Deionization cell for the extinction of the electric arc

Description

[0001] The present invention relates to a deionization cell for the extinction of an electric arc, particularly in the case of switches having an arc voltage somewhat high with respect to the circuit voltage in which these switches are to operate.

[0002] The known deionization cells are normally based on the principle of subdividing the electric arc into a certain number of partial arcs, each having a minimal self-supporting voltage, mainly determined by the kind of material or by the surface treatment of the material which forms the arc electrodes.

[0003] In a usual structure, the known deionization cell includes a fork formed by two jaws made of conductive and magnetizable material, these jaws being insulated from each other and diverging from the point where the arc is forming, such as the opening area of the switch-contacts (where the arc moves getting longer) and by a series of conductive lamellae located across this fork and oriented in such a way as to quench the arc.

[0004] Both the fork and the lamellae are located between two parallel walls of insulating material so that the arc, when formed, is pushed mainly by magnetic forces between the two jaws of the fork, getting longer and cooling and finally colliding with the lamellae, which subdivide it into several shorter and quicker extinguishable arcs.

[0005] The lamellae are generally parallel or slightly diverging and are iron made or iron surface- treated, for instance copper-covered or nickel- covered iron.

[0006] Although the lamellae are distributed between the diverging ends of the fork so that they attract the extended arc and these lamellae are provided with grooves opened towards the incoming arc, in order to facilitate the formation of the electric arc and the entrance and the subdivision of the arc itself, they are not always able to create an environment suitable for the extinction of the arc itself. In fact damaging phenomena may arise which help the arc persistance or protract the extinction time.

[0007] This is because the lamellae are obtained by shearing metal plates and their edges may have some indentations or even protuberances among which the electric arc tends to stabilize. This effect may be generated in correspondance both of the incoming and of the outcoming edges of the partial arc. Such tendency of the partial arc to settle at the edges of the lamellae is facilitated by the fact that the facing surfaces, parallel or slightly diverging of these lamellae, offer an unstable position to the partial arc so that the arc itself tends to move over these surfaces moving toward the mentioned edges. Sometimes it reaches a stability on these edges which resists to the thrust of the magnetic forces and delays the arc extinction, with possible disastrous consequences for the circuit to be protected.

[0008] In order to limit the generation of these harmful phenomena, normally the lamellae are placed along a line stretching between the outer ends of the fork jaws, so that the electric arc reaches the plates extended and cooled.

[0009] Such an arrangement, however, is not satisfactory as the arc needs a certain time to proceed along the fork, thus influencing the operation quickness of the switch. Operation times are extended to dangerous values under conditions of high short-circuit power. US-A-2,249,499 discloses an electric circuit interrupter provided in the arc chute with spaced metal pins or bars. This arrangement does not prevent the tendency of the arc to settle at the ends of the pins, thus causing the fusion of such ends.

[0010] The present invention proposes a new structure for the elements, designed to subdivide the electric arc and a new distribution of the same elements, in order to eliminate the above regrettable disadvantages.

[0011] The advantages of the proposed new system will be explained by presenting the various characteristics of the invention.

[0012] According to the invention, the deionization cell for the extinction of an electric arc formed when a movable contact is opened in respect of a fixed contact, comprising a fork with two jaws which diverge outward from said contacts, in such a way that the arc proceeds between the two jaws, getting longer and reaching a barrier of conductive elements or arc electrodes, among which the arc is subdivided into several shorter arcs, or partial arcs, is characterized in that said elements are made of conductive material and have an external surface which is defined entirely by a continuous convex curved surface, so that said partial arcs tend to stabilize between the closest points of pairs of adjacent elements.

[0013] This allows the control of the stability area of the partial arcs and permits a linear gradient of the partial arc voltages. This stability of the partial arc between two continuous convex curved surfaces is beneficial in relation to the arc control, particularly with reference to a linear voltage distribution, while presenting no resistance to the forces of the magnetic fields generated by the same arc. Therefore the best conditions for the cooling and the extinction of the partial arc itself are found.

[0014] In a preferred embodiment the above mentioned convex curved elements are made up of spheres, whose series production at low cost and with perfectly smoothed surfaces, is technologically well known. In an alternative, characteristic embodiment, these convex curved elements are ellipsoidal in shape.

[0015] These elements - in a preferred and characteristic embodiment - are distributed within the space limited by the jaws of the fork in such a way as to occupy totally or partially this space. In particular it is possible to arrange these elements much closer to the area where the arc is forming than by using the iron lamellae. Such an arrangement shortens strongly the arc path time before subdivision and offers an immediate and progressive subdivision which greatly reduces the extinction time, thus permitting an operation quickness of the switch provided with these elements.

[0016] Such elements, on the other hand, can be made up of ferrous material, thus providing a magnetic stabilization of the arc which prevents undesirable movements leading to harmful phenomena, should the arc come out of the deionization cell.

[0017] The ferrous material can be specially treated on the surface in order to increase the arc stability. Use of non-ferrous metallic material can also be contemplated and in this case the action of pushing the arc into the deionization cell is provided by magnetic circuits external to the deionization cell itself.

[0018] According to another characteristicembodi- ment of the invention, the elements can be made up of graphite. Graphite is not subjected to the formation of craters or to fusion phenomena and possesses a high specific heat which remarkably contributes to the arc cooling. It is therefore particularly advantageous in the subdivision of the electric arc.

[0019] The object of the invention, simply as a non limitative example, is shown in the enclosed drawings where:

figure 1 shows the deionization cell in a first embodiment;

figure 2 is a section according to the dotted line AA of figure 1;

figure 3 is a plan drawing of one of the containment insulated wall of the deionization cell;

figure 4 presents a different, preferred embodiment of the invention.

[0020] With reference to figure 1, it is indicated by 1 a portion of the wall of an electrical equipment housing, such as an automatic switch.

[0021] Schematically are indicated a movable contact 2 supported by a contact-holder 2' and a fixed contact 3 supported by a contact-holder 3', which extends externally of the housing up to the connecting terminal of an external conductor. In front of contacts 2 and 3 the fork of the deionization cell opens its two diverging jaws 4 and 5, whose narrower part is in front of contacts 2 and 3, in such a way as to attract the arc formed at the moment when movable contact 2 is opened in respect of the fixed contact 3. The extremities of the arc rest on the jaws 4 and 5 and the arc is pushed into the fork by the magnetic forces generated by the arc itself so that the arc extends while proceeding along the fork.

[0022] Between the two ends of the jaws 4 and 5, the arc movement is intercepted by subdividing elements made up by spheres 6 positioned in such a way that the mutual distance between contiguous pairs of spheres is almost equal. As already said, .the spherical shape of elements 6 is the preferred one, but the elements can be shaped in whatever different form, provided that their external surface be entirely a continuous, convex, curved one, without any discontinuity, for instance an elliptical or any equivalent form, presenting two continuous convex curved surfaces between two adjacent elementS: the partial arc can then stabilize between the two closest points.

[0023] Figure 1 also shows by dotted lines a possible progression in the arc subdivision. Although elements 6 have been indicated equal in size, they may have different dimensions for instance different diameter or axis length.

[0024] Again with reference to figure 2 and figure 3, it is easily perceived that spheres 6 (or differently shaped elements) are supported by two lateral walls 7 and 8, made up by insulating material presenting respectively holes 9 and 10 having a diameter smaller than the spheres one, so that they can hold the spheres on both sides; these walls 7 and 8 are connected to each other by means of transversal pins 11, differently positioned. Externally to the insulated supporting walls 7 and 8, two other continuous intermediate walls 12 and 13 exist, which insulate those portions of the spheres housed in holes 9 and 10. Finally, two more external walls 14 and 15 make up the housing of the electrical equipment.

[0025] As already said, elements 6 for the subdivision of the electric arc may be of ferrous material thus providing a magnetic stabilizing action by the arc and making it unlikely that the electric arc gets out of the deionization cell.

[0026] These elements, however, may be made up of ferrous material coated on the surface so obtaining a protective layer on the ferrous material and an increased stability of the arc.

[0027] The same elements 6 may be produced, with several advantages, in graphite for the reasons and with the benefits previously specified.

[0028] With reference now to figure 4 and in view of the advantages of the magnetic stabilization of the arc, of the possibility of partial arc stabilization between the two closest points of two convex surfaces perfectly smoothed, and of the reduction of fusion and crater formation, elements 6 for the arc subdivision are arranged within the area limited by the two jaws 4 and 5 of the fork, close to the contacts 2 and 3, so that the path of the arc before its subdivision is remarkably reduced, thus concurrently reducing its extinction time and therefore increasing the operation quickness of the switch.

[0029] As shown by the dashed lines in figure 4, the elements 6 for the arc subdivision may occupy the whole area comprised between the jaws 4 and 5, so that a labyrinth is offered to the arc where it is submitted to a progressive subdivision, the consequence being a greater quickness in cooling and extinction.

[0030] Of course, everything said for the elements of figure 1 is also valid for figure 4 as well as for the structure indicated in figure 2 for the support and the lateral insulation of elements 6.

Claims

1. A deionization cell for the extinction of an electric arc formed when a movable contact (2) is opened in respect of a fixed contact (3), comprising a fork with two jaws (4, 5) which diverge outward from said contacts (2, 3), in such a way that the arc proceeds between the two jaws (4, 5), getting longer and reaching a barrier of conductive elements (6) or arc electrodes, among which the arc is subdivided into several shorter arcs, or partial arcs, characterized in that said elements (6) are made of conductive material and have an external surface which is defined entirely by a continuous convex curved surface, so that said partial arcs tend to stabilize between the closest points of pairs of adjacent elements (6).

2. A deionization cell as in claim 1, wherein said elements (6) for the arc subdivision are constituted by spheres.

3. A deionization cell as in claim 1, wherein said elements (6) for the arc subdivison are ellipsoidal in shape.

4. A deionization cell as in claim 1, wherein said elements (6) for the arc subdivision are distributed within the area limited by the two jaws (4, 5) of the fork, so as to occupy totally or partially such area, and arranged in such a way that the distance between a pair of such elements (6) is constant.

5. A deionization cell as in claims 1 and 4, wherein said elements (6) for the arc subdivision are arranged within the area limited by the two jaws (4, 5) of the fork close to the contacts (2, 3).

6. A deionization cell as in claim 1, wherein said elements (6) for the arc subdivision are constituted by a ferrous material.

7. A deionization cell as in claim 1, wherein said elements (6) for the arc subdivision are constituted by a ferrous material coated on the surface.

8. A deionization cell as in claim 1, wherein said elements (6) for the arc subdivision are constituted by graphite.

Ansprüche

1. Entionisierungszelle zum Löschen eines elektrischen Bogens, gebildet bei Öffnung eines beweglichen Kontaktes (2) gegenüber einem festem Kontakt (3); bestehend aus einer Gabel mit zwei Abzweigungen (4, 5), die von genannten Kontakten (2, 3) derart auseinandergehen, dass der Bogen zwischen den beiden Abzweigungen (4, 5) verläuft, sich verlängert und eine Schranke leitender Elemente (6) oder Bogenelektroden erreicht, durch die der Bogen in mehrere kürzere Bogen oder Teilbogen aufgeteilt wird; mit dem Merkmal, dass genannte Elemente aus leitendem Material bestehen und eine Oberfläche haben, die gänzlich durch eine kontinuierliche, konvex gewölbte Fläche begrenzt ist, so dass besagte Teilbogen dazu neigen, sich jeweils zwischen den nächsten Punkten benachbarter Elemente (6) zu stabilisieren.

2. Entionisierungszelle laut Anspruch 1, wobei die genannten Elemente (6) zur Aufteilung des Bogens als Kugeln ausgeführt sind.

3. Entionisierungszelle laut Anspruch 1, wobei die genannten Elemente (6) als Ellipsoiden ausgeführt sind.

4. Entionisierungszelle laut Anspruch 1, wobei genannte Elemente (6) zur Aufteilung des Bogens innerhalb der von den beiden Abzweigungen (4, 5) begrenzten Zone verteilt sind, derart, dass sie diese Zone vollständig oder teilweise einnehmen und so angeordnet, dass der Abstand zwischen einem Paar Elemente (6) gleichbleibt.

5. Entionisierungszelle laut Ansprüchen 1 und 4, wobei die genannten Elemente (6) zur Aufteilung des Bogens innerhalb der Zone zwischen den beiden Abzweigungen (4,5) in Nähe der Kontakte (2, 3) angeordnet sind.

6. Entionisierungszelle laut Anspruch 1, wobei besagte Elemente (6) zur Aufteilung des Bogens aus Eisenmetall bestehen.

7. Entionisierungszelle laut Anspruch 1, wobei die genannten Elemente (6) zur Aufteilung des Bogens aus oberflächenbehandeltem Eisenmetall bestehen.

8. Entionisierungszelle laut Anspruch 1, wobei besagte Elemente (6) zur Aufteilung des Bogens aus Graphit bestehen.

Revendications

1. Une cellule déionisante pour l'extinction d'un arc électrique lorsqu'un contact mobile (2) est ouvert par rapport à un contact fixe (3), comprenant une fourche à deux mâchoires (4, 5) qui s'écartent vers l'extérieur des dits contacts (2, 3) de manière à ce que l'arc passe entre les deux mâchoires (4, 5), s'allongeant et atteignant une barrière d'éléments conducteurs (6) ou électrodes de l'arc, entre lesquels l'arc se subdivise en plusieurs arcs plus courts, ou arcs partiels, caractérisés par les dits éléments (6) faits de matériel conducteur et possèdent une surface externe entièrement définie par une surface continue convexe courbe, de manière à ce que les dits arcs partiels aient tendance à se stabiliser entre les points les plus rapprochés de paires d'éléments adjacents (6).

2. Une cellule déionisante comme à la revendication 1, où les dits éléments (6) pour la subdivision de l'arc sont constitués par des spères.

3. Une cellule déionisante comme à la revendication 1, où les dits éléments (6) pour la subdivision de l'arc sont ellipsoïdaux.

4. Une cellule déionisante comme à la revendication 1, où les dits éléments (6) pour la subdivision de l'arc sont distribués à l'intérieur de l'arc dans les limites des deux mâchoires (4, 5) de la fourche, de façon à occuper totalement ou partiellement cette zone, et placés de manière à ce que la distance entre une paire de ces éléments (6) soit constante.

5. Une cellule déionisante comme aux revendications 1 et 4, où les dits éléments (6) pour la subdivision de l'arc sont placés à l'intérieure de la zone délimitée par les deux mâchoires (4, 5) de la fourche à proximité des contacts (2, 3).

6. Une cellule déionisante comme à la revendication 1, où les dits éléments (6) pour la subdivision de l'arc sont faits de matériel ferreux.

7. Une cellule déionisante comme à la revendication 1, où les dits éléments (6) pour la subdivision de l'arc sont faits de matériel ferreux revêtu à la surface.

8. Une cellule déionisante comme à la revendication 1, où les dits éléments (6) pour la subdivision de l'arc sont en graphite.

Drawing