Vacuum bulb, circuit-breaker pole including such a vacuum bulb, and method to manufacture such devices
A vacuum bulb is provided, including a sealed chamber; two electrical contacts, which move relative to one another, the chamber including a cylindrical body of a dielectric material and closed at ends thereof by two metal covers, each of the two metal covers being connected to one of the two electrical contacts: and a dielectric coating, which covers an outer surface of the chamber, and includes at least two layers, including an overmolding layer of a synthetic material and an intermediate layer of silicone, the intermediate layer being interposed between the outer surface and the overmolding layer, the intermediate layer being discontinuous and localized on metal portions of the chamber so as to cover at least partially an outer surface of the metal portions, and the silicone includes compressible hollow bodies having a skin of a thermoplastic material.
1. A vacuum bulb, comprising:
a sealed chamber;
two electrical contacts, which move relative to one another,
wherein the sealed chamber includes a cylindrical body made of a dielectric material and closed at ends thereof by two metal covers,
wherein each of the two metal covers is connected to one of the two electrical contacts; and
a dielectric coating, which covers an outer surface of the sealed chamber,
wherein the dielectric coating includes at least two layers, including an overmoulding layer made of a synthetic material and an intermediate layer made of silicone,
wherein the intermediate layer is interposed between the outer surface of the sealed chamber and the overmoulding layer,
wherein the intermediate layer is discontinuous and localised in direct contact with at least a portion of each of the two metal covers, so as to cover at least partially an outer surface of the two metal covers, and
wherein the silicone of the intermediate layer includes hollow bodies that are compressible and have a skin made of a thermoplastic material.
2. The vacuum bulb according to claim 1 , wherein the hollow bodies are microspheres having an average diameter of between 1 μm and 800 μm.
3. The vacuum bulb according to claim 1 , wherein an interface between the dielectric coating and the outer surface of the sealed chamber is sealed.
4. The vacuum bulb according to claim 1 , further comprising at least one protective metal screen positioned inside the sealed chamber and attached to the sealed chamber.
5. The vacuum bulb according to claim 4 , wherein the cylindrical body includes at least one first portion and one second portion, the protective metal screen is attached to the sealed chamber by an attachment means interposed between the at least one first portion and one second portion, and the intermediate layer is also localised on the attachment means so as to cover at least an entire outer surface of the attachment means.
6. The vacuum bulb according to claim 1 , wherein the cylindrical body is made of a ceramic material.
7. The vacuum bulb according to claim 6 , wherein the ceramic material is alumina.
8. The vacuum bulb according to claim 7 , wherein the ceramic material is enameled.
9. The vacuum bulb according to claim 1 , wherein the overmoulding layer is made of a thermosetting polymer.
10. The vacuum bulb according to claim 1 , further comprising a shielding layer positioned on the dielectric coating.
11. A medium-voltage switchgear including at least one vacuum bulb according to claim 1 .
12. A circuit-breaker pole including an assembly formed of a vacuum bulb according to claim 1 and of two electrically conductive connections, wherein the assembly is coated by the overmoulding layer.
13. The circuit-breaker pole according to claim 12 , wherein the overmoulding layer is coated by a shielding layer positioned on the dielectric coating.
14. The vacuum bulb according to claim 1 , wherein the hollow bodies are microspheres having an average diameter of between 10 μm and 80 μm.
15. The vacuum bulb according to claim 1 , wherein the overmoulding layer is made of an epoxide polymer.
16. The vacuum bulb according to claim 1 , wherein the two metal covers are provided with elements protruding from the two metal covers and the intermediate layer is localised in direct contact with at least a portion of each of the two metal covers so as to cover at least entirely an outer surface of the elements.
17. The vacuum bulb according to claim 1 , wherein the intermediate layer is localised in direct contact with at least a portion of each of the two metal covers so as to cover at least entirely the outer surface of the two metal covers.
18. The vacuum bulb according to claim 1 , wherein the intermediate layer is also localised in direct contact with portions of the cylindrical body, at least in an area of an edge of each of the two metal covers that is joined to the dielectric material of the cylindrical body.