Metal-clad electrical equipment including a particle trap

Abstract

Metal-clad electrical equipment comprises a metal vessel (4) and an exhaust constituted by an arcing contact support tube (9) and a casing (16) surrounding the support tube (9) and co-operating therewith to define an annular volume (20). At one end, the support tube has an inlet for passing arc gas. Exhaust holes (17) are provided through the casing to allow arc gas to escape into the vessel. The equipment includes a particle trap (22) situated in the exhaust between the arcing contact support tube (9) and the exhaust casing (16).

Description

Other characteristics and advantages of the invention appear further on reading the following description of an embodiment given by way of illustration and with reference to the accompanying figures. In the figures:

FIG. 1 is a diagrammatic section view of metal-clad electrical equipment in accordance with the present invention;

FIG. 2 is a diagram showing the flow of gas within the electrical equipment; and

FIG. 3 is a detail view of a particle trap in accordance with the present invention.

In FIG. 1, overall reference 2 designates metal-clad electrical equipment in accordance with the present invention. The equipment comprises a vessel 4 constituted by a cylindrical container 6 and a hemispherical end 8 mounted at the end shown of the vessel. A similar end is provided at the portion of the vessel that is not shown. The vessel 4 is connected to ground. Inside the vessel there are parking contacts (not shown) for breaking an electric current. An arcing contact support tube 9 is cantilevered out from the end of a nozzle 10. The tube 9 is connected to an electrical bus bar 13 (see FIG. 2) that is received in a socket 12 (FIG. 1). An arcing contact support 14 is provided inside the tube 9. The tube 9 is mounted inside a casing 16 that has an end wall 18. The tube 9 co-operates with the casing 16 to define an annular volume 20.

When breaking a circuit, an arc appears between the arcing contacts. This arc gives rise to hot gas (arc gas) that travels along the tube 9 at high speed from left to right (in FIGS. 1 and 2) as represented by arrow 15 (see FIG. 2). This gas changes direction at the end 18 of the exhaust casing and then travels along the annular volume 20 lying between the outer portion of the tube 19 and the inside wall of the casing 16. The cross-section of the annular volume is greater than the cross-section of the tube 9. As a result, the speed of the gas is slower in the annular volume 20 than in the tube 9. The hot gas then leaves the exhaust via a hole 17 (see FIG. 2) formed through the casing 16.

In accordance with the invention, a particle trap 22 is provided inside the casing 16. The particle trap is situated in a zone that is not subjected to an electric field. The tube 9 and the casing 16 are electrically connected together and are consequently at the same potential. The electric charge spreads over the periphery of the casing 16 and a Faraday cage effect is produced inside the casing. The electric field thus exists between the outside wall of the casing 16 and the vessel 4, the electric field being about five times stronger in the proximity of the casing 16 than in the proximity of the vessel 4. By way of example, the magnitude of the field is 30 kilovolts per millimeter (kV/mm). Given that the particle trap 22 is situated in a zone that is not subjected to an electric field, there is no need for it to be designed in accordance with the rules that apply to zones that are subjected to a dielectric field. Its shape and the material(s) from which it is made can therefore be selected much more freely, and in particular it is possible to select shapes that enable particles to be trapped more effectively. Thus, a grid with pointed metal laminations could be used as a trap in the present invention even though it would be impossible to put the same trap in a zone that is subjected to an electric field. It should also be observed that the particle trap is situated in the bottom portion of the exhaust. Furthermore, its position is remote from the position of the hole 17 provided through the casing 16. Thus, the trap is situated in a zone that is calm, where the speed of the gas is slow.

FIG. 3 shows an embodiment of a particle trap in accordance with the invention. The trap comprises a support 23 carrying flexible lashes or bristles 24. These bristles or lashes lie down while gas is escaping so that they do not reduce the flow section offered to gas. The bristles 24 also serve to retain particles. They prevent particles being entrained away from the exhaust by puffing due to the gas.

In a variant embodiment, the trap is made of a material that is porous or in the form of a foam. Under all circumstances, the material constituting the trap is selected so as to be capable of withstanding hot gas.

Claims

1. Metal-clad electrical equipment comprising a metal vessel (4) and an exhaust constituted by an arcing contact support tube (9) and a casing (16) surrounding the support tube (9) and co-operating therewith to define an annular volume (20), the support tube having at one end an inlet for passing arc gas, exhaust holes (17) being provided through the casing to allow arc gas to escape into the vessel, the equipment being characterized in that it includes a particle trap (22) situated in the exhaust between the arcing contact support tube (9) and the exhaust casing (16).

2. Electrical equipment according to claim 1, characterized in that the particle trap is situated in a zone without an electric field.

3. Electrical equipment according to claim 1, characterized in that the cross-section of the annular volume (20) in which the particle trap (22) is located is greater than the cross-section of the arcing contact support tube (8).

4. Electrical equipment according to any one of claim 1, characterized in that the trap (22) is situated in the bottom portion of the exhaust.

5. Electrical equipment according to any one of claim 14, characterized in that the particle trap (22) is not situated close to the exhaust hole (17) provided through the casing (16).

6. Electrical equipment according to any one of claim 1, characterized in that the particle trap (22) comprises elements (24) that are floppy or flexible.

7. Electrical equipment according to claim 6, characterized in that the floppy or flexible elements are bristles (24), lashes, or laminations.

8. Electrical equipment according to any one of claim 1, characterized in that the particle trap is made of a material that withstands hot gas.

9. Electrical equipment according to any one of claim 1, characterized in that the trap is made of a material that is porous or in the form of a foam.

10. Electrical equipment according to claim 2, characterized in that the cross-section of the annular volume (20) in which the particle trap (22) is located is greater than the cross-section of the arcing contact support tube (8).