EP0859382B1 - Gas insulated transformer - Google Patents

Abstract

The transformer (15) has a magnetic core and primary and secondary coils contained within or are in contact with its casing (11). Within the casing, there is moulded resin (14) and pumped dielectric gas in the spaces between the coils. A disc (10) is held directly between the casing and its cover (12) which fixes on cover and forms a channel between the disc and the exterior of the casing. The cover is screwed onto the casing and a ring seal (13) is placed between the disc and the cover. The cover has a series of openings (19) to allow the gas to escape should the disc break. The casing may cover the whole of the core and the primary and secondary coils. Alternatively, it may be a single piece covering the part of the transformer necessary to form the channel between the core and coils and the disc.

Description

The present invention relates to a gas-insulated transformer comprising a magnetic core associated with primary and secondary windings, the magnetic core and the primary and secondary windings being contained in a housing mounted around part or all of the transformer core and molded inside a resin case.

These transformers are conventional elements in high or medium voltage lines of an electricity distribution network and use an inert gas, such as silicon hexafluoride (SF ₆ ) to provide thermal and electrical insulation. During the manufacture of the transformer, the gas is pumped inside the interior envelope of the resin case, either directly inside the spaces located between the layers of the transformer winding, or where a case in plastic material is mounted around the core and the windings before they are immersed in the resin, inside the plastic housing.

Despite the insulating presence of the inert gas, faults affecting the electrical circuit of the transformer can cause combustion of the windings, in particular electrically insulating sheets which are placed between the windings, which can lead to the release of certain quantities of gas in the envelope. inside the housing. Failure to use protection against such pressure increases may cause the housing to rupture or explode.

In an attempt to minimize the risk of this happening, newer models of a gas-insulated transformer have been fitted with a burst disc, usually made of carbon, arranged between the inner shell and the atmosphere, and designed to rupture when the pressure inside the transformer exceeds a certain level.

In most models of simple transformers, a recess is formed in the mold so as to provide a channel leading to the inner envelope of the transformer containing the core and the windings or, if present, the plastic casing. A simple carbon disc is then adjusted in this recess and held in place by the injection of a resin carried out during a second molding phase. Despite the fact that these models are relatively inexpensive compared to the material costs, the need to provide a second molding phase increases the production cost of these transformers.

Alternatively, more complex models use a commercially available safety cap, of the type produced by Elfab-Hughes or Carbon Lorraine. These safety plugs generally include a carbon disc held in place between two pieces of a steel plug body, the pieces of the plug body engaging with each other via a threaded joint. . The external body of the plug is itself threaded so that it can be screwed in place during use.

These devices have the disadvantage of being relatively complex and expensive components, for example, compared with a simple carbon disc of the type described above. More particularly, the use of two threaded parts engaging one inside the other in the body of the stopper to hold the disc in place, increases the cost. Furthermore, the production of a plug of this type often requires a certain number of other parts, for example an O-ring, between the carbon disc and the body of the plug, as well as between the plug and the transformer, a once it has been put in place. These considerations show that these devices provide a relatively complex solution to the problem posed by the transformer model presented above.

The present invention therefore aims to remedy the drawbacks associated with the prior art and to provide a transformer model using a safety element allowing the expulsion of gas in the event of overpressure inside the transformer, but which avoids the need for a second molding phase to keep the element in place, and which is less expensive than the conventional safety plugs available commercially and described above.

The transformer of the present invention is characterized in that it comprises a rupture disc held in place directly between the housing and the cover, the cover being fixed to the housing and forming a channel between the rupture disc and the outside of the housing.

The use of a cover which engages directly on the transformer case to hold the rupture disc in place, implies that the transformer as a whole, that is to say the case, the cover and the disc, can be assembled before molding and after that only one molding step is required to hold all the elements in place.

Furthermore, the presence of a single cover designed specifically engaging directly on the housing surrounding the transformer core, avoids the problem of duplication of elements and high price, due to the use of standardized safety caps. commercially available. In addition to replacing a plug comprising two or more elements machined by a single piece forming a cover, the invention also makes it possible to reduce the number of other elements involved in the design, as will be described below.

In one embodiment of the present invention, the cover and the housing are joined to each other by means of a threaded joint. Other embodiments are also possible, for example in which the cover is joined to the housing by means of a adhesive, but the use of a threaded joint has the advantage of leading to a secure joint, while avoiding the need to use other materials in construction.

In one embodiment, a single sealing ring is disposed between the rupture disc and the cover part. As mentioned in the introduction, commercially available safety caps are normally used with a pair of sealing rings, a first inner ring in the cap, at the position of the disc, inside the cap, and a second ring located outside the plug, at the point of contact between the plug and the transformer. During the implementation of the present invention, only one sealing ring is needed to ensure that the seal is gas tight while protecting the disc against rupture by compression of the cover. against the housing.

It is preferable that the cover portion has substantially the shape of a cap provided with one or more openings to allow the escape of gas in the event of rupture of the disc. By this means, the disc is protected from accidental rupture due to the intrusion of elements external to the transformer without preventing the element from fulfilling its essential function of safety valve.

In one of the embodiments, the housing surrounding the transformer covers practically the entire core and windings of the transformer. In other embodiments, the housing may include a single element covering only the part of the transformer that is needed to form a channel from the core and the windings of the transformer to the rupture disc.

It is preferable that the rupture disc is formed of carbon, while the housing and the cover portion are formed of plastic and metal, respectively.

• la figure 1 est une vue en coupe transversale d'une soupape de sécurité utilisée conformément à l'art antérieur ;
• la figure 2 est une vue en coupe transversale d'une soupape de sécurité d'un transformateur de la présente invention ;
• la figure 3 représente une vue en coupe transversale de la soupape de sécurité de la figure 2, lorsqu'elle est placée à l'intérieur du corps du transformateur ;
• la figure 4 représente une autre variante de la figure 3, dans laquelle le boîtier comprend un seul élément ne recouvrant qu'une partie du transformateur.

An example of a transformer model of the prior art will be described below, without limitation, in association with one or more embodiments of the present invention, with reference to the accompanying drawings, in which:

• Figure 1 is a cross-sectional view of a safety valve used in accordance with the prior art;
• Figure 2 is a cross-sectional view of a safety valve of a transformer of the present invention;
• Figure 3 shows a cross-sectional view of the safety valve of Figure 2, when placed inside the transformer body;
• FIG. 4 represents another variant of FIG. 3, in which the housing comprises a single element covering only part of the transformer.

Referring to Figure 1, there is shown a safety valve structure of the prior art intended for a transformer which comprises a conical recess 1 formed in the resin mold 2, constituting a channel between the windings of transformer 3 and the atmosphere. A carbon disc 4 is sealed inside the recess, against the windings 3 of the transformer. A second molding step was carried out and led to the formation of a second layer of resin 5 making it possible to fix the disc in position. The insulating gas is pumped inside the mold and the transformer windings. When using this system, in case of abnormally high pressure inside the transformer, for example due to a short circuit, the carbon disc bursts and allows the gas to escape.

As described in the introduction, this form of device suffers from the drawback that a two-stage molding operation is necessary to fix the disc in position. Furthermore, as can be seen from the Figure 1, this particular structure suffers from the drawback that the disc is exposed to the outside and can be pierced, for example by intrusion of external objects.

Turning now to FIG. 2, this illustrates a device forming a safety valve in a transformer according to an embodiment of the invention, which comprises a rupture disc 10 made of carbon engaged on a plastic housing 11 surrounding the core and the transformer windings (not shown) and held in position by a part 12 forming a steel cover which rests on the rupture disc by means of an O-ring 13 d ' sealing made of rubber or plastic. The assembly is held inside the resin case 14 of the transformer 15.

The use of a plastic casing to surround all or part of the core and the transformer windings so as to form an interior space inside the resin casing, in which an insulating gas (such as SF ₆ ) can be pumped, is known in the case of existing transformers. In the present case, the housing 11 has an opening 16 over which the rupture disc 10 is sealed in place, in association with a cylindrical part 17 projecting from the surface of the housing. The internal surface of the cylindrical part 17 is threaded so as to receive an external surface threaded in the same way of the part forming the cover 12 to form a threaded joint 18.

The use of a threaded joint is preferable for several reasons, including ease of assembly and mechanical safety. However, in other embodiments, the surfaces in mutual contact of the housing and the cover part can be smooth and the joint formed between them can be fixed by means of an adhesive.

The part forming the cover 12 has the form of a cap provided with a number of openings 19 around its periphery. The outermost face 20 of the cover has an uninterrupted protective surface for the user. As will become clear, the risks of accidental rupture of the disc by objects penetrating inside the cover-forming part are reduced, since the openings leading towards the interior of the part are not directly in front of the disc.

During the manufacture of the transformer, the housing 11 is fixed around the core and the windings of the transformer, of the disc 10 and of the sealing ring 13 which is then placed inside the cylindrical part 17 of the housing and is held in place. place by screwing the part forming the cover 12 in position in the housing. The assembly is then placed in the mold and resin is poured around it. Once the resin has hardened, insulating gas is pumped inside the transformer by means of a plastic tube (not shown) connecting the interior envelope of the mold to the exterior.

In the event of an increase in pressure in the transformer, the carbon disc 10 ruptures and allows the gas to escape to the atmosphere via the pipe formed by the housing 11 and the cover 12 and through the openings 19.

A cross-sectional view of a transformer 15 according to an embodiment is shown in Figure 3, in which the housing 11 completely surrounds the core and the annular windings 22 of the transformer. In this example the housing is formed of two halves which are pinched around the ring forming the transformer and are sealed in place. The sealed assembly is then placed in the resin mold.

In practice, the housing can be fixed around only part of the circumference of the transformer ring or, as illustrated in Figure 4, only on the surface of the windings which is close to the safety valve. In this embodiment, the core and the windings 24 of the transformer are directly molded in the resin, the insulating gas being contained inside the interstitial spaces between the windings, and the housing 23 is arranged so as to form a channel with the carbon disc 10 and the cover forming part 12.

Claims (7)

1. Gas-insulated transformer (15) comprising a magnetic core in association with primary and secondary windings contained in a casing (11) or in contact with it, this casing being adjusted around the whole or part of the core and windings and being moulded inside a resin casing (14), and characterized in that it comprises a rupture disc (10) held directly in place on casing (11) and a member forming a cover (12), the cover-forming part (12) being fixed to casing (11) and forming a channel between the rupture disc (10) and the outside of the casing.
2. Gas-insulated transformer as in claim 1, in which the cover-forming part (12) and casing (11) are joined together by means of a threaded joint.
3. Gas-insulated transformer as in claim 1 or 2, in which a gasket (13) is provided between the rupture disk and cover-forming part.
4. Gas-insulated transformer as in any of the preceding claims, in which the cover-forming part (12) is substantially in the form of a lid comprising one or more openings (19) to allow the gas to escape in the event of disc rupture.
5. Gas-insulated transformer as in any of the preceding claims, in which casing (11) covers substantially the entirety of the core and windings of the transformer.
6. Gas-insulated transformer as in any of claims 1 to 4, in which the casing comprises a single member covering only that part of the transformer needed to form a channel extending from the core and windings of the transformer to the rupture disc.
7. Gas-insulated transformer as in any of the preceding claims, in which the rupture disc is made of carbon.