Gas-filled spark gap with high follow current extinction capacity

Abstract

A gas-filled spark gap 2 for the protection of an electrical installation includes a gastight casing 4 and two elongate electrodes 13, 14 delimiting between them an inter-electrode space. The inter-electrode space includes successively a striking chamber 17 and an arc-extinguishing chamber 20 for extinguishing the electrical arc. The arc-extinguishing chamber 20 includes mutually spaced divider plates 29. The gas-filled spark gap 2 also includes two connecting terminals 11, 12 accessible from outside the casing 4 and intended to enable electrical connection of the gas-filled spark gap 2 to the electrical installation. The two connecting terminals 11, 12 are respectively electrically connected to the two electrodes 13, 14. Finally, the gas-filled spark gap 2 includes an inert gas trapped in the casing 4.

Claims

1. A gas-filled spark gap (2, 102) for the protection of an electrical installation, including: a casing (4, 104) delimiting an internal space (5), the casing (4, 104) being gastight; two elongate electrodes (13, 113, 14, 114) along a propagation trajectory (T) and housed in the internal space (5), the two electrodes (13, 113, 14, 114) delimiting between them an inter-electrode space, the two electrodes (13, 113, 14, 114) being arranged in such a manner that the inter-electrode space includes successively along the propagation trajectory (T) a striking chamber (17) situated between first portions (18, 19) of the two electrodes (13, 113, 14, 114) to strike an electrical arc between the first portions (18, 19) of the two electrodes (13, 113, 14, 114) and an arc-extinguishing chamber (20) situated between second portions (21, 22) of the two electrodes (13, 113, 14, 114) to extinguish the electrical arc, an isolation distance (d.sub.i) being defined as a shortest distance between the two electrodes (13, 113, 14, 114) in a plane transverse to said propagation trajectory (T), the isolation distance (d.sub.i) between the second portions (21, 22) of the two electrodes (13, 113, 14, 114) being greater than the isolation distance (d.sub.i) between the first portions (18, 19) of the two electrodes (13, 113, 14, 114), said arc-extinguishing chamber (20) including mutually spaced divider plates (29, 129) distributed between the second portions (21, 22) of the two electrodes (13, 113, 14, 114); two connecting terminals (11, 111, 12, 112) accessible from outside the casing (4, 104) and intended to enable electrical connection of said gas-filled spark gap (2, 102) to the electrical installation, the two connecting terminals (11, 111, 12, 112) being respectively electrically connected to said two electrodes (13, 113, 14, 114); and an inert gas trapped in the internal space (5) of the casing (4, 104).

2. The gas-filled spark gap (2, 102) according to claim 1, further including a striking element (27) to encourage the striking of the electrical arc, the striking element (27) being positioned between the first portions (18, 19) of the two electrodes (13, 113, 14, 114) and fixed to an electrically-insulative support.

3. The gas-filled spark gap (2, 102) according to claim 2, in which the striking element (27) takes the form of a thin layer of graphite in the form of a line.

4. The gas-filled spark gap (2, 102) according to claim 1, in which each of the two electrodes (13, 113, 14, 114) includes a third portion (24, 25) situated between the first portion (18, 19) and the second portion (21, 22) and the inter-electrode space further includes an elongation chamber (23) situated between the third portions (24, 25) of the two electrodes (13, 113, 14, 114) to lengthen the electrical arc, the elongation chamber (23) being inserted between the striking chamber (17) and the arc-extinguishing chamber (20), the two electrodes (13, 113, 14, 114) being arranged so that the isolation distance (d.sub.i) between the third portions (24, 25) of the two electrodes (13, 14) increases from said striking chamber (17) towards said arc-extinguishing chamber (20).

5. The gas-filled spark gap (2, 102) according to claim 4, in which a variation of the isolation distance (d.sub.i) between the first portions (18, 19) of the two electrodes (13, 113, 14, 114) in the striking chamber (17) is less than the variation of the isolation distance (d.sub.i) between the third portions (24, 25) of the two electrodes (13, 113, 14, 114) in the elongation chamber (23).

6. The gas-filled spark gap (2, 102) according to claim 1, in which the first portions (18, 19) of the two electrodes (13, 113, 14, 114) in the striking chamber (17) are parallel.

7. The gas-filled spark gap (2, 102) according to claim 1, in which the two electrodes (13, 113, 14, 114) are arranged so that the inter-electrode space is horn-shaped.

8. The gas-filled spark gap (2, 102) according to claim 1, in which the divider plates (29, 129) include notches, each notch having an opening oriented toward the striking chamber (17).

9. The gas-filled spark gap (2, 102) according to claim 1, in which the second portions (21, 22) of the two electrodes (13, 113, 14, 114) are parallel in the arc-extinguishing chamber (20) and in which the divider plates (29, 129) are parallel to the second portions (21, 22) of the two electrodes (13, 113, 14, 114) and disposed at regular intervals perpendicular to the plane transverse to the propagation trajectory (T).

10. The gas-filled spark gap (2, 102) according to claim 9 including an insulative material stop plate (34, 134) positioned perpendicularly to the propagation trajectory (T) downstream of the divider plates (29, 129) along said propagation trajectory (T).

11. The gas-filled spark gap (2, 102) according to claim 4, further including two insulating plates (32, 132a, 132b) disposed in the internal space (5) of the casing (4, 104), the two insulating plates (32, 132a, 132b) being arranged so as to surround some or all of the first portions (18, 19) of the two electrodes (13, 113, 14, 114) and the third portions (24, 25) of the two electrodes (13, 113, 14, 114).

12. The gas-filled spark gap (2, 102) according to claim 11, further including two deflector plates (33) housed in the internal space (5) of the casing (4), each deflector plate (33) being inserted between said casing (4) and a respective insulating plate (32) at the level of the elongation chamber (23).

13. The gas-filled spark gap (2, 102) according to claim 1, in which the casing (4) includes an insulating base (6) and an insulating lid (7) connected in gastight manner, the sealed connection between the insulating base (6) and the insulating lid (7) being made by solder (28), for example AgCu solder.

14. The gas-filled spark gap (2, 102) according to claim 13, in which the insulating base (6) has open ends intended to be in gastight contact with the insulating lid (7), the open ends including a layer of molybdenum-manganese covered with a layer of nickel.

15. The gas-filled spark gap (2, 102) according to claim 13, in which the insulating base (6) includes at least two facing walls (9) and a bottom wall (8), the second portions (21, 22) of the two electrodes (13, 14) being respectively pressed against the two walls (9), the bottom wall (8) including two electrode grooves (26) in the striking chamber (17) and plate grooves (31) in the arc-extinguishing chamber (20), the two electrodes (13, 14) being mounted in the two electrode grooves (26) and the divider plates (29) being mounted in the plate grooves (31).

16. The gas-filled spark gap (2, 102) according to claim 1, in which the casing (104) includes an insulative material peripheral wall (136) having two opposite open ends, the two connecting terminals (111, 112) being formed by two metal plates covering the respective opposite ends in gastight manner, the sealed connection between the peripheral wall (136) and each of the two connecting terminals (111, 112) being made by solder (128).

17. The gas-filled spark gap (2, 102) according to claim 16, further including: two insulating plates (132a, 132b) disposed in the internal space of the casing (104), the two insulating plates (132a, 132b) being arranged so as to surround the two electrodes (113, 114); and two deflector plates (133) respectively inserted between the two insulating plates (132a, 132b) and the two connecting terminals (111, 112).

18. The gas-filled spark gap (2, 102) according to claim 1, in which the two electrodes (13, 113, 14, 114) are made of a metal selected in the group consisting of copper and its alloys.

19. The gas-filled spark gap (2, 102) according to claim 1, in which the inert gas trapped in the internal space (5) of the casing (4, 104) is selected from the group consisting of argon, neon, dihydrogen, dinitrogen, rare gases and mixtures of those gases.

20. The gas-filled spark gap (2, 102) according to claim 19, in which the inert gas includes dihydrogen.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0061] The invention will be better understood and other aims, details, features and advantages thereof will become more clearly apparent in the course of the following description of particular embodiments of the invention given by way of non-limiting illustration only with reference to the appended drawings.

[0062] FIG. 1 is a schematic representation of an electrical network including a protection device taking the form of a gas-filled spark gap.

[0063] FIG. 2 is a perspective view of a gas-filled spark gap according to the invention.

[0064] FIG. 3 is an exploded perspective view of the gas-filled spark gap from FIG. 2.

[0065] FIG. 4 is a view in section from above of the gas-filled spark gap from FIG. 2.

[0066] FIG. 5 is a perspective view of the insulating base of the casing of the gas-filled spark gap from FIG. 2.

[0067] FIG. 6 is a cutaway perspective view of the gas-filled spark gap from FIG. 2, the insulating lid of the casing being omitted.

[0068] FIG. 7 is an exploded perspective view of another embodiment of a gas-filled spark gap.

DESCRIPTION OF EMBODIMENTS

[0069] The following embodiments are described in connection with a gas-filled spark gap intended to limit transient voltage surges in an electrical or data transmission network including an electrical line to be protected, for example a telecommunication network, a very high power energy transport network such as a high-voltage network, or a medium- or low-voltage network.

[0070] The gas-filled spark gap described hereinafter is more generally intended to be connected to any type of apparatus, installation or network powered electrically and liable to be subjected to transient disturbances, caused in particular by lightning. A gas-filled spark gap of this kind can therefore advantageously constitute an arrester.

[0071] Referring to FIG. 1, an electrical line 1 to be protected is connected by a gas-filled spark gap 2 to another electrical line 3, for example an earthing connection, another discharge line, or any other electrical line of the network. The gas-filled spark gap 2 is therefore shunt-connected (or parallel-connected) to the electrical line 1 to be protected.

[0072] The electrical line 1 to be protected carries an AC or DC voltage.

[0073] Referring to FIG. 2, the gas-filled spark gap 2 includes a hollow parallelepiped-shaped casing 4 delimiting an internal space 5 (visible in FIG. 3). The casing 4 is made of ceramic materials for example, preferably alumina. The casing 4 is preferably covered by an enclosure or a coating providing mechanical protection and electrical insulation, for example made of plastic material, in particular PBT or PA. Alternatively, insulating materials other than ceramics may be employed to produce the casing 4.

[0074] The casing 4 includes an insulating base 6 and an insulating lid 7. The insulating base 6 includes a bottom wall 8 and two longitudinal walls 9 interconnected by two transverse walls 10. As represented here, the longitudinal walls 9 have a dimension greater than that of the transverse walls 10.

[0075] One of the transverse walls 10 of the insulating base 6 includes a first connecting terminal 11 and a second connecting terminal 12. The first connecting terminal 11 and the second connecting terminal 12 form electrical connection interfaces between the interior and the exterior of the casing 4 in order to enable connection of the gas-filled spark gap 2 to the electrical line 1 to be protected.

[0076] For example, the first connecting terminal 11 may be electrically connected to the electrical line 1 to be protected and the second connecting terminal 12 may be electrically connected to an earth connection.

[0077] In FIGS. 2 to 4 the first connecting terminal 11 and the second connecting terminal 12 take the form of connecting studs, made of copper for example, a copper and tungsten alloy or any other appropriate metal or alloy.

[0078] In a variant (not represented) the first connecting terminal 11 and the second connecting terminal 12 may in particular take the form of tags, spring clamps or metal screw-cage assemblies, typically intended to be engaged on the end of a cable, a terminal block or a conductive rail connected to the electrical line 1 to be protected.

[0079] Referring to FIGS. 3 and 4 the hollow casing 4 delimits an internal space 5 inside which are housed two electrodes 13, 14. Each electrode 13, 14 is electrically connected to a connecting terminal 11, 12 by a connecting means 15, 16.

[0080] The electrodes 13, 14 and the connecting means 15, 16 advantageously form one-piece members. An arrangement of this kind makes it possible to eliminate connecting means (rivets, screws or filler metal) to avoid delicate and costly assembly operations.

[0081] Each electrode 13, 14 takes the form of a metal strip extending along a propagation trajectory T of an electrical arc and the thickness of which is of the order of the height of the insulating base 6 of the casing 4. The two electrodes 13, 14 may be made of copper, an alloy of copper and tungsten or any other appropriate metal or alloy.

[0082] The two electrodes 13, 14 delimit an inter-electrode space including a striking chamber 17 situated between first portions 18, 19 of the two electrodes 13, 14 to strike an electrical arc, an arc-extinguishing chamber 20 situated between the second portions 21, 22 of the two electrodes 13, 14 to extinguish the electrical arc, and an elongation chamber 23 situated between third portions 24, 25 of the two electrodes 13, 14 to lengthen said electrical arc. The elongation chamber 23 is inserted between the striking chamber 17 and the arc-extinguishing chamber 20.

[0083] Referring to FIGS. 4 and 5, the insulating base 6 of the casing 4 advantageously includes electrode grooves 26 in the striking chamber 17. The electrode grooves 26 are then crossed by the first portions 18, 19 of the two electrodes 13, 14, which enables positioning of the two electrodes 13, 14 in the internal space 5 of the casing 4. Alternatively, the electrode grooves 26 may be placed in the elongation chamber 23; they are then crossed by the third portions 24, 25 of the two electrodes 13, 14.

[0084] The isolation distance, denoted d.sub.i, is the distance that the electric arc has to travel to connect the two electrodes 13, 14 electrically. The propagation trajectory T corresponds to the trajectory of the electrical arc in the inter-electrode space. At a point on the propagation trajectory T the isolation distance d.sub.i is identified as being the shortest distance between the two electrodes 13, 14 in the plane perpendicular to the tangent at the point concerned of the propagation trajectory T.

[0085] As can be seen in FIG. 4, the isolation distance d.sub.i increases from the striking chamber 17 to the arc-extinguishing chamber 20 via the elongation chamber 23. In particular, the isolation distance d.sub.i is minimal between the first portions 18, 19 of the two electrodes 13, 14 in the striking chamber 17. It increases between the third portions 24, 25 of the two electrodes 13, 14 in the elongation chamber 23. Finally, the isolation distance d.sub.i is maximal between the second portions 21, 22 of the two electrodes 13, 14 in the arc-extinguishing chamber 20.

[0086] Given the composition and the pressure of the inert gas trapped in the internal space 5 of the casing 4, the minimal isolation distance d.sub.i participates in the definition of the striking voltage from which the gas-filled spark gap 2 is activated, that is to say from which electrical current the gas-filled spark gap 2 diverts said current to an earth line or more generally a discharge line.

[0087] Referring to FIG. 6, to encourage striking of an electrical arc in the striking chamber 17 the gas-filled spark gap 2 includes a conductive striking element 27, for example a line of graphite, fixed to the internal isolating surface 28 of the casing 4 so as to cause a disruptive discharge to appear between the first portions 18, 19 of the two electrodes 13, 14.

[0088] The inert gas trapped in the casing 4 of the gas-filled spark gap 2 is for example argon Ar, neon Ne, dinitrogen N.sub.2, dihydrogen H.sub.2, helium He, a mixture of these or other gases. The inert gas advantageously includes dihydrogen H.sub.2. This inert gas is at an absolute pressure in the gas-filled spark gap 2 from 0.5 bar (50 kPa) to 2 bar (200 kPa). As indicated, this pressure influences the striking voltage of the gas-filled spark gap 2. The inert gas can therefore be trapped in the gas-filled spark gap 2 at different pressures depending on the required striking voltage.

[0089] In order to trap the inert gas in the gas-filled spark gap 2 the internal space 5 of the casing 4 is sealed. The seal is made between the insulating base 6 and the insulating lid 7 by any appropriate means.

[0090] For example, a molybdenum-manganese layer may be used to cover an edge region of the edges of the insulating base 6 and a corresponding surface of the insulating lid 7, this molybdenum-manganese layer being itself covered by a layer of nickel. The seal between the insulating base 6 and the insulating lid 7 may be made by melting AgCu solder, denoted 28, between the insulating lid 7 and the layer of nickel, typically in a furnace at 780? C.

[0091] Alternatively, the seal between the insulating base 6 and the insulating lid 7 may be produced by AgCuTi solder deposited directly on the insulating base 6 and the ceramic (alumina) insulating lid 7.

[0092] Another way to provide this seal is gluing by means of a glue compatible with alumina. A further technique consists in using a seal and mechanical clamping of the two parts onto that seal.

[0093] If a transient voltage surge associated with an impulse current exceeds the striking voltage of the gas-filled spark gap 2 an electrical arc is struck in the striking chamber 17 where the isolation distance d.sub.i between the first portions 18, 19 of the two electrodes 13, 14 is the minimum distance.

[0094] This electrical arc is subjected to the Lorentz force induced by the flow of an electrical current between the two electrodes 13, 14. The electrical arc is then located in a current loop and so the Lorentz force exerted on the loop tends to open the loop (this effect is sometimes called the loop effect). The Lorentz force exerted on the electrical arc therefore tends to push it toward the elongation chamber 23.

[0095] In the elongation chamber 23 the electrical arc is guided by the third portions 24, 25 of the two electrodes 13, 14. The electrical arc is lengthened as it propagates toward the arc-extinguishing chamber 20, which weakens it.

[0096] The arc-extinguishing chamber 20 includes plane dividing plates 29 stacked at regular intervals between the second portions 21, 22 of the two electrodes 13, 14 parallel to the longitudinal walls 9 of the insulating base 6 of the casing 4. The height of the dividing plates 29 is substantially equal to the height of the insulating base 6 of the casing 4 and thus substantially equal to the thickness of the two electrodes 13, 14. The divider plates 29 are preferably made of a ferromagnetic metal, for example mild steel.

[0097] Referring to FIG. 5, the bottom wall 8 of the insulating base 6 of the casing 4 includes a plate support 30. The plate support 30 includes plate ribs 31 in which the divider plates 29 are nested and fixed. Mounting the divider plates 29 in the plate ribs 31 of the plate support 30 enables a rigid arc-extinguishing chamber 20 to be formed. The bottom wall 8 and the plate support 30 advantageously form a one-piece assembly.

[0098] When the electrical arc reaches the arc-extinguishing chamber 20 it is divided into a succession of electrical sub-arcs between the stacked divider plates 29. The voltage of the electric arc being equivalent to the sum of the voltages of the electrical sub-arcs, the electrical arc is in the end spontaneously extinguished between the stacked divider plates 29.

[0099] Twelve divider plates 29 are represented in FIGS. 3 and 4. Alternatively, the arc-extinguishing chamber 20 may include more than or fewer than twelve divider plates 29. Note that the arc extinguishing capacity of the gas-filled spark gap 2 is a function of the number of divider plates 29 stacked in the arc-extinguishing chamber 20. This number can therefore be adapted according to the nature of the electrical device (circuit, network, equipment, installation, etc.) to be protected.

[0100] To prevent expansion of the electrical arc over the two deflector plates 33 the gas-filled spark gap 2 includes two insulating plates 32 housed in the internal space 5 of the casing 4 and adapted to surround some of the first portions 18, 19 of the two electrodes 13, 14 and the third portions 24, 25 of the two electrodes 13, 14. As depicted here, the two insulating plates 32 extend parallel to the insulating lid 7 and to the bottom wall 8 of the casing 4.

[0101] The gas-filled spark gap 2 further includes two deflector plates 33 housed in the internal space 5 of the casing 4, each deflector plate 33 being inserted between said casing 4 and the insulating plate 32 at the level of the elongation chamber 23.

[0102] The greater the electrical current discharged by the electrical arc, the greater the Lorentz force exerted on the electrical arc. The electrical arc therefore propagates commensurately more rapidly toward the arc-extinguishing chamber 20. An electrical arc struck by an impulse current generated for example by a lightning strike, although of brief duration, can therefore propagate sufficiently rapidly to reach the arc-extinguishing chamber 20 and to be extinguished therein by dividing it.

[0103] Now, the discharge of the impulse currents in the arc-extinguishing chamber 20 imposes important constraints on the dimensions of the gas-filled spark gap 2 and recourse to heat resistant materials, in particular for the divider plates 29, which impacts the cost of manufacturing the gas-filled spark gap 2.

[0104] To reduce or even to eliminate the proportion of impulse current electrical arcs that migrate toward the extinguishing chamber 20 their speed must be selectively slowed. Indeed, once the propagation speed has decreased, the impulse current electrical arcs, which already have short discharge times, are extinguished before reaching the arc-extinguishing chamber 20. On the other hand, electrical arcs struck by follow currents, which generally have longer discharge times, have time to propagate as far as the arc-extinguishing chamber 20 to be extinguished therein by dividing them.

[0105] The propagation speed of an electrical arc depends on numerous parameters and in particular the materials of the electrodes 13, 14, the insulation resistance in the internal space 5 (which depends on the composition of the trapped inert gas and obstacles placed on the propagation trajectory T of the electrical arc) and the nature and the intensity of the forces exerted on the electrical arc.

[0106] Referring to FIG. 4, there can be seen the isolation distance d.sub.i between the first portions 18, 19 of the two electrodes 13, 14 that is maintained equal to or close to the minimum isolation distance d.sub.i. In the striking chamber 17 the first portions 18, 19 of the two electrodes 13, 14 are therefore essentially parallel and the inter-electrode space widens slightly on approaching the elongation chamber 23.

[0107] The Lorentz force exerted on the electrical arcs struck in the striking chamber is therefore minimised since the intensity of that force is proportional to the isolation distance d.sub.i, which makes it possible to slow the propagation speed of the electrical arc in the striking chamber 17.

[0108] The two electrodes 13, 14 are advantageously adapted to confer on the inter-electrode space a horn shape the mouth of which is situated at the level of the striking chamber 17 and the bell of which extends in the elongation chamber 23.

[0109] Indeed, unlike a follow current electrical arc, the discharge of an electrical arc struck by an impulse current reduces local pressure waves that propagate from the striking chamber 17 in the horn-shaped part of the inter-electrode space so as to be reflected into the elongation chamber 23 or at the level of or downstream of the arc-extinguishing chamber 20. These reflected pressure waves exert on the electrical arc a force tending to oppose the Lorentz force, which limits the speed of propagation of the electrical arc toward the arc-extinguishing chamber 20.

[0110] Referring to FIGS. 4 and 5, to accentuate the effect of reflection of pressure waves generated by the discharge of impulse currents, a stop plate 34 made of ceramic material, for example alumina, is advantageously positioned perpendicularly to the propagation trajectory T, downstream of the divider plates 29. As represented here, the stop plate 34 is still situated in the arc-extinguishing chamber 20. Alternatively, the stop plate 34 could be located downstream of the divider plates 29 outside the inter-electrode space.

[0111] Referring to FIG. 3, the divider plates 29 advantageously include V-shaped notches the openings of which are oriented toward the striking chamber. The isolation resistance and thus the resistance to flow of current therefore remain high at the inlet of the arc-extinguishing chamber 20.

Example

[0112] The dimensions of the casing 4 are for example 58?44?16 mm or less.

[0113] FIG. 7 shows a gas-filled spark gap 102 in accordance with another embodiment in an exploded perspective view. Elements analogous or identical to those in FIGS. 2 to 6 bear the same reference number increased by 100.

[0114] In this embodiment the casing 104 of the gas-filled spark gap 102 is of cylindrical shape. The two connecting terminals 111 and 112 are metal discs that respectively form the two lids of the casing 104. The lateral wall 136 of the casing 104 is for example made of ceramic materials, preferably alumina. It is preferably covered by an enclosure or a coating providing mechanical protection and electrical insulation, for example one made of plastic material, in particular PBT or PA. Alternatively, insulating materials other than ceramics may be employed to produce the lateral wall 136. The seal between the lateral wall 136 and the two connecting terminals 111, 112 is produced by solder, as described above.

[0115] The gas-filled spark gap 102 also differs from the gas-filled spark gap 2, depicted in particular in FIG. 3, in that the electrodes grooves 126a, 126b and the plate grooves 131 are produced on the insulating plates 132a, 132b. To be more precise, in FIG. 7 an electrode groove 126a is produced on the insulating plate 132a espousing the shape of the electrode 113 from the striking chamber as far as the arc-extinguishing chamber and an electrode groove 126b is produced on the insulating plate 132b in the striking chamber. The plate grooves 131 are produced on the insulating plate 132a. In this embodiment the insulating plates 132a, 132b are not symmetrical.

[0116] The gas-filled spark gap 102 further includes an insulating spacer 135 positioned between the two electrodes 113, 114 in the striking chamber to maintain a gap between them. The insulating spacer 135 also makes it possible to maintain the insulating plate 132a pressed against the connecting terminal 111 and the insulating plate 132b pressed against the connecting terminal 112.

[0117] Although the invention has been described with reference to particular embodiments it is obvious that it is in no way limited to them and that it encompasses all technical equivalents of the means described and combinations thereof if the latter fall within the scope of the invention.

[0118] Use of the verb to include or to comprise and conjugate forms thereof does not exclude the presence of elements or steps other than those stated in a claim.

[0119] In the claims, any reference sign between parentheses should not be interpreted as a limitation of the claim.