EP2264731B1 - Contact for medium-voltage vacuum bottle with improved arc cutting, vacuum bottle and circuit breaker, such as an associated generator breaker - Google Patents

Description

TECHNICAL AREA

The invention relates to the field of medium voltage vacuum switches, commonly called vacuum bulbs or vacuum bulbs.

It relates more particularly to the improvement of their short-circuit current arc breaking capacity.

The main application is one in which a vacuum interrupter is used as a break switch in a circuit breaker, such as an alternator disconnect switch at the output of the power plants.

PRIOR ART

Vacuum bulbs have been used for many years in medium voltage distribution switchgear to cut short-circuit currents of the order of a few kA, typically 25 kA, in a few kV, typically 36 kV. In this type of distribution apparatus, the vacuum bulbs must also support the permanent current flow, typically of the order of 1250 A, without undergoing excessive heating. Indeed, their location in the distribution network means that such vacuum bulbs are closed position in normal operation of the network and are traversed by the permanent nominal current.

It is known that to cut these short-circuit currents, it is necessary to design the arcing contacts so that at their end facing each other, intense axial magnetic fluxes are generated in order to perform the extinction of the arc during the mutual separation of the contacts. The higher the short-circuit currents, the greater the magnetic flux generated must be with optimal distribution between contacts, that is to say as uniformly as possible on their surface, to obtain an effective arc cut.

Because of the need for these vacuum interrupters to have to withstand the permanent current, their constituent material (s) was (are) generally based on copper or strong alloys. percentage of copper, that is to say materials with low electrical resistivity and therefore undergoing a low temperature when passed through the permanent current. However, these materials have a tendency to limit the magnetic flux by eddy currents passing through them.

Thus, in this implementation application in the distribution power grid, there is a certain incompatibility in the realization of contacts between the need for them to withstand a permanent current and therefore, to have a relatively low electrical resistivity and the need for them to achieve an effective arc cut by the magnetic flux they generate and therefore, to have a relatively high electrical resistivity.

Several solutions have already been proposed to improve the magnetic flux generated by the contacts of a vacuum interrupter while allowing them to withstand permanent currents in the closed position.

Some existing solutions involve either implanting additional ferromagnetic materials into the contact winding portion and / or the electrode portion or making slots in the contact body to reduce eddy currents locally or to combine the two.

With regard to the implantation of ferromagnetic materials, mention may be made of the patent US 6,747,233 B1 which discloses the use of magnetic rings with different μ saturations and permittivities in order to have magnetic fields of different profile and value depending on the value of the current, that is to say different for weak or strong currents . More precisely, the combined implantation of a saturable magnetic material 101, 401 with a non-saturable magnetic material 102, 402 in a contact body 104, 404 which is solid and essentially conductive itself is integral with a part mechanical connecting rod 103 essentially conductive. According to the embodiment envisaged, the relative value of electrical resistivity of the saturable materials is opposite to that of the non-saturable materials. So, depending on the mode of illustrated by Figures 1A to 3 the saturable material 101 has a high electrical resistivity and is implanted around a non-saturable material 102 of low electrical resistivity. It can be considered that the major disadvantage of the use of ferromagnetic materials in a contact is related to the fact that they are magnetized and thus undergo somehow the force created by the magnetic field. This force is reversed every 10 ms for a sinusoidal alternating current at 50 Hz. The presence of this force permanently on the materials supposed to control the arc in short circuit tends to weaken the proper structure of the contact. In addition, the value of the magnetic field obtained by inserting ferromagnetic materials is not necessarily greater than that obtained without them.

We can mention patents DE 195 03 661 and US 4, 390, 762 which each disclose a combined slit-forming solution and additional implantation of ferromagnetic materials.

More specifically, the patent DE 195 03 661 discloses a contact 1 comprising a hollow cylindrical tube 2, as a mechanical connecting rod portion, which is secured to the actual contact portion 3 which is magnetic. This magnetic contact portion 3 is recessed in its center and comprises a solid cylindrical winding portion 4 and an electrode disk portion 8 separated from each other by a magnetic wedge 9 and a stainless steel or ceramic plate 10. Three identical slots 5 are practiced spirally by being distributed at 120 ° one of the other in the contact 3 recessed from its internal diameter 7 coincides with the outer diameter of the tube 2 to its outer diameter 6. Such a geometry allows to obtain a magnetic field that extends axially while being distributed radially and thus, creating a rotating arc that reaches a larger contact area. In other words, this document discloses the generation of a radial magnetic field which rotates the arc on an annular zone at the periphery of the contacts.

The patent US 4, 390, 762 discloses, for its part, a contact with a tubular mechanical connection rod portion 1 to which is fixed a cylindrical base 2 recessed at its center which constitutes the winding portion of the contact and on which is fixed an annular contact ring of low height 4 The mechanical connection rod 1 and the cylindrical base consist essentially of copper while the annular contact ring 4 consists of a chromium matrix saturated with copper. As visible on the figure 2 , the winding part 2 comprises two concentric parts 3 separated from each other by a high grade steel 6 which fills an annular recess 5 which extends vertically. On part of the height of each of these parts 3 are made rectilinear slots which extend radially. These slots are distributed uniformly over the periphery and are oriented at the same inclination with respect to the axis of the cylinder 2, without intersecting the latter. The structure thus disclosed in this document increases the mechanical strength of the contacts.

Another existing solution is that described in the publication on behalf of the company TOSHIBA, in Proceedings ISDEIV 1988, page 131, and entitled "Recent Technical Developments of high-voltage and high-power vacuum circuit breakers" . This solution relates to the choice of different contact materials. If the contact is usually made of copper in almost all, the two faces in contact with the arc are preferably made of copper alloy. The winding structure described has 90 ° sections. Another existing solution is that described in the publication on behalf of the company TOSHIBA, in Proceedings ISDEIV 1998, pages 417-418, entitled "Physical and theoretical aspects of a new vacuum arc control technology". . This solution consists in adding a second winding smaller than the first winding. The disadvantage of these two solutions is that the magnetic fields generated by the windings described oppose each other, which tends to significantly reduce the effective total magnetic field.

With regard to the production of slots, these usually consist of straight or inclined cuts in the part of the contacts (electrodes) which are in mutual abutment with each other: these sections generally extend radially to one another. axis of the vacuum bulb. The result obtained is that the path taken by the Foucault currents is interrupted by these slits. What reduces the harmful effect of these eddy currents. The disadvantage of such slots is that they can not be made in all contact configurations: indeed, in some configurations, their presence could induce a reboot between contacts and thus be the cause of a decrease in dielectric withstand performance and capacitance breaking capabilities.

In addition, in recent years, the increase in performance of vacuum bulbs allows their use as a switch-off output direct generator alternator of power generation. However, the voltages to which they are subjected are of the order of 36 kV with short-circuit currents to be cut a few kilo amperes, typically 63 kA, 80 kA up to 160 kA. Permanent currents at the direct output of alternators can also reach considerable values of 9.5kA up to 26 kA. Also, to make a vacuum bulb capable of both supporting these permanent currents and to cut these short-circuit currents of very high value may return to give it unacceptable dimensions in terms of costs.

Also, the plaintiff has already proposed in patent applications WO 2007/110251 and WO 2007/082858 a kinematic solution consisting in inserting a cut-off switch in the electric circuit only during a short-circuit arc break and thus isolating it from the main electrical circuit to prevent him from being traversed by the permanent current.

Documents are known JP 06103859 and JP 200208009 a vacuum bulb contact with two hollow cylindrical windings inclined slots, the two windings being centered on the longitudinal axis of the contact and concentric with one another. Each winding is capable of generating a magnetic field, the magnetic fields superimposed to generate a total axial magnetic field.

The object of the invention is to propose an improved vacuum bulb design that allows it to be inserted into an electrical circuit during a very high-value short-circuit break, or to be crossed. by the rated current in a continuous (permanent) way.

A particular object of the invention is to provide a vacuum bulb design that allows it to be used as a circuit breaker direct output of alternator power generation plants.

STATEMENT OF THE INVENTION

• une partie de connexion mécanique qui s'étend selon l'axe longitudinal Y,
• un corps de contact comprenant:
  • un premier cylindre creux qui comprend des fentes réalisées en hélice autour de son axe et débouchant chacune de part et d'autre de son épaisseur, ledit premier cylindre creux étant centré sur l'axe longitudinal Y en ayant une extrémité solidarisée à la partie de connexion mécanique, le creux du cylindre premier étant dépourvu de matériau, le premier cylindre constituant un premier enroulement adapté pour engendrer un champ magnétique,
  • un deuxième enroulement monté électriquement en parallèle avec le premier enroulement et adapté pour engendrer un champ magnétique qui se superpose au champ magnétique engendré par le premier enroulement,
  • une plaque circulaire de même diamètre que celui extérieur du cylindre creux, ladite plaque étant également centrée sur l'axe longitudinal Y et solidarisée à l'extrémité du premier cylindre creux opposée à celle solidarisée à la partie de connexion mécanique.

To do this, the invention relates to an electrical contact for a medium-voltage vacuum bulb extending along a longitudinal axis Y and comprising:

• a mechanical connection part which extends along the longitudinal axis Y,
• a contact body comprising:
  • a first hollow cylinder which comprises slots made helically around its axis and opening each on either side of its thickness, said first hollow cylinder being centered on the longitudinal axis Y while having an end secured to the connecting part mechanical, the hollow of the first cylinder being devoid of material, the first cylinder constituting a first winding adapted to generate a magnetic field,
  • a second winding electrically mounted in parallel with the first winding and adapted to generate a magnetic field which is superimposed on the magnetic field generated by the first winding,
  • a circular plate of the same diameter as the outside of the hollow cylinder, said plate being also centered on the longitudinal axis Y and secured to the end of the first hollow cylinder opposite to that secured to the mechanical connection portion.

According to the invention, the second winding consists of an additional solid part which comprises two cylindrical portions and an annular ring not closed on itself and centered on the two cylindrical portions, each end of the crown not closed on itself being secured by means of an arm to one of the cylindrical portions. The arrangement of this additional piece is such that the two cylindrical portions are centered on the longitudinal axis and the annular ring concentrically arranged at the first winding. One of the cylindrical portions is secured to the mechanical connection portion and the other of the cylindrical portions is secured to the circular contact plate. The hollow of the first winding and the space between the annular ring and the solid cylindrical portions are devoid of material

Mastering the value and distribution of the magnetic field that occurs along the longitudinal axis of a switch or vacuum interrupter is a key parameter for controlling an arc. Thus, avoiding any contraction of the bow is a guarantee of a successful bow cut. A magnetic field of high value and distributed uniformly facing the contact surfaces allows diffusion of the arc on all these surfaces. For application as an alternator circuit breaker, it is necessary to cut currents above 63 kA. The inventors have found that with contact dimensions necessary to cut such arcs, of the order of 90 to 150 mm, and with structures and materials according to the state of the art, there was a subsidence of the field magnetic generated in the central part of the contacts.

Compared with the solutions according to the state of the art without second winding, the solution according to the invention makes it possible to obtain an axial magnetic field of higher value and distributed in a constant manner on the contact surface. It also allows a current supply on the central part of the contact surface. The arc between contacts can thus be better controlled and, thus, the performance breaking a short-circuit current for a given contact diameter increased.

Compared with a solution according to the state of the art with a second winding in the form of a hollow cylinder, the additional solid part with annular ring makes it possible to increase the axial magnetic field AMF generated by a value of 25 to 30 %, for a given relative amount of current and with identical elements (mechanical connection part, contact body, first winding, end circular plate).

• configurer l'allure du champ magnétique total effectif dans une large gamme,
• alimenter en courant le centre et la périphérie des contacts selon un ratio défini entre eux: en effet, les deux enroulements sont montés électriquement en parallèle et constituent donc des résistances électriques en parallèle, ils permettent d'avoir un pourcentage donné de courant qui passe dans l'un et dans l'autre ;
• réduire la résistance totale de l'ampoule à vide.

In other words, thanks to the invention, one can:

• configure the pace of the total effective magnetic field in a wide range,
• supply current to the center and the periphery of the contacts according to a ratio defined between them: in fact, the two windings are electrically connected in parallel and therefore constitute electrical resistances in parallel, they allow to have a given percentage of current which passes through one and the other;
• reduce the total resistance of the vacuum bulb.

The outer diameter of the first winding and the circular plate is between 90 and 150 mm, which is perfectly suitable for an application in which the short-circuit currents to be cut have a value beyond 63 kA.

The invention also relates to a medium voltage vacuum bulb comprising at least one electrical contact described above.

The vacuum bulb may comprise a pair of electrical contacts with a fixed contact described above and a movable contact described above.

The invention also relates to a circuit breaker, such as an alternator disconnect circuit breaker comprising at least one vacuum interrupter as above.

Finally, the invention relates to the use of such a circuit breaker, such as an alternator disconnecting switch according to which the vacuum interrupter is traversed only by a short-circuit current.

BRIEF DESCRIPTION OF THE DRAWINGS

• la figure 1 est une vue en coupe verticale partielle d'une ampoule à vide moyenne tension conforme à l'invention,
• la figure 2 est une vue en perspective et en coupe partielle réalisée au niveau d'un contact selon l'état de l'art,
• les figures 3A et 3B sont respectivement une vue en perspective et en coupe partielle réalisée au niveau d'un contact selon l'invention,
• la figure 3C est une vue en coupe longitudinale d'un contact selon les figures 3A et 3B;
• la figure 4A est une vue schématique réalisée au niveau d'un contact d'une ampoule à vide moyenne tension et montrant un profil de champ magnétique généré par un contact selon l'état de l'art avec un seul enroulement,
• les figures 4B à 4D sont des vues schématiques réalisées au niveau d'un contact d'une ampoule à vide moyenne tension et montrant différents profils de champ magnétique généré par un contact à deux enroulements,
• la figure 5 est une vue en coupe transversale réalisée au niveau d'un enroulement d'un contact selon l'invention et projetée dans un plan.

Other advantages and characteristics of the invention will emerge more clearly on reading the detailed description given by way of nonlimiting illustration with reference to the following figures among which:

• the figure 1 is a partial vertical sectional view of a medium voltage vacuum bulb according to the invention,
• the figure 2 is a perspective view and partial section made at a contact according to the state of the art,
• the Figures 3A and 3B are respectively a perspective and partial sectional view taken at a contact according to the invention,
• the figure 3C is a longitudinal sectional view of a contact according to the Figures 3A and 3B ;
• the Figure 4A is a schematic view taken at a contact of a medium voltage vacuum bulb and showing a magnetic field profile generated by a contact according to the state of the art with a single winding,
• the Figures 4B to 4D are schematic views made at a contact of a medium-voltage vacuum interrupter and showing different magnetic field profiles generated by a contact with two windings,
• the figure 5 is a cross-sectional view taken at a winding of a contact according to the invention and projected in a plane.

DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

As represented in figure 1 , a vacuum interrupter 1 according to the invention extends along a longitudinal axis Y and essentially comprises a pair of contacts one of which is fixed and the other 3 is movable between an open position (see the part shown in FIG. right) and a closed position (see the part shown on the left) under the action of an operating rod 4. The contacts 2 and 3 are large (diameter> 35mm).

The separation of the contacts 2, 3 in a vacuum bulb is usually intended to cut a current arc that may occur in the separation space between these contacts.

Whatever the closed or open position of the contacts 2, 3, they are arranged in a screen 6 itself inside the envelope 7 of the bulb inside which the vacuum prevails.

Cutting high AC currents requires control of the arc that is created. The arc control means are usually an integral part of the vacuum bulb. They must therefore ensure that the energy of the arc at the contacts 2, 3 remains below acceptable limits to be able to cut off the current and maintain the transient recovery voltage TTR. One type of known arc control is commonly called Axial Magnetic Field (AMF) arc control. These AMF axial magnetic field arc control means consist in creating a magnetic field parallel to the longitudinal axis Y of the bulb 1.

These AMF arc control means according to the state of the art are supposed to prevent a contraction of the arc and, consequently, to widen it over an area of the contact surfaces facing each other which is the widest possible. This normally results in distributing the energy of the arc over a larger area and thus allowing the breaking of the current to the natural zero of the alternating current.

In other words, effective AMF arc control means require a truly winding-generated magnetic field to be raised and distributed uniformly to efficiently diffuse the arc onto the contact surfaces facing each other. the other.

These AMF arc control means are thus constituted according to the state of the art by an element in the form of a coil or in other words a winding which is a hollow cylinder 8 arranged as shown in FIG. figure 2 that is to say which extends to the periphery of the contact. The hollow 80 of the winding 8 is devoid of material. The hollow cylindrical winding 8 comprises slots 81 made helically around the longitudinal axis Y and opening at least on its outside.

Each contact 2, 3 according to the state of the art comprises a mechanical connection portion 20, 30 and a contact body 21, 31 secured to this mechanical connection. The body 21, 31 comprises the winding 8 and an electrode portion 22, 32 in the form of a circular plate. This plate 22 or 32 constitutes the mutual physical contact surface with the other plate 32 or 22 when the contacts are in the closed position. These contact surfaces 22, 32 are the surfaces on which the arc must be diffused as uniformly and as widely as possible.

The windings 8 are each secured to both the mechanical connection portion 20 or 30 and to the circular plate 22 or 32.

Typically, the windings 8 and the electrode portions 22, 32 according to the state of the art have an outer diameter ∅ _ext between 50 and 80 mm to cut currents between 30 and 50 kA.

However, for applications in which the current to be cut has a value greater than 63 kA, for example 80 kA or above, it is necessary to increase the outer diameters of contacts and therefore those of the windings. Such a particularly targeted application is that in which the vacuum interrupter is used as an alternator circuit breaker at the output of a power plant. The outer diameters may be between 90 and 150 mm, for example of the order of 120 mm.

However, the inventors have demonstrated that contacts with such diameters greater than 100 and 150 mm and made in the same materials and with the same geometry as in the state of the art, a non-homogeneous distribution occurred. on the physical contact surface of the AMF magnetic field created with sagging in the central part. The phenomenon is highlighted by the dashed curve on the Figure 4A which is representative of the AMF magnetic field created by a contact according to the state of the art and calculated by FEA 3D modeling software. It can be seen on this curve that the magnetic field AMF undergoes a collapse near the longitudinal axis Y of the bulb along the radial axis X of the bulb. In addition, the current to be cut reaches the periphery of the electrode surfaces 22, 32. By construction, the current flows from the portion 20 towards the portion 8 which is at the periphery of the contact.

Thus, for contacts 2, 3 of large diameter (between 90 and 150 mm), and made in the materials and with the structures according to the state of the art, the effectiveness of the arc control means by field Axial magnetic AMF is reduced. The bow to cut therefore tends to contract and / or focus on the periphery of the contacts.

A solution already proposed according to the state of the art consists in arranging a second winding 9 concentrically in the first winding 8. This second winding 9 is thus electrically mounted in parallel with the first winding 8 and is adapted to generate a field magnetic superimposed on the magnetic field generated by the first cylinder 8 and therefore increases the total effective magnetic field in the central part of the contact.

The two windings 8, 9 or 8, 10 are provided to circulate the current in the same direction so that the two magnetic fields created by the passage of it are superimposed or otherwise added.

Different AMF axial magnetic field profiles can be obtained as shown in FIGS. Figures 4B to 4D : flat, with a subsidence or elevation in the central part of the contacts. These different profiles can be obtained by varying the parameters that are the properties and dimensions of the second winding: diameter, materials constituting it, thickness, height ... It is specified here that the different curves illustrating the different magnetic field profiles to Figures 4B to 4D were also calculated from the FEA 3D software. It goes without saying that the curves shown are indicative and not limiting.

These same parameters can also influence the amount of current flowing through the central part of the contact: this makes it possible to reduce or even prevent the interaction between the plasma (created between the contact surfaces 22, 32 of the end facing at the time of a break current) and the screen 6. In addition, this allows better distribution of the current on the end contact surface and thus better distribute the arc current. Finally, the implantation of a second winding makes it possible to reduce the total electrical resistance of the vacuum interrupter 1.

An embodiment of a second winding according to the state of the art is that illustrated in FIG. figure 2 .

It consists of a second hollow cylinder 9 comprising slots 91 made helically around its axis and opening at least on its outside. This second hollow cylinder 9 is centered on the longitudinal axis Y, arranged concentrically with the first cylinder 8, having one end secured to the mechanical connection portion and the other end secured to the circular plate 22. In this embodiment, the troughs 80, 90 of the cylinders are devoid of material.

As illustrated, the second hollow cylinder 9 is in fact homothetic of the first hollow cylinder 8.

The material (s) constituting this second hollow cylindrical winding 9, its diameter, the number of slots 91 and the angle they form are chosen as a function of the outside diameter of the contact 2. The profile of the total effective AMF axial magnetic field is the result of the choice of these parameters. The solution according to figure 2 , has the important advantage of maintaining the cylindrical symmetry of the magnetic field over the entire contact surface 22.

According to a particularly advantageous embodiment, the two hollow cylinders are made from the same machined or milled cylindrical crown: it is thus possible to obtain a mechanical reinforcement base 89 between them (see FIG. figure 2 ).

The two windings 8 and 9 are electrically connected in parallel: thus the two cylinders are secured to the connection base 20 and to the electrode plate 22, typically by brazing. It is the same for the windings (not shown) of the contact 3 vis-à-vis the contact 2.

Since the winding 8 at the periphery and the winding 9 at the center of the contact 2 constitute electrical resistances in parallel, they make it possible to have a given percentage of current passing through the one 8 and the other 9.

• compenser complètement l'affaissement du champ magnétique axial AMF, comme représenté en figure 4C,
• créer une surélévation du champ magnétique axial AMF dans la partie centrale du contact, comme représenté en figure 4D. Dans ce cas, le champ magnétique a tendance à légèrement diminuer à la périphérie du contact.

A hollow cylindrical winding 9 of small diameter, typically of outside diameter Dext of the order of 30% of the internal diameter ∅ _int of the first winding 8 has the effect of increasing the axial magnetic field in the central part of the contact 2. It can including:

• completely compensate for the collapse of the AMF axial magnetic field, as shown in figure 4C ,
• create an elevation of the axial magnetic field AMF in the central part of the contact, as represented in FIG. figure 4D . In this case, the magnetic field tends to slightly decrease at the periphery of the contact.

A hollow cylindrical winding 9 of large diameter, typically of outside diameter Dext of the order of 80% of the inside diameter ∅ _int of the first winding, has the effect of less compensation for the sagging of the field in the central part but an increase in the field in the intermediate zone between the central part and the periphery of the contact, as visible in Figure 4B .

A second winding 10 according to the invention is illustrated in FIGS. Figures 3A and 3B .

According to the invention, the second winding consists of an additional solid part 10 which comprises two cylindrical portions 100a, 100b and an annular ring 102 not closed on itself and centered on two cylindrical portions 100a, 100b. Each end 1020, 1021 of the ring 102 not closed on itself is secured by means of an arm 101, 103 to one of the cylindrical portions 100a, 100b.

The distance provided between the two ends 1020 and 1021 of the annular ring is minimal and thus has no influence on the value of the magnetic field created by the second winding 10 (FIG. figure 3A and 3C ).

The arrangement of this additional piece 10 is such that the two full cylindrical portions 100a and 100b are centered on the longitudinal axis Y and its annular ring 102 concentric with the first cylinder 8. The solid cylindrical portion 100b is secured to the mechanical connection portion 20. The cylindrical portion 100b is secured to the circular contact plate 22. The hollow 80 of the first cylinder 8 and the space between the annular ring 102 and the cylindrical portions 100a and 100b are devoid of material.

As visible on the Figure 4B , so that the current flowing in the additional winding 10 and the current flowing in the first winding 8 have the same direction of flow (from bottom to top and following a counterclockwise path in the ring 102), the arm 103 which secures the end 1020 of the ring 102 to the cylindrical portion 100b is below the arm 101 which secures the other end 1021 of the ring 102 to the cylindrical portion 100a. As visible on the Figure 4B the current I ₁₀ which reaches the base of the cylindrical portion 100b travels the ring 102 in a counterclockwise direction before reaching the top of the other cylindrical portion 100a. As visible on this same Figure 4B the current I ₈ reaching the base of the winding 8 flows in a helical path also anti-clockwise.

Here too, the material (s) constituting this additional piece 10, its height, its thickness, and the outside diameter of the annular ring 102 are chosen taking into account the dimensions of the contact 2 and the first winding 8 and depending on the desired AMF axial magnetic field profile.

It will thus be possible to provide an annular ring 102 with an outside diameter Dext of between 30 and 80% of the inside diameter ∅ _int of the cylinder of the first winding 8. The precise profile of the axial magnetic field AMF is a function of the outside diameter Dext of the annular ring 102 and of the proportion of current passing through it with respect to the quantity passing through the first winding. figure 3B The direction and distribution of the current I have been schematized since its arrival from the mechanical connection part 20 to its end plate 22.

A piece 10 with a ring 102 of small diameter, typically of outside diameter Dext of the order of 30% of the inside diameter ∅ _int of the first winding 8, has the effect of increasing the total magnetic field as visible in FIG. figure 4C .

A piece 10 with a ring 102 of large diameter, typically of outside diameter Dext of the order of 80% of the inside diameter ∅ _int of the first winding 8, has the effect of less compensation for the sagging of the field in the central part but a increase of the field in the intermediate zone between the central part and the periphery of the contact, as visible in Figure 4B .

The thickness of the first cylindrical winding 8 is determined by the current density that passes through as well as the desired total resistance for the vacuum bulb. Indeed, the total resistance of the vacuum bulb decreases if the thickness of the windings 8, 9 or 10 increases. The thickness of the second winding 9 or 10 is limited only by the available space defined between the mechanical connection portion 20, the first winding 8, and the end contact plate 22. The material (s) constituting the second winding 9 or 10 is (are) advantageously the (s) same (s) as that (those) constituting the first winding 8. They can of course be different insofar as they have close electrical properties. A preferred material for both first winding 8 and second winding 9 or 10 is copper of high purity, for example of OFHC type. OFHC copper is known for its low electrical resistance and its ability to be brazed to other metallic materials.

For a value of current I given on arrival in the mechanical connection part 20, the second winding according to the invention in the form of the solid part 10 makes it possible to generate a higher axial AMF magnetic field in the center of the contact than that only generated by a winding according to the state of the art in the form of hollow cylinder 8 with slots 81: the difference in value can go up to a factor of two to three. In other words, the total axial AMF magnetic field generated in the center of the contact by a solid-filled piece 100 and annular ring 102 arranged in the hollow 80 of the cylinder 8 can be two to three times greater than that generated solely by a hollow cylinder. 8.

The amount of current flowing through the solid part 10 can advantageously be understood between 5 and 30% of the total amount of the current I which passes through the contact 2. Thus, it is possible to choose dimensions and a material constituting a solid part 10 so that it is traversed by a current whose quantity is equal to 10% of the total amount of current I passing through contact 2. For this relative quantity of current and with identical elements (mechanical connection part 20, contact body 21, first winding 8, end circular plate 22), the magnetic field AMF axial generated by the full piece 10 to annular ring 102 according to the invention is 25 to 30% greater than the axial magnetic field AMF generated by a second winding 9 of hollow cylindrical shape according to the state of the art.

As represented in Figures 3A and 3B , the cylindrical winding 8 may be integral with a base 800, recessed to let the cylinder 100 in contact with the electrode plate 22. This base 80 thus serves as a mechanical reinforcement without the major drawback of reducing the magnetic field because the eddy currents flowing through it are negligible because of its high electrical resistivity.

The slots 81, 91 are cut in the first 8 and the second 9 cylindrical windings, respectively, so as to create helical sections around the axis of each of the cylinders considered and which extend from one of their ends. towards the other ( figure 2 ).

The figure 5 is an example of a schematic representation for cross-sectional view, that is to say in a section parallel to the surface 22 made at the first cylinder 8 and projected in the same plane.

According to this section, it can be seen that the slot portions 81 are uniformly distributed over the diameter of the winding 8 (12 in number) and all of the same size.

• augmenter et donner un profil donné au champ magnétique axial AMF effectif sur la surface de contact d'extrémité,
• avec un deuxième enroulement à pièce pleine avec couronne annulaire, augmenter davantage le champ magnétique axial AMF effectif,
• permettre une répartition du courant en guidant un pourcentage de sa quantité vers la partie centrale du contact, ce qui augmente la surface disponible pour la diffusion de l'arc lors d'une coupure,
• rendre moins élevée la probabilité pour un arc d'être créé à la périphérie du contact.

The invention which has just been described makes it possible to obtain the following advantages:

• increase and give a given profile to the effective AMF axial magnetic field on the end contact surface,
• with a second full-body winding with annular ring, further increase the effective axial AMF magnetic field,
• allow a distribution of the current by guiding a percentage of its quantity towards the central part of the contact, which increases the surface available for the diffusion of the arc during a cut,
• lower the probability of an arc being created on the periphery of the contact.

Claims (6)

1. An electrical contact (2, 3) for a medium-voltage vacuum circuit-breaker (1), extending along a longitudinal axis Y and comprising:

   a mechanical connection portion (20, 30) that extends along the longitudinal axis Y;

   a contact body (21, 31) that comprises:

   a first hollow cylinder (8) that includes helical slots (81) about its axis and opening out at least to its exterior, said first hollow cylinder being centered on the longitudinal axis Y and having one end fastened to the mechanical connection portion, the hollow (80) of the first cylinder being empty of material, and the first cylinder constituting a first winding adapted to generate a magnetic field;

   a second winding (9, 10) that is connected electrically in parallel with the first winding (8) and that is adapted to generate a magnetic field that is superposed on the magnetic field generated by the first winding (8); and

   characterized in that the electrical contact comprises:

   a circular plate (22, 32) that has a diameter equal to the outside diameter of the first hollow cylinder, said plate (22, 32) also being centered on the longitudinal axis Y and being fastened to the end of the first hollow cylinder opposite from its end fastened to the mechanical connection portion,

   wherein the second winding consists of an additional solid part (10), the part comprising two cylindrical portions (100a, 100b) and an annular ring (102) that is not looped and that is centered on the two cylindrical portions (100a, 100b), each non-looped end (1020, 1021) of the ring (102) being fastened by an arm (101, 103) to one of the cylindrical portions (100a, 100b), the arrangement of this additional part (10) being such that the two cylindrical portions (100a, 100b) are centered on the longitudinal axis Y and the annular ring (102) is concentric with the first winding (8), one cylindrical portion (100a) being fastened to the mechanical connection portion (20) and the other cylindrical portion (100b) being fastened to the circular contact plate (22), the hollow (80) of the first winding (8) and the space between the annular ring (102) and the two solid cylindrical portions (100a, 100b) being empty of material.
2. An electrical contact according to claim 1, wherein the outer diameter of the first winding and of the circular plate is between 90 mm and 150 mm.
3. A medium-voltage vacuum circuit-breaker (1) including at least one electrical contact (2, 3) according to claim 1 or 2.
4. A vacuum circuit-breaker according to claim 3, including a pair of electrical contacts with a fixed contact (2) according to claim 1 or 2 and a movable contact (3) according to claim 1 or 2.
5. A circuit-breaker, such as an AC generator disconnector circuit-breaker, including at least one vacuum circuit-breaker (1) according to claim 3 or 4.
6. Use of a circuit-breaker, such as an AC generator disconnector circuit-breaker according to claim 5, such that the vacuum circuit-breaker carries only a short-circuit current.

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