ARC CHAMBER FOR A LOW-VOLTAGE SWITCHING DEVICE

Abstract

An arc chamber 10, 20, 30, 40, 50 for a low voltage switching device comprising an insulating casing 1, having a first and a second lateral walls 2,3, a rear and a front wall 4,5, that defines an internal space housing a number of arc-breaking plates, a top wall 6 of said casing having a discharge opening 101 for venting off the gases from said internal space, said discharge opening 101 being covered by a top cover 7, 37, 47, 57. The arc chamber for a low voltage switching device comprises a filter 11, 21, 31, 41, 51 made of an open cell metal foam is positioned at said discharge opening 101.

Claims

1. An arc chamber for a low voltage switching device comprising an insulating casing (1), having a first and a second lateral walls a rear and a front wall, that defines an internal space housing a number of arc-breaking plates, a top wall of said casing having a discharge opening for venting off the gases from said internal space, said discharge opening being covered by a top cover, and a filter made of an open cell metal foam is positioned at said discharge opening.

2. The arc chamber for a low voltage switching device, according to claim 1, wherein said filter made of an open cell metal foam covers entirely said discharge opening.

3. The arc chamber for a low voltage switching device, according to claim 1, wherein said open cell metal foam of said filter has a porosity of greater than 70%, preferably greater than 80%, more preferably greater than 85%.

4. The arc chamber for a low voltage switching device, according to claim 3, wherein said open cell metal foam of said filter has a thermal conductivity of lower than 15 W.Math.m.sup.−1.Math.K.sup.−1.

5. The arc chamber for a low voltage switching device, according to claim 4, wherein said open cell metal foam of said filter has a tensile strength of greater than 5 MPa.

6. The arc chamber for a low voltage switching device, according to claim 5, wherein said open cell metal foam of said filter is provided with a structure having randomly distributed channels.

7. The arc chamber for a low voltage switching device, according to claim 6, wherein said filter made of an open cell metal foam is interposed between said discharge opening and said top cover.

8. The arc chamber for a low voltage switching device, according to claim 7, further comprising a perforated sheets positioned between said filter made of an open cell metal foam and said discharge opening, a spacer interposed between said perforated sheets and said filter made of an open cell metal foam, said top cover being superimposed onto said filter made of an open cell metal foam.

9. The arc chamber for a low voltage switching device, according to claim 1 wherein said filter made of an open cell metal foam is inserted into said top cover.

10. The arc chamber for a low voltage switching device, according to claim 1, wherein said filter made of an open cell metal foam is integrally made within said top cover.

11. The arc chamber for a low voltage switching device, according to claim 1, wherein said top cover is entirely made with said filter made of said open cell metal foam.

12. A low voltage switching device comprising an arc chamber according to claim 1.

13. The arc chamber for a low voltage switching device, according to claim 1, wherein said open cell metal foam of said filter has a thermal conductivity of lower than 15 W.Math.m.sup.−1.Math.K.sup.−1.

14. The arc chamber for a low voltage switching device, according to claim 1, wherein said open cell metal foam of said filter has a tensile strength of greater than 5 MPa. cm 15. The arc chamber for a low voltage switching device, according to claim 1, wherein said open cell metal foam of said filter is provided with a structure having randomly distributed channels.

16. The arc chamber for a low voltage switching device, according to claim 1, wherein said filter made of an open cell metal foam is interposed between said discharge opening and said top cover.

17. The arc chamber for a low voltage switching device, according to claim 1, further comprising a perforated sheets positioned between said filter made of an open cell metal foam and said discharge opening a spacer interposed between said perforated sheets and said filter made of an open cell metal foam, said top cover being superimposed onto said filter made of an open cell metal foam.

18. The arc chamber for a low voltage switching device, according to claim 13, wherein said open cell metal foam of said filter has a thermal conductivity of lower than 12 W.Math.m.sup.−1.Math.K.sup.−1.

19. The arc chamber for a low voltage switching device, according to claim 14, wherein said open cell metal foam of said filter has a tensile strength of greater than 10 MPa.

20. The arc chamber for a low voltage switching device, according to claim 3, wherein said open cell metal foam of said filter is provided with a structure having randomly distributed channels.

Description

[0053] Further features and advantages of the present invention will be more clear from the description of preferred but not exclusive embodiments of the arc chamber for a low-voltage switching device of the present invention, shown by way of examples in the accompanying drawings, wherein:

[0054] FIG. 1 is a perspective view of a prior art embodiment of an arc chamber for a low-voltage switching device;

[0055] FIG. 2 is a perspective view of a first embodiment of an arc chamber for a low-voltage switching device according to the invention;

[0056] FIG. 3 is an exploded view of a first embodiment of an arc chamber for a low-voltage switching device according to the invention;

[0057] FIG. 4 is an exploded view of a second embodiment of an arc chamber for a low-voltage switching device according to the invention;

[0058] FIG. 5 is an exploded view of a third embodiment of an arc chamber for a low-voltage switching device according to the invention;

[0059] FIG. 6 is an exploded view of a fourth embodiment of an arc chamber for a low-voltage switching device according to the invention;

[0060] FIG. 7 is an exploded view of a fifth embodiment of an arc chamber for a low-voltage switching device according to the invention;

[0061] FIG. 8 is an exploded view of a pole of a low voltage power circuit breaker housing an arc chamber according to the invention;

[0062] FIG. 9 is a perspective view of a low voltage power circuit breaker housing an arc chamber according to the invention.

[0063] With reference to the attached figures, the arc chamber for a low voltage switching device of the present invention comprises an insulating casing 1, having a first and a second lateral walls 2, 3 a rear and a front wall 4, 5.

[0064] The casing 1 defines an internal space which houses a number of arc-breaking plates. The set-up of such plates in the arc chamber depend on the kind of switching device and is in general well known and therefore will not be described with further details.

[0065] The casing 1 of the arc chamber 10, 20, 30, 40, 50 is provided with which a top wall 6 which has a discharge opening 101 for venting off the gases from said internal space, said discharge opening 101 being in general covered by a top cover 7, 37, 47, 57.

[0066] One of the distinguishing features of the arc chamber 10, 20, 30, 40, 50 of the present invention in given by the fact that a filter 11, 21, 31, 41, 51 made of an open cell metal foam is positioned at said discharge opening 101.

[0067] As previously explained a filter made of an open cell metal foam is provided with a well-balanced set of mechanical, thermal and flow control properties that make it perfectly suited for the intended scopes.

[0068] In this regard, the open cell metal foam of said filter 11, 21, 31, 41, 51 preferably has the following properties:

[0069] a porosity of greater than 70%, preferably greater than 80%, more preferably greater than 85%;

[0070] a thermal conductivity of lower than 15 W.Math.m.sup.−1.Math.K.sup.−1, preferably lower than 12 W.Math.m.sup.−1.Math.K.sup.−1, more preferably lower than 10 W.Math.m.sup.−1.Math.K.sup.−1;

[0071] a tensile strength of greater than 5 MPa, preferably greater than 10 MPa, more preferably greater than 15 MPa.

[0072] Moreover, in order to guarantee an increase of the turbulence of the gas flow, the open cell metal foam of said filter 11, 21, 31, 41, 51 is conveniently provided with a structure having randomly distributed channels.

[0073] Thus, in general, the filter 11, 21, 31, 41, 51 made of an open cell metal foam is positioned at said discharge opening 101 so as cover entirely said discharge opening 101, thereby fully controlling the discharge of the hot gases from the internal space of the arc chamber 10, 20, 30, 40, 50 to the external ambient.

[0074] With reference to FIGS. 2 and 3, in a first exemplary embodiment of an arc chamber 10 for a low-voltage switching device according to the invention, said filter 11 made of an open cell metal foam is directly interposed between the discharge opening 101 of the casing 1 of the arc chamber 10 and said top cover 7. It is clear, by comparing such embodiment with the prior art embodiment of FIG. 1 that the former is much simpler than the latter, since it is made by one single piece, instead of the at least three pieces of the prior art filter. Moreover, as previously explained the mechanical, thermal and flow control properties of the filter 11 can easily be tailored so as to better match the practical needs with respect to the prior art filters made by a combination of different parts.

[0075] However, with reference to FIG. 4 which shows a second exemplary embodiment of an arc chamber 20 for a low-voltage switching device according to the invention, if so desired, a filter 21 made of an open cell metal foam may be combined also with other component parts as in prior art filters.

[0076] In such a case, the arc chamber 20 for a low voltage switching device, according to this embodiment, comprises a perforated sheets 8 which is positioned between said filter 21 made of an open cell metal foam and the discharge opening 101 of the casing 1 of the arc chamber 20. A spacer 9 is then interposed between said perforated sheets 8 and said filter 21 made of an open cell metal foam and a top cover 7 is superimposed onto said filter 21 made of an open cell metal foam to complete the assembly.

[0077] With reference to FIG. 5, a much simpler implementation of a filter as herein disclosed is given in a third exemplary embodiment of an arc chamber 30 for a low-voltage switching device according to the invention.

[0078] In such embodiment of the arc chamber 30, the filter 31 made of an open cell metal foam is inserted into a top cover 37. In particular, the top cover 37 is provided with a seat that matches the discharge opening 101 of the casing 1 of the arc chamber 30 and the filter 31 is inserted and secured into said seat, thereby realizing an assembly that can be directly fixed on the top wall 6 of the casing 1 of the arc chamber 30. Such solution can be used when the top cover 37 and the filter 31 are made of different materials. The manufacturing and assembly processes are therefore further simplified with respect to the prior art systems.

[0079] A further simplified form of implementation of a filter as herein disclosed is given in FIG. 6 which shows a fourth exemplary embodiment of an arc chamber 40 for a low-voltage switching device according to the invention, which is particularly suited when the top cover and the filter are made of the same materials.

[0080] In this case, the filter 41 made of an open cell metal foam is integrally made within said top cover 47 thereby realizing a single-piece element that combines the functions of the filter and of the top cover. In practice, the single piece element comprises a frame having the structure of the cover 47 and a core having the structure of the filter 41.

[0081] With reference to FIG. 7, which shows a fifth exemplary embodiment of an arc chamber 50 for a low-voltage switching device according to the invention, a still simplified form of implementation of a filter as herein disclosed can be obtained when said top cover 57 is entirely made with said filter 51 made of said open cell metal foam. In other words, in this embodiment of the arc chamber 50, the top cover 57 and the filter 51 totally coincide, being the one and same thing.

[0082] With respect to the other embodiments shown beforehand, this latter has the following advantages, maintaining at the same time the same advantages over the prior art systems:

[0083] Improved compactness;

[0084] Higher mechanical stability;

[0085] Improved assembly easiness;

[0086] Further cost reduction.

[0087] In a further aspect the present invention also relates to a low voltage switching device, including but not limited to, a circuit breaker, a disconnector, or a contactor, comprises an arc chamber as disclosed herein.

[0088] In particular, with reference to FIGS. 8 and 9, the presently disclosed arc chambers are particularly suitable for use in low voltage power circuit breakers, such as air insulated circuit breakers or molded case circuit breakers (MCCB), which generally comprise one or more electrical poles 110.

[0089] With particular reference to FIG. 8, a typical pole 110 of low voltage power circuit breaker has an internal space delimited by an enclosure which, in the embodiment shown, is made of two half-enclosures coupled to each other.

[0090] Within said internal space of the pole 110, there is a contact area 111 and an arc extinguishing area 112, located proximate to said contact area 111. A fixed contact assembly 121 and a movable contact assembly 122 are respectively positioned in said contact area 111, said movable contact assembly 122 being movable between a closed position in which it is into contact with said fixed contact assembly 121 and an open position in which it is spaced apart from said fixed contact assembly 121. The set-up of a pole of circuit breaker of this kind is well known in the art and will not be described with further details.

[0091] Inside the internal space of the pole 110 there is also an arc extinguishing area 112 into which an insulating casing 1 of an arc chamber 10, 20, 30, 40, 50 of the present invention can be easily fitted, according to embodiments which are well known in the art.

[0092] It is clear from the above description that the low voltage power circuit breaker of the present invention, fully achieve the intended aims and solved the above-highlighted problems of the existing electrical cabinets.

[0093] In practice, as previously explained, in the arc chamber of the present invention, the use of a filter made of an open cell metal foam allows to achieve at least the following advantages with respect to the arc chambers of known type:

[0094] Temperature decrease of the hot stream;

[0095] Flow control;

[0096] Acoustic control;

[0097] Mechanical thermo-elastic dumping of induced vibrations;

[0098] Fire protection;

[0099] Increased mechanical stiffness at the discharge section of the breaker.

[0100] Several variations can be made to the arc chamber for low voltage switching device thus conceived, all falling within the scope of the attached claims. In practice, the materials used and the contingent dimensions and shapes can be any, according to requirements and to the state of the art.