EP1667180A1 - Electrical contactor and electric arc extinguishing chamber with deionisation blades - Google Patents

Abstract

The switchgear has an electric arc extinguishing chamber, opening on an opening volume (35), with a stack of de-ionization blades separated by an exchange gap. Free leading edges of the blades are exposed to an electric arc and delimit a recess (9) of asymmetrical form and formed to create, when the blades are alternatively stacked, chimneys (15) whose passages are closed in a plane perpendicular to chimneys` longitudinal axis.

Description

TECHNICAL FIELD OF THE INVENTION

The invention relates to an electrical cut-off device comprising a housing having a reference longitudinal geometric plane, a pair of separable electrical contacts disposed in an opening volume, an arc extinction chamber opening on the volume opening and being delimited by two parallel side walls and placed on either side of the geometric reference plane, a rear wall remote from the opening volume, a bottom wall and an upper wall. The arc extinguishing chamber comprises a stack of at least two deionization fins separated from each other by an exchange space, each fin having a leading edge to be exposed to the arc. At least one exchange space is connected to at least one evacuation duct via at least one evacuation hole.

STATE OF THE ART

The presence of electrical faults inside switching devices such as circuit breakers, switches or electrical contactors causes a sudden opening of their electrical contacts. This rapid separation of the contacts is usually accompanied by the birth of an electric arc. The energy of the arc and the gas discharges accompanying the birth of said arc give rise to significant constraints on the mechanisms and may damage the device.

In order to reduce the time of occurrence of the short-circuit current and thus to reduce the thermal load borne by the electrical breaking device, the arc voltage is raised as rapidly as possible until it becomes greater than the applied voltage. This causes the cancellation of the short circuit current. The dielectric resistance of the air between the separated contacts then prevents a reboot or other arcing.

The electric arc must be cooled as quickly as possible while remaining away from the electrical contacts. This cooling is commonly done by placing the arc inside an arc extinguishing chamber comprising a stack of metal plates called deionization fins. In practice, the electric arc, which has just been born, is pushed into the chamber by electrodynamic forces induced by a magnetic field of the current flowing in the conductors.

During its movement, the arc tends to move between the side walls of the arc extinguishing chamber, generally borrowing the recesses present in the fins. These recesses favor the migration of the arc towards the bottom of the chamber. In addition, the stack of fins causes a cutting of the arc and facilitates its insertion into the arc extinguishing chamber 10. The fins provide the arc a heat exchange surface throughout the cut. As the bow progresses in the room, it tends to expand to invade all available space. The fins contain this expansion by interacting with the periphery of the arc. The arc voltage increases as the arc cools. In addition, the pressure in the breaking volume increases sharply.

If the shape of the recesses is not optimized, we can witness repetitive arc recoblings between the contacts.

Some documents (FR2839195) disclose recesses terminating in a chimney which tends to stabilize the arc in a region remote from the opening volume of the contacts. However, the shape of the recess characterized by the presence of a corridor running from the birth zone of the arc to the chimney can cause a sending of hot gases and vapors towards the opening area of the contacts and thus causing a leak of the arc from the chamber to the contacts. This leak is accompanied by repetitive repetitions.

Moreover, the birth of the arc causes concomitantly the birth of a large amount of metal vapor or gas, which may, if they are not evacuated, be responsible in particular for a connecting arc between the phases of the electrical device cut and create an explosion.

Many existing solutions provide at least one exhaust channel for said gases outside the area near the contacts. These gases are generally expelled outside the electrical cut-off device.

These solutions, although having advantages, may nevertheless generate nuisances in the premises where the cut-off devices are placed. Indeed, these gases are still hot and strongly ionized, can cause adverse effects.

In order to avoid this pollution of the external environment, other solutions offer internal gas recycling (GB2285889, US5731561, FR1400079).

These solutions may have certain disadvantages. This internal gas recirculation is generally accompanied by an increase in the volume of the electrical cut-off device. Indeed, the gases are generally conducted in specific volumes located beyond the arc extinction chamber. In addition, the channels used for the gas duct can, due to their geometry, induce pressure caps responsible for poor evacuation or slowing of said gases.

SUMMARY OF THE INVENTION

The invention therefore aims to overcome the drawbacks of the state of the art, so as to provide an electrical cutoff device comprising deionization fins for rapid cooling of the electric arc.

The free edge of attack of at least two of the fins of the device according to the invention delimits a recess opening of asymmetrical shape and forming two lateral branches, said recess being made so as to create, when said fins are stacked alternately, at least one chimney whose duct appears as substantially closed in a plane perpendicular to the longitudinal axis of said chimney.

Advantageously, the device comprises, along the axis z, at least two alignment zones between a lateral branch of a first fin and at least one lateral branch of a second fin having undergone, with respect to said first fin, a rotation 180 ° around its longitudinal axis.

In a preferred embodiment of the invention, the free edge of attack fins is in contact at least twice with the longitudinal axis of said fins.

In a preferred embodiment of the invention, the free cutting edge of the fins cuts at least twice the longitudinal axis of said fins.

Advantageously, the cut-off device comprises, along the z-axis, at least one overlap zone between a lateral branch of a first fin and at least one lateral branch of a second fin having undergone, with respect to said first fin, a rotation of 180 ° around its longitudinal axis.

Preferably, the free leading edge of the recess delimits a first flared front portion opening on the opening volume and a second longitudinal posterior portion extending towards the posterior wall, the first flared front portion is cut by the longitudinal axis of the fins.

According to one embodiment of the invention, each fin is positioned next to another fin which has been rotated 180 ° relative to its longitudinal axis.

According to a particular embodiment of the invention, at least one evacuation duct extends from at least one evacuation hole to an opening, along at least one side wall, said duct comprising, according to z axis of the gas inlet at their outlet of said duct, a substantially constant or increasing section, said opening (18) being at least equal to the largest section of said duct and being placed facing the electrical contacts of the volume opening.

Preferably, each exchange space of the extinguishing chamber comprises at least one evacuation hole connected to at least one evacuation duct.

Preferably, the device comprises at least two exhaust ducts, at least one duct extending along each side wall of the arc extinguishing chamber.

Advantageously, the exchange spaces of the extinguishing chamber comprise at least two evacuation holes, at least one hole being connected to each of the evacuation conduits extending along each wall.

Preferably, the drain holes are placed in an area between the rear wall and the center axis of the fins.

The drain holes are placed in the side walls.

The drainage holes are placed in the posterior wall.

The exhaust ducts have a substantially parallelepiped shape.

BRIEF DESCRIPTION OF THE FIGURES

• la figure 1 représente une vue de coté d'un dispositif électrique de coupure selon un premier mode de réalisation préférentiel de l'invention ;
• la figure 2 représente une vue en coupe selon un plan Il d'un dispositif électrique de coupure selon la figure 1 ;
• la figure 3 représente une vue en coupe selon un plan JJ d'un dispositif électrique de coupure selon la figure 2 ;
• la figure 4A représente une vue détaillée d'une ailette de désionisation d'un dispositif électrique de coupure selon la figure 1 ;
• la figure 4B représente une vue détaillée d'un empilement d'ailettes de désionisation selon la figure 4A ;
• les figures 5A, 5B représentent respectivement une vue détaillée d'une ailette et d'un empilement d'ailettes de désionisation d'un dispositif électrique de coupure selon une variante du premier mode de réalisation préférentiel de l'invention ;
• la figure 6A représente une vue détaillée d'une ailette de désionisation d'un dispositif électrique de coupure selon un seconde mode de réalisation préférentiel ;
• la figure 6B représente une vue détaillée d'un empilement d'ailettes de désionisation selon la figure 6A ;
• les figures 7A, 7B représentent respectivement une vue détaillée d'une ailette et d'un empilement d'ailettes de désionisation d'un dispositif électrique de coupure selon une variante du second mode de réalisation préférentiel de l'invention ;
• les figures 9A à 10B représentent des variantes de réalisation d'ailettes de désioniation de la chambre d'extinction d'arc.
• la figure 11 représente une variante de réalisation d'un dispositif électrique de coupure selon la figure 1.

Other advantages and features will emerge more clearly from the following description of a particular embodiment of the invention, given by way of non-limiting example, and represented in the accompanying drawings in which:

• FIG. 1 represents a side view of an electrical cut-off device according to a first preferred embodiment of the invention;
• FIG. 2 represents a sectional view along a plane II of an electrical cut-off device according to FIG. 1;
• FIG. 3 represents a sectional view along a plane JJ of an electric cut-off device according to FIG. 2;
• FIG. 4A represents a detailed view of a deionization fin of an electric breaking device according to FIG. 1;
• FIG. 4B represents a detailed view of a stack of deionization vanes according to FIG. 4A;
• FIGS. 5A and 5B respectively represent a detailed view of a fin and a stack of deionization vanes of an electric switching device according to a variant of the first preferred embodiment of the invention;
• FIG. 6A represents a detailed view of a deionization fin of an electric breaking device according to a second preferred embodiment;
• FIG. 6B shows a detailed view of a stack of deionization fins according to FIG. 6A;
• FIGS. 7A and 7B respectively represent a detailed view of a fin and a stack of deionization vanes of an electric switching device according to a variant of the second preferred embodiment of the invention;
• FIGS. 9A to 10B show alternative embodiments of fins for deionizing the arc extinction chamber.
• FIG. 11 represents an alternative embodiment of an electric switching device according to FIG. 1.

DETAILED DESCRIPTION OF AN EMBODIMENT

According to a first preferred embodiment shown in FIGS. 1, 2 and 3, the electrical cut-off device 30 comprises a casing 31 made of molded plastic material in which at least one fixed contact 32 associated with at least one movable contact 33 is arranged. One or more fault detection devices including short-circuit, act on an actuating mechanism 34 controlling the opening of the movable contact 33.

The housing 31, because of its shape, defines a reference longitudinal geometric plane xz.

In this embodiment shown, the electrical cut-off device comprises two U-shaped fixed contacts 32 connected to a terminal respectively. electrical connection. The movable contact 33, which can move in translation under the action of the actuating device 34, makes it possible to connect the two fixed contacts 32 electrically. The movable contact 33 has two contact zones 36 each capable of collaborating respectively with a fixed contact 32 Two opening volumes 35 corresponding to the space in which a fixed contact 32 and a contact zone 36 associated with the moving contact 33 are thus defined.

In addition, each opening volume 35 is associated with an arc extinguishing chamber 10. The arc extinguishing chamber 10 opening on the opening volume 35 is delimited by two parallel side walls 11 and placed on either side of the longitudinal geometric reference plane xz, a rear wall 6 remote from the opening volume 35, a bottom wall 7 and an upper wall 8.

The arc extinguishing chamber 10 comprises a stack of at least two deionization fins 1 planar and perpendicular to the reference longitudinal geometric plane xz. Said fins are of substantially rectangular shape and have a longitudinal axis 12 and a median axis 13. Said fins comprise two main parts: a first front portion 13a facing the opening volume 35 and extending from the front face of the extinguishing chamber 10 at the median axis 13, and a second posterior portion 13b extending from the median axis 13 to the posterior wall 6.

Each fin 1 has a free leading edge 5 intended to be exposed to the arc. The free leading edge 5 forms a recess 9 opening and extending along the longitudinal axis 12, from the anterior face of the extinguishing chamber 10 to the posterior wall 6. This recess 9 delimits two lateral branches 1a, 1b.

The recess 9 of at least two fins 1 is asymmetrically shaped and has two portions. It comprises a first flared front portion 9a facing the contacts 32, 33 placed in the opening volume 35 and a second narrower rear longitudinal portion 9b.

According to a preferred embodiment of the invention, as shown in FIGS. 6A, 7A, the leading edge 5 traversing the flat surface of the said at least two fins is at least twice in contact at points a, b with the longitudinal axis 12 of the fins. In another preferred embodiment of the invention, as shown in Figures 4A and 5A, the leading edge 5 cuts three times at points a, b, c the longitudinal axis 12 of said at least two fins.

According to these preferred embodiments of the invention, the recess 9 is made so that when two fins are stacked alternately, there are, along the z axis, at least two alignment zones a and b between a lateral branch 1a of a first fin 1 and at least one lateral branch 1a of a second fin 1 placed in an alternating position. One fin is in an alternating position with respect to another when it has been rotated 180 ° about its longitudinal axis 12. Preferably, the first alignment zone a is located in the front portion 13a of the fin 1 .

When the leading edge 5 cuts three times the longitudinal axis 12, there are three alignment zones a, b and c between a lateral branch 1a of a first fin 1 and at least one lateral branch 1a of a second fin 1 placed in an alternating position. There is then a recovery zone 50 of the lateral branches 1a. Each fin has a covering zone 50 delimited by the intersection, at points a and b, between the longitudinal axis 12 and the leading edge 5 of the first lateral branch 1a.

According to these two preferred embodiments of the invention, the two lateral branches 1a, 1b are substantially placed on either side of said longitudinal axis 12 and the first flared front portion 9a is cut by the longitudinal axis 12.

In the exemplary embodiments as represented in FIGS. 1 to 11, all the fins placed in the arc extinguishing chamber 10 comprise the same recess 9. The stack of all the fins 1 of the chamber extinction of arc 10 is realized so that at least two of the fins are stacked alternately so that the shapes of their recess 9 do not coincide.

Advantageously, all the fins 1 are stacked alternately, so that each fin 1 is positioned next to another fin having been rotated 180 ° relative to its longitudinal axis 12.

Due to the asymmetrical shape of the recesses 9 of the fins 1 and because of the alternating stack of said fins, is formed a chimney 15 whose conduit appears as substantially closed in a xy plane perpendicular to the longitudinal axis 16 of said chimney 15.

In the exemplary embodiment, the chimney 15 extends over the entire height of the chamber, from the bottom wall 8 to the top wall 7.

Depending on the shape of the recesses 9 of the fins 1, the axis 16 of the chimney 15 will be more or less close to the rear wall 6 of the arc extinguishing chamber 10. The chimney 15 is preferably positioned at the median axis 13 of the fin 1 or beyond said axis to the posterior wall 6.

The fins are made of conductive material based on steel. The deionization fins 1 stacked one on the other are separated from each other by an exchange space 2. The thickness of each exchange space 2, slightly greater than the thickness of the fins.

The gases or metal vapors present in the arc extinguishing chamber 10 can be evacuated in the traditional way by means of at least one evacuation channel connected to one or more exchange space 2 via evacuation holes. . The gases may be expelled outside the electrical cut-off device, as this may cause nuisance in the rooms where the cut-off devices are placed.

In a particular embodiment of the invention, gas recycling means are then used. At least one exchange space 2 is connected to at least one evacuation duct 3 via at least one evacuation hole 4. Said at least one evacuation duct 3 is intended on the one hand for evacuation of gases of the extinguishing chamber 10 and on the other hand the injection of said gases, via an opening 18, at the level of the contacts 32, 33 of the opening volume 35. In addition, said at least one exhaust duct 3, s extends from at least one discharge hole 4 to the opening 18, along at least one side wall 11. Said opening 18 is placed facing the electrical contacts 32, 33 of the opening volume 35

The gases then take a flow duct composed of at least one evacuation hole 4, at least one evacuation duct 3 and at least one opening 18. Said evacuation ducts 3 comprise, over any their length and along the x-axis, a constant or increasing section A. In addition, said evacuation ducts 3 also preferably comprise a constant section along the y and z axes. In other words, from the inlet to the gas outlet of the exhaust ducts 3, the section of said ducts is substantially constant. Advantageously, the section of said ducts may be increasing. The opening 18 is at least equal to the largest section A of said duct.

In general, the section of a flow path taken by the gases must at least remain constant or increase. This geometrical feature promotes the flow of gases from the exchange spaces 2 and thus limits the creation of pressure caps that can form along the flow conduit. A decrease in the section of the flow conduit, particularly at the outlet duct 3 or the opening 18, could cause the creation of pressure plugs. These pressure caps could cause braking in the progression of gases and in the progression of the electric arc.

Advantageously, in the preferred embodiment of the invention shown in FIGS. 1 to 3, each exchange space 2 is connected to at least one evacuation duct 3 via at least one evacuation hole 4. The shape and size of the discharge holes 4 are such that the gas flow does not cause the passage of the arc through these holes. In order to avoid short circuits between the fins 1, via the electrical art, the drain holes are made independently and do not communicate with each other.

Preferably, at least two exhaust ducts 3 are present in such a way that at least one duct 3 extends along each side wall 11 of the arc extinguishing chamber 10. In the example of embodiment shown in Figures 1 and 2, each discharge duct placed next to a side wall 11 extends from the discharge holes 4 to an opening 18, the bottom wall 8 to the upper wall 7 and the along the side wall 11.

In a preferred embodiment according to the invention as shown in Figures 1 to 3, two exhaust ducts 3 are used. An evacuation duct 3 is placed next to each of the side walls 11 of the arc extinguishing chamber 10. Each exchange space 2 comprises at least one evacuation hole 4 connected to an evacuation duct 3 The drainage holes 4, placed in the side walls 11, are positioned in an area between the rear wall 6 and the central axis 13 of the fins 1. In addition, the ducts are substantially parallelepipedal in shape.

The apparatus operates in the following manner. During the appearance of a short circuit, the electromagnetic field induced by the current flowing in the conductors and in particular in the fixed contact 32, generates in the moving contact 33 electrodynamic forces that push the movable contact in separation position, this movement being subsequently confirmed by the opening of the actuating mechanism via the mechanism 34. Upon separation of the contacts 32, 33, an electric arc arises between said contacts. This arc is pushed into the arc extinction chamber 10 by the electrodynamic forces. During its movement towards the chimney 15 and the rear wall 6, the arc remains halfway between the side walls 11, since it tends to borrow the recesses 9 open between the fins.

The fins 1 offer the arc a heat exchange surface during the entire cut, especially in their part near the edges 5. During its progression in the arc extinguishing chamber 10 or when installed in the chimney 15, the arch tends to expand to invade all the available space. The fins 1 contain this expansion by interacting with the periphery of the arc. When the arc is in the chimney 15, the heat exchange is distributed in a uniform way around the arc and thus optimizes its cooling and accelerates its extinction. The arc voltage increases as the arc cools which eventually allows the extinction of the arc when the current passes through zero.

The recesses 9 promote the migration of the arc towards the bottom of the arc extinguishing chamber 10, and the chimney 15 stabilizes the arc in this region. This stack 15, remote from the opening volume allows the arc to stabilize and not re-slamming repeatedly between the contacts. It is therefore the conjunction of the shape of the recess and the respective position of the fins relative to each other which allows to quickly and sustainably move the arc contacts.

Furthermore, via the exhaust ducts 3, a gas convection is established so that the progression of the arc to the rear wall 6 is not hindered by an increase in pressure. The foot of the arc migrates rapidly from the fixed contact 32 to the stack 15, before the movable contact 33 has reached its final separation position.

In practice, the gases emitted at the periphery of the arc and present in the exchange spaces 2 are injected into the opening volume 35 via the flow conduits composed of the evacuation holes 4, the evacuation ducts 3 and openings 18. The homogeneous and even distribution of the gases evacuated by the flow ducts reduces the risk of pressure plugs responsible for slowing the progression of the gases and the progression of the arc. Indeed, a local increase in pressure or the presence of cold gas, in front of the arc, may cause a slowdown in its movement.

The flow of gases in the flow conduits towards the electrical contacts 32, 33 of the opening volume 35 allows decompression of said gases and a faster cooling thereof.

The injection of the cooled gases at the contacts 32, 33 present in the opening volume 35 makes it possible to increase the dielectric strength in this case. space and avoid inadvertent re-breakdown of the electric arc. In addition, this injection at the level of the contacts makes it possible to subject the plasma present in the opening volume 35 and the arc extinguishing chamber 10 to a rear flow of cold and weakly ionized gases. This causes a cooling of the rear area of the arc but also the sending of the hot gases in front of the arc. Due to its cooling by the rear, the arc tending to develop in the presence of ionized hot gases associated with metal vapors, moves towards the posterior face 6 of the extinguishing chamber 10 and thus moves away from the contact opening area.

According to a first series of alternative embodiments as shown in FIGS. 6A and 7A, the leading edge 5 traversing the flat surface of the fins 1 and forming the recess 9 of asymmetrical shape, cuts five times at the points a, b , c, d, e the longitudinal axis 12 of said fins. Because of the asymmetric shape of the recesses 9 of each fin 1 and because of the alternating stack of said fins, are formed two chimneys 15 whose ducts 16 appear respectively substantially closed in a plane perpendicular xy to the longitudinal axis 16 said chimneys 15.

According to a second series of alternative embodiments as shown in FIGS. 10a and 10b, the leading edge 5 traversing the flat surface of the fin and forming the recess 9 of asymmetrical shape cuts twice the longitudinal axis 12 of said fin. In addition, the first flared longitudinal portion 9a is positioned beyond the longitudinal axis 12 of the fins 1.

In another alternative embodiment as shown in FIG. 11, the exchange spaces 2 comprise at least one evacuation hole 4 placed in the rear wall 6 and connected to a discharge duct 3. According to this exemplary embodiment each exchange space 2 has two discharge holes 4; each of the holes is respectively connected to a discharge duct 3.

In another variant embodiment, each hole 4 is connected autonomously to an opening 18 via its own evacuation duct 3. indeed, each evacuation duct 3 remains independent of the other evacuation ducts.

Claims (15)

Electrical cutoff device comprising: A housing (31) having a reference longitudinal geometric plane (xz), A pair of separable electrical contacts (32, 33) disposed in an opening volume (35), An arc extinguishing chamber (10) opening on the opening volume (35) and being delimited by two parallel side walls (11) and placed on either side of the geometric reference plane (xz ), a rear wall (6) remote from the opening volume (35), a bottom wall (7) and a top wall (8), At least two deionization vanes (1) having a leading edge (5) intended to be exposed to the arc and delimiting a recess (9) opening asymmetrically and forming two lateral branches (1a, 1b) , said at least two fins being stacked alternately, the fins being placed inside the arc extinguishing chamber (10) characterized in that said recess (9) of said at least two fins (1) being made to create at least one chimney whose duct appears as substantially closed (15) in a plane perpendicular (xy) to the longitudinal axis ( 16) of said chimney (15). Electrical cut-off device according to claim 1, characterized in that it comprises, along the axis (z), at least two alignment zones (a, b) between a lateral branch (1a) of a first fin (1). ) and at least one side branch (1a) of a second fin (1) having, relative to said first fin (1), a rotation of 180 ° about its longitudinal axis (12). Electrical cut-off device according to claims 1 or 2 characterized in that the free edge of attack (5) fins (1) is in contact at least twice with the longitudinal axis (12) of said fin. Electrical cut-off device according to claim 3, characterized in that the free leading edge (5) of the fins (1) cuts at least twice the longitudinal axis (12) of said fin. Electrical cut-off device according to Claim 4, characterized in that at least one overlapping zone (50) is arranged between a lateral branch (1a) of a first fin (1) and at the end of the axis (z). minus one lateral branch (1a) of a second fin (1) having, relative to said first fin (1), a rotation of 180 ° about its longitudinal axis (12). Electrical cut-off device according to any one of the preceding claims, characterized in that the free leading edge (5) of the recess (9) delimits a first flared front portion (9a) opening onto the opening volume ( 35) and a second longitudinal posterior portion (9b) extending towards the posterior wall (6), the first flared front portion (9a) is cut by the longitudinal axis of the fins (12). Electrical cut-off device according to any one of the preceding claims characterized in that each fin (1) is positioned next to another fin (1) which has been rotated 180 ° relative to its longitudinal axis (12). Electrical cut-off device according to any one of the preceding claims, characterized in that at least one discharge pipe (3) is connected to at least one exchange space (2) separating two fins (1) via at least one drain hole (4), said at least one exhaust duct (3) extending from at least one drain hole (4) to an opening (18) along at least one side wall (11), said duct (3) having, along the axis (x) of the gas inlet at their outlet of said duct, a substantially constant or increasing section (A), said opening (18) being at least equal to the largest section (A) of said duct (3) and being placed opposite the electrical contacts (32, 33) of the opening volume (35). Electrical cut-off device according to claim 8 characterized in that each exchange space (2) of the extinguishing chamber (10) comprises at least one evacuation hole (4) connected to at least one evacuation duct ( 3). Electrical cut-off device according to claims 8 or 9, characterized in that it comprises at least two discharge ducts (3), at least one duct (3) extending along each side wall (11) of the chamber arc extinction (10). Electric arc cutting device according to claim 10, characterized in that the exchange spaces (2) of the extinguishing chamber (10) comprise at least two discharge holes (4), at least one hole being connected to each of the exhaust ducts (3) extending along each wall (11). Electric arc cutting device according to any one of the preceding claims, characterized in that the discharge holes (4) are placed in an area between the rear wall (6) and the median axis (13) of the fins. (1). Electric arc cutting device according to claim 12, characterized in that the discharge holes (4) are placed in the side walls (11). Electric arc cutting device according to claim 12, characterized in that the discharge holes (4) are placed in the rear wall (6). Electrical cut-off device according to any one of the preceding claims, characterized in that the discharge ducts (3) have a substantially parallelepiped shape.

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