Termination devices for shielded wire with mineral insulation

Abstract

A terminal device (1) for mineral insulated wires, comprising a metal sleeve (3) one end of which is intended to be fixed to the end of the insulated wire (2), and a ceramic insulating element (4), the ceramic insulating element consisting of a cylinder (4) housed in the sleeve (3) with one end protruding from the sleeve (3) and an end opposite the one end having a hole (41) housed in the sleeve (3), the end of the cylinder (4) housed in the sleeve (3) having a tapered shape.

Description

[Technical field]

[0001] The present invention relates to termination equipment for shielded mineral insulated wire that provides good sealing and very good dielectric strength at high temperatures up to several thousand volts, specifically up to 1000°C. [Background technology]

[0002] Shielded mineral insulated wire is a wire made of a metallic center conductor and a cylindrical hollow metallic cladding, between which is inserted a powdered refractory insulation such as a mineral, e.g., magnesia, alumina, or silica, and an outer cladding made of stainless steel, copper, or a Ni-Cr alloy, such as the Ni-Cr alloy known by the trade name Inconel 600.

[0003] Such covered wires are fire resistant and are used in places frequented by the public, such as shopping centers, airports, reception halls, etc., or in industrial environments involving hazardous areas, such as nuclear power plants, etc. Such covered wires are particularly used in many areas of factories involving the use of sensors, heating elements, or electrical signal transmission covered wires that must be resistant to environments that present increasingly demanding conditions (temperature, high pressure, humidity, etc.).

[0004] As a result, such covered wires are useful for connecting devices that are spaced apart from one another, and therefore it is necessary to provide means for connecting these covered wires to the devices, or indeed to each other.

[0005] Wire termination devices, and more generally connectors, are a very important part of these components since they must ensure the continuity of the conductors and prevent the migration of moisture into the insulation while preserving the dielectric strength of the wire.

[0006] In particular, this is often a weakness as it can sometimes be difficult to ensure all of these properties simultaneously in a high temperature environment.

[0007] Thus, the shielded wire may be an electric heating element or signal transmission coated wire with a mineral insulation such as magnesia, alumina, or silica, and with an outer coating made from stainless steel, copper, or a Ni-Cr alloy.

[0008] When a shielded mineral insulated wire is stripped to mate with an end device such as a connector, so that the outer jacket and mineral insulation are removed to reveal the metallic conductor, the inherent dielectric barrier of the wire at the connector / wire interface is greatly weakened. Specifically, after this operation, the in principle dense mineral insulation leaves room for air, and the dielectric strength then depends only on the distance between the conductor and the jacket, and on the environmental parameters such as temperature, pressure, etc. at this interface.

[0009] In order to maintain the dielectric strength, various types of terminal devices have been proposed. In the French patent 1150390(A) an accessory for insulating electric covered wires is proposed, consisting of two ceramic plugs, each with a conical end and connected to each other by a glass seal. These two plugs are housed in a metal tube and have a central through-hole in which the conductor of the covered wire can be accommodated. The electric covered wire consists of a central conductor housed in an outer sheath, and a hygroscopic mineral insulation is placed between the outer sheath and the central conductor. The mineral insulation at the end of the covered wire has a cone-shaped annular cavity that receives the cone-shaped ends of the ceramic plugs that constitute the insulation. The cone-shaped ends of the ceramic plugs are composed of two ceramic plugs connected to glass seals, and these two plugs are housed in a metal sheath. The conical ends of the insulation are received in the conical cavities at the end of the covered wire, while the metal sheath of the insulation is welded to the outer sheath of the covered wire. These assembly conditions ensure that the hygroscopic insulation is protected against moisture.

[0010] French patent 2832558(A) describes a cylindrical coupling sleeve with a first filling port that can be mounted on the outer circumference of the metallic coating of a first mineral insulated wire and a second end mounted on the outer circumference of a second insulated wire or of a complementary device, the sleeve thus mounted being welded directly to the outer circumference of the connected elements. The sleeve then forms a cavity in which an electric conductor is connected. The sleeve has an opening that allows said cavity to be filled with insulating material. However, it is difficult to guarantee the dielectric strength of such a connector device, since the degree of compression of the introduced mineral insulating material cannot be controlled in practice.

[0011] It has also been proposed to terminate mineral insulated wires using epoxy or acrylic resins. These resins, even if they provide good voltage resistance and good sealing, cannot withstand temperatures above 230°C. This type of device is described in detail in U.S. Pat. No. 6,437,246 (B), which discloses a metal sleeve crimped onto the outer coating of the coated wire, filled with epoxy resin inside, which surrounds the free end of the conductor or has a connection to another conductor. Similarly, terminations can be made using a ceramic adhesive or even fusible glass. The fusible glass solution has the disadvantages of low resistance to high temperatures and frequent cracking which reduces the coated wire's resistance to moisture.

[0012] US 9583933(B) proposes a termination device for mineral insulated wires, with a conductive element forming a pin and with a cavity for receiving the electric conductor corresponding to the end of the stripped wire, which pin engages around the conductor up to the wire itself. Around this pin, a sealing ring is also fitted between the metal pin and the mineral insulation contained in the coating at the wire. An insulating sleeve fits around the metal pin. In order to prevent moisture from damaging the mineral insulation, the end is heated during assembly. However, with assembly in mind, the sealing ring is inserted between the mineral insulation and the electric conductor after removing a portion of the mineral insulation around the conductor, or the end of the termination device is conical so as to be pressed into the mineral insulation. Such devices also require an O-ring to ensure tightness, which limits their use at high temperatures. The seals can therefore deteriorate over time due to aging of the material, moisture can get in, etc.

[0013] Furthermore, terminal devices such as glass-to-metal sealed double-sided connectors, typically resistant to 500°C, or ceramic metal sealed double-sided connectors resistant up to 1000°C, have also been proposed. However, this type of connector requires exposure of the ceramic insulation and conductor of the coated wire during stripping, leaving the possibility of electrical arcing between the conductor and the shield during use. This risk is exacerbated when the coated wire operates at high voltages (e.g., due to a shielded heating element, or a signal-carrying coated wire connected to a special detector). As a result, high voltages cannot be applied for long periods of time.

[0014] As a result, in French patent FR 2 988 514 (B) a termination element is described in which the end of a mineral insulated wire carries a termination sleeve consisting of a sleeve tube equipped at one end with a ceramic insulating element having two through holes in which the termination tube is received, and at the other end mounted on the end of the stripped wire, the mineral insulating material being inserted between the end of the wire and the ceramic element. The bare conductor then passes through the insulating material and then the ceramic element passes through the termination tube. To ensure the dielectric strength, the empty space of the termination sleeve is filled with a mineral insulation that is placed between the end of the wire and the ceramic insulating element. Again, the degree of compression of the mineral insulation is difficult to control. [Prior art documents] [Patent documents]

[0015] [Patent Document 1] French Patent Invention No. 1150390(A) [Patent Document 2] French Patent Invention No. 2832558(A) [Patent Document 3] US Patent No. 6437246(B) [Patent Document 4] US Patent No. 9583933(B) [Patent Document 5] French Patent Invention No. 2988514(B) Summary of the Invention [Problem to be solved by the invention]

[0016] In order to overcome the drawbacks of the prior art devices, the present invention proposes a terminal device that can be used under harsh environmental conditions, e.g. at high temperatures up to 1000° C., while being simple in design and easy to implement on the shielded mineral insulated wire, and guaranteeing a dielectric strength (up to several thousand volts). [Means for solving the problem]

[0017] To this end, the present invention relates to a terminal device for mineral insulated wires, meaning for example a device forming an end of a wire or a device forming a connector with another wire or device, which makes it possible to overcome the drawbacks of existing devices.

[0018] In particular, the present invention relates to a terminal device for a mineral insulated cable, comprising a metal sleeve, one end of which is intended to be fixed to the end of the insulated cable, and a ceramic insulating element, characterized in that the ceramic insulating element consists of a cylinder housed in the sleeve, having one end protruding from the sleeve and an end opposite the one end having a hole, the end of the cylinder housed in the sleeve having a tapered shape.

[0019] Advantageously, such a termination device may then be mounted on the end of a stripped mineral insulated wire such that the stripped conductor of the wire may engage in the sleeve and then in the bore of the ceramic insulating element, the sleeve being positioned over the wire so as to be fixed onto the wire, the tapered shape of the insulating element allowing the cylindrical insulating element to move gradually forward towards the mineral insulation, so that the ceramic cylinder can apply a compressive stress to the surface of the mineral insulation. In this way, since the compressibility of the insulation is locally lost due to stripping of the insulation, the compressive stress applied to this insulation by the tapered tip of the ceramic insulating element restores this compressibility, so that the wire includes a uniform dielectric barrier without weak spots.

[0020] As a result, the leakage path is advantageously longer since the conductor and the metal coating of the coated wire are no longer facing each other. In order for an electric arc to occur, the electric arc must travel a much longer leakage path outside the terminal equipment. This means a much higher breakdown voltage.

[0021] Preferably, the bushing is secured to the ceramic insulating element by brazing.

[0022] According to a preferred embodiment of the invention, the tapered end of the ceramic cylinder is conical.

[0023] According to a first embodiment, the ceramic insulating element has a hole, the end of which protruding from the sleeve can be blocked, so that the termination device constitutes a device for terminating a mineral insulated wire.

[0024] As a result, advantageously, the stripped conductor engages within the bushing so as to engage within the bore, and the bushing engages over the outer circumference of the covered wire so as to be fixed onto the covered wire, while the tapered end of the cylinder surrounding the conductor presses against the mineral insulation surrounding the conductor to compress the mineral insulation. When the stripped conductor end is received within the bore, the bore is sealed and the termination device forms the terminal end of the covered wire.

[0025] According to a second embodiment, the ceramic insulating element has a through hole, at the end of which a metal tube is mounted on the end of the insulating element protruding from the bushing and fixed on the ceramic insulating element, for example by brazing, so that the end device constitutes a connector device.

[0026] Advantageously, this terminal device may then be fixed to the end of a previously stripped mineral-coated wire, so that the stripped conductor engages in the through hole of the cylinder and engages in the bushing so as to protrude from the terminal device through the tube, and the bushing engages on the outer periphery of the coated wire so as to be fixed onto the coated wire, while the tapered end of the cylinder surrounding the conductor presses against the surface of the mineral insulation surrounding the conductor to compress the mineral insulation.

[0027] According to an alternative embodiment, the end device may further comprise a sleeve in which the ceramic insulating element and the metal tube are mounted, the sleeve being mounted within the bushing.

[0028] The end of the bushing which is intended to be mounted on the outer circumference of the covered wire may be fixed to the outer covering of the covered wire by crimping.

[0029] According to a preferred embodiment, the end of the bushing has fastening means intended to interact with complementary fastening means provided on the outer periphery of the end of the covered wire, the interaction between the bushing fastening means and the covered wire fastening means preferably making it possible to generate a compressive force exerted on the mineral insulation by the tapered tip of the cylinder.

[0030] Preferably, the complementary fixing means consist of an internal thread formed on the inner wall of the bushing and a threaded ring provided on the outer coating of the insulated wire, screwing the bushing onto said ring advantageously making it possible to generate a compressive force of the cylindrical tip against the mineral insulation.

[0031] As a result, after assembly, the mineral insulation of the covered wire and the ceramic insulation element remain in compression, thereby providing dielectric strength to the covered wire even under high temperature conditions.

[0032] Advantageously, the bushing / sleeve assembly may accommodate several ceramic insulating elements and associated metal tubes, all of which may be accommodated within the bushing / sleeve assembly, each with holes adapted to different conductor diameters, which generally translate into different coated wire diameters, in which case the threaded ring interacting with the bushing is adapted to the diameter of the coated wire.

[0033] The end device according to the invention therefore makes it possible to obtain coated wires with a completely sealed device, using only metals and ceramics, whether it serves as a termination or a connector, without any organic materials or any seals, in particular sealed by high-temperature brazing.

[0034] In addition, the insulation is compressed in a strong manner on the cone, which ensures a stable interface between the insulated wire and the insulation, which is necessary for high voltage resistance.

[0035] The main concerns of the device according to the invention centre around "harsh environment" use and safety (eg nuclear power plants).

[0036] As a result, the device can be used at operating temperatures of 800° C. or even 1000° C. with maximum operating voltages of up to 6000 VAC (with 6 mm diameter coated wire) and is resistant to rapid thermal cycling.

[0037] The device also does not contain any organic compounds and is therefore helium-free (leak rate <10 -8 atm·cm 3 / sec), pressure resistance (>250 bar) and very good stability over time.

[0038] The present invention also relates to a shielded covered wire with a conductor, a metal coating, and a mineral insulation made of a mineral insulating material inserted between the two, the shielded covered wire having at one end a terminal device comprising a metal sleeve fixed to the outer periphery of the end of the covered wire, and a ceramic insulating element, the ceramic insulating element being composed of a cylinder received in the sleeve via an end having a hole through which the conductor of the covered wire stripped of its coating is inserted, the end of the cylinder received in the sleeve further having a tapered shape in compression against the mineral insulation surrounding the conductor.

[0039] The invention will now be explained in more detail with reference to the drawings, which show namely: [Brief description of the drawings]

[0040] [Figure 1] 1 shows a longitudinal section of a first embodiment of a terminal device according to the invention; [Diagram 2] FIG. 2 is a longitudinal cross-sectional view of a mineral insulated wire equipped with a terminal device according to FIG. 1. [Diagram 3] 1 is a perspective view of a terminal device according to the present invention as mounted on a covered wire; [Figure 4] FIG. 2 is a side perspective view of the covered wire according to FIG. [Diagram 5] FIG. 2 is a perspective view of a second embodiment of an end device according to the present invention; [Figure 6] FIG. 2 is a longitudinal cross-sectional view of a third embodiment of a terminal device according to the invention. [Figure 7] FIG. 11 is a longitudinal cross-sectional view of a fourth embodiment of a terminal device according to the invention. [Figure 8] FIG. 11 is a longitudinal cross-sectional view of a fifth embodiment of a terminal device according to the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0041] The terminal device 1 according to the invention is intended to be fitted onto a coated wire 2 with mineral insulation.

[0042] Such a covered wire 2 consists of a metallic central conductor 21 and a metallic outer coating 22 surrounding said conductor 21, between which a mineral insulating material 23 is inserted. To complete such a covered wire 2, a terminal device 1 according to the invention is fitted to the end of the covered wire 2. To fit the terminal device, the covered wire 2 is stripped of its coating, exposing the central conductor 21 over a certain length.

[0043] The device 1 comprises a ceramic insulating element consisting of a metal bushing 3 and a cylinder 4 housed within said bushing 3. The bushing 3 or the base (or fitting) is brazed to the ceramic insulating element 4. This type of termination can be called a monoblock.

[0044] The sleeve 3 has an end for fixing to the end of the covered wire 2, in particular by positioning itself around the outer jacket 22. To this end, the sleeve 3 is provided with means for fixing to the covered wire 2.

[0045] According to a preferred embodiment, these fastening means consist of an internal thread, formed on the inner wall of the fixed end of the bushing 3, intended to interact with an external thread, formed on the outer wall of a ring 5 fixed to the end of the outer jacket 22. This ring 5 is fixed to the jacket 22, in particular by brazing.

[0046] Preferably, a shoulder 31 is provided in the internal bore of the bushing 3 so that by screwing the bushing 3 onto the ring 5, an end of the ring 5 and / or an end of the covering 22 can come to abut against said shoulder 31. This defines a fixing part 32 of the bushing 3 extending between the end of the bushing 3 and the shoulder 31 and having, for example, an internal thread, and a receiving part 33 past the shoulder 31 to the other end of the bushing 3 in which the ceramic cylinder 4 is received.

[0047] The ceramic cylinder 4 of the device of the present invention preferably has a central through hole 41. This hole 41 is shaped to receive the central conductor 21 of the stripped coated wire 2.

[0048] Mounted at one end of the bore 41, and therefore at one end of the cylinder 4, is a metal tube 6 which may also engage the stripped conductor wire 21, which extends partially into the bore 41 and partially protrudes from the cylinder. This tube 6 is attached to the ceramic insulating element 4 by brazing. The bore 41 may also be sealed once the conductor wire is engaged, thus forming a coated wire with a terminating end formed by the device.

[0049] As can be seen in FIG. 5, the metal tube 6 may take the form of a cap 60 secured to the end of the cylinder 4 .

[0050] The cylinder 4 has, in its receiving portion, a circular cross section whose diameter is equal to the inner diameter of the bushing 3. The end 42 of the cylinder 4 housed in the bushing 3 is further tapered and is preferably conical.

[0051] The barrel 4 has a length that enables it to fit within the bushing 3 such that the conical tip 42 extends beyond the shoulder 31 but is positioned away from the fixed end of the bushing 3 .

[0052] As a result, during assembly of the terminal device 1, the metal conductor 21 at the end of the stripped coated wire 2 engages in the through hole 41, while the device 1 engages on the metal conductor 21 at the end of the stripped coated wire 2 so that the bushing 3 is screwed onto the ring 5 held by the outer coating 22.

[0053] During screwing, the conical tip 42 of the cylinder 4 comes into contact with the mineral insulation 23 and compresses the surface of this insulation 23 .

[0054] As a result, the leakage path is longer since the conductor 21 and the outer jacket 22 no longer face each other and the conical tip 42 presses the mineral insulation 23 away from the end 22a of the jacket 22. Thus, for an electric arc to occur, the electric arc must travel a longer leakage path than if it were located outside the terminal device. The breakdown voltage is therefore higher.

[0055] The compressive force that the conical tip 42 exerts on the mineral insulation 23 occurs when the bushing 3 is screwed onto the ring 5, and this compression is managed by controlling the tightening torque.

[0056] Furthermore, a preform may be made on the mineral insulation 23 using special tools, which optimizes the interface with the ceramic cylinder 4. As a result, by making a preform in the friable, hygroscopic insulation of the covered wire, contact is maximized and stress on the tip of the conical ceramic is limited.

[0057] To seal the end device 1 onto the covered wire 2, the bushing 3 is brazed to the ring 5. After assembly, the mineral insulation 23 and the ceramic cylinder 4 remain in compression, thereby providing a new dielectric barrier for the covered wire 2.

[0058] A metal conductor 21 protrudes from the protruding end of the metal tube 6 and is brazed or soldered therebetween.

[0059] Preferably, bushing 3 and tube 6 are made from an iron / nickel alloy such as FN42, although any other type of alloy or pure metal that has a coefficient of expansion close to that of alumina is suitable.

[0060] The ring 5 is preferably made from stainless steel, but may also be made from copper or a nickel-chromium alloy.

[0061] Advantageously, the end device according to the present invention is a connector device and may be used under temperature conditions up to 700° C., the braze between the ceramic cylinder and the sleeve being made of Ag / Cu eutectic alloy. For very high temperature use conditions up to 1000° C., the braze is preferably 100% copper.

[0062] The braze joining the sleeve 3 to the outer coating of the coated wire 2 may be an Ag / Cu / Zn / Sn alloy such as AG102, which is resistant to temperatures up to 600°C, or a B / C / Cr / Fe / Si / Ni alloy, such as the alloy known under the trade name "Nicrobraz LM", which is resistant to temperatures up to 1000°C.

[0063] The end device 1 may further comprise a sleeve 7 in which the ceramic insulating element 4 and the metal tube 6 are mounted, the sleeve 7 being mounted within the bushing 3. The sleeve 7 is preferably made from alumina.

[0064] Advantageously, the bushing 3 / sleeve 7 assembly may then accommodate different ceramic insulating elements and associated metal tubes 6 for different conductor diameters. As can be seen in Figures 6, 7 and 8, the covered wires 2a, 2b, 2c have different diameters, in particular conductors of different diameters. As a result, with the same bushing 3 / sleeve 7 assembly it is possible to fit a ceramic insulating cylinder 4a and tube 6a adapted to the diameter of the conductor 23a, a cylinder 4b and tube 6b adapted to the covered wire 23b, in addition to a cylinder 4c and tube 6c adapted to the conductor 23c. However, the tube 6 may remain the same, since in this case it has a size adapted to conductors of several diameters. This type of termination is called adaptive.

[0065] As a result, threaded rings 5a, 5b, 5c of a diameter adapted to the outer diameter of the coated wires 2a, 2b, 2c are selected to interact with the bushing 3.

Claims

1. A terminal device (1) for a mineral insulated wire (2), comprising a metal sleeve (3) intended at one end to be fixed to the end of the wire (2) and a ceramic insulating element (4), The ceramic insulating element is composed of a cylinder (4) housed in the sleeve (3) with one end protruding from the sleeve (3) and an end housed in the sleeve (3) opposite the one end having a hole (41), the end of the cylinder (4) housed in the sleeve (3) opposite the one end having a tapered shape, The coated wire is composed of a conductor, a metallic coating, and a mineral insulation interposed therebetween; The terminal device (1) is characterized in that one end of the sleeve is positioned on the outer circumference of the covered wire so as to be fixed onto the covered wire, and the tapered shape of the end of the ceramic insulation element opposite to the one end housed in the sleeve allows the ceramic insulation element to gradually move forward toward the mineral insulation, thereby allowing the ceramic insulation element to apply compressive stress to the surface of the mineral insulation.

2. 2. The terminal device (1) according to claim 1, characterized in that the tapered end (42) opposite the one end of the ceramic insulating element (4) is conical.

3. The terminal device (1) according to claim 1 or 2, characterized in that the ceramic insulating element (4) has a hole, and the hole at the one end protruding from the bushing can be sealed, so that the terminal device constitutes a terminating device.

4. The terminal device (1) according to claim 1 or 2, characterized in that the ceramic insulating element (4) has, at the one end of the insulating element (4) protruding from the bushing (3), a through hole (41) in which a metal tube (6) is mounted, so that the terminal device constitutes a connector device.

5. The terminal device (1) according to any one of claims 1 to 4, characterized in that the one end of the bushing (3) which is fixed to the end of the covered wire has fastening means which are intended to interact with complementary fastening means provided on the outer periphery of the end of the covered wire.

6. The terminal device (1) according to claim 5, characterized in that the complementary fixing means consist of an internal thread formed on the inner wall of the bushing (3) and a threaded ring (5) intended to be mounted on the outer coating (22) of the coated wire (2).

7. 5. Terminal device (1) according to claim 4, characterized in that the ceramic insulating element (4) and the metal tube (6) are mounted in a sleeve (7) mounted in the bushing (3).

8. A shielded coated wire comprising a mineral insulating coated wire (2) and a terminal device (1) as described in any one of claims 1 to 7, wherein the coated wire is composed of a conductor, a metal coating, and a mineral insulator inserted between the two, and the terminal device is fitted onto the coated wire.

9. 9. The shielded wire (2, 2a, 2b, 2c) according to claim 8, characterized in that the one end of the sleeve (3) that is fixed to the end of the covered wire (2) is fixed onto the outer periphery of the end of the covered wire (2) by crimping.

10. A shielded coated wire (2, 2a, 2b, 2c) as described in claim 9, characterized in that it has complementary fixing means on the outer periphery of the end of the coated wire (2) fixed to the sleeve (3), which are complementary to the fixing means provided on the sleeve (3) of the terminal device (1).

11. 11. The shielded wire (2, 2a, 2b, 2c) according to claim 10, characterized in that the complementary fastening means consist of an internal thread formed on the inner wall of the bushing (3) and a threaded ring (5) fastened by brazing onto the metallic outer sheath (22) of the shielded wire (2).

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