FR2508230A1 - LV circuit breaker arc extinction chamber - uses porous screen of fine refractory insulating material to filter gas leaving arcing chamber - Google Patents

Abstract

The arc extinction chamber (16) has, for each pole,: (1) a pair of contacts, one fixed (20) and one mobile (22), (2) an operating mechanism for the mobile contact (22) which moves between the opened and closed positions, and (3) metal cooling plates (24) to draw the arc between the contacts during their separation. An orifice (38) allows gas to escape from the arc chamber (16). A porous screen (40) is fitted in the orifice to filter the escaping gas. The porous screen (40) is of a fibrous (41) structure using refractory insulating material of either mineral or synthetic origin. The fibres are of less than 1mm dia. and may be formed as a mesh or as a tissue.

Description

POROUS EXHAUST SCREEN FOR ARC EXTINGUISHING CHAMBER.

The invention relates to an arc extinguishing chamber for a low-voltage multipolar circuit breaker with bolier made of molded insulating material, comprising by pole: - a pair of separable fixed and movable contacts, - a mechanism for actuating the movable movable contact between closed and open positions, - metal sheets for cooling the arc drawn between said contacts when they separate after tripping of the circuit breaker,
a cut-off gas exhaust opening in the bolt bowl at the outlet of said chamber,
- And a porous screen arranged in the exhaust orifice to filter the cut gases expelled to the outside environment.

According to a known circuit breaker of the kind mentioned, the exhaust screen comprises metallic grids with fine meshes, in particular made of steel, housed in the exhaust orifices. The breaking gases generated in the extinguishing chamber during the breaking are ventilated towards the outside environment after passage through the grids acting as flame arresters, and it has been found that these gases were still strongly ionized at the outlet of the bedroom.

To improve the filtering of the breaking gases, other deionization devices have already been proposed, in particular a labyrinth formed by a plurality of screens with offset windows, a reflection grid, cooling tubes, but the bulk. important of these devices does not allow their use in compact extinguishing chambers for molded case circuit breakers.

According to another known device, the exhaust screen comprises a porous structure formed from agglomerated metal elements. Under the effect of hot gases, however, there are still risks of clogging of the pores which impede the escape of the gases to the outside.

The object of the invention is to avoid the aforementioned drawbacks and to allow the production of an extinguishing chamber with high breaking capacity, equipped with an improved exhaust screen of small size allowing efficient filtering and exhausting. cut gases expelled to the outside environment.

The arc extinguishing chamber according to the invention is characterized in that the porous exhaust screen comprises a refractory fibrous structure made of mineral or synthetic insulating material. The refractory fibrous structure is arranged to form a fabric, braid or felt.

According to a characteristic of the invention, the mineral insulating material of the refractory structure comprises glass wool.

According to another characteristic of the invention, the refractory fibrous structure is attached in the exhaust orifice to a perforated grid. The perforated grid is either metallic or made of insulating material molded with the case of the circuit breaker.

Other advantages and characteristics will emerge more clearly from the description which follows of an embodiment of the invention, given by way of nonlimiting example and represented in the appended drawing, in which FIG. 1 is a longitudinal section view of urn arc extinguishing chamber of a circuit breaker equipped with an exhaust screen according to the invention.

In FIG. 1, the low-voltage circuit breaker 10 with a boot 12 made of molded insulating material and with a lever 14 for manual control, comprises, by pole, an arc extinguishing chamber 16 housed in a lower compartment 18 of the case 12.

Each arc extinguishing chamber 16 comprises a pair of separable contacts 20, 22 and a stack of V-shaped notched cooling sheets 24, extending transversely to the direction of extension of the arc drawn between the contacts 20 , 22 during their separation after tripping of the circuit breaker. The fixed contact 20 is supported by a conductor 26 in the form of a U-shaped pin, positioned on an intermediate wall 27 of the boot 12 and in electrical connection with an external connection pad 28. A metal shielding element 30 is inserted between the two branches of the conductor pin 26, and is provided with an extension 32 acting as an end separator. The movable contact 22 is integral with a contact arm 4 associated with a pivoting bar of the actuating mechanism (not shown) common to all the poles. A connecting shunt 36 connects the opposite end of the arm 34 to the thermal and electromagnetic trip elements (not shown) of each pole. The transverse face of the lower compartment of the boot 12 is provided with an orifice 38 for exhaust of the cut-off gases formed at the outlet from each arc extinguishing chamber 16.

According to the invention, a porous exhaust screen, designated by the general reference 40, is disposed in the exhaust orifice 38 of each pole to reduce the external manifestations of the ionized gases. The porous exhaust screen 40 is formed by a fibrous structure or refractory mesh fabric 41 based on wires or mineral insulating fibers, in particular asbestos or glass wool. The spacing of the threads or fibers intertwined with the fabric 41 is less than 1 mm, and the fibers are braided or woven so as to constitute a very fine filter capable of retaining small conductive particles, in particular metallic and carbon, while allowing the escape of hot gases arising during the cutting of the arc. Any risk of blockage of the pores of the fabric under the effect of hot gases is avoided by the use of refractory fibers or wires.

The fabric 41 or the braid of refractory material of the porous screen 40 has a certain rigidity to be used separately and independently of any other support member. In the case where the thickness of the fabric 41 does not give sufficient rigidity, a metal grid 42 is associated with the fabric 41 to form a screen 40 of mixed exhaust. The diameter of the holes of the grid 42 is greater than that of the pores of the fabric 41. The latter can be trapped in the metal grid 42 in the form of a U-shaped stirrup. In addition to its support function, the grid 42 allows cooling of the cut-off gases filtered by the internal fabric 41.

According to an alternative embodiment (not shown), the metal grid 42 is housed inside the fabric 41.

According to another variant, the grid 42 is formed by two perforated and parallel walls made of insulating material obtained from molding with the housing 12. During mounting of the circuit breaker, the fabric 41 of glass wool is inserted in the space provided between the two walls to form the porous exhaust screen 40.

An additional wall 44 made of insulating material, is arranged in the exhaust zone of each arc extinguishing chamber 16, in the gap formed between the ends of the arc deionization sheets 24 and the screen. exhaust 40. The wall 44 extends in the height direction between the bottom 45 of the boot 12 and the intermediate wall 27, and is pierced with a plurality of holes 46 arranged opposite the screen 40.

When the arc is cut in the extinguishing chamber 16, the cutting gases after passing through the holes 46 of the insulating wall 44 are effectively filtered in the screen 40 and escape towards the outside environment. The metallic and carbon particles resulting from the cut are retained by the very fine meshes of the screen 40.

The invention is of course by no means limited to the mode of implementation more particularly described and represented in the appended drawing, but it extends quite the contrary to any variant remaining within the framework of electrotechnical equivalences, in particular that in which the fabric 41 of screen glass fibers 40 would be replaced by another fibrous structure (braid or felt) based on mineral or synthetic fibers, or a non-woven material.

Claims (7)

1. Arc extinguishing chamber (16) for low-voltage circuit breaker (10) in molded insulating material, comprising by pole - a pair of separable fixed (20) and movable (22) contacts, - a mechanism for actuation of the movable contact (22) displaceable between closed and open positions, - metal sheets (24) for cooling the arc drawn between said contacts during their separation after tripping of the circuit breaker, - an orifice (38 ) exhaust of the cut-off gases formed in the case at the outlet of said chamber (16), - and a porous screen (40) arranged in the exhaust orifice to filter the cut-off gases expelled to the outside environment, characterized in that the porous exhaust screen (40) comprises a refractory fibrous structure (41) made of mineral or synthetic insulating material. 2. Arc extinguishing chamber according to claim 1, characterized in that the spacing of the interlaced wires or fibers of the refractory structure (41) of the screen (40) is less than I mm, so as to constitute a very fine mesh filter. 3. Arc extinguishing chamber according to claim 1 or 2, characterized in that the mineral insulating material of the refractory structure Cl) comprises glass wool. 4. Arc extinguishing chamber according to claim 1, 2 or 3, characterized in that the refractory fibrous struct.ure (41) is arranged to form a fabric, a braid or a felt. 5. arc extinguishing chamber according to claim 4, characterized in that the fibrous structure (41) refractory-- is contiguous in the orifice (38) of exhaust to a grid (42) perforated. 6. Arc extinguishing chamber according to claim 5, characterized in that the perforated grid (42) is metallic and that the fibrous structure (41) is arranged inside or outside the grid (42 ) metallic. 7. Arc extinguishing chamber according to claim 5, characterized in that the perforated grid (42) is formed by two insulating walls obtained by molding with the boot (12), the refractory fibrous structure (41) being inserted into the gap between the two parallel walls of the grid (42) when mounting the circuit breaker.