrically insulating fixing means.

As a variant or in combination, at least one of the discharge electrodes comprises, on the one hand, an active portion having, at least downstream of the electric arc trip zone, the shape of a cylindrical rod and, on the other hand, a passive portion in the form of a flat plate, said plate and rod being distant from each other and arranged so that the rod extends between the plate and the other unloading electrode, parallel to said plate and close to it.

Advantageously and according to the invention, the spark gap comprises a housing inside which are placed the discharge electrodes. Said housing may comprise at least one conductive wall acting as a passive portion (in the form of a flat plate) of an unloading electrode.

As a variant or in combination, at least one of the discharge electrodes comprises an elongate flat plate, a longitudinal connection end of which is connected to the connector. The active portion of the electrode consists of a downstream fraction of said plate and at least one rod or rod of length and width respectively lower than those of the plate, fixed on an upstream fraction of said plate. The passive portion of the electrode is essentially constituted by the upstream fraction of the plate. The rod preferably extends away from the passive portion at least downstream of the electric arc trip zone, so that when an electric arc is triggered and an electric current is established, the electric charges circulating in the electrode are channeled and concentrated in the rod - at least as long as the electric arc extends between the rod and the other electrode - to induce a high magnetic field.

Advantageously and according to the invention, the spark gap comprises several pairs of discharge electrodes, said pairs being arranged in parallel. Thus, the amount of charges conducted can be multiplied by the number of pairs of electrodes operating in parallel. In a first version of the invention, at least one of the discharge electrodes of each pair is connected to a connector of the spark gap that is specific to it. In other words, the spark gap comprises at least, on the one hand, a connector per pair of discharge electrodes, and on the other hand, a single connector or a connector pair of electrodes. Electrical decoupling means (inductive, resistive, temporal ...) are, in this case, arranged between the current generator and a series of connectors (one per pair of electrodes). In a second version of the invention where the spark gap comprises only two connectors, it incorporates electrical decoupling means (inductive, resistive, temporal ...) between one of the two connectors and one of the electrodes of each pair. A third version, which corresponds to a combination of the two previous ones and in which the spark gap integrates means of internal decoupling and is used in association with external decoupling means, is also in accordance with the invention.

The invention also relates to a spark gap characterized in combination by all or some of the characteristics mentioned above and below.

• la figure 1 est une vue schématique en coupe selon un plan longitudinal d'un premier éclateur selon l'invention,
• la figure 2 est une vue schématique en coupe selon un plan transversal du premier éclateur selon l'invention,
• la figure 3 est une vue schématique en coupe selon un premier plan longitudinal d'un deuxième éclateur selon l'invention,
• la figure 4 est une vue schématique en coupe selon un deuxième plan longitudinal AA -orthogonal au premier plan longitudinal- du deuxième éclateur selon l'invention.

Other objects, features and advantages of the invention will appear on reading the following description which refers to the appended figures representing preferred embodiments of the invention given solely by way of non-limiting examples, and in which:

• the figure 1 is a schematic sectional view along a longitudinal plane of a first spark gap according to the invention,
• the figure 2 is a schematic sectional view along a transverse plane of the first spark gap according to the invention,
• the figure 3 is a schematic sectional view along a first longitudinal plane of a second spark gap according to the invention,
• the figure 4 is a schematic sectional view along a second longitudinal plane AA-orthogonal to the first longitudinal plane of the second spark gap according to the invention.

The first spark gap according to the invention illustrated in Figures 1 and 2 comprises a stainless steel conductive parallelepipedic housing 1, a first discharge electrode 2, a second discharge electrode 3 and an electric arc release electrode 4.

Each discharge electrode 2, 3 has a generally elongated and straight shape, defining a longitudinal direction of the electrode. It comprises a straight elongated active portion, described below, whose longitudinal direction (guideline) coincides with that of the electrode. The electrodes extend facing one another in a transverse direction Z, said unloading direction, so that their longitudinal directions are parallel and define a common longitudinal direction X.

The trip electrode 4 extends between the discharge electrodes, in a transverse direction Y, orthogonal to the longitudinal direction X and to the unloading direction Z. It extends more precisely between the active portions (described below). unloading electrodes, near the connection ends of said active portions. It defines a zone 21 for triggering an electric arc.

The discharge electrode 2 comprises on the one hand a passive portion comprising a hollow cylindrical tube 9, called a passive tube, which has an inner radius of the order of 55 mm, an outer radius of about 75 mm and a longitudinal slot 22 over almost all of its length. Said passive portion has a downstream longitudinal end formed by a tip 16, electrically insulated (both the housing 1 and the active portion of the electrode). The passive portion is also connected to a connector 11 via a nozzle 17 and a portion of tube 50 (of short length) extending the passive tube 9 upstream, said tip and tube portion forming part of the active portion (described later). The connector 11 passes through the housing 1 for the connection of the electrode 2 to an electrical circuit, and in particular to one or more capacitors (s) high voltage. The connector 11 comprises a conductive rod 12, a longitudinal end of which is welded in the endpiece 17, and a sleeve 13 of electrically insulating material for embedding the connector in the housing 1.

The passive portion of the discharge electrode 2 has a useful surface 23 oriented towards the electrode 3, formed by the portion of the external surface of the passive tube 9 located "below" (on the Figures 1 and 2 ) a "horizontal" median plane-orthogonal to the unloading direction-passing through a diameter of the tube.

The discharge electrode 2 further comprises an active portion comprising a cylindrical rod 10, called an active rod, of circular section having a substantially constant diameter of the order of 10 mm, and of length substantially corresponding to that of the passive tube. 9. The active portion has a longitudinal connection end which extends said active rod 10, and which comprises the tip 17, the tube portion 50 and a lug 15 for fixing the rod 10 to said tube portion 50. The active portion also has a downstream longitudinal end 18, carried by the longitudinal end downstream 6 of the passive portion to which it is connected by a pin 14 of electrically insulating material. The active rod 10 extends opposite, in the unloading direction Z, of the slot 22 of the passive tube 9, so as to protrude slightly (in the said unloading direction Z) from the useful surface 23 of the passive portion and to extend between this useful surface and the discharge electrode 3.

The active portion of the discharge electrode 2 has a useful surface 24 formed by the portion of the outer surface of the rod 10 which is directed towards the electrode 3 (this portion is cylindrical with a semicircular section) and which is extends, in the longitudinal direction, between the trigger electrode 4 and the downstream end 18 of the rod.

The discharge electrode 3 comprises on the one hand a passive portion formed by a plate or wall 6 of the housing 1, said passive wall. Said wall 6 of the housing is connected at one end 27 to a connector 7 for connecting said wall to ground. The connector 7 has a conductive rod passing through the wall 6 (which provides the connection between said connector and the passive wall 6), and a mortise receiving the connection end of the active portion (described below) of the electrode 3. The discharge electrodes 2 and 3, provided with their respective connector 11, 7, are arranged so that said connectors are facing in the transverse direction of unloading.

The passive portion of the discharge electrode 3 has a planar working surface formed by the portion of the inner face (facing the electrode 2) of the wall 6 of the housing which extends, in the longitudinal direction, between the tip 17 and the tip 16 of the electrode 2.

The discharge electrode 3 further comprises an active monobloc portion consisting of a cylindrical rod 5, called active rod, of circular section having a substantially constant diameter of the order of 10 mm. The active portion has, on the one hand, a longitudinal end of formed connection by the longitudinal end 28 of the active rod, welded in the mortise of the connector 7, and secondly, a downstream longitudinal end formed by the opposite longitudinal end 20 of the active rod 5, carried by a wall 29 of the housing 1 in which it is fixed by an anchor 8 of electrically insulating material. The downstream end of the active portion of the electrode 3 is thus electrically isolated. The active rod 5 of the electrode 3 extends parallel to the passive wall 6 and close to the latter also extends parallel to the active rod 10 of the electrode 2.

The active portion of the discharge electrode 3 has a useful surface 26 formed by the portion of the outer surface of the rod 5 which is oriented towards the electrode 2 (this part is cylindrical with a semicircular section) and which extends, in the longitudinal direction, between the trigger electrode 4 and the free end 16 of the electrode 2.

To make a shot, plug connector 11 to one or more capacitors, the connector 7 and the housing 1 being connected to ground. The discharge electrodes 2 and 3 are thus brought to distinct potentials, the difference of which can be up to 50 kV. The electrical charges are distributed over the useful surfaces of the active and passive portions of the discharge electrodes, and an electric field appears between the two electrodes. Because of their shape and their extent, the useful surfaces 23 and 25 of the passive portions of the electrodes act as reducers of the electric field, thus limiting the risks of self-priming of the spark gap under normal conditions of use of the spark plug. this.

Arc formation is then initiated between the active rods 10 and 5 of said electrodes, in the electric arcing trip zone 21, by bringing the trigger electrode 4 to a suitable given potential. The presence of the trigger electrode, when brought to this potential, locally increases the electric field and causes a breakdown in the electric arc trip zone.

A current is thus established between the conductive rods of the connectors 11 and 7. This current flows essentially in the active portions of the electrodes: the electric charges propagate in the tip 17, the tube portion 50, the fixing lug 15 and the active rod 10 of the discharge electrode 2; they are transferred to the discharge electrode 3 by the electric arc formed between the active rods 10 and 5, which arc extends substantially in the transverse direction of unloading; then they propagate in the active rod 5 of the discharge electrode 3 to the connector 7. The current is channeled into the active rods 10 and 5.

Note that the trigger electrode extends near the connection ends of the active portions of the two discharge electrodes, slightly downstream (and not facing) of said connection ends. Therefore, when a current is established, it flows in the active rod of each electrode over a length which corresponds, at the time of the establishment of the current, to the distance - along the longitudinal direction - between the end of connection of the active portion and the electric arc trip zone. From its establishment, the current therefore has a component in the longitudinal direction X, immediately upstream of the electric arc. In the discharge electrode 2, the current flows towards the downstream end 18 of the rod 10, while it flows in the opposite direction in the discharge electrode 3, towards the connection end 28 of the rod 5. The flow of current in each of the active rods 10, 5 induces a magnetic field with substantially circular field lines in the vicinity of the rods. Between said rods, in the plane of the arc (plane comprising the two rods and in which the arc is formed and moves), the resulting magnetic field (sum of the fields induced by the two electrodes) has a direction substantially orthogonal to the longitudinal and transverse directions of unloading, and a sense "returning" on the figure 1 . The resulting induced magnetic field moves the electric arc in the longitudinal direction towards the downstream ends 18 and 20 of the active rods 10 and 5, along said rods which provide a straight range of displacement of the arc. The terms "upstream" and "downstream" are defined with reference to this direction of movement of the electric arc.

The active rods 10 and 5 having small diameters, their useful surfaces 24 and 26 have a small width. The density of the current flowing in the active rods, along these useful surfaces 24 and 26, is therefore particularly high, so that the induced magnetic field is strong and the resulting Laplace force important. The speed of displacement of the arc obtained is sufficiently high to considerably reduce, or even avoid, the damage due to erosion of the electrodes by the electric arc. Unlike known spark gaps, it is therefore not necessary to use a special expensive alloy to make the electrodes (a basic material such as a simple steel is suitable), or to provide a geometry that allows the arc to pass several times in the same place during the same shot.

The second spark gap according to the invention illustrated in figures 3 and 4 comprises: a parallelepipedal box 30, conductive or not, made of a steel or any synthetic material; two identical discharge electrodes 31 and 32; and an electrode 42 for triggering an electric arc.

Similarly to the first spark gap, each discharge electrode 31, 32 has a generally elongate and straight shape, defining a longitudinal direction of the electrode. Each electrode comprises a straight elongated active portion, described below, whose longitudinal direction (guideline) coincides with that of the electrode. The electrodes are arranged parallel to one another and symmetrically; they extend opposite one another in the transverse direction Z of unloading, and their parallel guidelines define a longitudinal direction X common.

The trigger electrode 42 also extends in the longitudinal direction X, and has, between the discharge electrodes, a free end defining in its vicinity a region 41 of electric arc triggering. The trigger electrode 42 is mounted on a wall 48 of the housing 30 by means of a sleeve of insulating material, which allows both to fix the electrode on the housing 30 , to isolate the electrode from the housing, and to protect the fraction of the electrode which extends outside the housing 30 .

Each discharge electrode 31, 32 comprises an elongated flat plate 33 and a rod 34, whose respective longitudinal directions coincide with the longitudinal direction X of the electrode. The rod 34 is fixed to the flat plate by a fixing flange 46 and screw means or bolts, so as to extend facing an upstream fraction of said plate. The flat plate has a length of the order of 700 mm and a width (dimension in a transverse direction orthogonal to the longitudinal direction X and the discharge direction Z) of the order of 100 mm. The rod 34 has a length of the order of 200 mm and a width of the order of 25 mm.

The active portion of each discharge electrode 31, 32 is formed by the rod 34 and by a downstream fraction 44 of the plate which extends in the extension of a downstream longitudinal end 47 of the rod 34 towards a free end 35 of the plaque. This active portion has a longitudinal connection end formed by an upstream longitudinal end 40 of the rod 34, and a downstream end formed by the free end 35 of the plate.

Note that each rod 34 is slightly curved in a plane containing the two rods (plane of formation and displacement of the electric arc), so that the spacing between the two rods is variable: it is minimal in the zone 41 arc tripping, then increases downstream, towards the ends 47 of the rods 34. When the discharge electrodes are brought to different potentials, the electric field induced between the rods 34 is maximum in the zone of electric arc trigger. The triggering of an electric arc is facilitated.

The passive portion of each electrode 31, 32 is formed by an upstream fraction 45 of the plate 33, which extends from an upstream end 36 of the plate 33 to the downstream end 47 of the rod 34. Said passive portion is directly connected to a connector by its upstream end 36.

The connection ends 40 and 36 of the active and passive portions of each electrode are traversed by the conductive rod 38 of a connector 37. The mechanical connection thus formed is electrically conductive; it makes it possible to connect the electrode in an electric circuit. In particular, one of the connectors 37 can be connected to one or more capacitors and the other connector to a load. The conductive rod 38 of the connector is surrounded by an insulating sleeve 39, for its installation in a wall of the housing 30 and its attachment to said wall.

Similarly to the first spark gap, the trigger electrode 42, when raised to a given potential, locally changes the electric field in the electric arc trip zone and initiates the formation of an electric arc between the rods. 34. The established current, channeled into the rods 34, flows in the longitudinal direction X, downstream - that is to say towards the free end 35 - in the electrode connected to the generator, and to the upstream-that is, towards the connection end 40- in the electrode connected to the load.

The established current induces a magnetic field between the electrodes, whose direction in the arc plane is orthogonal to the longitudinal direction and the discharge direction. The induced magnetic field moves the arc toward the free ends of the active portions.

The discharge of a capacitor comprises an initial period during which the current flowing through the spark gap has an increasing intensity (initially zero). The active portion of each electrode in the vicinity of the electric arc trip zone is advantageously formed by the rod 34, the useful surface of which has a small width in order to concentrate the electric charges, increase the current density and thus generate a high magnetic field in this area despite the low intensity of the current at the beginning of the discharge. The induced field is sufficient to move the electric arc at a speed capable of limiting erosion. The rods are advantageously dimensioned so that, as long as the intensity of the current is not sufficiently high, the moving electric arc still extends between the rods.

Note that, for each discharge electrode 31, 32, an element 43 of electrically insulating material is arranged between the active rod 34 and the passive upstream fraction 45 of the plate, downstream of the electric arc trip zone. This element 43 can channel in the rod 34 the established current, at least until the moving electric arc has not reached the downstream end 47 of the rod. The electrical insulation that the element 43 provides could also be obtained by leaving a space between the rod 34 and the passive upstream fraction 45, that is to say by removing the element 43, the gas contained in the housing 30. realizing an insulator.

After the electric arc reaches the end 47 of the rod 34, its movement is along the downstream fraction 44 of the plate. Said plates having a width greater than that of the rods 34, the current density flowing on the useful surface of these plates is less than that flowing on the useful surface of the rods. The induced field between the facing plates 33 in this zone is therefore smaller, but is nevertheless sufficient to move the arc at a high speed, since the intensity of the current in the electric arc is now high (the initial phase being completed).

The obtained speeds of displacement of the electric arc between the rods 34 and between the downstream fractions 44 of the plates, are sufficiently high to limit the erosion of said downstream rods and fractions to the point of allowing the use of a basic material ( any copper or steel for example) for their manufacture, or to allow to transfer charge quantities and / or current intensities higher than those usually transferred.

It goes without saying that the invention may be subject to numerous variants with respect to the embodiments previously described and shown in the figures.

In particular and especially, a spark gap comprising an unloading electrode devoid of passive portion is in accordance with the invention, since the other electrode has one.

Furthermore, a spark gap comprising two identical discharge electrodes, similar to either electrode 2 or electrode 3 represented in the figures, is in accordance with the invention. Similarly, a spark gap comprising one of the electrodes 2 or 3 shown, associated with an electrode such as the electrode 31, is in accordance with the invention.

In addition, the spark gap shown in Figures 1 and 2 could be used by connecting one of the electrodes to one or more capacitors (s) and the other electrode to a load, by means of a modification of the electrode 3 (such as the addition of an insulating sleeve around the connector 7 ) to isolate the latter from the housing 1.

Furthermore, the arcing trip means are not limited to the trigger electrodes shown. In particular, it is possible to use a needle-shaped electrode which passes through (in the unloading direction) without contact the active portion of one of the discharge electrodes. When brought to a given given potential, such an electrode creates a plasma in its vicinity, which propagates so as to form an electric arc. In a variant, the spark gap is devoid of a trip electrode. It is closed either by applying a voltage higher than the minimum self-priming voltage, or by temporarily creating, between its discharge electrodes, an overvoltage greater than said self-priming voltage. Alternatively, the pressure of the gas inside the spark gap housing (by opening a corresponding regulating valve) is reduced.

More generally, the shape and structure of the electrodes are not limited to those illustrated. In particular, the active portions of the electrodes may have a curved guideline, to form, for example, a turn or circular ring open (or possibly closed). The passive portions of the electrodes may have various shapes, provided that these shapes are adapted (in particular by the extent and arrangement of their useful surface) to prevent inadvertent self-priming of the spark gap.

Claims (27)

1. spark-gap device comprising two rigid discharge electrodes which are mounted fixedly and distantly from each other, and at least two connectors, each electrode being connected to one of the connectors to connect said electrodes to an electrical circuit including a current generator, in which:

   - each discharge electrode (2; 3; 31) has an extended conducting portion (10; 5; 34, 44), called the active portion, which has a longitudinal extremity (15, 50, 17; 28; 40), called the connection longitudinal extremity, which is connected to the connector (11; 7; 37), and an opposite longitudinal extremity (18; 20; 35), called the downstream extremity,

   - initiating means (4; 42) are suitable for initiating the formation of an electrical arc between the active portions of the electrodes, in a region (21; 41) called the electrical arc initiation region,

   - the active portions of the discharge electrodes are arranged to be able to channel an electric current, and to be able to form an extended range of movement of the electrical arc by the effect of a magnetic field induced by said current,

   - at least one discharge electrode (2; 3; 31) has at least one other conducting portion (9, 16; 6; 45), called the passive portion, which is connected electrically to the connector and/or to the active portion, said passive portion having a surface (23, 25), called the useful surface, defined as that part of the surface of the passive portion which extends opposite the other electrode, having a minimum radius of curvature which is greater than a threshold radius below which the intensity of the electrical field between the discharge electrodes is greater than a minimum self-striking value in normal conditions of use of the spark-gap device, said passive portion being suitable for preventing any ill-timed spontaneous formation of an electrical arc in said normal conditions of use of the spark-gap device.
2. Spark-gap device according to Claim 1, characterized in that each discharge electrode has a passive portion.
3. Spark-gap device according to any one of Claims 1 or 2, characterized in that the active and passive portions of at least one of the discharge electrodes are separated at least by a fraction of the length of the active portion downstream from the electrical arc initiation region.
4. Spark-gap device according to any one of Claims 1 to 3, characterized in that it includes an initiating device (4; 42), which is suitable for initiating the formation of an electrical arc in the electrical arc initiation region (21; 41).
5. Spark-gap device according to any one of Claims 1 to 4, characterized in that the active portions (10, 5) of the discharge electrodes extend approximately facing each other, at least downstream of the electrical arc initiation region (21; 41).
6. Spark-gap device according to any one of Claims 1 to 5, characterized in that the active portions of the discharge electrodes have connection longitudinal extremities (17, 50, 15; 28; 40) which are arranged on one side of the spark-gap device.
7. Spark-gap device according to any one of Claims 1 to 6, characterized in that the active portions (10, 5; 34, 44) of the discharge electrodes have approximately parallel directrices.
8. Spark-gap device according to any one of Claims 1 to 7, characterized in that the active portion (10; 5; 34, 44) of at least one of the discharge electrodes has a directrix, called longitudinal direction, which is approximately straight, at least downstream of the electrical are initiation region (21; 41).
9. Spark-gap device according to any one of Claims 1 to 8, characterized in that the active portions (10, 5; 34, 44) of the discharge electrodes have similar overall shapes.
10. Spark-gap device according to any one of Claims 1 to 9, characterized in that the active portion of each electrode has a surface (24; 26), called the useful surface, of suitable dimensions so that the induced magnetic field moves the electrical arc at sufficient speed to avoid eroding the active portions by local melting and/or vaporisation, said useful surface of the active portion being defined as that part of the surface of the active portion which extends opposite the other electrode, downstream from the electrical arc initiation region.
11. Spark-gap device according to Claim 10, which is suitable for transmitting an electric current of intensity between 1 kA and 1 MA, and for transferring a quantity of charge between 0.1 and 200 C, characterized in that the useful surface (24; 26) of the active portion of each discharge electrode has a length between 5 and 200 cm, and a width less than 50 cm on this length, and less than 7 cm at least on an upstream fraction of this length.
12. Spark-gap device according to any one of Claims 1 to 11, characterized in that the active portions (10, 5; 34, 44) of the discharge electrodes are of a basic conducting material such as a steel, a stainless steel, a brass, aluminium, copper, a copper-based alloy.
13. Spark-gap device according to any one of Claims 1 to 12, characterized in that at least one (2; 3) of the discharge electrodes has an active portion (10; 5) having the shape of a cylindrical rod, at least between the electrical arc initiation region and its downstream extremity.
14. Spark-gap device according to any one of Claims 1 to 13, characterized in that at least one (2; 3) of the discharge electrodes has an active portion having the shape of a rod (10; 5) of circular transverse cross-section, at least between the electrical arc initiation region and its downstream extremity.
15. Spark-gap device according to Claim 14, characterized in that said rod has a transverse cross-section of approximately constant diameter.
16. Spark-gap device according to Claim 14, characterized in that said rod has a transverse cross-section having a diameter which increases in the downstream direction.
17. Spark-gap device according to any one of Claims 1 to 16, characterized in that the active portion of at least one of the discharge electrodes has an electrically insulated downstream extremity.
18. Spark-gap device according to any one of Claims 1 to 17, characterized in that each passive portion (45) extends along at least one upstream fraction (34) of the active portion of the discharge electrode, projecting from a longitudinal edge of said active portion and in such a way as not to cross a separating space which extends between the active portions of the two electrodes.
19. Spark-gap device according to any one of Claims 1 to 18, characterized in that the passive portion of at least one (3) discharge electrode has a plane useful surface (25).
20. Spark-gap device according to any one of Claims 1 to 19, characterized in that at least one (2) of the discharge electrodes includes an active portion which has, at least downstream from the electrical arc initiation region, a shape of a cylindrical rod (10) of circular cross-section, called the active rod, and a passive portion which has the shape of a hollow cylindrical tube (9) of greater cross-section than that of the active rod, said tube having a longitudinal slot (22) facing which the active rod (10) extends, the downstream longitudinal extremity (18) of the active rod being carried by a downstream longitudinal extremity (16) of the tube.
21. Spark-gap device according to any one of Claims 1 to 20, characterized in that at least one (3) of the discharge electrodes includes an active portion (5) which has, at least downstream from the electrical arc initiation region, a shape of a cylindrical rod, and a passive portion (6) in the form of a plane plate, said plate and rod being distant from each other, and arranged in such a way that the rod extends between the plate and the other electrode, parallel and near to said plate.
22. Spark-gap device according to any one of Claims 1 to 21, characterized in that it includes a box (1; 30), inside which the discharge electrodes are placed.
23. Spark-gap device according to Claim 22, characterized in that the box includes at least one conducting wall (6), which acts as a passive portion of a discharge electrode (3).
24. Spark-gap device according to any one of Claims 1 to 23, characterized in that at least one (31, 32) of the discharge electrodes includes an extended plane plate (33), and in that the active portion of the electrode consists of a downstream fraction (44) of said plate and at least one rod (34) of length and width respectively less than those of the plate, said rod being fixed on an upstream fraction (45) of said plate, the passive portion of the electrode consisting of the upstream fraction (45) of the plate.
25. Spark-gap device according to any one of Claims 1 to 24, characterized in that it comprises multiple pairs of discharge electrodes, arranged in parallel.
26. Spark-gap device according to Claim 25, characterized in that it includes means for electrical decoupling between one cf its connectors and one of the electrodes of each pair.
27. Spark-gap device according to any one of Claims 25 or 26, characterized in that at least one of the discharge electrodes of each pair is connected to a connector of the spark-gap device which is specific to it.

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