GB2215140A

GB2215140A - Co-axial conductive coupler

Info

Publication number: GB2215140A
Application number: GB8802880A
Authority: GB
Inventors: Den Steen Leon Van
Original assignee: Shell Internationale Research Maatschappij BV
Current assignee: Shell Internationale Research Maatschappij BV
Priority date: 1988-02-09
Filing date: 1988-02-09
Publication date: 1989-09-13
Anticipated expiration: 2008-02-09
Also published as: DE3903587A1; NO890541D0; NO890541L; GB2215140B; BR8900526A; GB8802880D0

Description

19 9215140 CO-AXIAL INDUCTIVE COUPLER The invention relates to a co-axial

inductive coupler.

Inductive couplers are commonly used for interconnecting electrical power or data transfer conduits in a releasable manner in environments, such as in an explosive atmosphere or underwater, 5 where normal pin-box electrical connectors cannot be employed.

The operation of inductive couplers is based upon the alternating current transformer principle, which implies that with the aid of a magnetic circuit a voltage is induced from a primary winding to a secondary winding without making any physical electrical connection between the windings.

An inductive coupler where the primary and secundary windings and associated core members are co-axially arranged in a plug and socket part of the connector is disclosed in British patent specification No. 2058474 and in the article "Inductive couplers in underwater power distribution networks - Improving their applicabim lity" in the magazine "Underwater Technology" (Volume 12 NLL ber Autumn 1986). This article describes that an advantage of the co-axial coupler is the high efficiency thereof but that a disadvantage thereof is the difficult construction of the inner and outer core member as because of their rotational symmetry they cannot be constructed from laminated transformer iron. In the co-axial inductive coupler disclosed in British patent specification No. 2058474 ferrite is used as core material. However, ferrite is very brittle and not suitable for the construction of rugged underwater equipment. Moreover, it has a low saturation flux density, leading to a large cross sectional area of the core.

It has furthermore been proposed to make the core from composite ferromagnetic material, such as COROVAC (Trade Mark). This material is almost anisotropic for the magnetic flux direction g and it can easily be machined into virtually any desired shape. The relative magnetic permeability of this composite material, however. is limited to about five hundred. This prohibits application of composite material throughout the core as this would entail a high 5 magnetising current.

Accordingly it is an object of the present invention to remedy these drawbacks and to provide a co-axial inductive coupler having a core which can be easily constructed and which has simultaneously a high magnetic permeability.

The inductive coupler according to the invention thereto comprises a plug part and a socket part, which parts are co-axially arranged, the plug part comprising a first winding surrounding an elongated central core member and the socket part comprising a second winding which is surrounded by a cylindrical outer core member, wherein at least part of one of said cores is built from a bundle of ferromagnetic wires.

In a preferred embodiment of the coupler the central core member comprises disc-shaped end portions which are surrounded by ring-shaped end portions forming part of the outer core member, said end portions of the inner and outer core member being made of a composite material consisting of ferromagnetic particles embedded in an epoxy resin. In this manner it is accomplished that the end portions of the core members, which have a complex shape, can be easily machined while the tubular or cylindrical shaped other parts of the core members have a high magnetic permeability.

These and other features and advantages of the coupler according to the invention will be evident from the following detailed description read in conjunction with the accompanying drawings, in which; Fig. 1 is a sectional view of a coupler according to the invention, and Fig. 2 is a sectional view of an alternative form of the coupler.

The coupler shown in Fig. 1 comprises a cylindrical plug part, and an annular socket part 2, which parts are co-axial to a central i - 3 axis I. The socket part 2 is mounted inside a cup-shaped housing 3, whereas the plug part is secured to an end flange 4 which closes the housing during operation of the coupler.

The cylindrical plug part comprises an elongated central core member 6 around which an annular first winding 7 is arranged. The annular socket part:Z comprises an elongated outer core member 5 which surrounds an annular second winding 8.

The first winding 7 is connected to an alternating current source (not shown) by an electrical feed cable 9 whereas the second winding is connected to an electrical load by an electrical supply cable 10. The first and second winding 7 and 8 are embedded in bodies 11 of epoxy resin.

The inner and outer core member 5 and 6 form together a "pot"core through which the magnetic circuit surrounding the windings 7,8 is guided such that the magnetic flux lines 13 have a toroidal shape. Along the length of the windings 7 and 8 the magnetic flux lines 13 have an axial direction whereas beyond the ends of the windings the flux lines make each a 180' turn.

To accomplish that the core members 5 and 6 have a high magnetic permeability along the major part of the trajectory of the magnetic flux lines 13 the parts where the flux lines 13 are oriented in axial direction are built from bundles 5A, 6A of axially or helically oriented ferromagnetic wires, such as wires made of PERMENORM 5000 H2 (Trade Mark), a material comprising about 70% Iron and 30% Nickel. To reduce eddy current losses the wires are separated from each other by thin insulation sheaths (not shown).

To accomplish that the end portions of the core members 5, 6 which protrude beyond the windings 7,8 can be easily machined and to allow a smooth transfer of the magnetic flux between the end portions of the core members 5,6 the inner core member 6 comprises a pair of disc-shaped end portions 6B while the outer core member 5 comprises a pair of ring-shaped end portions 5B, which end portions 5B, 6B are each made of a composite ferromagnetic material, such as COROVAC (Trade Mark). The mating surfaces of the disc-shaped and surrounding ring-shaped end portions are separated by a small gap 15. As the end portions 5B, 6B are the only portions of the magnetic circuit which are in direct contact with the environment the corrosion resistance of the material is of importance, because corrosion products in the gaps 15 could result in seizure of the plug part 1 in the socket part 2 of the coupler. Hence, if the coupler is used in a dry atmosphere said end portions 5B, 6B may be made of silicon -iron particles embedded in epoxy resin such COROVAC (Trade Mark), whereas if the coupler is used in a wet environment it is preferred to use a more corrosion resistant composite material such as a material consisting of Chromium. alloyed PERMALLOY (Trade Mark). Both above mentioned composite materials can be easily machined and are anisotropic for the magnetic flux direction, which is important since within the end portions 5B, 6B the flux lines 13 have a complex shape.

The wire bundle 6A of the inner core member 6 has at the outer circumference thereof a length which at least equals the length of the windings 7 and 8 whereas the length of said wire bundle 6A increases in a radial direction towards the central axis I.

The wire bundle 5A of the outer core member 5, on the other hand, has at the inner circumference thereof a length which at least equals the length of the windings 7 and 8 whereas the length of said wire bundle 5A increases in a radial direction away from the central axis I.

Due to the varying lengths of the wire bundles 5A, 6A conical. transition areas 18 and 17 are formed between the wire bundles 5A, 6A and the end portions 5B, 6B. In this manner it is accomplished that the magnetic field is guided over the maximum possible length through the wires, which have a high magnetic permeability, while the magnetic flux lines 13 are guided in an equally distributed pattern into the end portions 5B, 6B and through the gaps 15, thereby reducing eddy current losses and associated heating of the coupler to a minimum.

The end portions 5B, 6B may be bonded to the wire bundles 5A, 6A after machining them into the desired shape. The wires of the wire bundles 5A, 6A may have a circular or rectangular shape. The wires may also consist of ferromagnetic strips or laminations.

In the embodiment of the coupler shown in Fig 1 the plug part 1 has along the total length thereof a cylindrical shape whereas the socket part 2 has an annular inner surface having along the total length thereof a width which is slightly larger than the outer diameter of the plug part 1. As a modification the annular gap can be increased somewhat along the length of the windings 7,8 so as to increase the tolerance to manufacturing errors and debris trapped in the gap between the windings.

As can be seen in the alternative embodiment of the coupler shown in Fig 2 the plug and socket part may also have another co-axial shape.

The coupler shown in Fig 2 comprises a plug part 20 having a primary winding 21 which is carried by an inner core member consis ting of an cylindrical wire bundle 22 and two end portions 23 and 24, which have a conical outer surface.

The coupler further comprises a socket part 25 having a secundary winding 26 which is carried by an outer core member consisting of an annular wire bundle 27 and two end portions 29 and having a conical inner surface.

The conical surfaces of the end portions 23, 24, 29 and 30 of 0 the inner and outer core member point each in an inward direction along the central axis II of the socket part 25 so as to enable easy insertion and removal of the plug part 20 into and from said socket part 25. A further advantage of the conical shape of said surfaces is that debris in the gaps 31 between said surfaces will not result in seizure of the plug part 20 in the socket part 25.

Apart from the different shape of the end portions 23, 24, 29 and 30 the construction and operation of the coupler shown in Fig 2 are similar to those of the coupler shown in Fig 1. Accordingly it is a key feature of the coupler shown in Fig 2 that the inner and outer core member comprise bundles 22, 27 of ferromagnetic wires which have a high magnetic permeability. In addition it is an z k important feature of the coupler that the end portions 23, 24, 29 and 30 of the inner and outer core member consist of a composite ferromagnetic material which can be easily machined. Moreover, the conical transition areas 32, 33 between the ends of the wire bundles 22, 27 and the end portions 23, 24, 29 and 30 ensure equal distribution of magnetic flux lines throughout the length of the t9roidal magnetic circuit formed by the core members.

1 S W 4

Claims

C L A I M S

1. An inductive coupler comprising a plug part and a socket part, which parts are co-axially arranged, the plug part comprising a first winding surrounding an elongated central core member and the socket part comprising a second winding which is surrounded by an annular outer core member, wherein at least part of one of said core members is built from a bundle of ferromagnetic wires.

2. The inductive coupler of claim 1 wherein both core members are partly built from a bundle of ferromagnetic wires, said wires having a substantially axial orientation.

3. The inductive coupler of claim 1 wherein the central core member further comprises disc-shaped end portions which are surrounded by ring-shaped end portions forming part of the outer core member, said end portions of the central and outer core member being made of a ferromagnetic material.

4. The inductive coupler of claim 3 wherein said ferromagnetic material is a composite material consisting of ferromagnetic particles embedded in a resin.

5. The inductive coupler of claim 4 wherein said ferromagnetic particles are silicon-iron particles.

6. The inductive coupler of claim 4 wherein said ferromagnetic particles are chromium alloyed PERMALLOY particles.

7. The inductive coupler of claim 3 wherein the wire bundle of the central core member has at the outer circumference thereof a length which at least equals the length of the first winding whereas the length of said wire bundle gradually increases in a radial direction towards the central axis of the coupler, thereby forming a conical transition area between said wire bundle and each of the disc- shaped end portions of the central core member.

8. The inductive coupler of claim 3 wherein the wire bundle of the outer core member has at the inner cimcumference thereof a length which at least equals the length of the second winding whereas the length of said wire bundle gradually increases in a radial direction from the central axis of the coupler, thereby forming a conical transition area between said wire bundle and each of said ring-shaped end portions of the outer core member.

9. The inductive coupler of claim 1 wherein the plug part has along the length of the first winding a cylindrical shape and the socket part has along the length of the second winding an annular inner circumference having a width which is slightly larger than the outer diameter of said cylindrical portion of the plug part.

10. The inductive coupler of claim 9 wherein the plug part has along the length thereof a cylindrical shape and the socket part has along the length thereof an annular inner circumference having a width which is slightly larger than the outer diameter of the plug part.

11. The inductive coupler of claim 3 wherein the disc-shaped end portions of the plug part have each a conical outer surface and the ring-shaped end portions of the socket part have each a conical inner surface, each of said conical surfaces pointing in the same direction along the central axis of the coupler.

12. An inductive coupler according to claim 1 substantially as described with reference to the accompanying drawing.

Published 1989 at The Patent Office, State House, 66 71 High Holborn, London WC1R 4TP. Purther copies maybe obtained from The Patent Office. Sales Branch, St Mary Cray, Orpington, Rent BR5 3113). Printed by Multiplex techniques Itd, St Mary Cray, Kent, Con. 1/87 -c