GB2037498A - Electric Couplings - Google Patents

Abstract

A separable coupling (1) is contained in a fluid-tight enclosure (2, 3) having in it, or in communication with it, a fluid reservoir 6 of variable volume. This allows the coupling, filled with insulating liquid, to withstand very large pressure changes such as occur in 'sub-sea' installations normally operating at sea-bed pressure but pumped out to near- atmospheric pressure whilst alterations or adjustments are made. In the preferred form of reservoir, a piston 8 is sealed to the entering cable 5 and the surrounding wall by resilient skirts 9, so obviating the need for a separate seal round the cable. In another embodiments (Fig. 5, not shown) the fluid reservoir (18) is outside the enclosure (2, 3). <IMAGE>

Description

SPECIFICATION Electric Couplings This invention relates to separable electric couplings of the kinds used to connect electriccables to one another or to electrical apparatus of various kinds, or occasionally to connect two pieces of apparatus together without the use of cables.

More specifically it is concerned with couplings suitable for applications in which large changes in ambient pressure will be encountered in service.

A specific instance arises in sea-bed installations, such as well-heads used in the exploitation of oil reserves on the continental shelf.

For most of the time such installations may operate automatically under the natural sea-bed pressure, which under typical oil-exploitation conditions is likely to be of the order of 1-2 MN/m2, but for maintenance and other operations involving human intervention the installation may be enclosed in a rigid working chamber and pumped out to a more convenient working pressure, probably not greatly different from atmospheric pressure (about 0.1 MN/m2).

Under this procedure, electrical couplings will be made and broken always at low pressure but will be subject whilst coupled to very large changes in pressure, often exceeding 1 MN/m2.

In accordance with the invention, a separable electric coupling comprises at least two parts carrying mutually engageable electric contacts, a fluid-tight enclosure surrounding the said parts when engaged and, in or in communication with the enclosure, a fluid-tight reservoir of variable volume.

The contents may be engaged by virtue of inherent resilience (as plug and socket contacts for instance) or resilient biassing (e.g. bayonet or other stud contacts) or by clamping (e.g. with screws).

Normally at lest one valved port will be provided in the wall of the enclosure. In use, the enclosure is filled with insulating fluid, and the range of variation in the volume of the reservoir shouid be sufficient to accommodate the change in the volume of the whole of the chosen fluid due to the change for which the fitting is designed, usually at least 0.5 MN/m2 and preferably at least 1.0 or even 1.5 MN/m2.

Two forms of reservoir of variable volume are known for other purposes, and both of them can be used in the present invention. In the first, the reservoir is hermetically sealed and has at least one flexible wall, typically made of thin sheet material with corrugations to enhance flexibility.

In the second, the walls are rigid and variations in volume arise from sliding movement of a piston that engages the walls and forms a boundary for the insulating fluid, the other side of the piston being exposed to the exterior.

The inventors have devised a special form of the second type of reservoir which has the advantages of low susceptibility to impact damage and of a reduced total number of seals. In accordance with this aspect of the invention, the reservoir is formed by an annular wall surrounding a cable that enters the coupler and an annular piston acting within an annular space between the cable and the wall and in fluid-tight but slidable engagement with both of them.

Preferably the annular piston is sealed to the cable and the wall by resilient flexible skirts on at least one of its end faces, and a resiliently-biassed pressure ring may be urged between concentric skirts to ensure an adequate inital seal (ie. when there is no pressure differential). The biassing ring or rings preferably also urge the piston, in the absence of pressure differential, away from the low-volume extreme of its travel and preferably to a position away from the high-volume extreme also.

In the accompanying drawings: Figures 1-4 show a first form of coupling in accordance with the invention; Figure 1 being a longitudinal cross-section, Figure 2 being an end elevation, Figure 3 being a simplified cross-section on the line Ill-Ill in figure 1, and Figure 4 being a composite cross-section of an end part of the joint on the radii IV, IV in figure 3; Figures 5-8 show a second form of coupling in accordance with the invention:: Figure 5 being a longitudinal cross-section, Figure 6 being a corresponding elevation, Figure 7 being an end view, and Figure 8 being a simplified cross-section on the line VIlI-VIlI in figure 5; Figures 9-11 1 are fragmentary views illustrating modifications to the coupling of figures 5-8; Figures 12-1 5 show a third form of coupling in accordance with the invention: Figure 12 being a longitudinal cross-section, Figure 13 being a corresponding elevation, and Figures 14 and 15 being opposite end-views of one half of the coupler; Figure 1 6 is a diagram illustrating a modification to the coupler of figures 12-1 5; Figures 17-20 show a fourth form of coupling in accordance with the invention:: Figure 1 7 being a cut-away elevation of approximately half the coupling, Figures 1 8 and 1 9 being cross-sections on the lines XVlII-XVlII and XIX-XIX respectively in figure 17, and Figure 20 being a side elevation, on a smaller scale, of the whole coupling; Figure 21 is a cross-section showing a major component of the coupling of figures 1 7-20 prepared for towing to its working position; Figure 22 is a diagram illustrating the use of the couplings of the invention; and Figure 23 is a further diagram illustrating a modification.

In the coupler of figures 1-4, a standard industrial coupler 1 (one of those sold by the Applicant company as a "BICC Marechal Decontactor") is housed in a cylindrical chamber made from an extruded stainless steel tube 2 and cast bronze end-members 3 secured with tie bolts 4. Each of the entering cables 5, 5 is equipped with a variable-volume reservoir 6 comprising an annular chamber 7 bounded on the inside by the cable 5 and on the outside by a cylindrical wall of the end-member 3 and housing a piston 8 sealed to the cable and the wall by resilient skirts 9.

Pressure rings 10, 11 biassed by respective springs 12, 1 3 engage the adjacent pair of skirts when the piston approaces its respective limits of travel, serving the dual purpose of (i) improving the security of sealing when the pressure differential is low (whether the pressures and consequently the volume of fluid 14 in the chamber, is high or low) and (ii) biassing the piston away from its limits of travel. The chamber is filled with the insulating fluid 14 after assembly using the valves 1 5 visible in figures 2 and 4. It will be appreciated that the cone grips 1 6 acting on the cable outside the chamber are purely mechanical grips and are not fluid-tight: they may for example have split phosphor-bronze cones.

Figures 5-8 illustrate a second form of coupler in which the cables 5 are sealed at fixed positions in the ends of the chamber 1 7, and a separate reservoir 1 8 is fitted. This allows endparts 1 9 of the chamber to be filled with a viscous or elastic insulating compound, so reducing the volume of insulating fluid 14 that has to be supplied when making and withdrawn when breaking the connection.

Figure 9 shows a minor modification in which a mechanical clamp 20 for gripping armour wires 21 of the cable is provided. In figures 5-8, the halves of the chamber 1 7 are secured together by half-rings 22 of channel section, pivoted together at 23 and secured together at their opposite ends 24. Figures 10 and 11 show a toggle mechanism 25 that may be substituted for the screw to provide a quick-release version.

Figures 12-1 5 show a third form of coupling, differing from the second form in a variety of ways, notably the use of quick-release eye bolt couplings 26 and the use of dowel pins 27 to locate the halves independently of the electric contacts. The whole chamber is filled with fluid 14 in this case, and the variable-volume reservoir 1 8 may be attached in any convenient position.

The coupler 1 is in this case a conventional pin and socket type. Figure 1 6 shows a modification to the internal layout (compare figure 14) in which the coupler 1 is eccentrically positioned to allow more convenient space for auxiliary connections 28, for instance between hydraulic lines incorporated in the structure of the cable 5.

Figures 1 7-21 show a coupler for relatively high voltages. The specific form illustrated is for three-phase operation but (for enhanced fiexibility) the cable 29 has six cores 30, two for each phase. Appropriate pairs of cores are connected to bushing terminals 31 in a bulkhead 32 and the core screens are terminated, as best seen in figure 18, on another bulkhead 33. Tie bolts 34 secure the bulkheads with respect to the armour-grip 35 and a sleeve 36 with welded flanges 37 completes a substantially fluid-tight half-coupler 38.

The two half-couplers are interconnected electrically by jumper leads 39 bolted to the terminals 31; they are interconnected mechanically and hydraulically by a longitudinally divided centre housing section 40. Each of the sections 38, 38, 40 is filled with a suitable insulating fluid and has its own reservoir 1 8 to maintain filling when pressure changes.

Figure 21 shows one of the half-couplers 38 (with its reservoir 1 8 removed, a suitable valve preserving sealing) installed in a "bulinosed" casing 41 and attached thereby to a hawser 42 to facilitate towing the cable 29 to the required position on the sea-bed.

Figure 22 iilustrates a typical installation in which the coupler of figures 1 7-21 may be used. The installation provides a connection between a sea-bed installation 43, such as a wellhead, and a surface termination 44, say on the associated oil-production platform. A first coupling 45 in accordance with the invention connects a flexible cable 46 extending from the surface termination to a relatively rigid cable 47 extending along the sea-bed. If the length of the cable 47 makes it necessary, sections may be coupled by one or more further couplings 48 in accordance with the invention, and the coupling 49 between the cable 47 and the sea-bed installation may also be in accordance with the invention.

When the nature of the sea-bed installation makes a single point entry inappropriate, a further coupling 50 in accordance with the invention can be used to subdivide the electrical and other (if any) services to provide a number of separate leads 51 for connection to individual electrical or where appropriate hydraulic, pneumatic or other connection points on the sea-bed installation.

In general, any insulating fluid that has no deleterious effect on the other materials of the coupling can be used, but in most cases either hydrocarbon oils or silicone oils will be preferred, the latter being more expensive but allowing a wider range of elastomeric materials to be used for seals.

The couplings may incorporate hydraulic connections as well as electric power and/or telecommunication circuit connections. Use on power circuits up to 16 kV and 500 A is contemplated, and higher voltages and currents could be used.

Claims (9)

Claims

1. A separable electric coupling comprising at least two parts carrying mutually engageable electric contacts, a fluid-tight enclosure surrounding the said parts and, in or in communication with the enclosure, a fluid-tight reservoir of variable volume.

2. A coupling as claimed in Claim 1 in which the reservoir is hermetically sealed and has at least one flexible wall.

3. A coupling as claimed in Claim 1 in which the reservoir has rigid walls and a piston in sliding engagement with the walls forms a boundary for the insulating fluid, the other side of the piston being exposed to the exterior.

4. A separable electric coupling comprising at least two parts carrying mutually engageable electric contacts, at least one of the parts having a cable connected to it, a fluid-tight enclosure surrounding the said parts and providing an annular wall surrounding the said cable, and an annular piston action within the annular space between the cable and the wall and in fluid-tight but slidable engagement with both of them so that the piston forms with the annular space a fluid-tight reservoir of variable volume.

5. A coupling as claimed in Claim 4 in which the piston is sealed to the cable and the wall by resilient flexible skirts on at least one of its end faces and a resiliently-biassed pressure ring is urged between concentric skirts to ensure an adequate initial seal.

6. A coupling substantially as described with reference to figures 1-4.

7. A coupling substantially as described with reference to figures 5-8 with or without figures 9-11.

8. A coupling substantially as described with reference to figures 12-1 5 with or without figure 16.

9. A coupling substantially as described with reference to figures 1 7-20.