EP2223319B1 - Insulation of a current interrupter of the vacuum bulb type by overmoulding - Google Patents

Description

TECHNICAL AREA

The invention relates to switches and switchgear, in particular vacuum interrupters, operating in particular at high and medium voltage. The invention relates to the insulation of such equipment by coating with a suitable material.

The invention relates to the isolation of a cutting member by injection of an elastomer in order to overmold said member. To overcome a rupture of its envelope, or even possible infiltrations of the elastomer in the chamber of the cutoff device, the junction areas of the envelope are protected by mechanical reinforcements, also dielectric baffles.

STATE OF THE ART

A vacuum interrupter is constituted by a breaking chamber in which a low pressure prevails and in which there is a pair of contacts that can take a closed position allowing the passage of current and an open position in which the two contacts are separated so as to interrupt the current. Usually, a contact is fixed, secured to a bottom of the envelope; the other contact is mobile with a bellows surrounding it and allows to mechanically isolate the interior of the room.

The envelope of the chamber of a vacuum interrupter comprises an insulating casing, sometimes also called bulb, made of ceramic or glass, which constitutes the first generally tubular central part; the tube is closed at its ends by lids, usually metal, also called bowls or caps, to which are connected the contacts.

Vacuum bulbs require a dielectric environment to counter discharges when triggered by opening contacts. A free space around the bulb can be enough; however, especially when the operating voltage is high, an option is the location of the bulb in a sealed chamber comprising a dielectric fluid, empty or SF ₆ . These solutions generate a significant bulk around the bulb, the latter being moreover heavy to implement.

For reasons of compactness, cost and reliability, solid insulators have been developed for coating vacuum bulbs, including an overmoulding epoxy such as for example presented in the document EP 0 866 481 . This type of overmolding is however not optimized, despite the possible interposition of a flexible or elastic layer between the coating and the bulb, due to the different coefficients of thermal expansion of the ceramic cylinder, metal bowls and the epoxy coating, which can lead to cracking or even fractures of the insulation.

Certain thermosetting elastomers certainly combine a very good dielectric strength with suitable mechanical properties. Their use as a vacuum bulb coating has, however, been restricted because of the conditions of their shaping: overmoulding by such a material, which is carried out under high pressure, may damage the coated components, in particular fragile elements such as vacuum interrupters or fuses that include welds. For example, overmolding directly a vacuum bulb with an EPDM elastomer or silicone deforms or destroys parts constituting it. In fact, as described in the document US 5,864,942 , a thermoset elastomer is used, for a device whose vacuum chamber is delimited by several components, as a complement to a first coating, with establishment of a rigid protective layer around the bulb before overmolding.

Finally, the document WO 86/00464 A discloses a device according to the preamble of claim 1.

SUMMARY OF THE INVENTION

Among other advantages, the invention aims at overcoming the drawbacks of the insulation of existing controlled atmosphere cut-off devices, and at allowing the direct use of elastomers on multi-component waterproof envelopes.

In particular, in one aspect, the invention relates to a method according to claim 11 for isolating a switching device whose chamber, isolated with respect to the fluidic exchanges, is delimited by a multi-component envelope, it is that is to say a sealed envelope having areas of weakness, and in particular comprising solder-bonded ceramic and metal parts, in particular on the edge of the wall of a cover comprising a bottom extended by metal side walls coupled on the periphery to the side wall of a ceramic part. The insulation is made by a step of overmolding by injection at high pressure of an elastomer which is vulcanized. Before the introduction of the cutoff device into the injection mold, it is assembled with protective covers that cover the areas of weakness. In particular, for a vacuum-type device in which the central tubular portion is closed by conductive covers, the covers are fitted on the covers and exceed the junction area between insulator and conductor; the shape of the covers is also optimized for a role of mechanical reinforcement.

In a preferred embodiment, the surfaces of the envelope of the cut-off device which will be in contact with the injected elastomer, that is to say the protective covers and / or a large part of the central tube, are prepared. , for example with a bonding agent, to facilitate the adhesion of the elastomer. The elastomer may in particular be EPDM or silicone, and the process is preferably continued by a step of painting or overmolding said elastomer loaded with conductive particles in order to electrostatically shield the cut-off device.

In another aspect, the invention relates to a cut-off device according to claim 1 made by this method.

More generally, a breaking device according to the invention, which is preferably axisymmetric, comprises a sealed chamber extending along a longitudinal axis. The chamber is delimited by an envelope which comprises an insulating tubular part, preferably ceramic, open at its ends, which is associated with conductive covers, advantageously metallic monobloc, closing the tubular part; in particular, the connection between the various components of the envelope defines a junction zone, which is advantageously a solder between the thickness of the tubular portion and thickness of the wall of the lids which are in the form of cylinders closed by a bottom at one end.

The sealed chamber comprises two movable contacts relatively to each other along its axis; preferably, one of the two contacts is fixed and the other mobile, each of them being coupled to one of the two covers. In a preferred embodiment, low pressure prevails in the chamber, and the cutoff device is a vacuum interrupter.

The cut-off device according to the invention further comprises two covers covering each of the covers and protecting their junction zone with the tubular part; in particular, the covers are in the form of bowls, with a bottom wall substantially normal to the axis of the cut-off device, and a peripheral wall extending along this axis a distance sufficient to cover the wall side of the cover and also an end portion of the insulating tube. The thickness of the lid is determined by its role of mechanical reinforcement, with removal of brittle points type protruding angles. Means, for example a direct contact, are provided to avoid the creation of a potential difference between them. A conductive spacer may spread the bottom of the lid of the bottom of the lid in the longitudinal direction so as to facilitate the connection of the assembly means of the cut-off device.

The covers are rigid enough to serve as mechanical reinforcements, and advantageously they are designed to serve as dielectric baffles; in particular, they do not have sharp corners on their outer surface, and may have bulges at the junction points between insulator and conductor. It is furthermore preferred that a seal be present between the insulating tubular part and the cover, so as to protect the junction zone between the cover and the tubular part by locating it in a clean space; the seal may be of elastomer, and is advantageously put in place in a suitable groove of the cover. Thus, in addition to the mechanical protection against an upper external pressure, the solder is protected against fluid infiltration.

The cut-off device according to the invention finally comprises an elastomeric coating, preferably made of EPDM, around the envelope of the chamber and protective covers with which it is in direct contact: the interface is "adhered", that is to say that it is waterproof, devoid of empty spaces. The elastomer is advantageously coated with a conductive electrostatic shielding layer, for example the same charged elastomer; this elastomer can be used for the joint.

BRIEF DESCRIPTION OF THE FIGURES

• La figure 1 représente une ampoule à vide selon un mode de réalisation préféré de l'invention.
• La figure 2 illustre la protection mécanique avant surmoulage selon un mode de réalisation préféré de l'invention.

Other advantages and features will emerge more clearly from the following description of particular embodiments of the invention, given by way of illustration and in no way limiting, represented in the appended figures.

• The figure 1 represents a vacuum interrupter according to a preferred embodiment of the invention.
• The figure 2 illustrates the mechanical protection before overmolding according to a preferred embodiment of the invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

A vacuum interrupter 1 according to the invention, illustrated in figure 1 , is intended for use in a switch for making the cut in an electric circuit. The bulb 1 according to the invention is preferably arranged to operate at high or medium voltage, that is to say between 1 and 75 kV or 52 kV, although low voltage use is possible. The ampoule 1 comprises a sealed chamber or cartridge 2 in which there is preferably a controlled low pressure of air or other dielectric fluid, that is to say a "vacuum"; the chamber 2 is defined by a longitudinal envelope extending along an axis AA, and which is advantageously axisymmetric (symmetrical of revolution) for reasons of manufacture and assembly.

The envelope of the chamber 2 comprises a first main part, central, insulating 4, preferably ceramic although glass may be an option. The insulating part 4 is tubular, preferably cylindrical of revolution to optimize its resistances mechanical and dielectric, as well as to facilitate its manufacture; in the preferred embodiment, each open end of the tube 4 is delimited by an orthogonal section of its wall, thus forming two superimposable rings. The orifices of the tube 4 are partially closed by conductive covers 6 ₁ , 6 ₂ ; in the illustrated frame, the covers, or caps, 6 are metallic and each comprise a substantially plane bottom normal to the axis AA, extended on its periphery by an orthogonal side wall 7 of the same shape as the tube 4 at its ends; the side wall 7 ₁ , 7 ₂ is longer or shorter depending on the use, but anyway extends the bottom to optimize the construction of the bulb 1. To optimize their mechanical strength, the covers 6 are advantageously formed in one piece and substantially constant thickness between the peripheral walls 7 and bottom.

The conductive covers 6 are tightly secured to the insulating tube 4 according to a junction zone 8. Although any known technique can be used, according to the preferred embodiment, the junction zone 8 is limited to a line corresponding to a brazing of the peripheral wall 7 of the covers 6 on the insulating tubular wall 4. Advantageously, the thickness of the tube 4, homogeneous (for example of the order of 6 mm for a bulb 1 of internal diameter 65 mm operating at 17.5kV ) is greater than the thickness of the cover 6 (for example of the order of 1.5 to 2 mm), and the two ends are placed edge to edge, with vacuum brazing of the cap 6 substantially in the center of the wall of the tube 4.

The chamber 2 delimited by the ceramic tube 4 and the covers 6 comprises a pair of arcing contacts 10 ₁ , 10 ₂ movable relative to each other along the axis AA of the bulb 1. Each contact 10 comprises a contact pad 12 of suitable material, such as CuCr, fixed on a longitudinal electrode 14 made of copper. Preferably and as illustrated, a first contact 10 ₁ is fixed, integral with one of the end caps 6 _{1 to} which its electrode 14 is coupled to close it, for example by welding or mechanical assembly; the second contact 10 ₂ is mounted to slide axially inside the cartridge 2, with its electrode 14 being able to move through the other bowl 6 ₂ . To allow the movement of the movable contact 10 ₂ and keep the controlled atmosphere, a sealing bellows 16 is interposed between the mobile electrode 14, to which it can by for example be welded at one end, and the corresponding cover 6 ₂ , thus isolating the opening of the cover 6 ₂ of the chamber 2. A dielectric screen 18 can be placed around the bellows seal 16, at its end coupled to the electrode 14 to protect it against projections caused by a cut.

The sealed chamber 2 further preferably comprises a dielectric screen 20 positioned at the contact pads 12 regardless of their position in order to protect the ceramic 4 possible projections. Advantageously, the internal dielectric screen 20 is fixedly attached to one of the covers 6 _{1 in} order to simplify the manufacturing process and limit the number of solderings on the ceramic tube 4.

The ampoule 1 according to the invention is preferably used in tight spaces, which can also be aggressive: so that the cut-off device is insensitive to the environment (pollution, dust, other dirt) and reduce the dimensions, solid insulation 22 is used to concentrate the dielectric stresses inside the insulator 22; a shield 24 may be associated with it to confine them by removing any electric field from the ambient air. Furthermore, the ampoule 1 according to the invention is preferably suitable for storage conditions of up to -40 ° C and to tolerate large temperature differences in operation, in particular an ambient temperature of -25 ° C to 55 ° C. C, to which are added the local heating due to the operation (of the order of 45 ° C): an amplitude of -40 ° C to + 100 ° C for the vacuum bottle 1 preferably expands the metallic elements 6, 10, 16, 18, 20 of the cartridge 2.

According to the invention, the dielectric insulating coating 22 of the vacuum ampoule 1 is chosen from elastomers that are sufficiently flexible to compensate for the different expansions of the components of the envelope of the ampoule 1 to which it is joined, for example of Shore hardness. A between 40 and 80. Silicones, especially injectable silicone, rubbers or other thermoset elastomers can be envisaged; in the preferred embodiment of the invention, the dielectric coating is made of an ethylene-propylene-diene terpolymer or EPDM (for: "Ethylene-Propylene Diene Monomer rubber") sufficiently flexible but which has sufficient mechanical strength to a protection The advantage of this material, besides its cost, lies in its known dielectric qualities of other electrical applications.

Conventionally, for an elastomer such as EPDM whose properties are adapted to the application according to the invention, the material is injected at a temperature of the order of 60 to 80 ° C., that is to say in a viscous state or liquid, in a heated mold between 140 and 170 ° C under a pressure of 100 to 150 bar. It is important to protect in particular the junction zone between the components 4, 6 of the envelope, in particular to eliminate any failure of the solder 8: according to the invention, a suitable means is put in place, with a reinforcement The presence of such an additional element whose main role is mechanical can also be used to reduce the electric fields, and the mechanical reinforcement 26 used according to the invention. is advantageously shaped to serve as a dielectric baffle.

A preferred embodiment of a reinforcing cover 26 comprises a bottom extended at its periphery by a side wall, defining a recess in which the cover 6 of the bulb 1 can be put in place; the peripheral wall extends along the axis AA of sufficient length to cover the junction zone 8. To avoid the peak effects and the areas of mechanical weakness, if the internal recess may comprise sharp angles, the outer surface of the hood 26 is smooth, with blunted, rounded corners; the cover 26 is advantageously axisymmetric, and its external shape is determined according to the mechanical and dielectric stresses. In particular, the end portion of the peripheral wall, being set up at the level of the ceramic wall 4 and / or the conductive solder 8, that is to say in an area where the field constraints are the higher, comprises an annular bulge 28. For example, of general thickness of the order of 4 mm, or at least sufficient for the mechanical stresses it undergoes, the dielectric cover 26 may comprise a swollen end portion 28 up to 8 mm thick, the length of which is about 16 mm along the axis AA is substantially distributed on each side of the solder 8.

The cover 26 may be made of a thermoplastic or thermosetting conductive material; advantageously, the cover 26 is made of a single piece of metal whose mechanical strength is proven, for example steel. Its general shape is preferably standardized, with, as illustrated in figure 1 , an adaptation of the size of the cylindrical part of its wall to that of the lid 6; Furthermore the bottom of the reinforcement 26 comprises an orifice 30 allowing the passage of the electrode 14 and means 32 to which the contact 10, and more generally the bulb 1, are coupled.

In an embodiment illustrated in figure 2 , a spacer 34 takes up the mechanical forces between the cover 6 and the bottom of the cover 26. The spacer 34 can be conductive and provide the same potential between the cover 6 and cover 26; it allows the assembly with the coupling means 32 of the bulb 1. Other geometric possibilities for the covers 26 may be derived from the constraints by the skilled person; whatever the solution, contact is made between the parts 6, 26 under tension to prevent the remaining space is crossed field lines.

Prior to overmolding, the vacuum bottle 1 is thus protected at its ends by placing covers 26 on its end covers 6 and through which the connection means 32 pass. The dielectric covers 26 cover by their peripheral wall, at the the level of a bulge 28, the junction zones 8 and a portion of the ceramic tube 4. Advantageously, the internal arrangement of the wall of the cover 26 allows adequate positioning at the junction braking 8, with sufficient space to do not solicit this weak point during the installation of the cover 26.

In view of the injection pressure, in order to eliminate the infiltration of elastomer likely to stress the solder 8 and thus avoid the deformation of the cut-off device 1, it is preferred to position sealing means between the cover 26 and the ceramic tube 4. Any means can be envisaged, but, for example, the inner surface of the peripheral wall of the cover 26 is provided with an annular groove 36 in which a seal 38 is put in place. The seal 38 is of insulating or conductive material; it may be of any shape, for example toric, but advantageously, its geometry is complementary to that of the groove 36 of the deflector 26 to distribute the forces on the ceramic 4 during the injection of the insulating material; the seal 38 may also make it possible to center the mechanical cap 26 on the cut-off member 1.

The seal 38 is made of elastomer whose compatibility with the insulator 22 overmoulding is good, preferably of the same nature as the insulating coating 22 (here of the EPDM), in order to maintain the same mechanical properties, and its hardness is compatible with the ceramic rib tolerances 4. Depending on the relative shape of the groove 36 and the seal 38, the latter may be inserted or adhered to the peripheral wall of the bulge 28.

Once the ampoule 1 is assembled with the covers 26 and the seal 38, it is placed in a mold of suitable size and shape, preferably with centering means. The EPDM is injected into the residual space, whose overmolding thickness is determined by the lightning strike, and vulcanized; the ampoule 1 is then demolded.

Preferably, the external interface surface between the envelope of the chamber 2 and the coating 22, in particular that of the ceramic tube 4 and the dielectric cover 26, is prepared in order to optimize the attachment of the elastomer 22 and to guarantee a waterproof direct adherence, with no residual spaces likely to contain air; in particular, a bonding agent can be used to optimize the interface and counteract partial discharges.

Preferably, the dielectric overmolding 22 itself is covered with a conductive or semi-conductive layer 24 called shielding, in particular a conductive EPDM overmoulding, which may be grounded. Thus, the field lines are held inside the coating 22, which allows the positioning of other electrical equipment in the vicinity of the bulb 1 according to the invention and the insensitivity of the latter to the environment.

It should be noted that the role of mechanical protection of the cover 26 is essential with a large pressure difference between the injection of the elastomer 22 and the interior of the chamber 2; however, even when this difference decreases, or even vanishes, the dielectric action of the cover 26 is maintained, and it may be recommended to keep the covers 26 also for overmolding at ambient pressure, for example epoxy. In the latter case, to overcome the problems of differential thermal expansion, the dielectric cover 26 advantageously retains its mechanical role by being made of material flexible, for example EPDM loaded to absorb the different deformations between coating 22, cover 6 (and ceramic 4); possibly, orifices or games-type arrangements may be made to serve as compression spaces.

Although the invention has been described with reference to a vacuum interrupter, it is not limited thereto: other elements may be concerned by the invention, which is delimited by the scope of the claims. In particular, an overmoulding as performed according to the invention may also be implemented on any device in which the chamber under controlled atmosphere has a "fragile" junction between two materials. In particular, the invention finds an application for fuse-type switchgear with a sealed envelope.

Claims (13)

1. Current interrupter device (1) comprising a sealed chamber (2) extending along a longitudinal axis (AA) in which are housed two contacts (10) that are mobile relative to one another along the axis (AA), the enclosure of the chamber (2) comprising a tubular part (4) open at its ends, and two conductive covers (6) secured to the tubular part (4) by a junction zone (8), said current interrupter (1) further comprising an elastomer insulating coating (22) of said enclosure of the chamber (2), characterized:

   - in that each of the covers (6) comprises a bottom extended on its periphery by a lateral wall;

   - in that two conductive caps (26) surround the covers (6), each of the caps (26) comprising a bottom wall and a peripheral lateral wall extending along the axis (AA) such that the junction zone (8) and an end of the tubular part (4) are located in the cap (26); and

   - in that the interface between coating (22) and tubular part (24), respectively caps (26), is sealed.
2. Device according to Claim 1, in which the outer surface of the caps (26) has no sharp corners.
3. Device according to one of Claims 1 and 2, in which the outer surface of the caps (26) is designed for dielectric deflection.
4. Device according to one of Claims 1 to 3, in which the tubular part (4) is insulating and made of ceramic, the cover (6) is made of metal and brazed onto the end of the tubular part (4), the junction zone (8) defining a line on the wall of the tubular part (4).
5. Device according to one of Claims 1 to 4, further comprising at least one seal (38) between the tubular part (4) and the peripheral wall of a cap (26), such that the junction zone (8) is separated in a sealed manner from the coating (22).
6. Device according to Claim 5, in which the seal (38) is manufactured in an elastomer of the same nature as the coating (22).
7. Device according to one of Claims 1 to 6, further comprising a conductive covering (24) around the insulating coating (22) to serve as electrostatic shielding.
8. Device according to one of Claims 1 to 7, in which the insulating coating (22) is produced in EPDM or in silicone.
9. Device according to one of Claims 1 to 8, in which the longitudinal axis (AA) of the device (1) is an axis of symmetry.
10. Vacuum interrupter comprising a device (1) according to one of the preceding claims, in which the chamber (2) is at a pressure less than atmospheric pressure, one of the contacts (10₁) is fixed and secured to one of the covers (6₁) and the other contact (10₂) is mobile through the other cover (6₂) and its cap (26).
11. Method for insulating a current interrupter device according to Claim 1 at controlled atmosphere (1) comprising a sealed chamber (2) delimited by an enclosure of which the central tubular part (4) is closed by two conductive end covers (6) at a junction zone (8), each end cover (6) each comprising a bottom extended on its periphery by a lateral wall (7) comprising the junction zone (8), said method comprising:

    - the protection of the covers (6) by caps (26) which are extended to also overlap the junction zones (8);

    - the positioning of the current interrupter device (1) secured to the caps (26) in a mould;

    - the injection of an elastomer into the mould and the vulcanisation thereof.
12. Method according to Claim 11, further comprising a step of preparing the outer surfaces of the tubular part (4) and/or of the caps (26) in order to facilitate the adherence of the elastomer (22).
13. Method according to one of Claims 11 and 12, further comprising a step of covering the vulcanised elastomer (22) with a conductive layer (24).

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