GB2028602A - Cable terminations and electrical cables therewith - Google Patents

Abstract

A terminal arrangement for a cable (1) e.g. of a kind making connexion to a thermocouple junction has a metal outer sleeve (10) that is welded about its rear end (14) only to a metal inner sleeve 15. The inner sleeve (15) is welded about its forward end only to the forward end (16) of a metal sheath (2) of the cable (1) within which extend two flexible thermocouple wires (3 and 4) of a nickel chromium and of a nickel aluminium alloy. The forward end (17) of the outer sleeve (10) is welded to the forward end only of a further inner sleeve (18) that supports an electrically-insulative filling (19) of compacted magnesium oxide. The filling (19) supports two rigid wires (6 and 7) that are joined at their rear ends to respective ones of the thermocouple wires (3 and 4), the rigid wires being of the same material as the thermocouple wires. The intermediate portion (12) may be filled with a glass material. This filling would prevent the passage of moisture between the magnesium oxide filling (19) and the cable (1). The siting (14, 16, 17) of the welds allows differential thermal expansion of the arrangement without subjecting the joints (20, 21) to high stress in the case of thermocouple use. <IMAGE>

Description

SPECIFICATION Terminal arrangements and electrical cables including them This invention relates to terminal arrangements for electrical cables and to electrical cable assemblies including such terminal arrangements.

The invention is especially applicable to terminal arrangements for thermocçouple cables.

In many applications it is necessary to make secure electrical connection to relatively fine wires contained within an electrical cable. Difficulties have been experienced in the past in making such connection, especially where the connection is required to be capable of being repeatedly disconnected and reconnected and where the connection is required to withstand high temperatures, or temperature changes, and high levels of vibration. One such application is in temperature sensors used in gas-turbine engines where it is necessary regularly to disconnect cables leading to the sensors so as to enable the sensors to be checked, serviced or replaced, and where it is especially important that electrical connection to the cables be capable of withstanding the high temperatures and levels of vibration commonly experienced.

It is an object of the present invention to provide a terminal arrangement for electrical cables and cable assemblies that can be used substantially to alleviate the above-mentioned difficulties.

According to one aspect of the present invention there is provided a terminal arrangement for an electrical cable of the kind including an electrically-conductive wire extending within a metal outer sheath, the arrangement including a metal outer sleeve adapted to be welded at one end about an end of said cable such that said sleeve extends beyond the end of said cable, and at least one rigid elongate conductor element arranged such that one end of said conductor element projects from said sleeve and is supported by an electrically-insulative member in said sleeve, the other end of said element being adapted to be electrically-connected within said sleeve with said wire.

In this way, connection can be made to the cable via the rigid conductor element whilst the wire within the cable is protected by the sleeve.

The terminal arrangement may include a metal inner sleeve that extends within said one end of the outer sleeve, the said outer sleeve being welded to said'inner sleeve at one point only along the length of said inner sleeve. The terminal arrangement may include a further metal inner sleeve that extends within said other end of the outer sleeve, the said outer sleeve being welded to said further inner sleeve close to one end only of said further inner sleeve, and the said insulative member being supported within said further inner sleeve.

According to another aspect of the present invention there is provided a cable assembly comprising a terminal arrangement according to the above-specified one aspect of the present invention and an electrical cable of the kind including an electrically-conductive wire extending within a metal outer sheath, the terminal arrangement being welded at one end to an end of said cable. The terminal arrangement of the cable assembly may include a metal inner sleeve that extends within the one end of the outer sleeve of the terminal arrangement, the inner sleeve being welded to said sheath at one point only along the length of said inner sleeve. The outer sleeve may be welded to the inner sleeve close to one end only of said inner sleeve and said inner sleeve may be welded to said sheath close to the other end of said inner sleeve.

A terminal arrangement and a thermocouple cable assembly including such arrangement, both in accordance with the present invention will now be described, by way of example, with reference to the accompanying drawing which is a crosssection elevation through a terminal arrangement mounted at one end of a cable.

A mineral insulated cable 1 of the kind making connection to a thermocouple junction (not shown) comprises an outer sheath 2 of inconel having two fine wires 3 and 4 of a nickel chromium alloy and a nickel aluminium alloy respectively extending through it. The wires 3 and 4 project a short distance from the forward end of the cable 1 and are supported along their length by a filling 5 of a compacted mineral insulant such as, for example, magnesium oxide. The wires 3 and 4 are welded at their forward end to the rear of a thicker short terminal wire 6 of a nickel chromium alloy and to a similar wire 7 of a nickel aluminium alloy respectively.The terminal wires 6 and 7 provide rigid conductor elements and are formed into loops 8 and 9 respectively at their forward ends such that electrical connection to the terminal wires, and hence the cable wires 3 and 4, can be made by welding, crimping or otherwise securing to these lodps.

The terminal wires 6 and 7 are supported by means of an outer sleeve 10 of inconel. The outer sleeve 10 comprises a rear cylindrical portion 11 which embraces the forward end of the cable 1, an intermediate, frusto-conical portion 12 which flares outwardly to a forward portion 13 of a large diameter. The rear end of the rear portion 11 is welded about its circumference 1 4 to the outer surface of an inconel inner sleeve 1 5, a short distance from the rear of the inner sleeve. The sleeve 15 embraces the forward end of the cable 1 and is in turn welded about its forward end to the forward end 16 of the cable's metal sheath 2.

The forward end of the forward portion 13 of the outeresleeve 10 is welded about its circumference 17 to the forward end of another inconel inner sleeve 18 which extends coaxially as a close fit within the forward portion 13. The forward inner sleeve 8 contains an electricallyinsulative filling 1 9 of a compacted mineral powder such as, for example, magnesium oxide.

The terminal wires 6 and 7 extend through, and are supported by, this filling. The rear ends of the terminal wires project from the rear end of the filling 1 9 and are welded to the fine cable wires 3 and 4 such that welded joints 20 and 21 between the two pairs of wires are located within the intermediate portion 12 of the sleeve 10.

By joining relatively thick and rigid terminal wires 6 and 7 to the end of the fine cable wires 3 and 4 in this way electrical connection can be made by external conductors without subjecting the cable wires to stress upon movement of these conductors. Repeated connection and disconnection can also be made to the loops 8 and 9 without stressing the cable wires 3 and 4.

The cavity within the intermediate portion 12 may be filled with a glass material. Such a filling would further support the joint between the wires and would also prevent any moisture that might be absorbed by the filling 19 in the forward sleeve 1 8 entering the cable 1. The glass filling may be formed by drilling a small hole in the intermediate portion 12, introducing glass chips into the cavity, and heating to melt the chips. The weld about the circumference 14 of the rear portion 11 is preferably made after any filling within the intermediate portion 12 has cooled and solidified.

In this way, thermal stresses between the inner sleeve 1 5 and the rear portion 11 that might otherwise arise during heating of the glass filling are avoided.

Arranging the welded joints between the outer sleeve 10 and the inner sleeves 1 5 and 18, and between the rear inner sleeve 1 5 and the sheath 2 in the manner described, ensures that the joints between the various components are not subjected to high stress upon differential thermal expansion between them. More particularly, since the outer sleeve í O is joined to the rear inner sleeve 1 5 at one point only, that is, close to the rear end of the inner sleeve, these two components are free to expand relative to one another along their lengths, from the joint between them. Similarly, the rear inner sleeve 15 is free to expand along its length relative to the sheath 2 of the cable 1 since the sleeve is joined to the sheath at one point only, that is at its forward end. In the same way, the forward portion 13 of the outer sleeve 10 is free to expand along its length relative to the forward inner sleeve 1 8 since it is joined to the inner sleeve at only one end 17.

The arrangement described is especially useful for forming terminals at the end of cables used for making connection to thermocouples employedin temperature sensors in gas-turbine engines, and in other applications where cables might be subjected to high temperatures, temperature changes and levels of vibration. The arrangement is not, however, restricted to use with thermocouple cables but may find application with other cables.

Claims (18)

1. A terminal arrangement for an electrical cable of the kind including an electricallyconductive wire extending within a metal outer sheath, the arrangement including a metal outer sleeve adapted to be welded at one end about an end of said cable such that said sleeve extends beyond the end of said cable, and at least one rigid elongate conductor element arranged such that one end of said conductor element projects from said sleeve and is supported by 'an electricallyinsulative member in said sleeve, the other end of said element being adapted to be eiectricallyconnected within said sleeve with said wire.

2. A terminal arrangement according to Claim 1 including a metal inner sleeve that extends within said one end of the outer sleeve, wherein said outer sleeve is welded to said inner sleeve at one point only along the length of said inner sleeve.

3. A terminal arrangement according to Claim 2, wherein said inner sleeve and said outer sleeve are of inconel.

4. A terminal arrangement according to any one of the preceding claims including a further metal inner sleeve that extends within the other end of said outer sleeve, wherein said outer sleeve is welded to said further inner sleeve close to one end only of said further inner sleeve, and wherein said insulative member is supported within said further inner sleeve.

5. A terminal arrangement according to Claim 4, wherein said further inner sleeve is of inconel.

6. A terminal arrangement according to any one of the preceding claims, wherein said insulative member is of a compacted mineral powder.

7. A terminal arrangement according to Claim 6, wherein said mineral powder is magnesium oxide.

8. A terminal arrangement according to any one of the preceding claims, wherein the said one and other ends of said outer sleeve are of cylindrical shape and wherein an intermediate portion of frusto-conical shape extends between the said one and other ends.

9. A terminal arrangement according to Claim 8, wherein the other end of said conductor element terminates within said intermediate portion.

10. A cable assembly comprising a terminal arrangement according to any one of the preceding claims and an electrical cable of the kind including an electrically-conductive wire extending within a metal outer sheath, said terminal arrangement being welded to an end of said cable.

1 A cable assembly according to Claim 10 and Claim 2, wherein said inner sleeve is welded to said sheath at one point only along the length of said inner sleeve.

12. A cable assembly according to Claim 11, wherein said outer sleeve is welded to said inner sleeve close to one end only of said inner sleeve and wherein said inner sleeve is welded to said sheath close to the other end only of said inner sleeve.

13. A cable assembly according to any one of Claims 10 to 12, wherein said cable includes a plurality of electrically-conductive wires extending within a metal outer sheath, and wherein said terminal arrangement includes a plurality of conductor elements.

14. A cable assembly according to Claim 13, wherein each said conductor element is connected with a respective wire of the same material.

1 5. A cable assembly according to Claim 14 for making connection with a thermocouple, wherein one of said conductor elements and a respective one of said wires is of a nickel chromium alloy, and wherein another of said conductor elements and a respective other of said wires is of a nickel aluminium alloy.

16. A cable assembly according to any one of Claims 10 to 1 5, wherein said sheath is of inconel.

17. A terminal arrangement substantially as hereinbefore described with reference to the accompanying drawing.

18. A cable assembly including a terminal arrangement according to any one of the prece,ding claims.

1 9. A cable assembly substantially as hereinbefore described with reference to the accompanying drawing.