FR2788369A1 - CURRENT CROSSING FOR MEDIUM VOLTAGE ELECTRIC CELL WITH HERMETIC METAL ENCLOSURE - Google Patents

Abstract

The invention concerns a plug-in feed-through for connecting an element such as a single-pole cable to a medium voltage electric cell with a sealed metal casing usually filled with gas. The feed-through comprises a body made of insulating material (13) run through by a solid connecting conductor (12) projecting from the body by its ends, and an annular flange (15) whereof the peripheral edge (15A) projects from the body to enable a welding for blocking the feed-through in a casing aperture. The annular flange comprises an internal edge (15B) embedded in the feed-through body, constituting a support for a semiconductor elastomer material layer (17) forming a shield controlling for the electric field. Said part is coated with an insulating elastomer material (16) separating it from the shielding semiconductor elastomer material layer (17), which is itself embedded in the elastomer material constituting the insulating body (13).

Description

The invention relates to a plug-in type current bushing,

  intended to ensure the connection of an external conductive element, such as a medium-voltage unipolar cable, to a cell comprising a hermetic metallic envelope, usually filled with insulating gas, as is conventional with shielded cells. As is known and as shown in FIG. 1, such bushings include a body 1 made of insulating material impermeable to gas which is longitudinally traversed by a solid axial conductive element 2. The body of known plug-in bushings is made of epoxy resin or made of polyurethane, it traps a metal fixing flange 3 intended to come to be assembled and fixed by welding at the level of an opening formed in an appropriate manner in

  a wall 4 of a metallic cell envelope.

  In this type of assembly and as shown in FIG. 1, provision is made to place a spacer 6 made of elastomeric material between the flange and the insulating resin to ensure the tightness of the assembly. The necessary adhesion between the resin and the elastomer is difficult to obtain due to the difference in nature existing between these materials and due to the shrinkage of material occurring during the molding of the resin. Indeed, this withdrawal, which is done in the direction of the axis of the crossing, leads to a separation which occurs between the resin body and the elastomer interlayer. This separation results in the appearance of partial electric discharges when the part is electrically energized. We therefore use special glues or primers to promote adhesion between resin and

  elastomer, which makes crossing operations difficult.

  As is also known, an electromagnetic screen 7 is provided embedded in the insulating material of the body of a bushing. This screen, of cylindrical appearance, is for example constituted by a piece of metallized plastic and it is electrically connected to an external terminal 8 allowing its connection to a capacitive system for indicating the presence of voltage. The positioning of such a screen, in a resin injection mold intended for the manufacture of a bushing body, is difficult to achieve and the problems of detachment and withdrawal

  mentioned above arise again at this level.

  The invention therefore proposes a current crossing, of the plug-in type, for the connection of an external conductive element, usually of the unipolar cable type, to an electric cell, medium voltage, with a hermetic metal envelope, said crossing comprising a body of revolution. of insulating material, axially traversed by a solid conductive connecting element projecting out of the body at its ends, as well as an annular and metallic flange for transverse fixing including a peripheral edge protruding out of the body to allow immobilization of the crossing in a opening, made for this purpose in a wall of the envelope, which it closes hermetically, after welding the edge to the wall at the periphery of the opening, said annular fixing flange having an internal edge embedded in the body crossing and shaped so as to constitute a support for a layer of semi-elastomeric material conductor forming an electric field control screen around the solid conductive element for connection to the level provided for the

  fixing of the bushing in said opening.

  According to a characteristic of the invention, the fixing flange part, which is contained in the insulating body and which comprises at least the internal edge, is coated with an insulating layer of elastomeric material which separates it from the layer of semi-elastomeric material. - screen conductor in elastomeric material

constituting the insulating body.

  According to a characteristic of the invention, a connection terminal is provided, a part of which is embedded in the screen layer to which it is therefore electrically connected and of which another part projects into a receiving conduit, for wire connection end piece. , which opens out of the insulating body near the peripheral edge of the fixing flange, to allow a

  insulated and sealed connection of wire via a connection member.

  The invention, its characteristics and its advantages are specified in the description

  which follows in connection with FIG. 3 of the list of figures mentioned below o: - FIG. 1 shows an example of a first known current crossing; - Figures 2 and 3 respectively show a sectional view along II-II and the corresponding front view of a current crossing according to the invention; - Figure 4 shows a cutaway relating to a detail of embodiment of a terminal

  associated with a flange according to the invention.

  The current crossing 10, according to the invention, which is illustrated in Figures 2, 3 is intended to come to be mounted at an opening provided for it in a metal wall 11 of a metal casing of an electrical cell medium voltage. It is intended to allow the connection of an external conductive element, usually a medium-voltage unipolar cable, to a conductive element of this cell, via a solid axial conductive element 12 of the crossing. The external conductive element and the conductive element located in the cell are not shown here, since they are only related

  indirect with the object of the invention.

  The metal wall 11 is assumed to be part of a medium voltage electrical cell envelope. This envelope is assumed to be hermetic in order to be able to be placed under vacuum or more commonly filled with an electrically insulating gas. The bushing according to the invention is therefore designed to hermetically seal the wall opening 11, provided for it and where it is mounted. To this end, a bushing 10, according to the invention, comprises a body 13 made of insulating material and impermeable to gases, preferably of revolution and at the center of which the solid conducting element 12 extends longitudinally so as to project through each of its two ends. In the embodiment illustrated in Figure 3, there is provided a thread 14, blind and axial, at each end of the solid conductive element. These threads allow the connection of a cell conductive element located in the enclosure and of the medium voltage cable external to the solid conductive element 12, either directly or via a

  suitable arrangement, as known to those skilled in the art.

  The insulating body 13 here forms a solid of revolution whose axis corresponds to that of the solid conductive element 12. It can be made of resin. It is preferably made of an elastomeric material of sufficient Shore hardness, by

example greater than 70.

  In the example presented, this solid of revolution is composed of a frustoconical part 13A extending an acorn 13B between which is positioned an external fixing flange 15. The acorn 13B is intended to enter the envelope

  the outside of which the frustoconical part 13A must remain.

  The fixing flange 15 is here assumed to be produced in the form of a metal ring, preferably of steel, it is for example obtained by stamping. In the embodiment presented, it comprises two concentric borders 15A, 15B linked together by an annular element and both projecting from the same side of this element with a height here assumed to be greater for the internal border than for the external border, as shown in the

section presented in figure 2.

  The internal border 15B of the ring formed by the fixing flange 15 is housed in the insulating body with a part of the annular flange element which connects it to the external border 15A. It has the same longitudinal axis as the solid conductive element 12 and forms an electrode for an electric field control screen between this element and the wall 11 at the opening of this wall where the outer edge is positioned and welded. This electrode is in the form of a tubular element centered on the axis of the solid conductive connecting element 12 which it surrounds at the level provided for fixing the bushing in the opening provided for it in the wall 11 It is assumed here that this wall is connected to the ground as conventional in this field, consequently the fixing flange is also at the ground potential insofar as it is welded on the wall, as indicated below and it is of course the same for its

internal border.

  The outer edge of the ring formed by the fixing flange 15 is said to be fixing and welding. It protrudes outside the insulating body 13 which it surrounds in order to ensure the positioning of the crossing which comprises it in an opening provided for it in a wall 1 1 of the envelope. The height of this border is chosen to allow welding of the ring in position in the opening provided for it in the wall 11 around the entire periphery of this

  opening. This is then hermetically sealed by the crossing.

  The use of a body made of elastomeric material makes it possible without difficulty to bond the insulating material to the metal constituting the flange. It also makes it possible to carry out a flange welding on the wall in good conditions and without risk for the crossing because of the temperature resistance which is likely

  to be obtained with this type of material.

  According to the invention and for reasons of electric field control, the part of the fixing flange 15 which is housed in the insulating body 13 is associated with a layer of semiconductor elastomer 17 forming an electric field control screen. This layer 17 surrounds the internal border 15A from which it is separated by an insulating elastomer layer 16. The insulating elastomer layer 16 here covers the internal border and the part of the annular element of the flange which is housed in the body. insulating. The elastomer constituting the insulating body 13 envelops the layer of screen semiconductor elastomer 17 and the part of annular flange element which is here housed in the body, without being covered by the

  layer of semiconductor elastomer, as shown in Figure 4.

  For this purpose, the crossing is for example carried out by a series of three successive overmoldings. A first overmolding allows a thin layer of insulating elastomer to be coated on the part of the metal fixing flange 15 which is intended to be embedded in the insulating body 13 of the bushing. An overmolding of a screen of semiconductor elastomer 17 is then carried out on the part of the fixing flange which is coated with insulating elastomer and on a part of a terminal 18 which is electrically in contact with the screen where it is partially drowned. This makes it possible to isolate the screen and the terminal from the fixing flange and to prevent this screen and this terminal from being earthed by the flange, once the latter is welded to a wall of metal casing. connected to the earth. It thus becomes possible to connect a capacitive divider making it possible to supply a voltage measuring device, not shown, this divider having a primary consisting of the two concentric electrodes which constitute the conductive element 12 and the layer of semiconductor elastomer screen 17. This second overmolding is then followed by overmolding during which the insulating body 13 is made of a hard, insulating elastomer material which surrounds the solid conductive element 12 with a volume of material whose axis of revolution corresponds to the axis of this massive conducting element. This insulating body 13 then includes the flange part 15 covered by two layers of elastomer, one insulating and the other semiconductor, as well as the terminal part 18 covered by

the semiconductor layer.

  The realization of the field control screen and capacitive tap around the fixing flange solves the problems of screen positioning, the screen layer of semiconductor material being obtained by overmolding on this flange

  before overmolding of the body, in the proposed embodiment.

  It is possible to produce the insulating body 13 in resin, as is known in this field, but it is considered here that the use of materials having an elastic nature, as can be the elastomers, offers the advantage of eliminating the problems of differential thermal expansion between the materials used. A male connection part of the terminal 18 is here represented in the form of a protruding pin in the center of a conduit 19 formed in the material of the insulating body 13 outside of which it opens, here near the edge device of the fixing flange. This duct is designed to receive a complementary female connection member 20 which is, for example, mounted at the end of an electric wire 21, sheathed in insulation, and which is surrounded by an insulating end piece 22, preferably made of elastomeric material, the shape of which and the dimensions are complementary to that of the duct 19, to ensure insulation and good

  tightness of the connection made for the wire.

Claims (2)

  1 / Current bushing, plug-in type, for connection of an external conductive element, usually of the unipolar cable type, to an electric cell, medium voltage, with a hermetic metal envelope, said bushing comprising a body of revolution made of insulating material ( 13), axially traversed by a solid conductive connecting element (12) projecting from the body at its ends, as well as an annular and metallic transverse fixing flange (15) including a peripheral edge (15A) protruding outside the body to allow immobilization of the bushing in an opening, formed for this purpose in a wall of the envelope, which it closes hermetically, after welding the edge to the wall at the periphery of the opening, said annular fixing flange having an internal border (15B) embedded in the bushing body and shaped so as to constitute a support for a layer of semi-elastomeric material -conductor (17) forming an electric field control screen around the solid conductive element for connection at the level provided for fixing the bushing in said opening, characterized in that the part of the fixing flange, which is contained in the insulating body and which comprises at least the internal border (15B) is coated with an insulating layer of material   elastomer (16) which separates it from the layer of semi-elastomeric material   screen conductor (17) in the elastomeric material constituting the insulating body (13). 2 / Current crossing, according to claim 1, in which is provided a connection terminal (18) of which a part is embedded in the screen layer to which it is therefore electrically connected and of which another part projects into a receiving conduit (19), for wire connection end piece (22), which opens out of the insulating body near the peripheral edge of the fixing flange, to allow an insulated and sealed connection of wire through a connection member (22).