FR2661546A1 - WALL CROSSING FOR AN ELECTRIC CABLE. - Google Patents

Abstract

The invention relates to a wall feed-through for an electric cable. According to the invention, the bushing comprises an insulating sleeve (2), extending along an axis (3) and carrying, at least on a portion of the axially median outer surface, a coating (10) capable of ensuring a guide of an electric field originating in the sleeve (2); a conductive core (11) extending axially inside the sleeve (2); fixing means (20) for fixing the sleeve (2) on a wall (40); and electrical connection means (20, 40) for electrically connecting the conductive coating (10) to a reference potential.

Description

The invention relates to a wall penetration for an electric cable

  It relates in particular to a transformer housing through or an apparatus

  such as a switchgear.

  Such a crossing must, in addition to providing insulation with respect to the wall which is often metallic, also provide a reference for guiding an electric field originating in the crossing The crossing, which comprises an insulating sleeve, may comprise for this purpose conductive elements embedded in the sleeve and connected to the earth, which constitute a screen Such a solution is however expensive because of the complexity of manufacture

of the sleeve.

  The first problem that the invention aims to solve is therefore to propose a crossing whose means for guiding the electric field can be

made in a simple way.

  The wall penetration according to the invention comprises, for this purpose, an insulating sleeve, extending along an axis and carrying, at least on an axially median outer surface portion, a coating capable of guiding an electric field. arising in the sleeve; a conductive core extending axially inside the sleeve; fastening means for fixing the sleeve to a wall; and electrical connection means for electrically connecting the conductive coating to a reference potential. Thus, according to the invention, the electric field guiding means comprise only an outer coating of the sleeve, which can be made in a simple manner, in particular by painting, vacuum projection, or

hot projection.

  Another problem that the invention aims to solve is to ensure electrical isolation between an end of the conductive core and the wall or said coating, when this end opens in the open air or in a fluid

insulation such as oil.

  For this purpose, the sleeve carries, at least one

  end, protuberances forming isolation fins.

  Another problem that the invention aims to solve is to fix the sleeve on the wall without having to provide fixing lugs on the sleeve and corresponding fixing means on the wall. For this purpose, the sleeve attachment means comprise a threading carried by the outer surface of the sleeve and arranged to cooperate

  with tapping carried by the wall.

  Advantageously, said electrical connection means comprise an electrical contact surface between said coating and a conductive portion of the wall. This single contact electrical connection avoids the need for conductive braid or bolt connections. In the case where the bushing must be fixed on a wall having no threaded hole, but standard fastening means such as a plurality of threaded rods, it is necessary to adapt the sleeve to these fastening means, if possible. without having to design a

new type of sleeve.

  This problem is solved according to the invention by the fact that the bushing comprises a conductive base arranged to support the sleeve in the region bearing the coating, and bear on the wall It is sufficient to design the base in a suitable form each time to the fixing means provided on the wall The base may for example comprise fixing lugs intended to be

  crossed by threaded rods.

  It will be noted that, advantageously, this base ensures both the support function of the sleeve and the

  electrical connection function of the coating.

  According to a preferred embodiment, the base comprises a peripheral crown portion intended to cooperate with the wall, and a central cylinder portion

  intended to cooperate with the sleeve.

  Advantageously, said tapping is carried by the

central cylinder portion.

  Advantageously, the bushing comprises an insulating flange covering a face of the conductive base intended to be remote from the wall, in which case it cooperates with a clabot itself mounted on a rod.

threaded integral with the wall.

  In some cases, the bushing receives a cable end connection device which is simply fitted onto the bushing. It is then necessary to couple this device to the bushing to ensure absolute fixing thereof. For this purpose the insulating flange carries attachment means for cooperating with fastening means arranged to secure a

  end of cable on the crossing.

  Because the flange is insulating, the cable end connection device is isolated from the wall, which facilitates the implementation of a test of electrical resistance of the cable sheath, known under the name

"Sheath test".

  It may be that the device for connecting the cable end, such as a T-shaped or L-shaped socket, hinders access to one of the collar attachment means. In this case, it is possible to modify the relative angular position of the connecting device

relative to the attachment means.

  For this purpose, the insulating flange is rotatably mounted crossing In these conditions, it is sufficient to modify the angular position of the flange for

solve the problem mentioned above.

  Other details and advantages of the invention

  will appear in the following description of a form

  preferred embodiment but not limiting, with reference to the accompanying drawings in which: Figure 1 is an elevational view in section of a bushing according to the invention, mounted on a transformer and cooperating with electrical cables; and FIG. 2 is an exploded perspective view of

the crossing of Figure 1.

  The bushing 1 shown in FIG. 1 comprises an electrically insulating core 2, consisting in particular of epoxy resin, which is in the general form of a hollow cylinder of circular section, having an axis 3. An outer surface of the core 2 carries, in an axially central region, threaded corrugations 4, and in an end region, other corrugations forming electrical isolation fins 5 The core 2 further comprises an annular rim 6 disposed at one end of the thread 4 furthest from the fins 5

  other regions of core 2 are smooth.

  Core 2 carries, all over its surface

  thread 4 and that of a portion between

  ci and fins 5, a conductive coating 10 reported by any suitable means, including painting, projection

under vacuum, or hot projection.

  Inside the core 2 is housed a conductive core 11 In this example, one end 12 of the core opens out of the core 2 and is threaded, while another end 13 is substantially flush with the adjacent end of the core 2. core and has an elastic member of electrical contact The conductive core 11 is made of metal,

especially copper or brass.

  The bushing also comprises an electrically conductive base 20, in particular a light metal alloy. The base 20 comprises a crown portion 21 and a cylinder portion 22. It is coaxial with the

core 2.

  The circular crown portion extends substantially in a plane and carries, on one side, an annular flange 23 extending axially in a radially median region. If necessary, a plurality of fastening tabs 24, only one of which is visible in FIG. 1, are distributed around the axis 3 and extend in the plane

  of the crown, radially outward.

  The crown portion 21 has a radially inner circular opening. The cylinder portion 22 has an inside diameter substantially equal to that of the opening 25 and is supported at one end on an edge of this opening on one side of the portion. forming crown 21 which is the farthest

from the rim 23.

  The cylinder portion 22 carries, on an inner face, a thread corresponding to the thread 4 carried by the core 2 and extending axially on the same length It has, at an end remote from the crown portion 21, an inner annular groove

26 housing an O-ring 27.

  The bushing 1 finally comprises a flange 30 made of an electrically insulating material, such as a thermoplastic or thermosetting material. The collar 30 is bell-shaped. It has a circular central opening 31 of dimensions corresponding to the diameter of the cylinder portion 22 of the cylinder. This base 31 is surrounded by an annular flange 32 extending

axially outward.

  The flange 30 has an outer diameter equal to that of the crown portion 21 of the base In its thickness, are formed several through holes 33 distributed peripherally and intended to accommodate fastening elements such as perforated lugs 34 or a threaded insert not shown for coupling a cable connecting piece such as a plug These fixing elements are slid into the holes 33 by a lower face of the flange 30 and cooperate with a

  shoulder of the holes forming axial stop.

  FIG. 1 partially shows a metal cover 40 of a LV low voltage / medium voltage electrical transformer tank having a circular opening 41 of diameter slightly greater than the diameter of the annular flange 23 of the base 20. The base rests, by its crown portion 21, on the cover 40, with the interposition of a flat gasket 42 Its flange 23 extends axially slightly inside the opening 41 of the cover 40 In the case where the transformer encloses gases under a particularly high pressure, the flat gasket 42 is replaced by an O-ring disposed in an annular groove of

the base 20.

  The flange 30 caps the cylinder portion 22 of the base 20 and bears on its crown portion 21 The core 2 of the bushing 1 is screwed into the base 20 to abut on the end of the portion forming a cylinder 22 of the base 20 and compressing the O-ring 27 An electrical contact exists between the conductive coating 10 of the core 2 and the base 20, over the entire surface of the thread 4 of the core. The core 2 is immobilized in rotation relative to at the base 20, for example by means of a bead of localized glue This glue bead can be designed to complete the tightness achieved by the O-ring 27 or even ensure by itself

seal.

  The annular rim 6 of the core 2 faces that 32 of the collar but is moved away from a slight axial play, so that the collar is free in rotation

around axis 3.

  According to a variant of attachment of the core 2 on the base 20, the core has no thread 4 but is fitly fitted in the crown portion 22 of the base 20 and is immobilized axially by an annular pin. The lid 40 carries a plurality of threaded rods 43 distributed around its circular opening 41. The fixing of the bushing 1 on the lid 40 can be effected notably in one of the two following ways. According to the first way (on the left, FIG. On each threaded rod 43, is threaded a metal clapper 44 supported by one end on the cover 40 and another end on the flange 30 Each clasp 44 is held by a nut 45 The electrical connection between the base 20 and the cover 40 is provided by a sheet metal contact 39 pinched at one end between the base 20 and the flange 30, and at another end between the flange 30 and one of the cleats 44. A second way to fix the bushing 1 on the lid 40 is to provide the base 20 with tabs 24 to be traversed by the threaded rods 43 A nut 38 is then mounted on each threaded rod and bears on the base 20 C this fastening ensures at the same time

  the electrical connection between the base 20 and the cover 40.

  At the end 12 of the conductive core 11 located in the transformer is fixed one end of a cable 46 via a connecting sleeve 47 fixed by

a nut 48.

  The transformer is filled with oil to a level 49 such that the fins 5 of the core 2 are immersed as well as one end of the adjacent conductive coating 10

of these fins.

  In this example, a male plug 50 in the shape of a square, in particular L-shaped, externally cap the core 2 It comprises in particular an inner conductive layer 51 covering one end of the core 2 over a short axial length, an insulating layer 52 the covering the rim 6, and an outer conductive layer 53 covering the flange 6. The outer conductive layer 53 has an end disposed substantially opposite one end of the conductive coating 10 so as to ensure continuous guidance of a field electric taking

  birth in the socket 50 and the nucleus 2.

  A stirrup 54 comprises several tie rods 55 hooked into the perforated lugs 34 of the collar: as necessary, the collar 30 is angularly displaced around the axis 3 to arrange the legs

  perforated 34 in front of the tie rods 55.

  The yoke 54 also supports centrally

  on the socket 50 via a threaded hook 56.

  When current flows through the bushing 1, electric field lines extend along the insulating layer 52 of the plug 50 and along the core 2, thanks to a screen constituted by the outer conductive layer 53 of the plug 50. and the conductive coating 10 of the core 2 In the transformer, the field lines pass through the core 2 and

flourish in the oil.

Claims (7)

RESUME ICAT IONS   1. Wall penetration for an electric cable, characterized in that it comprises: an insulating sleeve (2) extending along an axis (3) and carrying, at least on an axially median outer surface portion, a coating (10) adapted to guiding an electric field originating in the sleeve (2); a conductive core (11) extending axially inside the sleeve (2); fastening means (20) for securing the sleeve (2) to a wall (40); and electrical connection means (20, 40) for electrically connecting the conductive coating (10) to a reference potential.   2. Crossing according to claim 1, wherein the sleeve (2) carries, at least at one end,   protuberances (5) forming isolation fins.   3. Crossing according to claim 1 or claim 2, wherein said means for fixing the sleeve (2) comprises a thread (4) carried by the outer surface of the sleeve (2) and arranged to cooperate with a   tapping carried by the wall (40).   4. Crossing according to any of the   preceding claims, wherein said means for   electrical connection comprises an electrical contact surface between said coating (10) and a portion conductor of the wall (40).   5. Crossing according to any one of   preceding claims, which comprises a base   conductor (20) arranged to support the sleeve (2) in the region carrying the coating (10), and to bear on the wall (40).   6. Crossing according to claim 5, wherein the base (20) comprises a peripheral ring portion (21) intended to cooperate with the wall (40), and a central cylinder portion (22) for cooperating with the sleeve (2).   1 7 Crossing according to claim 3 and claim 6 taken together, wherein said tapping is carried by the central cylinder portion (22).   8. Crossing according to any of the   preceding claims, which includes a flange   insulation (30) covering a face of the conductive base   (20) intended to be remote from the wall (40).   9 Crossing according to claim 8, wherein the insulating flange (30) carries fastening means (34,35) for cooperating with fastening means (54,55) arranged to attach a cable end on the crossing.   Crossing according to claim 9, wherein the insulating flange (30) is rotatably mounted on the crossing.