EP2905796A1 - Deflecting cover for overmoulded vacuum interrupter - Google Patents

Abstract

In order to improve the quality of the epoxy overmoulding of a vacuum bulb (1), the thin walls of the covers (6 1, 6 2) of the ceramic tube (4), comprising a side wall (7 1, 7 2) extending along the axis (AA) of the bulb (1) and a bottom wall, are associated with covers (26 1, 26 2) which surround them. The thermal inertia of the metal closure means of the ceramic tube (4) is thus increased.

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, and relates to the establishment of a cover around the lids of the bulb to optimize the reliability of overmolding by an insulating material .

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 a 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 . 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 .

To avoid partial discharges, the triple points can be reinforced by conductive material ( WO 2007/116661 , GB 2,160,710 ), sometimes associated with deflectors ( EP 1 680 792 ). In addition, in order to overcome insulator cracking that may occur due to differences in the thermal expansion coefficient of the ceramic cylinder, metal bowls and epoxy coating, various solutions of interposition of flexible or elastic layers between the coating and the bulb, on all or part of the interface, have been proposed: see for example JP 2004306528 , WO 2013/113499 .

However, it appears that cracks and / or a lack of compactness of the fern-type resin and / or detachment at the interface with the lid can, despite the previous solutions, appear within the epoxy overmoulding and generate partial discharges.

SUMMARY OF THE INVENTION

Among other advantages, the invention aims to overcome the disadvantages of existing bulbs and minimize the risk of occurrence of cracks and lack of compactness within the epoxy coating at the metal caps of a ceramic bulb.

In particular, the invention relates to a cut-off device, in particular a vacuum interrupter, comprising a sealed chamber extending along a longitudinal axis, preferably an axis of symmetry. The sealed chamber houses two movable contacts relatively to each other along the axis, and integral electrodes that extend out of the chamber. The interrupting chamber is coated with an insulating coating made of thermosetting resin, preferably an epoxy or epoxy resin, advantageously itself coated with a conductive coating serving as electrostatic shielding.

The interrupting chamber comprises a tubular portion, preferably ceramic, open at its ends, and closed by closure means which are secured thereto. At at least one end, the closure means comprise a conductive cover, in particular a metal cover, with a bottom that is substantially flat and orthogonal to the longitudinal axis in which a contact electrode can pass, and a side wall that is coupled to the tubular part, advantageously by brazing, at a junction zone, which can define a line on the tubular wall. The closing means at each end may be similar, the length of the side walls of the lids may in turn differ; alternatively one of the ends may be closed by other means.

Each closure lid of the tubular portion is itself housed without play in a conductive cover, preferably in wire mesh, comprising a bottom wall against which is backed its bottom and a peripheral side wall extending on the length of the side wall of the lid. The peripheral side wall may be extended by an end portion which then houses the junction zone and an end of the tubular portion; the end portion may be thicker than the rest of the cap, and may be spaced apart from the tubular portion by a gap, in which a seal may be provided. The outer surface of the cover is preferably devoid of sharp angles.

The invention also relates to a vacuum interrupter comprising the preceding cutoff device, wherein the chamber is under a pressure lower than atmospheric pressure, one of the contacts being fixed and secured to the lid.

BRIEF DESCRIPTION OF THE FIGURES

• La figure 1 représente une ampoule à vide selon un mode de réalisation de l'invention.
• Les figures 2A et 2B illustrent plus particulièrement le couvercle et le capot dans 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 one embodiment of the invention.
• The Figures 2A and 2B illustrate more particularly the cover and the cover in 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, 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 mechanical and dielectric strengths, 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 side 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 66 mm internal diameter operating at 17.5 kV) is greater than the thickness of the lid 6 (For example of the order of 1 to 2.5 mm), and the two ends are placed edge to edge, with vacuum brazing of the cap 6 on 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 ₁ , 10 ₂ 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 enable movement of the movable contact 10 ₂ and to maintain the controlled atmosphere, a sealing bellows 16 is interposed between the movable electrode 14, to which it can 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 may be placed around the sealing bellows 16, at its end coupled to the electrode 14 to protect it against projections caused by a cut.

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.

Solid insulation is conventionally produced by overmolding a thermosetting resin 22, in particular epoxy resin, commonly known as epoxy, optionally in composite form with fiberglass fabric. By its very nature, the introduction of the solid insulation 22 involves the positioning of the casing 2 of the chamber within a heated mold in order to inject the resin. Despite all the precautions, it can happen that fissures, detachments or faults of the fern type, appear at the level of lids 6 of the vacuum chamber 2, which causes the appearance of partial discharges during the commissioning of a circuit breaker 1 containing it.

In order to allow overmolding without ferns, according to the invention, covers 26 ₁ , 26 ₂ are associated with lids 6 ₁ , 6 ₂ , and follow the shapes.

In particular, as illustrated also in figures 2 , a cover 26 comprises a bottom 28 which is set up perpendicular to the longitudinal axis AA against the cover 6, said bottom 28 being extended at its periphery by a peripheral side wall 30, defining a recess in which the cover 6 of the bulb 1 can be put in place. The bottom 28 of the cover 26 comprises an orifice 32 allowing the passage of the electrode 14. The peripheral wall 30 of the deflector 26 extends along the axis AA along the entire length of the wall 7 of the cover 6 to reach the zone junction 8.

The cover 26 made of metal is in close contact with the cover 6: the presence of the cover 26 thus increases the mass of a cap assembly 6, 26, which increases its thermal inertia. With this system, the cover assembly 26 + cover 6 can have a cooling coefficient substantially equal to that of the electrode rod 14, formed of solid copper, and the ceramic 4. Thanks to the homogeneity of the coefficient of cooling thus obtained, during the establishment of the chamber 2 in the overmolding mold, and during overmoulding by the epoxy 22, the envelope of the chamber 2 behaves uniformly, resulting in fewer constraints within epoxy 22, and significantly reducing the lack of compactness, the detachment at the interface and the presence of cracks.

In fact, in the prior art, despite preheating of the ampoule in an oven prior to placement in a hot mold for epoxy injection, during the displacement of the envelope of the chamber 2 of the oven towards the mold, as the cover 6 has a large surface and a relatively low copper thickness, it cools very quickly: the temperature is therefore lower in this so-called "cold" zone, with a large difference between the temperatures of the epoxy resin and the cold zone. In addition, this difference is much greater than the difference between the temperature of the epoxy resin 22 and that of the electrode 14 (made of thick monobloc copper, which cools slowly) or that of the ceramic (refractory by nature). The cold zone can cause during the overmolding defects such as cracking, ferns or detachments. The thickness of the new metal screen 26 adds to the copper thickness in the cold zone and thus improves the thermal management of the closure means 6 of the chamber 2.

Advantageously, the cover 26 is made of copper, preferably perforated in order to allow the penetration of epoxy, and in particular copper-plated wire mesh, for example brass, which prevents the sandwich structure when the lid 6 is placed in the hood 26, very harmful to the resistance to partial discharges in the presence of a high electric field. Although a contact is necessary between the cover 26 and the cover 6 to ensure thermal continuity, the use of mesh also limits the problems of adjustment: the cover 26 thus preferably forms a cup shape complementary to that lid 6 which can be inserted with a few points of contact, obtained for example by compression during insertion. In particular, it is possible to possibly provide a slight spacing, for example less than 0.5 mm, between cover 26 and cover 6.

Preferably, the cover 26 also covers the junction zone 8, and the side wall 30 is extended by an end portion 34 so that the length of the cover 26 exceeds that of the cover 6. The end portion 34 may be of internal diameter greater than the side wall 30 in which the lid 6 is housed to take into account the offset formed by the thickness of the ceramic tube 4, thus forming a flange. Moreover, as the end flange 34 is put in place 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 highest, it may be of greater thickness than that of the part of the cover 26 in which the cover 6 rests. For example, with a general thickness of the order of 0.5 mm, the dielectric cover 26 may comprise a swollen portion of end 34 up to 2 mm thick, over a length of about 18 mm beyond the solder 8.

In fact, the flange 34 has a function different from the rest of the side wall 30, and the bottom wall 28, of the cover 26, which are associated with copper parts 6 of thickness conventionally less than 4 mm to increase thermal inertia: it is here more especially to serve as a deflector. The flange 34 may thus be further away from the envelope 2, with a gap between the ceramic 4 and the copper 34. According to the illustrated embodiment, it is possible to deliberately remove the flange 34 of the cover 26 of the ceramic tube. 4, so that the epoxy can be inserted between the grill of the hood 34 and the ceramic 4; it can then be advantageous to set up a seal 36 at the solder 8, in particular to cover the salient points at the terminals of the triple points of the vacuum bottle 1.

To avoid peak effects and areas of mechanical weakness, if the internal recess may include sharp corners, the outer surface of the baffle 26 is smooth, with blunt, rounded corners; the cover 26 is advantageously axisymmetric, and its external shape is determined according to the mechanical and dielectric stresses.

• les champs électriques au point triple de l'ampoule à vide sont gérés de façon similaire à celle des déflecteurs standards qui correspondent au rebord 34 du capot 26 ;
• le problème de fougère, initié par un écart thermique entre le couvercle 6, de faible épaisseur de cuivre, et la résine epoxy 22 est résolu ;
• la tenue au cycle thermique et donc la tenue dans le temps du pôle surmoulé 1 est améliorée ;
• l'adhérence de l'époxy au niveau de l'ensemble capot 26/couvercle 6 est optimisée ;
• le capot 26 et le couvercle 6 créent une cage de Faraday, étant donné que le rebord 34 et la paroi latérale 30 sont au même potentiel diélectrique que le couvercle 6, ce qui augmente encore la fiabilité en cas de présence résiduelle de défaut dans l'époxy, la cage de Faraday confinant les décharges partielles entre capot 26 et couvercle 6.

Thanks to this solution for installing hoods 26 screen baffles, the following results are obtained:

• the electric fields at the triple point of the vacuum interrupter are managed in a manner similar to that of the standard deflectors which correspond to the rim 34 of the cover 26;
• the fern problem, initiated by a thermal gap between the lid 6, of small thickness of copper, and the epoxy resin 22 is solved;
• the resistance to the thermal cycle and therefore the behavior in time of the overmolded pole 1 is improved;
• the adhesion of the epoxy at the cover 26 / cover 6 assembly is optimized;
• the cover 26 and the cover 6 create a Faraday cage, since the rim 34 and the side wall 30 are at the same dielectric potential as the cover 6, which further increases the reliability in the event of a residual presence of defect in the epoxy, the Faraday cage confining the partial discharges between cover 26 and cover 6.

Thus in addition, in a preferred embodiment according to the invention, it is possible not to sand the generatrix of the vacuum bulb covers in the zone protected by the Faraday cage formed between cover 26 and cover 6, which allows sandblasting of the insulating part 4 before placing the internal elements. For example, a mask can be used, but in fact, this possibility reduces the roughness constraints on sandblasting, including checks at this location, including when sanding is performed for the entire envelope of the chamber to empty 2.

• sablage de l'ampoule à vide 1 munie de ses deux couvercles 6₁, 6₂ ;
• assemblage de deux capots 26₁, 26₂ dont la forme épouse la forme des couvercles 6₁, 6₂, en grillage métallique sur la chambre 2, avantageusment avec logement de joints 36 en matière synthétique à l'intérieur des extrémités déflectrices 34 pour couvrir les points saillants aux bornes des points triples de l'ampoule à vide 1 et éviter toute amorce à la rupture ;
• nettoyage dans un bain à ultrasons pour éliminer toute trace de salissure, séchage ;
• préchauffage de l'assemblage à une température supérieure à la température du moule pendant une durée suffisante pour que l'assemblage ait une température proche de celle du moule afin d'optimiser la qualité du surmoulage - par exemple, l'assemblage est préchauffé à 170°C pendant plus d'une heure pour un moule chauffé à 150°C ;
• surmoulage de l'enveloppe 2 d'ampoule à vide 1 par la résine epoxy 22, par exemple par gélification automatique sous pression APG (« Automatic Pressure Gelation ») maîtrisant le retrait de la résine et améliorant la compacité de l'époxy ;
• sablage du pôle et métallisation 24.

The realization of the bulb can thus include the following steps:

• sandblasting of the vacuum bottle 1 provided with its two covers 6 ₁ , 6 ₂ ;
• assembly of two covers 26 ₁ , 26 ₂ whose shape matches the shape of the covers 6 ₁ , 6 ₂ , metal mesh on the chamber 2, preferably with housing of joints 36 of synthetic material inside the deflector ends 34 to cover the salient points at the terminals of the triple points of the vacuum interrupter 1 and avoid any primer at break;
• cleaning in an ultrasonic bath to remove all traces of soiling, drying;
• preheating the assembly to a temperature above the mold temperature for a time sufficient for the assembly to have a temperature close to that of the mold to optimize the quality of overmolding - for example, the assembly is preheated to 170 ° C for more than one hour for a mold heated to 150 ° C;
• over-molding of the vacuum bag envelope 2 with the epoxy resin 22, for example by automatic pressure gelation APG (" Automatic Pressure Gelation ") controlling the removal of the resin and improving the compactness of the epoxy;
• sandblasting of the pole and metallization 24.

It is thus possible to manufacture a compact panel with a vacuum circuit breaker whose poles are derived from a shielded solid insulation technology. Despite the very high dielectric stresses given the application of the voltage to a small thickness of solid insulation (generally less than 20 mm for a shielded pole of 17.5 kV), the partial discharge resistance is ensured, and at least in accordance with the relevant requirements.

Although the invention has been described with reference to a vacuum interrupter in which the two metal covers 6 ₁ , 6 ₂ extend longitudinally to extend the space tubular ceramic, it is not limited to other elements may be concerned by the invention. In particular, the ceramic tube 4 could be closed only by a cover 6 having a side wall 7, the other end of the tube 4 being closed by suitable means, in which case the presence of a cover 26 at this end can to be superfluous. Of course, the invention can be applied to a longitudinal enclosure containing no relatively movable contacts and serving for example fuse.

Claims (10)

Cutoff device (1) comprising a sealed chamber (2) extending along a longitudinal axis (AA) in which are housed two contacts (10) movable relative to one another along the axis (AA), said contacts (10) being integral with electrodes (14) extending along the axis (AA) out of the sealed chamber (2), wherein: - The casing of the chamber (2) comprises a tubular portion (4) open at its ends, a first conductive cover (6 ₁ ) secured to a first end of the tubular portion (4) by a first junction zone (8). ), and means for closing the second end of the tubular portion (4); - The first cover (6 ₁ ) comprises a bottom substantially orthogonal to the longitudinal axis (AA) within which passes a first contact electrode (14), extended on its periphery by a side wall (7 ₁ ) to the junction area (8); - The first cover (6 ₁ ) is housed without play within a first conductive cover (26) comprising a bottom wall (28) against which is backed the bottom of said first cover (6 ₁ ), and a peripheral side wall. (30) extending parallel to the side wall (7 ₁ ) of said first cover (6 ₁ ) and on the same length; the chamber (2) is coated with an insulating coating made of thermosetting resin (22). Cutoff device according to claim 1 wherein the first cover (26) comprises an end portion (34) extending the side wall (30) and in which are located the junction zone (8) and an end of the tubular portion (4). Cutoff device according to claim 2 wherein the thickness of the end portion (34) is greater than the thickness of the side wall (30) and the bottom wall (28) of the first cover (26). Cutoff device according to claim 3 comprising a seal (36) between the end portion (34) of the first cover (26) and the junction area (8). Device according to one of claims 1 to 4 wherein the outer surface of the first cover (26) is devoid of sharp angles. Device according to one of claims 1 to 5 wherein the first cover (26) is formed by a metal mesh, including copper. Device according to one of claims 1 to 6 wherein the tubular portion (4) is insulating ceramic, the first cover (6 ₁ ) is metal and brazed to the end of the tubular portion (4), the zone of junction (8) defining a line on the wall of the tubular portion (4). Device according to one of claims 1 to 7 wherein the closure means of the second end of the tubular portion (4) comprises a second cover (6 ₂ ) comprising a bottom substantially orthogonal to the longitudinal axis (AA) within which passes the second electrode (14) of contact, extended on its periphery by a side wall (7 ₂ ) to the junction area (8), said second cover (6 ₂ ) being housed without play within a second conductive cover (26) similar to the first cover and comprising in particular a bottom wall (28) against which the bottom of said second cover (6 ₂ ) is leaned against, and a peripheral side wall (30) extending parallel to the side wall (7 ₂ ) of said second cover (6 ₂ ) and on the same length. Device according to one of claims 1 to 8 further comprising a conductive coating (24) around the insulating coating (22) to serve as electrostatic shielding, the insulating coating (22) being preferably made of epoxy resin. Vacuum bulb comprising a device (1) according to one of the preceding claims wherein the chamber (2) is under a pressure lower than the pressure atmospheric, one of the contacts (10 ₁ ) is fixed and secured to the first cover (6 ₁ ) and the other contact (10 ₂ ) is movable.

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