EP2483900A1

EP2483900A1 - Winding for a contact of a medium-voltage vacuum bulb having improved arc cutoff, and related vacuum bulb and circuit breaker, such as an alternator disconnect circuit breaker

Info

Publication number: EP2483900A1
Application number: EP10765768A
Authority: EP
Inventors: Saïd Kantas
Original assignee: Schneider Electric Energy France SAS
Current assignee: Schneider Electric Energy France SAS
Priority date: 2009-09-29
Filing date: 2010-09-27
Publication date: 2012-08-08
Also published as: US20120181254A1; FR2950729A1; CN102668002B; WO2011039133A1; CN102668002A; US8835790B2; FR2950729B1

Abstract

The invention relates to a novel design for a winding (8) made of a material having low electrical resistivity, such as copper, and a diameter typically larger than 90 mm, intended for generating a magnetic field in an electric contact (2, 3) for a medium-voltage vacuum bulb (1), consisting of a hollow cylinder (8) including slots (81) free of material and formed helically about the longitudinal axis thereof, and being in communication with both the cavity and the outside of the cylinder. According to the invention, the angular length of each helix is at least equal to 360°. The invention enables an increase in the level of the magnetic field AMF obtained by the winding(s) integrated into an electric contact of a vacuum bulb while enhancing uniformity and field symmetry, and reducing production costs.

Description

WINDING FOR CONTACT OF MEDIUM VOLTAGE VACUUM BULB WITH IMPROVED ARC BREAKER, VACUUM BULB AND CIRCUIT BREAKER, SUCH AS CIRCUIT BREAKER

OF ALTERNATOR

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 improving the arc breaking of such vacuum bulbs.

The main application is that in which a vacuum interrupter is used as a break switch in a generator disconnect circuit breaker 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, in order to cut off these short-circuit currents, it is necessary to design the arcing contacts so that at their end facing each other, axial intense magnetic fluxes (usually called AMF , abbreviation of "Axial Magnetic Flux" in English) or radial (usually called RMF, abbreviation of "Radial Magnetic Flux" in English) are generated in order to realize the control of the arc during the mutual separation of the contacts.

In other words, the breaking of high currents in vacuum interrupters requires the integration of these arc control means into the arcing contacts: these are therefore an integral part of the vacuum interrupter.

The desired function for these arc control means is that the density of the arc energy created through the arcing contacts during a break remains below the limits required for both breaking the current and sustaining the recovery voltage in the vacuum space immediately after the interruption of the current.

The aforementioned AMF fluxes are generated parallel to the axis of the vacuum interrupter while the aforementioned RMF fluxes also create a magnetic force which will cause a rotation of the arc at the periphery of the mechanical contact surface.

These AMF or RMF magnetic fluxes are created by the current itself flowing through the contacts of the arc control. Typically, the arc control means generating AMF or RMF flows comprise two windings, one of which is mounted in the moving arc contact and the other in the fixed arc contact of a vacuum bulb. If the current flows in the same direction in both windings, the resulting magnetic fluxes are added in an axial direction of the vacuum interrupter in the void space between the two arcing contacts in the open or separate position. one of the other. If the current flows in a given winding in a direction opposite to that in the other winding, this results in a magnetic flux which extends radially in the void space between the two separate arc contacts.

The arc control means generating AMF fluxes theoretically have the primary technical effect of preventing contraction of the arc in a specific area. In other words, they must widen the arc to the widest possible contact area. The result that we seek to achieve is a distribution of the arc energy over as wide a surface as possible and thus allow the breaking of the alternating current to the natural passage to zero.

Efficient AMF flux arc control means must therefore generate a high and homogeneous magnetic flux over the entire contact surface.

Typically, the breaking of currents in the range of 30 to 50 kA requires the use of contacts of diameter between 50 and 80 mm. For such diameters, the AMF arc control means currently implemented give overall satisfaction.

However, some vacuum bulbs by their application can be subjected to short circuit currents to cut a few kilo amperes, typically 63 kA, 80kA up to 160 kA. This necessarily requires the use of upper diameter contacts typically between 90 and 150 mm.

With such diameters, the inventors have been able to observe that a non-homogeneous distribution occurs on the physical contact surface of the AMF magnetic field created with a slump in the central part, which has the consequence of lowering the breaking performance of the the vacuum bulb.

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.

As regards the implantation of ferromagnetic materials, mention may be made of US Pat. No. 6,747,233 B1, which discloses the use of magnetic rings with saturation and permittivity μ different 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. Thus, according to the embodiment illustrated in FIGS. 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.

Patent DE 195 03 661 and

US 4,390,762 which each disclose a solution combined slit production and additional implantation of ferromagnetic materials.

More specifically, 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 contact portion itself 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 made spirally by being distributed at 120 ° to each other in the contact 3 hollowed 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, to create 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.

US Pat. No. 4,390,762 discloses, in turn, 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 4. The mechanical connecting 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 can be seen in FIG. 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 makes it possible to increase the mechanical strength of the contacts.

Another existing solution is that described in the publication on behalf of the company TOSHIBA, in the Proceedings ISDEIV 1998, pages 417-418, and 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 this solution is that the magnetic fields generated by the windings described oppose each other, which tends to reduce significantly the total effective magnetic field.

To solve this problem, the applicant has proposed in the patent application FR 09 53852 filed June 10, 2009 entitled "CONTACT FOR VACUUM BULB MEDIUM VOLTAGE IMPROVED ARC BREAKER, BULB VACUUM AND CIRCUIT BREAKER ALTERNATOR ASSOCIATED ", To mount a second winding electrically 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.

This solution is generally satisfactory insofar as it makes it possible to increase and avoid the collapse of the axial magnetic field AMF at its center by giving it an effective given profile over the entire end contact surface.

DE 195 13790 discloses a winding 33 for generating an axial magnetic field AMF in a vacuum interrupter contact, which in its embodiment of FIG. 5 comprises slits 50 in a helix of limited length which does not allow to have a uniform magnetic field on both the surface of the arc control contacts and in the space between the contacts of the bulb.

The object of the invention is to propose an improved solution that makes it possible to further increase the axial magnetic field AMF in an electrical contact for a medium voltage vacuum bulb, while preventing it from sagging in the center of the contact.

Another object of the invention is to improve the uniformity of the magnetic field on the surface of the contacts and in the space between the contacts of a vacuum interrupter while reducing the cost of manufacture.

STATEMENT OF THE INVENTION

To do this, the invention relates to a winding based on a material of low electrical resistivity, such as copper, and diameter typically greater than 90 mm, intended to generate a magnetic field in an electrical contact for a medium-voltage vacuum bulb, consisting of a hollow cylinder comprising mutually parallel slits devoid of material and made helically around its longitudinal axis and opening into both the hollow and the outside of the cylinder.

According to the invention, the angular length of each helix is at least equal to 360 °. It is specified here that the notion of "angular length" of the helices is to be understood as usually in the mathematical sense: thus, considering the projection of a helix on a plane perpendicular to its axis, the angular length of a helix is the value the angle traveled between its two ends along its length.

By methodically producing parallel helical slots with an angular length of at least 360 °, the disadvantages of the windings according to the state of the art are overcome.

In fact, the inventors have been able to observe that shorter helical slot windings according to the state of the art generate a nonhomogeneity of the magnetic fluxes at the time of the creation of the arc in a concentrated zone, in particular in periphery of contact which is provided with it. Indeed, in the windings according to the state of the art, the current flows, for at least a certain duration, only in a limited part of the turns delimited individually by two slots. This is because the arc can start at any point on the surface (the last point of contact of two electrodes before their separation). It is indeed very rare or impossible to have more than one point of separation between the two surfaces of the two contacts. The other part of the turns does little or nothing to generate the total magnetic flux. This is what focuses the AMF magnetic flux while it should be spread over the entire surface of the arc to diffuse the arc. In addition, and even if the arc arrives very quickly to be fed by all the turns of the arc control, there remain areas of weak fields or in other words field sinks created by the discontinuity of the turns between them. These areas of weak fields increase the risk of constriction. These zones of nonuniformity of the magnetic field of a winding imply zones of nonuniformity of the magnetic field in the space between the two contacts and are thus regions of disturbance of the plasma during a power failure. The detrimental consequence is the obtaining of a non-uniform thermal load on the surface of the contacts. For large short-circuit current values, this can affect the breaking performance of a vacuum interrupter. The larger the diameter of the arc control, the smaller these fields are. The smaller the number of turns, the larger these areas are (in the case of a geometry similar to that according to the state of the art of FIG. 3).

The axial magnetic flux (field) AMF generated by a winding according to the invention implanted in a medium-voltage contact is homogeneous, that is to say symmetrical and constant, both on the surface of the contact and in the space between contacts, and much higher value than those generated by windings according to the state of the art.

For a value of angular length of at least 360 °, a winding according to the invention can generate an axial magnetic flux AMF increased by a factor of 2 to 3 compared to that generated by a winding according to the state of the art.

In addition, a winding according to the invention makes it possible to increase the mechanical endurance of a contact 2, 3 of large size, typically between 90 mm and 150 mm, which incorporates it.

In addition, the stability of the AMF arc control during a power failure is improved with a winding according to the invention. Indeed, the inventors have found that for winding lengths less than 360 °, the AMF magnetic field was not necessarily homogeneous at the moment when the arc is created locally. In this case, the current will, at least for a certain time, flow preferably only in one or two turns of the winding. Thus, the other turns do little or no contribution to obtaining the total magnetic field. This results in locating the AMF magnetic field while for it to be effective it must be distributed over the largest possible area of contact. Thus, a winding according to the invention with angular helix lengths of slots at least equal to 360 ° generates a high and uniform AMF magnetic field regardless of the position of the initial arc. Preferably, the width of each slot is less than 0.5 mm for an outer diameter Oext of the hollow cylinder greater than 90 mm.

More preferably, each turn delimited individually by two consecutive helical slots has a section in section parallel to the longitudinal axis of the winding which is substantially rectangular and identical over the entire height of the winding.

According to an advantageous characteristic, the number of helical slots parallel to each other is at least equal to two, advantageously equal to 6.

The invention also relates to a method for producing a winding based on a material of low electrical resistivity, such as copper, for generating a magnetic field in an electrical contact for a medium voltage vacuum bulb, comprising: step of producing a hollow cylinder with helical slots around its longitudinal axis and opening into both the hollow and the outside of the cylinder, being devoid of material, a step in which the angular length of each helix is at least less than 360 °.

Advantageously, the helical slots of angular length greater than or equal to 300 ° are produced by electroerosion. The method of producing a winding according to the invention has a reduced cost because the number of operations to make the slots is.

Compared to the geometry of FIG. 3, the new geometry of a winding according to the invention only has a number of six turns instead of twelve. In addition, the production of the twelve turns in a winding according to the state of the art of FIG. 3 requires an equal number (twelve) of cross sections. However, the realization of the six turns in the new geometry of the winding according to the invention requires only three cuts passes. Thus, thanks to the invention, there is a reduction factor equal to four in the number of section passes.

The invention also 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 winding as described above,

• A circular plate of the same diameter as the outside of the first hollow cylinder, said plate is 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 one variant, the helices of the slots of the first winding are of the dextral type from the mechanical connection part to the circular contact plate. It is specified here that the term "dexter" is that used in mathematics and means that an observer placed outside the contact sees the propellers mounted from left to right from the mechanical connection portion to the circular plate. According to an advantageous embodiment, the contact comprises a second winding and whose arrangement is the subject of the patent application FR 09 53852 filed on June 10, 2009 by the applicant and entitled "CONTACT FOR VACUUM BULB AT MEDIUM VOLTAGE A IMPROVED ARC BREAKER, VACUUM BULB AND CIRCUIT BREAKER, SUCH AS AN ASSOCIATED ALTERNATOR DISCONNECT CIRCUIT BREAKER.

This second winding is thus 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.

According to a first variant, the second winding may consist of a winding according to the invention, with an angular length of each slot at least equal to 360 °.

The second hollow cylinder is then centered on the longitudinal axis Y, arranged concentrically with the first cylinder, having one end secured to the mechanical connection portion and the other end secured to the circular plate, the hollow of the cylinders being devoid of material .

The helices of the slots of the second winding may be dextral type from the mechanical connection portion to the circular contact plate.

The manufacturing method used (wire EDM) allows the realization of the second winding at the same time as the main winding and cutting in the same block of material. There is no room or additional cutting passage.

According to an advantageous embodiment, the contact comprises at least one column as claimed in the patent application FR 09 53853 filed on June 10, 2009 by the applicant and entitled "CONTACT FOR LOW-VOLTAGE MEDIUM-VOLTAGE BULB WITH REINFORCED STRUCTURE, BULB A VACUUM AND CIRCUIT BREAKER, SUCH AS AN ASSOCIATED CIRCUIT BREAKER CIRCUIT BREAKER. The column is thus distinct from (s) the winding (s) and arranged, in the hollow of the first cylinder, in a spacer between the mechanical connection portion and the circular plate of the contact body so as to avoid the collapse of this last during a closing maneuver and in the closed position of the vacuum bottle, the (the) column (s) having a high electrical resistivity such that when a given current flows in the contact, the amount of current which circulates in the (the) column (s) is negligible compared to that which circulates in the (the) coil (s).

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 greater than or equal to 63 kA, typically up to 100 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.

Preferably, in the vacuum bottle, the slots of the windings of angular length greater than 360 ° open on the side of the separation space between contacts where the arc is formed during the power failure.

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

Depending on the application, a vacuum interrupter according to the invention may or may not be traversed by the nominal load current and of course by the short-circuit current in the event of a fault.

BRIEF DESCRIPTION OF THE DRAWINGS

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:

FIG. 1 is a partial vertical sectional view of a medium voltage vacuum interrupter according to the invention,

FIG. 2 is a schematic view taken at the contacts of a medium-voltage vacuum interrupter and showing the magnetic field generated by an electrical contact incorporating a winding according to the state of the art (dashed curve), FIG. 3 is a cross-sectional view taken at the level of a copper-based winding according to the state of the art and projected in a plane;

FIG. 3A is a graphic illustration of the shape and level of the magnetic field generated by an electrical contact incorporating a winding according to FIG. 3;

FIG. 4 is a perspective view of a winding according to an embodiment of

The invention,

FIG. 5 is a perspective view of a winding according to another embodiment of the invention,

FIG. 5A is a graphic illustration of the shape and level of the magnetic field generated by an electrical contact incorporating a winding according to FIG. 5,

FIG. 6 is a graphic illustration of the shape and level of the magnetic field generated by an electrical contact incorporating a winding according to the invention and a winding according to the state of the art.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS As represented in FIG. 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 portion shown to the right) and a closed position (see part shown on the left) under the action of an operating rod 4. The contacts 2 and 3 are large (diameter> 35 mm).

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 integral parts of the vacuum bulb. They must therefore ensure that the energy density 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 are said to prevent contraction of the arc and, consequently, to widen it over an area of the contact surfaces facing each other which is the most wide 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, arc control means

Effective AMFs require a truly winding-generated magnetic field that is high and evenly distributed to efficiently diffuse the arc onto contact surfaces facing each other.

These AMF arc control means are thus constituted by at least one element in the form of a coil or in other words a copper-based winding which is a hollow cylinder 8 arranged as shown in FIG. 2, 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 the same time on the inside and the outside of the cylinder 8. The space between two consecutive slots 81 defines a turn 82 .

Each contact 2, 3 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 invention have an outside diameter of between 90 and 150 mm in applications in which the current to be cut has a value greater than or equal to 63 kA, for example 80 kA. or above.

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.

Figure 3 is an exemplary schematic representation for cross-sectional view of a winding 8 according to the state of the art, the cut being 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. The angular length of a slot 81 is of the order of 115 °. This configuration corresponds to that described in the patent application on behalf of the applicant FR 09 53855 filed on June 10, 2009 and entitled: "WINDING FOR CONTACT OF VACUUM BULB VACUUM MEDIUM VOLTAGE IMPROVED ENDURANCE, BULB VACUUM AND CIRCUIT BREAKER, TEL AN ALTERNATOR DISCONNECT CIRCUIT BREAKER ASSOCIATED ". FIG. 3A illustrates the shape and level of the AMF magnetic field obtained by an electrical contact integrating a winding according to FIG. 3, that is to say with slots made in a helix but with an angular length (X limited to 115 ° It is specified here that the contact is traversed by a normalized current I. The abscissa X of the illustrated curve represents the radial X axis of the contact 2. The magnetic field thus illustrated AMF is along this radial axis X.

As indicated on the ordinate, the maximum value of the AMF field obtained is of the order of 6.5.

The effective total magnetic field obtained with a winding according to the state of the art (FIG. 3) with an angular length of slots of the order of 115 ° therefore has a globally high value and presents a very small sag in the center (X = 0).

The inventors have sought to further increase the value of the magnetic field. The problem of the invention is in other words to generate a high value magnetic field by improving its uniformity at the contact surface and reducing the cost of manufacture.

To increase the effective total magnetic field in the contact, for contacts 2, 3 of large diameter (between 90 and 150 mm), the inventors have thought to increase the angular length of the helix of each slot 81.

FIG. 4 illustrates a first embodiment of a winding according to the invention. The winding consists of a hollow cylinder 8 which comprises two slots 810, 811 parallel to each other and made helically. Each propeller 810, 811 has an angular length approximately of the order of 360 °. This angular length of 360 ° corresponds to the angle traveled by each propeller 810, 811 between its two ends 8100, 8101 respectively 8110, 8111 along its length. The ends 8101, 8111 of the slots 810, 811 which open on the upper part of the cylinder 8 are diametrically opposed. The turns 82 of the hollow cylinder 8 delimited individually by the two slots 810, 811 also have substantially the same height in their central part with ends 820 of lower height, typically h of the order of 1 mm. The current I which passes through the winding 8 thus circulates in a dextral type helix by making a complete revolution over the entire height of the cylinder 8.

FIG. 5 illustrates another embodiment of a winding according to the invention. The hollow cylinder 8 constituting the winding comprises six slots 810, 811, 812, 813, 814, 815 parallel to each other and made helically. Each helix 810-815 has, as the embodiment of Figure 4 an angular length of the order of 360 °. The ends 8101, 8111, 8121, 8131, 8141 and 8151 which open on the upper part of the cylinder 8 are distributed uniformly, that is to say, being distant from each other by 60 °.

FIG. 5A illustrates the shape and level of the AMF magnetic field obtained by a contact electric integrating a winding according to Figure 5 that is to say with the six slits 810-815 made helically and each with an angular length of the order of 360 °. It is specified here that the test conditions are the same as for the winding contact according to the state of the art (FIG. 3): same winding dimensions 8, same arrangement with respect to the mechanical connection part 20 and plate contact circular 22 and the same normalized value of the current I _N which passes through the winding.

The paces of the fields obtained respectively in FIG. 3A and 5A are identical.

On the other hand, as indicated on the ordinate in FIG. 5A, the maximum value of the AMF field obtained for the winding according to the invention is of the order of 19.5.

Thus, the value gain of the AMF magnetic field by virtue of the invention is equal to 3 (ratio between the maximum value of 19.5 of FIG. 5A and the maximum value of 6.5 of FIG. 3A).

Another electrical contact has been made according to the invention: it comprises a first winding made according to FIG. 5 and a second winding as claimed in the patent application FR 09 53852 filed on June 10, 2009 by the applicant and entitled "CONTACT FOR BULB MEDIUM - VOLTAGE VACUUM WITH IMPROVED ARC CUTOUT, VACUUM BULB AND CIRCUIT BREAKER, SUCH AS AN ALTERNATOR DISCONNECT CIRCUIT BREAKER.

The second winding 9 is arranged concentrically in the first winding 8. This second winding 9 is thus electrically mounted in parallel with the first winding 8 and adapted to generate a magnetic field which is superimposed on the magnetic field generated by the first cylinder 8.

It consists of a second hollow cylinder 9 comprising slots (not shown) made helically around its axis and opening to the faith on the inside and outside of the cylinder. 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 20 and the other end secured to the circular plate 22.

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.

In contrast with the winding 8 according to the invention, each helix of the slots of the second winding 9 is made with an angular length of at least 360 °.

Preferably, the slots of angular length of at least 360 ° open on the plate 22 or 32, that is to say in the separation space 5 between the contacts 2, 3 where the arc is formed during the power failure.

FIG. 6 illustrates the shape and level of the AMF magnetic field obtained by an electrical contact integrating the two windings 8 and 9 as described above. It states here that the conditions are the same as for the winding contact according to the state of the art (FIG. 3): same winding dimensions 8, same arrangement with respect to the mechanical connection part 20 and the contact circular plate 22 and even normalized value of the current I _N passing through the winding.

The paces of the fields obtained respectively in FIG. 3A and 6 are different. Thus, the arrangement of a second winding 9 as described above makes it possible to obtain an AMF magnetic field without any sagging at the center of the contact provided with it.

On the other hand, as indicated on the ordinate in FIG. 6, the maximum value of the AMF field obtained for the contact according to the invention is of the order of 19.

Thus, the gain in value of the magnetic field AMF thanks to the invention is here of the order of 2.9 (ratio between the maximum value of 19 of FIG. 6 and the maximum value of 6.5 of FIG. 3A).

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

to increase the AMF magnetic field by a factor ranging from 2 to 3 with respect to the AMF magnetic fields obtained with windings according to the state of the art,

improve the distribution of the magnetic field generated by a winding according to the invention: the winding generates a better distributed magnetic field on the contact surface at the time of the ignition of the arc, which allows an effective cut of the currents of 'bow, - reduce the path of the eddy currents induced by the alternating current when it passes through the arc control. As is known, these induced currents generate a magnetic field that opposes the axial magnetic field useful for cutting: the slots according to the invention opening onto the surface create a discontinuity of the surface of the contact, which reduces the path of the eddy currents induced,

simplifying the method of producing the winding and thus reducing the cost thereof, making the slots by electroerosion two by two or four by four (in the case of an additional inner winding) being simpler,

- obtain slits of width less than 1 mm by the electroerosion process,

- Increase the mechanical stability of a contact of a vacuum interrupter comprising a winding according to the invention. Increasing the slot lengths and their constant thickness actually increases the length of the turns, and thus the mechanical stability. This mechanical stability makes it possible to meet ANSI or IEC standards. The mechanical endurance of the vacuum interrupter is significantly improved until 30,000 opening / closing cycles can be achieved. The angular length of the turns advantageously greater than or equal to 360 °, results in a linear length of the turns greater than that in the coils according to the state of the art. The electrical resistance of the turns is increased. This is a minor inconvenience of the invention with respect to a state-of-the-art geometry similar to that of FIG. 3, since the increase in resistance is small. And the contribution of the windings to the total resistance of the vacuum bulb is minimal. In addition, in the case where the vacuum interrupter is only required to cut the short-circuit current and not to conduct the nominal current permanently, the resistance of the vacuum interrupter has no effect on 1 heating circuit breaker.

- optimize (reduce) the size and cost of winding due to the better stability of the AMF arc control,

- to avoid the addition of additional ferromagnetic materials that could lead to the deterioration of the arc control,

- Overcoming the creation of slots at the contact surface 22 may reduce the strength or dielectric performance or change the electrical characteristics by erosion of the contacts.

Other improvements are possible within the scope of the invention, namely to achieve a winding 8 with slots 81 parallel to each other and made helically angular length at least equal to 360 °. As described at least in part above, it is possible to make an electrical contact 2, 3 which integrates the winding according to the invention and furthermore:

a second winding 9 as described and claimed in the patent application FR 09 53852 filed on June 10, 2009 and entitled "CONTACT FOR MEDIUM-VOLTAGE VACUUM BULB WITH IMPROVED ARC BREAKER, VACUUM BULB AND CIRCUIT BREAKER, SUCH AS AN ALTERNATOR DISCONNECT CIRCUIT BREAKER THEREFOR,

- At least one pillar 7 as described and claimed in the patent application FR 09 53853 filed June 10, 2009 and entitled "CONTACT FOR LOW VOLTAGE MEDIUM VOLTAGE BULB REINFORCED STRUCTURE, VACUUM BULB AND CIRCUIT BREAKER, AS A CIRCUIT BREAKER DISCONNECTOR OF ASSOCIATED ALTERNATOR ",

with a slot width 81 of less than 1 mm as described and claimed in the patent application FR 09 53855 filed on June 10, 2009 and entitled "WINDING FOR CONTACT OF EMPTY VENTILATED MEDIUM VOLTAGE BULB WITH IMPROVED ENDURANCE, VACUUM BULB AND CIRCUIT BREAKER, AS AN ALTERNATOR DISCONNECT CIRCUIT BREAKER ASSOCIATED ".

Claims

1. Winding (8) based on a material of low electrical resistivity, such as copper, and of diameter typically greater than 90 mm, for generating a magnetic field in an electrical contact (2, 3) for a vacuum interrupter (1) medium voltage, consisting of a hollow cylinder (8) comprising slots (81) parallel to each other, devoid of material and made helically around its longitudinal axis and opening into both the hollow and the outside the cylinder, winding in which the angular length of each helix is at least equal to 360 °.

2. Winding according to claim 1, wherein the width of each slot is 0.5 mm to 1 mm for an outer diameter Oext of the hollow cylinder greater than 90 mm.

3. Winding according to one of the preceding claims, wherein each turn delimited individually by two consecutive helical slots has a section in section parallel to the longitudinal axis of the winding which is substantially rectangular and identical over the entire height of the winding. 'winding.

4. Winding according to any one of the preceding claims, wherein the number of helical slots parallel to each other is at least two.

5. Winding according to claim 4, wherein the number of helical slots parallel to each other is equal to 6.

6. A method of producing a winding based on a material of low electrical resistivity, such as copper, for generating a magnetic field in an electrical contact (2, 3) for a medium voltage vacuum bulb (1) , comprising the step of producing a hollow cylinder with helical slots about its longitudinal axis and opening into both the hollow and the outside of the cylinder, being devoid of material, a step according to which the angular length of each helix is at least 360 °.

7. A method of producing a winding according to claim 6, wherein the helical slots of angular length greater than or equal to 360 ° are made by electroerosion.

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

a mechanical connection part (20,

30) which extends along the longitudinal axis Y,

a contact body (21, 31) comprising: a first winding according to one of claims 1 to 6,

· A circular plate (22, 32) of the same diameter as the outside of the first hollow cylinder, said plate (22, 32) also being centered on the longitudinal axis Y and secured to the end of the first hollow cylinder opposite to that secured to the mechanical connection part.

9. Electrical contact (2, 3) according to claim 8, wherein the helices of the slots of the first winding are dextral type from the mechanical connection portion to the circular contact plate.

Electrical contact (2, 3) according to claim 8 or 9, comprising a second winding (9, 10) electrically connected in parallel with the first winding (8) and adapted to generate a magnetic field which is superimposed on the magnetic field generated. by the first winding (8).

11. The electrical contact (2, 3) according to claim 11, wherein the second winding is a winding according to one of claims 1 to 5, the second hollow cylinder (9) being centered on the longitudinal axis Y, arranged concentrically. the first cylinder (8), having one end secured to the mechanical connection portion and the other end secured to the circular plate (22, 32), the recesses (80, 90) of the cylinders being devoid of material.

12. Electrical contact (2, 3) according to claim 11, wherein the helices of the slots of the second winding are dextral type from the mechanical connection portion to the circular contact plate.

13. Electrical contact (2, 3) according to one of claims 8 to 12, comprising at least one column (7) separate from (s) 1 'winding (s) and arranged in the hollow of the first cylinder (8). , in a spacer between the mechanical connection part (20, 30) and the circular plate (22, 32) of the contact body so as to avoid the collapse of the latter during a closing maneuver and in the closed position of the vacuum bulb, the (the) column (s) having a high electrical resistivity such that when a given current flows in the contact, the amount of current flowing in the (the) column (s) is negligible by relative to that which circulates in the winding (s).

An electrical contact according to any one of claims 8 to 13, wherein the outer diameter of the first winding and the circular plate is between 90 and 150 mm.

Medium voltage vacuum bulb (1) comprising at least one electrical contact (2, 3) according to one of claims 8 to 14.

Vacuum bulb (1) according to claim 15, comprising a pair of electrical contacts with a fixed contact (2) according to any one of claims 8 to 14 and a movable contact (3) according to any one of the claims. 8 to 14.

17. Vacuum bulb (1) according to claim 15 or 16, wherein the slots (81) of the windings of greater than or equal to 360 ° open on the side of the separation space (5) between contacts (2, 3). where the arc is formed during the power failure.

18. A circuit breaker, such as an alternator disconnect circuit breaker, comprising at least one vacuum interrupter (1) according to any one of claims 15 to 17.

19. Use of a vacuum interrupter according to one of claims 15 to 17 in which it is crossed by a short-circuit current in the event of a fault and, where applicable, the rated load current.