High breaking capacity circuit breaker

Abstract

 Circuit breaker (1) comprising an electric circuit having at least a fixed electric contact (25) and at least a movable electric contact (24), wherein the movable contact (24) is rotatable along a trajectory (T) lying in a plane and defined between a first operating position, in which the movable contact (24) abuts against the fixed contact (25) and a second operating position, in which the movable contact (24) is positioned at a predetermined distance from the fixed contact (25), wherein the circuit breaker (1) further comprises a holding element (20) for the fixed contact (25).
The circuit breaker (1) further comprises two generally plate-like parallel elements (27, 28), made of ferromagnetic material, positioned at a certain mutual distance on opposite sides with respect to said plane.

Description

[0001] The present invention relates to the field of circuit breakers and in particular to a high breaking capacity circuit breaker.

[0002] As is known, a circuit breaker, as a so called moulded case circuit breaker, comprises an electric circuit formed by a fixed electric contact and a movable electric contact. Generally, inside the circuit breaker, the fixed electric contact is integral with the circuit breaker body whereas the movable contact is rotatably hinged to the circuit breaker body, in order to be moved from an open to a closed position. In the open position, the movable electric contact is spaced apart from the fixed electric contact and the electric circuit of the circuit breaker is open. On the contrary, in the closed position, the movable electric contact abuts against the fixed contact and the electric circuit is closed. In order to extinguish electric arcs formed during the opening/closing operations of the electric circuit, the circuit breaker is typically provided with a deionizing cell, which is positioned near the electric fixed and movable contacts. The fixed contact, the end portion of the movable contact which interacts with the fixed contact and the deionizing cell are contained inside an internal chamber of the circuit breaker called deionizing chamber.

[0003] A characteristic parameter of a circuit breaker is the so-called breaking capacity, which may be defined as the maximum short-circuit current which may be interrupted by the circuit breaker. The current corresponding to the maximum breaking capacity is much higher (some orders of magnitude) with respect to the maximum nominal current of the circuit breaker. The latter is another characteristic property which may be defined as the maximum current the circuit breaker is able to withstand for an unlimited amount of time.

[0004] The breaking capacity of a circuit breaker is a parameter which depends on the constructive characteristics of the same circuit breaker, as for example the circuit breaker size and the dielectric properties of the medium interposed between the movable and the fixed contact.

[0005] The object of the present invention is to provide a circuit breaker having a breaking capacity higher than that of circuit breakers of the known art.

[0006] This object is achieved by providing a circuit breaker as defined in the annexed claim 1, in its broadest form, and as defined in the dependent claims, which refer to particular embodiments of the same.

[0007] The invention will be more easily understood in connection with the following detailed description of some of its embodiments, which are only provided as non limiting examples, with reference to the attached drawings, in which:

Fig. 1 shows an isometric view of the rear side of a particularly preferred embodiment of a circuit breaker according to the invention, wherein a component of said circuit breaker is shown separated from the circuit breaker,

Fig. 2 shows some of the components of the electric circuit of the circuit breaker of fig. 1,

Fig. 3 shows the arrangement of components of fig. 3 in the circuit breaker of fig. 1,

Fig. 4 shows a partial internal view of the circuit breaker of fig. 1, and

Fig. 5 shows a deionizing cell, which may be used in the circuit breaker of fig. 1.

[0008] In the figures, identical or similar elements are indicated by the same numeral references.

[0009] With reference to fig. 1, a particularly preferred illustrative and non limiting embodiment of the circuit breaker according to the invention, is generally indicated by numeral 1.

[0010] In the particular embodiment of fig. 1, the circuit breaker 1 is for example a so called moulded case circuit breaker. A moulded case circuit breaker, as opposed to a so called air circuit breaker, has a cased body 2 formed by insulating material, for holding the internal circuit breaker mechanism. Moulded case circuit breakers are generally used in automation industry as well as in the service and maintenance sector, for interrupting currents up to 1500 A.

[0011] In the example shown, the circuit breaker 1 is embodied in a non limiting way by a moulded case automatic three-pole circuit breaker.

[0012] The cased body 2 is formed by juxtaposing two shells, in particular a base shell, or base 3, and a lid shell, or lid 4. Such shells 3, 4 are juxtaposed and mutually fixed by fixing means, not shown in the figures, such as rivets, screws or bolts.

[0013] At lid 4, a front overhanging portion is provided, commonly called "DIN front", which is provided with a lever for operating circuit breaker 1, not shown.

[0014] The cased body 2 of the circuit breaker is provided on the upper side 6 with three screw clamps 7, or input terminals 7, for connecting the circuit breaker 1 to electric mains cables. Analogous clamps, or output terminals, not shown, are provided on the lower side of cased body 2.

[0015] The rear side 8 of cased body 2 is provided with suitable fixing means 9 for attaching the circuit breaker 1 to an electric panel. For instance, in a non limiting way, such fixing means allow to fix the circuit breaker 1 to a DIN rail by using a mounting device as the one described in Italian patent application nr. RM 2006 A 000145.

[0016] As shown in fig. 1, on the rear side 8 of cased body 2 openings 10 are provided for allowing the insertion, from the outside and from the rear side 8 of the circuit breaker 1, of the holding elements 20 for the fixed electric contacts of circuit breaker 1. Since in the example shown, the circuit breaker 1 is a three-pole circuit breaker, its rear side 8 is provided with three openings 10, each allowing the insertion of a respective holding element, or contact-holder 20, provided with a fixed electric contact. Preferably, but in a non limiting way, the contact holders 20 are comprised of copper or a copper alloy, for instance a copper and brass alloy.

[0017] Preferably, in order to fix the contact holders 20 to the rear of circuit breaker 1, fixing means, as for instance holes for corresponding screws 22, rivets or analogous fixing means are provided on the rear side 8 of circuit breaker 1, and on holding element 20 at least a hole 21 is provided, which cooperates with such fixing means.

[0018] Preferably, each of the contact holders 20 has a stepped end, provided with a hole 23 for receiving a corresponding screw, or a pin, of a connection screw terminal 7.

[0019] As known, since the circuit breaker 1 is of the three-pole type, it is provided with three separate electric circuits to be operated simultaneously by a single lever. Each of these circuits is provided in order to interrupt a respective phase and comprises a pair of contacts, i.e. a fixed and a movable electric contact.

[0020] A portion of the electric circuit of the circuit breaker 2 is illustrated in fig. 2, which shows a fixed electric contact 25 and a movable electric contact 24. These contacts are preferably copper contacts.

[0021] The fixed electric contact 25 is connected, for instance by welding or riveting, to the respective contact holder 20, already described with reference to fig. 1. The movable electric contact 24 is fixed, for instance by welding or riveting, to a holding arm 26, which is rotatable about axis R-R. In this way, the movable electric contact 24 is rotatable in either direction along an arched trajectory T, defined between a first operating position, in which the movable contact 24 abuts against the fixed contact 25 and a second operating position, in which the movable contact 24 is positioned at a predetermined distance from the fixed electric contact 25. The first operating position corresponds to a closed circuit condition, whereas the second operating position, illustrated in fig. 2, corresponds to an open circuit condition.

[0022] As shown in fig. 2, a circuit breaker 1 according to the present invention further comprises two generally plate-like parallel elements 27, 28, made of ferromagnetic material, preferably iron with a relative permeability of approximately 10.000. These elements are distanced from each other near the fixed and movable contacts 24, 25, and are opposed to each other with respect to a plane comprising the trajectory T of movable contact 24. Preferably, such plate-like elements 28, 28 extend approximately starting from the fixed contact 25 to such an extent that at least a significant portion of trajectory T lies between these elements 27, 28. For example, the significant portion corresponds at least to 50% of the total length of trajectory T. More preferably, this significant portion corresponds to at least 70% of the total length of said trajectory T.

[0023] In a particularly advantageous embodiment, as shown in fig. 2, the two plate-like elements 27, 28 are portions of an integral ferromagnetic piece, further comprising a crossbar 29 connected to a respective end portion of each of plate-like elements 27, 28. Preferably, this integral element, which from now on will be called ferromagnetic element, is generally "C" or "U" shaped.

[0024] In the particularly preferred embodiment of fig. 2, the crossbar 29 of ferromagnetic element 27, 28, 29 is positioned underneath the fixed electric contact 25. More in detail, the contact holder 20 is provided with a hook-shaped end portion, comprising a plate 31, on which the fixed contact 25 is fixed, wherein the crossbar 29 is positioned under said plate 31, and is interposed between the plate 31 and the remaining portion of contact holder 20.

[0025] In a particularly advantageous embodiment, the ferromagnetic component 27, 28, 29 has also the task to fix the fixed contact 25 and its holder 20 to the base 3 of circuit breaker 1. To this end, each of the two plate-like elements 27, 28 is provided, at its distal end, with respect to the fixed contact 25, with fixing means 32 in order to fix the ferromagnetic element 28, 29, 29 to the base 3 of circuit breaker 1. In the particular embodiment shown, these fixing means are formed by a pair of pins 32, wherein each pair has a plate-like element 27, 28 positioned on a respective end. The fixing procedure by means of pairs of pins 32 will be further explained in the following description.

[0026] Fig. 3 shows a portion of the circuit breaker of fig. 1, in which the base 3 of circuit breaker 1 is shown in a cross section A-A of fig. 1. In fig. 3, the movable electric contact 24 is in the closed position, i.e. it abuts against the fixed contact 25. This figure also shows the rotating mechanism 36 which acts on arm 26 holding the movable contact 24, in order to move it between its two operating positions.

[0027] Fig. 4 shows an internal view of a portion of base 3, wherein the rotating mechanism 36, the holding arm 26 and the movable contact 24 have been omitted.

[0028] As can be seen in fig. 3 and 4, the fixed contact 25 and the movable contact 24 are housed inside a chamber 35, usually called interruption chamber or deionizing chamber. In a particularly preferred embodiment, two lateral opposed walls 36, 37 of chamber 35 are provided with a respective wall portion 38, 39 projecting towards the inside of the interruption chamber 35 and provided with an internal cavity, which is best seen in fig. 3, which is substantially isolated from the deionizing chamber 35 and receives a corresponding plate-like element 27, 28 of ferromagnetic element 27, 28, 29.

[0029] As can be seen in fig. 3, each of the two cavities is closed on the upper side by a transverse wall 40, in which an opening is provided, through which a pair of pins 32 is to be inserted. The fixing of the ferromagnetic component 27, 28, 29 may for example be accomplished by means of metallic washers 33, in particular by inserting each pair of pins 32, after passing them through the openings provided on the transverse walls 40, into a respective washer 32, and then by parting the pins 32 of a same pair.

[0030] It is to be noted that by letting the crossbar 29 of the ferromagnetic component 27, 28, 29 pass underneath the plate 31 supporting the fixed contact 25 and by fixing the ferromagnetic component 27, 28, 29 to the base 2 of the circuit breaker 1, for example as shown above, the fixed contact 25 is firmly fixed to the base 2, forming a structural arrangement which is very resistant to concussions originating from the closing of the movable contact 25.

[0031] Furthermore it is to be noted that by providing the insertion of the two plate-like elements 27, 29 into cavities provided in said opposite (with respect to the plane of trajectory T) lateral walls, an advantage is achieved in that the lateral walls 36, 37 of the deionizing chamber 35 are greatly reinforced. These walls 36, 37 are normally very stressed by the ignition of electric arcs between fixed and movable contact, during opening and closing operations of circuit breaker 1. Such stresses are caused by a significant heating of gas inside the chamber 35, due to the generation of the electric arc, which determines a great increase of volume of said gas inside the chamber.

[0032] Since the circuit breaker 1 of the example shown is a three-pole circuit breaker, in fig. 4 three adjacent deionizing chambers 35 are at least partially shown. In one of these, a so called deionizing cell 50 is shown. Obviously, the other two chambers 35 are also normally provided with a respective deionizing cell 50, although in fig. 4 they are shown without such a cell.

[0033] A particularly preferred embodiment of a deionizing cell 50 is shown in fig. 5. The cell 50 comprises a group of densely packed parallel thin plates 51, which are joined together by opposite lateral bars 52. The thin plates 51 have an arched notch 53 in the portion directed towards the movable contact, so that a slot is defined inside the cell 50, which is generally parallel to trajectory T, and forms an invitation for the arc to be extinguished.

[0034] Simulations and experimental tests have shown that a circuit breaker according to the invention is able to achieve the goal previously described with reference to circuit breakers according to the known art.

[0035] In particular it has been observed that the presence of the plate-like elements 27, 28 of ferromagnetic material, when an arc is generated between the fixed and movable contact, allows the modification of the distribution of the magnetic field generated by said arc, since the plate-like elements cause the closing of the lines of flux of said field on the plate-like elements. It is to be noted that this magnetic field is generated since the arc can be considered equivalent to an electric conductor, in which a magnetic field is caused by an electric current flowing through it.

[0036] In other words, a confinement of the magnetic field between the plate-like elements 27, 28 has been observed, which causes, as opposed to an arrangement without plate-like elements, an induced electromagnetic field, having an intensity much greater in the area interposed between the two plate-like elements 27, 28. This causes a large increase of the force acting on the electric arc and therefore an increase of the expulsion effect acting on the electric arc, directed towards the deionizing cell 50. This allows to obtain a circuit breaker which, with respect to the circuit breakers of the known art, has better characteristics in terms of breaking capacity.

[0037] Obviously, a skilled in the art, in order to satisfy contingent and specific needs, may introduce various modifications and changes to the above described circuit breaker, wherein these modifications and changes are by the way all comprised in the scope of protection, as defined in the following claims.

Claims

1. Circuit breaker (1) comprising an electric circuit having at least a fixed electric contact (25) and at least a movable electric contact (24), wherein the movable contact (24) is rotatable along a trajectory (T) lying in a plane and defined between a first operating position, in which the movable contact (24) abuts against the fixed contact (25) and a second operating position, in which the movable contact (24) is positioned at a predetermined distance from the fixed contact (25), wherein the circuit breaker (1) further comprises a holding element (20) for the fixed contact (25),
characterized in that
the circuit breaker (1) further comprises two generally plate-like parallel elements (27, 28), made of ferromagnetic material, positioned at a certain mutual distance on opposite sides with respect to said plane.

2. Circuit breaker (1) according to claim 1, wherein the length of said elements (27, 28), starting from said fixed contact (25), is such that a significant portion of said trajectory (T) is interposed between said elements (27, 28).

3. Circuit breaker (1) according to claim 2, wherein said significant portion is at least equal to 50% of the total length of said trajectory (T).

4. Circuit breaker (1) according to claim 2, wherein said portion is at least equal to 75% of the total length of said trajectory (T).

5. Circuit breaker (1) according to any of the preceding claims, wherein the elements (27, 28) are portions of a single component (27, 28, 29) made of ferromagnetic material, further comprising a crossbar (19) connected to a respective end portion of said plate-like elements (27, 28).

6. Circuit breaker (1) according to claim 5, wherein said component (27, 28, 29) is substantially "C"- or "U" shaped.

7. Circuit breaker (1) according to claim 5, wherein the crossbar (29) is positioned underneath the fixed electric contact (25).

8. Circuit breaker (1) according to claim 7, wherein the holding element (20) is provided with a hooked end portion, comprising a holding plate (31), to which the fixed contact (25) is fixed, wherein the crossbar (29) is positioned between the holding plate (31) and an opposite portion of said hooked end.

9. Circuit breaker (1) according to claim 8, wherein the crossbar (29) is in contact with the holding plate (31).

10. Circuit breaker (1) according to claim 5, further comprising a cased body (2) with a base (3) of insulating material and a cover part (4), which may be put over the base (2), said component of ferromagnetic material (27, 28, 29) further forming a fixing element in order to fix the fixed contact (25) to the base (3).

11. Circuit breaker (1) according to claim 10, wherein the base comprises a deionizing chamber (35), housing the electric fixed (25) and movable (24) contacts, said chamber (35) being defined between two lateral opposite walls (35, 37), with respect to said plane, each of said walls comprising a cavity (38, 39) for receiving a respective one of said plate-like elements (27, 28).

12. Circuit breaker (1) according to claim 10 or 11, wherein each of said plate-like elements (27, 28) comprises an end portion, distally positioned with respect to said crossbar (29), and which is provided with means (32) for fixing said component to said base.

13. Circuit breaker (1) according to claim 12, wherein said means comprise for each plate-like element (27, 28) a pair of parallel pins (32), which may be parted after inserting said plate-like element in respective cavity (38, 39).

14. Circuit breaker (1) according to claim 10, wherein said component (27, 28, 29) and said holding element (20) may be joined to said base (3) by inserting them into the base (3) from the opposite side (8) of the base (3), with respect to said cover part (5).

15. Circuit breaker (1) according to any of the preceding claims, wherein said circuit breaker is a moulded case automatic circuit breaker.

16. Circuit breaker (1) according to claim 15, wherein said circuit breaker is a three-pole or a four-pole circuit breaker.

Drawing