Gas igniter

Abstract

The invention relates to a gas discharger (2) for the protection of an electrical installation, comprising: an electrically insulating body (10); two electrodes (11; 12) fixed to the electrically insulating body and spaced apart in a principal direction; an inter-electrode space (20) formed in the electrically insulating body between the two electrodes, the inter-electrode space being closed in a gas-tight manner; two connection terminals (31; 32) intended to allow an electrical connection of said gas discharger to the electrical installation, the two connection terminals being respectively electrically connected to said two electrodes; the inter-electrode space comprising a deflection channel (22) defining a propagation path (T) for an electric arc;a cross-section of the deflection channel (22) being between 2 and 8 mm², the deflection channel extending transversely or obliquely to the principal direction over at least part of the length of the deflection channel; and a gas trapped in the inter-electrode space, the gas being selected from argon Ar, neon Ne, dinitrogen N2, dihydrogen H2, helium He and mixtures thereof. Figure for the abstract: 3;

Description

Title of the invention: Gas spark gap technical field

[0001] The invention relates to the general field of protection devices against transient overvoltages of all types of circuits, installations, electrical equipment and networks.

[0002] The invention relates more particularly to the field of surge arresters or gas-gap surge arresters for the protection of electrical circuits, installations or equipment and networks against transient overvoltages, in particular due to lightning. Technological background

[0003] Electrical or data transmission networks can be subject to transient overvoltages and overcurrents. Industrial and switching disturbances, generated by the starting or stopping of motors or alternators, the switching of power networks, or the falling of electrical cables with different voltages, are examples of factors likely to cause transient overvoltages and overcurrents. Furthermore, when these networks include cables suspended above the ground, attached to utility poles or other structures, over long distances, they are particularly susceptible to lightning strikes.

[0004] Lightning is characterized by a high peak intensity pulse discharge current with a rise time on the order of microseconds. Typically, lightning can cause overvoltages of several million volts and overcurrents of thousands of amperes. However, electrical or data transmission networks are not designed to withstand such transient overvoltages and overcurrents.

[0005] To protect these networks, it is known to use protection devices generally referred to as "surge arresters", overvoltage arresters or "overvoltage arresters" which are intended to drain impulse currents to earth, which makes it possible to clip overvoltages to values ​​compatible with the performance of the electrical installation and the equipment to which they are connected.

[0006] Surge arresters with gas discharge tubes are known in particular from FR 3 017 004. Such a gas discharge tube is a hermetically sealed electrical component comprising two conductive electrodes separated by an insulating ceramic inside which a gas is trapped. In normal operation of the electrical network, i.e. in the absence of overvoltage, the gas discharge tube exhibits a very low insulation resistance. The potential difference is high, and can be considered virtually infinite. However, when subjected to a transient overvoltage exceeding the gas spark gap's opening voltage (determined by the gas pressure), an electric arc forms due to the ionization of the gas between the electrodes. The gas spark gap then abruptly opens and becomes conductive with very low impedance. The gas spark gap can then be considered a short circuit, diverting a strong discharge current to ground, corresponding to the transient overvoltage. This allows for the protection of electrical circuits downstream of the gas spark gap against impulse currents by diverting them to ground through the gas spark gap.

[0007] Thus, in the behavior of a spark gap, we can distinguish four operating domains: the resting domain, the effluvium domain, the arc regime and the extinction.

[0008] The resting domain is characterized by a practically infinite insulation resistance.

[0009] In the effluvium range, after ignition, the conductance increases abruptly. If the current flowing through the gas spark gap is less than approximately 0.5 amperes (an approximate value that varies with different types of spark gaps), the voltage, known as the effluvium voltage, at the terminals will be 80-100 volts.

[0010] Next, the arc regime is established: as the current increases, the gas spark gap transitions from the effluvium voltage to the arc voltage. It is in this range that the gas spark gap is most efficient, since the current flowing can reach several thousand amperes without significantly increasing the arc voltage at its terminals.

[0011] Finally comes the extinction of the spark gap: for a bias voltage approximately equivalent to the effluvium voltage, the spark gap recovers its initial insulation characteristics after the disturbance has dissipated.

[0012] Such gas dischargers are designed to exhibit good resistance to impulse currents, typically 100 kA. Impulse current is defined as the maximum resistance without destruction or dispersion of the electrical initiation characteristics following the passage of a 10 / 350 ps wave representative of the lightning current generated during a direct impact.

[0013] However, the weak point of a sealed gas discharge tube is its extinguishing capacity. Containing a gas in a sealed chamber, after the discharge tube is triggered and the lightning current passes through it, the gas becomes hot and ionized. Since the gas discharge tube is connected to the network, the network current can then flow through this ionized gas, theoretically indefinitely.

[0014] Indeed, once triggered, the gas discharger releases a portion of the mains current, then called the follow current. Unlike an air discharger, the gas cannot escape from the enclosure and therefore cannot be blown out, which would cause the circuit to shut down. current. This greatly limits their extinguishing capacity: the gas spark gap can only extinguish a low network current (on the order of a few hundred Amperes).

[0015] For the spark gap to extinguish correctly, the operating voltage of the network to be protected must be lower than the minimum spark gap arc voltage. Thus, it is advantageous to increase the arc voltage across the spark gap when it is in the arcing regime. Summary of the invention

[0016] One idea underlying the invention is to produce a gas spark gap with a better capacity for extinguishing the following current, while retaining its electrical characteristics of ignition and resistance to shock currents.

[0017] According to one embodiment, the invention provides a gas burst for the protection of an electrical installation, comprising:

[0018] - an electrically insulating body;

[0019] - two electrodes fixed to the electrically insulating body and spaced apart from each other in a main direction;

[0020] - an inter-electrode space provided in the electrically insulating body between the two electrodes, the inter-electrode space being closed in a gas-tight manner;

[0021] - two connection terminals intended to allow an electrical connection said gas spark gap to the electrical installation, the two connection terminals being respectively electrically connected to said two electrodes; the inter-electrode space comprising a deflection channel defining a propagation path for an electric arc; a cross-section of the deflection channel being between 2 and 8 mm2, the deflection channel extending transversely or obliquely to the main direction over at least part of the length of the deflection channel;

[0022] and a gas trapped in the inter-electrode space.

[0023] According to one embodiment, the gas is selected from argon Ar, neon Ne, dinitrogen N2, dihydrogen H2, helium He and mixtures thereof.

[0024] Thanks to these characteristics, the propagation path is defined by the deflection channel. In other words, first, the electric arc is forced to propagate along a propagation path defined by the shape of the deflection channel. Then, it is possible to lengthen the arc by defining a propagation path that includes at least one turn, or even at least a half-turn. Thus, the arc length is increased, resulting in a correspondingly increased arc voltage. The increased arc voltage facilitates arc extinction.

[0025] According to one embodiment, the gas spark gap further includes an ignition chamber formed at one end of the inter-electrode space to initiate an electric arc.

[0026] According to one embodiment, the gas burster further comprises at least one initiating element positioned in the initiation chamber.

[0027] According to one embodiment, the initiating element comprises an initiating electrode separated from the two electrodes and / or one or more graphite lines.

[0028] Thus, it is possible to initiate the arc by triggering a spark with the initiating element.

[0029] According to one embodiment, the initiation electrode is electrically connected to passive electronic components adapted to generate an electric arc initiation between the initiation electrode and one of the two electrodes following the reception of a transient overvoltage.

[0030] According to one embodiment, the length of the inter-electrode space is between 6 and 10 mm.

[0031] Thus, the arc has a length between 6 and 10 mm since the inter-electrode space defines the propagation trajectory thanks to its small cross-section.

[0032] According to one embodiment, the gas spark gap has a starting voltage greater than 200V.

[0033] According to one embodiment, the insulating body is made of ceramic, for example of alumina.

[0034] According to one embodiment, the electrodes are made of copper or of steel and nickel alloy or any other suitable metal or alloy.

[0035] According to one embodiment, the gas burster has the general shape of a straight cylinder with a rectangular or circular cross-section. Brief description of the figures

[0036] The invention will be better understood, and other objects, details, features and advantages thereof will become more apparent from the following description of several particular embodiments of the invention, given solely by way of illustration and not limitation, with reference to the accompanying drawings.

[0037] [Fig. 1] schematically represents an electrical installation in which embodiments of the invention can be used,

[0038] [Fig.2] schematically represents a gas burst according to a first mode of realization,

[0039] [Fig.3] is a cross-sectional view along line III-III of [Fig.2].

[0040] [Fig.4] is a view analogous to [Fig.3] which schematically represents a spark gap gas-powered according to a second embodiment,

[0041] [Fig.5] schematically represents a gas burst according to another mode of realization,

[0042] [Fig.6] schematically represents a gas burst according to another mode of realization,

[0043] [Fig.7] schematically represents a gas burst according to another mode of realization.

[0044] [Fig.8] is a graph representing the voltage across the terminals of a gas spark gap according to a method of implementation depending on the time available. Description of the implementation methods

[0045] The following embodiments are described in relation to a gas spark gap intended to limit transient overvoltages in an electrical or data transmission network comprising an electrical line to be protected, for example a telecommunications network, or a network for the transport of very high power energy such as a high voltage network, or even a medium or low voltage network.

[0046] The gas discharge tube described below is generally intended to be connected to all types of electrically powered devices, installations, or networks that are susceptible to transient disturbances, particularly those caused by lightning. Such a gas discharge tube can therefore advantageously serve as a surge arrester.

[0047] With reference to [Fig. 1], an electrical line to be protected 1 is connected by means of a gas discharge tube 2 to another electrical line 3, for example, a grounding connection, another discharge line, or any other electrical line in the network. The gas discharge tube 2 is thus connected in parallel with the electrical line to be protected 1.

[0048] The power line to be protected 1 carries an alternating or direct voltage.

[0049] Gas igniter

[0050] With reference to figures 2 and 3, the gas burst 2 comprises an insulating body 10, of parallelepiped shape, for example made of ceramic, at the ends of which are positioned two electrodes 11 and 12. The electrodes 11 and 12 are spaced apart from each other by the insulating body 10 along a principal direction of the gas burst 2.

[0051] The electrically insulating body 10 can be made of ceramic materials, preferably alumina. The electrically insulating body 10 is preferably covered with a casing or coating providing mechanical protection and electrical insulation, for example, made of plastic, in particular PBT or PA. Alternatively, insulating materials other than ceramics can be used for the construction of the electrically insulating body 10.

[0052] With reference to [Fig. 2], the electrodes 11 and 12 have external portions accessible from outside the insulating body and internal portions inserted into recesses machined into the insulating body 10. Thus, the external portions of the electrodes 11 and 12 extending outside the insulating body 10 form terminals of connection 31 and 32. These connection terminals 31 and 32 form electrical connection interfaces to allow the connection of the gas spark gap 2 to the electrical line to be protected 1.

[0053] For example, the first connection terminal 31 can be electrically connected to the power line to be protected 1 while the second connection terminal 32 can be electrically connected to an earthing link.

[0054] The connection terminal 31 or 32 and the electrode 11 or 12 form a single unit. Alternatively, each electrode 11, 12 is electrically connected to a connection terminal 31, 32 via a connecting means.

[0055] An inter-electrode space 20 is formed in the insulating body 10 between the first electrode 11 and the second electrode 12. The insulating body 10 and the two electrodes 11 and 12 are joined in a gas-tight manner, for example by brazing, so that the inter-electrode space 20 is completely isolated from the ambient atmosphere. In other words, the electrodes 11 and 12 are fixed to the insulating body 10 in a hermetic manner, for example by brazing.

[0056] The inter-electrode space 20 has the shape of a narrow channel that defines a propagation path T for an electric arc between the two electrodes 11 and 12. It comprises successively:

[0057] - a priming chamber 21 near the inner portion of the first electrode 11

[0058] - a deflection channel 22 deflecting the propagation trajectory T obliquely to the main direction for lengthening the propagation trajectory, and

[0059] - a contact chamber 23 near the internal portion of the second electrode 12.

[0060] According to an embodiment not shown, the deflection channel 22 comprises at least one half-turn or bend. In other words, the deflection channel 22 comprises a first portion extending from the first electrode 11 to the second electrode 12 and a second portion extending in the opposite direction, i.e., from the second electrode 12 to the first electrode 11. According to this embodiment, the deflection channel 22 may have a general "S" shape.

[0061] The ignition chamber 21 is the location where the electric arc is initiated. The electrode 11 forms at least one wall of the ignition chamber 21. The ignition chamber 21 may further include at least one initiating element, for example one or more graphite strips fixed to the insulating body 10 in the ignition chamber 21.

[0062] The initiating element further comprises an initiating electrode 40. This initiating electrode 40 can be electrically connected to passive electronic components such as resistors, inductors, and / or capacitors. These components Passive electronics generate the arc initiation in response to the transient overvoltage (lightning or other) received at the terminals of the gas spark gap 2.

[0063] Like the electrodes 11 and 12, the starting electrode 40 has external portions 45, 46 accessible from outside the insulating body and internal portions inserted into recesses machined into the insulating body 10. The insulating body 10 and the starting electrode 40 are assembled in a gas-tight manner, for example by brazing, so that the inter-electrode space 20 is completely isolated from the ambient atmosphere.

[0064] An internal portion 47 of the initiation electrode 40 is present within the inter-electrode space 20. With reference to [Fig.3], the internal portion 47 is located in the initiation chamber 21. In an embodiment not shown, the internal portion 47 may be located within the deflection channel 22.

[0065] The ignition generated by the transient overvoltage through the passive electronic components occurs between the internal portion 47 and the electrode 11, then the arc is established between the electrode 11 and the electrode 12. In an embodiment not shown, the ignition electrode 40 comprises several internal portions 47.

[0066] The inter-electrode space 20 has a cross-section between 1 and 10 mm2, for example between 2 and 8 mm2. According to one embodiment, the cross-section of the inter-electrode space is constant.

[0067] With reference to [Fig.3], the inter-electrode space 20 is formed by a space left free within the insulating body 10.

[0068] The walls of the inter-electrode space 20 are formed by the insulating body 10. In addition, a part of one of the electrodes 11, 12 can form a part of the walls of the inter-electrode space 20. For example, in [Fig.6], the electrode 12 forms a part of the wall of the inter-electrode space 20.

[0069] The inter-electrode space 20 therefore includes electrode 11 at one end and, at the second end, electrode 12.

[0070] With reference to figures 2 and 3, the main direction of the gas burst corresponds to the direction of insertion of the electrode 11 and the electrode 12 into the insulating body 10.

[0071] To ensure the gas is trapped within the gas burst 2, the burst is sealed. The gas trapped in the inter-electrode space 20 of the gas burst 2 is, for example, argon Ar, neon Ne, nitrogen N2, hydrogen H2, helium He, or a mixture of these gases. Advantageously, the gas contains hydrogen H2. This gas is stored in the gas burst 2 at an absolute pressure ranging from 0.5 bar (50 kPa) to 2 bar (200 kPa). As indicated, this pressure influences the opening voltage of the gas burst 2. The gas can thus be trapped in the gas burst 2 at different pressures depending on the desired opening voltage. According to one embodiment, the gas is an Argon-Hydrogen mixture with 10% hydrogen trapped at a pressure of 1300 mbar.

[0072] For example, a molybdenum-manganese layer can be used to seal the electrically insulating body 10, this molybdenum-manganese layer being itself coated with a nickel layer. The sealing of the electrically insulating body 10 can be achieved by melting the Ag-Cu brazing alloy.

[0073] Alternatively, the sealing of the electrically insulating body 10 can be achieved by an Ag-Cu-Ti brazing deposited directly on the surface of the insulating body 10 in contact with the electrode.

[0074] Another way to achieve this watertight seal is by bonding with an adhesive compatible with aluminas. Yet another technique consists of using a sealing gasket and mechanically clamping the two parts onto this gasket.

[0075] With reference to [Fig.8], we now describe a result obtained experimentally with a gas burster 2 as described previously.

[0076] A standardized 10 / 1000 ps current wave is sent to the terminals of the gas spark gap 2. In a known manner, a standardized 10 / 1000 ps current wave is a current wave characterized by a rise time of 10 ps and a total duration of 1000 ps.

[0077] Fig. 8 shows the arc voltage across the terminals of the gas spark gap 2 expressed in V on the ordinates as a function of time expressed in ms on the abscissas.

[0078] It is observed that an arc voltage of 200 V is established stably in less than 1 ms with a peak voltage of over 300 V. After 5 to 6 ms, the arc voltage becomes zero. In other words, the arc extinguishes after a duration of between 5 and 6 ms, or the arc extinction occurs after 5 to 6 ms.

[0079] The operation of a gas burster 2 as described previously is now described.

[0080] When a transient overvoltage associated with a pulsed current exceeds the ignition voltage of the gas spark gap 2, an electric arc is initiated in the ignition chamber 21.

[0081] In the inter-electrode space 20, the electric arc is guided by the gas present in the inter-electrode 20 between the ignition chamber 21 and the contact chamber 23 along the propagation path T.

[0082] As explained previously, the length of the propagation path T, i.e. the distance di, is increased by means of its transverse component(s).

[0083] Thus, the arc voltage is increased since the arc resistance is directly proportional to its length.

[0084] Furthermore, in addition to its ability to define the propagation trajectory T, the interelectrode space 20 allows for a reduction in the arc cross-section. Now, if the surface area of ​​the arc cross-section As the voltage is reduced, the voltage required to maintain the arc is increased. Thus, the cross-section of the discharge channel 22 allows for an increase in the arc voltage.

[0085] The gas spark gap 2 therefore makes it possible to obtain a sufficiently high arc voltage, which makes it easier to extinguish.

[0086] Thus, the gas spark gap 2 allows, while retaining the electrical characteristics of ignition and current holding of a gas spark gap, to improve the extinguishing power.

[0087] Other embodiments

[0088] With reference to [Fig. 4], a second embodiment of the gas burst 2 is now described. Elements similar or identical to those of the first embodiment are identified by the same reference numerals. Only the differences are described below.

[0089] According to this embodiment, the electrodes 11,12 are two metallic strips inserted from opposite faces of the electrically insulating body 10. Thus, the main direction of the inter-electrode space 20 corresponds globally to the horizontal direction of [Fig.4].

[0090] According to this embodiment, the electrodes 11,12 each include at their end a connecting terminal 31, 32. In this case, the main direction of the inter-electrode space 20 corresponds to the line passing through the two connecting terminals 31, 32.

[0091] According to this embodiment, the attachment of the electrodes 11, 12 to the electrically insulating body 10 is facilitated by ribs 51 of the electrically insulating body 10 engaged in notches 52 of the electrodes 11 and 12. The notches 52 are located on two opposite edges of the metal strips.

[0092] Furthermore, according to this embodiment, the gas burster 2 is closed by a cover (not shown).

[0093] According to another embodiment illustrated in [Fig. 5], with the electrodes 11, 12 inserted from the lower and upper faces of the electrically insulating body 10, the principal direction of the inter-electrode space 20 corresponds overall to the vertical direction of the figure. According to this embodiment, the gas burst 2 has a general rectangular or parallelepiped shape.

[0094] In a variant illustrated in figures 6 and 7, the gas burster may have a general shape of a straight cylinder.

[0095] Although the invention has been described in connection with several particular embodiments, it is clearly evident that it is by no means limited to them and that it includes all technical equivalents of the means described as well as their combinations if these fall within the scope of the invention.

[0096] The use of the verb "comprise", "comprendre" or "include" and its conjugated forms does not exclude the presence of other elements or other steps than those stated in a claim.

[0097] In the claims, any reference sign in parentheses shall not be interpreted as a limitation of the claim.

Claims

Demands

1. Gas spark gap (2) for the protection of an electrical installation, comprising: an electrically insulating body (10); two electrodes (11; 12) fixed to the electrically insulating body and spaced apart in a principal direction; an inter-electrode gap (20) formed in the electrically insulating body between the two electrodes, the inter-electrode gap being closed in a gas-tight manner; two connection terminals (31; 32) intended to allow electrical connection of said gas spark gap to the electrical installation, the two connection terminals being respectively electrically connected to said two electrodes; the inter-electrode gap comprising a deflection channel (22) defining a propagation path (T) for an electric arc;a section of the deflection channel (22) being between 2 and 8 mm2, the deflection channel extending transversely or obliquely to the main direction over at least part of the length of the deflection channel; and a gas trapped in the inter-electrode space, the gas being selected from argon Ar, neon Ne, dinitrogen N2, dihydrogen H2, helium He and mixtures thereof.;

2. Gas spark gap according to claim 1, further comprising an ignition chamber (21) formed at one end of the deflection channel for initiating an electric arc.

3. Gas igniter according to claim 2, further comprising at least one initiating element (40) positioned in the initiation chamber.

4. Gas spark gap according to claim 3, wherein the initiating element comprises an initiating electrode (40) separated from the two electrodes.

5. Gas spark gap according to claim 4, wherein the starting electrode is electrically connected to passive electronic components adapted to generate an electric arc initiation between the starting electrode and one of the two electrodes following the reception of a transient overvoltage.

6. Gas spark gap according to any one of claims 3 to 5, wherein the initiating element comprises one or more graphite strips.

7. Gas burster according to any one of the preceding claims, wherein a length of the deflection channel (22) is between 6 and 10 mm.

8. Gas spark gap according to any one of the preceding claims, wherein the two electrodes (11;12) are made of copper or of a steel and nickel alloy.

9. Gas igniter according to any one of the preceding claims, having the general form of a straight cylinder with a rectangular or circular cross-section.

10. Gas spark gap according to any one of the preceding claims wherein the insulating body is made of ceramic.

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