CONNECTOR ARRANGEMENT FOR ELECTRICAL CIRCUITS IN UNDERWATER INSTALLATIONS, AND TRANSFORMER PARTICULARLY FOR USE IN SUCH ARRANGEMENTS

Abstract: Transformer for current supply and/or signalling purposes, in particular for use in a connector arrangement for electrical circuits in underwater installations. The transformer comprises a magnet circuit (11, 12), a first winding having a plurality of turns (14, 16) and a second winding (15, 17) having one or very few turns, whereby turn portions of both windings pass essentially in parallel through one or more openings (10, 20) in the magnetic circuit (11, 12). For obtaining advantageous electrical properties turn portions of the first winding (14, 16) are so arranged that along a major part of their length which is surrounded by the magnetic circuit (11, 12), they are individually enclosed by that or those conductors (15, 17) which constitute the turn portions of the second winding being surrounded by the magnetic circuit (11, 12). A particularly interesting use of the transformer is in association with and assembled with inductive connectors for underwater installations.

Description: Connector Arrangement for electrical Circuits in Underwater Installations, and Transformer particularly for Use in such Arrangements«- In underwater installations as for example in associa¬ tion with offshore oil activity, the interconnection between cables or between cables and equipment modules being for example located at the sea bottom, represents serious pro¬ blems. A specific type of inductive connector is described in Norwegian Patent Application No. 84.0087. The present invention takes as a basis a corresponding situation as in the previous patent application, but as will appear from the following, the present invention has also in part more gene¬ ral uses. Corrosion and pitting of materials included in the struc¬ ture of such connectors or the like, constitute one of the greatest problems in underwater installations in sea water and, besides, frequently at other forms of electrical instal¬ lations, in which it cannot always be guaranteed that corro¬ sion protection and encapsulation will prevent penetration of for example water or moisture. In particular when there is ambient sea water it is to be noted that the voltage level in a part of the electrical installation has much signifi¬ cance to the corrosion rate. When the voltages exceed about 1 volt, the corrosion will take place much more quickly than at lower voltages. This recognition constitutes some of the background for the solutions set forth in the following. When transmitting and distributing electrical energy and signals respectively, through cables and wires there will normally be employed much higher voltage levels than 1 volt, depending upon the transmission distances concerned. This also applies to a high degree in underwater installa¬ tions in offshore oil activity. Thus, more specifically this invention in a first aspect which is rather fundamental, relates to a connector arrangement for electrical circuits in underwater installations, comprising two connector parts adapted for mutually separable interconnection, preferably by inductive coupling. What is novel and specific to the arrangement according to the invention consists therein that associated with at least one of the connector parts there is provided a transformer for transforming between a comparative¬ ly low voltage level over the connector and a comparatively high voltage level in an adjacent electrical circuit, for example a transmission cable. An advantageous embodiment in practice is obtained by assembling these coupling trans¬ formers with the connector into an integrated unit. Depending upon the electrical circuit in which the con¬ nector is included, it may be necessary to have a transformer at both sides or only at one side of the connector. Two- sided transformation will be the more normal, for example when the interconnection of two lengths of a transmission cable is concerned. Moreover, there may be situations in which the voltage level in the system is so high that step- down transforming to a low level across the connector must be effected by means of two or more transformers in series, as these individually in practical designswill have limi¬ tations with respect to the maximum conversion rate. The present arrangement with the so-called coupling transformers impose quite specific requirements to the transformer design. Another and essential aspect of this invention, thus, relates to a transformer being suitable for this purpose. It will be realized, however, that the transformer to be described in the following can also be employed with advantage in other areas than in underwater installations as discussed above. In this aspect the invention takes as a basis a trans¬ former for current supply and/or signalling purposes, in particular for use in an arrangement comprising a magnetic circuit, a first winding having a plurality of turns arid a second winding having one or very few turns, in which turn portions of both windings pass .substantially in parallel through one or more openings in the magnetic circuit. What is novel and specific to the transformer according to the invention consists therein that turn portions of a first winding along a major part of its length being surrounded by the magnetic circuit, are individually enclosed by that or those conductors which constitute the turn portion(s) of the second winding being enclosed by the magnetic circuit. With such a solution it will be possible to obtain a very low ohmic resistance in the transformer, which is an advantage primarily with respect to self heating in power transmission, but also concerning a low attenuation in sig¬ nal transmission. Besides, the transformer will have small leakage fields. This gives good properties at high signal frequencies and results in a low reactive voltage drop in power transmission. Various aspects of this invention shall be discussed more closely in the following with reference to the drawings, in which: Fig. 1 is a diagram showing in principle an arrangement according to the invention, Fig. 2 is a simplified longitudinal section through a trans¬ former designed according to the invention, Fig. 3 shows a cross-section along lines III-III in Fig. 2, Fig. 4 shows a cross-section through a magnetic circuit with windings as an alternative to the embodiment shown in Figs. 2 and 3, and Fig. 5 shows in principle an assembly of several (three) transformers connected into a group for obtaining a higher total conversion rate, possibly also an increased power capacity. Fig. 1 shows in principle and much simplified a portion of an underwater system with an electrical installation com¬ prising a cable 9 which for example can serve to supply energy in the form of electric current to an equipment module 10, possibly also to convey signals to or from the module 10. In such an installation it will very often be a need for a separable connection, i.e. in the form of a connector between the cable 9 and the equipment module 10. Corresponding requirements for a separable connection can also be present when two cable lengths shall be interconnected. In such situations there can for example be employed an induc¬ tive connector as described in the above Norwegian patent application. As previously mentioned it is of substantial significance both in such inductive connectors and in other types of connectors, to keep the voltage level low across the connector in order thereby to contribute to minimizing corrosion and pitting, if the existing corrosion protection or encapsulation should be damaged. In underwater systems or installations concerned the usual voltage level will be from 20 to 100 volt, depending inter alia upon the transmission distances. Thus, as shown in Fig. 1 and in accordance with the invention there are inserted transformers 2 and 3 connected to the equipment module 10 through wires 6 and 7 and to the cable 9 through wires 4 and 5, respectively. The transformer 3 is connected to a main part 1A of the connector 1, whereas the transformer 2 is connected to a separable part IB of the connector. As indicated by a broken line 8 around the connector and both transformers, these components can be built together into an assembled unit, which is a substantial advantage in practice, particularly in order to obtain the shortest possible electrical connections between the two transformers 2 and 3 at one side and the associated parts of the connec¬ tor 1 at the other side. Figures 2 and 3 show a particular embodiment of a transformer for the above purpose and possibly other pur¬ poses in which similar properties are required. This trans¬ former has a magnetic circuit composed of toroidal cores, preferably of aferrite material, in the form of two elongate tube-like core members 11 and 12. At the lower end of core member 11 there is specifically designated a toroidal core 11A. The transformer windings are passed through the through openings in both members of the magnetic circuit, with the major parts of the winding lengths or portions lying within these through openings and enclosed by the magnetic circuit. As will appear in particular from Fig. 2 the turn portions within the magnetic circuit members will extend generally in parallel and rectilinear. The windings in the embodiment of figures 2 and 3 can be regarded as provided by a form of coaxial wire having an inner conductor forming winding portions indicated inter alia at 14 and 16, and an outer conductor having correspon¬ ding turn portions 15 and 17, as well as an intermediate insulation which can consist of a usual insulating material applied according to some conventional manufacturing method. Conveniently the inner conductor and the outer conductor can consist of copper, for example having a conductor cross- section composed of individual threads. For the manufac¬ turing it is moreover an advantage to employ an outer conduc¬ tor in the form of a braided sleeve. The composite wire with inner conductor, intermediate insulation and outer conductor can be contemplated to be a finished product supplied by a cable manufacturer, or the sleeve mentioned can be pulled outside the winding portions during the application thereof on the magnetic circuit. Possibly there may also be provided an outer insulation around the outer conductor. This is not necessary if the winding formed by the outer conductors shall have only one single turn, which is a convenient embodiment in many cases. Fig. 3 shows inter alia a cross-section of the magnetic circuit member 12 in which the through opening 20 accommodates the windings which here consist of seven inner conductors, of which one inner conductor 14 is specifically indicated, with an associated outer conductor 15. A firstwinding, which can for example be considered to be the primary winding, is formed of all turns of the inner conductor, of which the turn portions 14 and 16 have been mentioned above. The first winding has an end for example as designated at 16A, and forms a total number of turns adjusted according to the desired conversion rate, to another winding end (not shown) which can also be located adjacent the upper end of the magnetic circuit in Fig. 2. The other winding which may be regarded as the secon¬ dary winding, comprises inter alia the above turn portions 15 and 17 which individually enclose the respective inner conductors 14 and 16. The outer conductor is interrupted however, for each turn of the inner conductor at the top of the magnetic circuit member 11B, where all these outer con¬ ductor parts are connected in parallel so as to form a single turn which constitutes the other winding. This paral¬ lel connection is effected thereby that the two free ends of the outer conductor sleeve which are formed by the above interruption or cutting thereof adjacent the top of the magnetic circuit member 11, are connected to output leads in the form of two coaxial copper tubes 21 and 23 the lower ends of which are shown at the top of Fig. 2. Between the copper tubes there is indicated an insulation layer 22. More specifically it appears from Fig. 2 that at the outer conductor 17 there are formed two output leads 17A and 17B which for example by soldering are connected to the respective copper tubes 23 and 21. Correspondingly at the outer conductor 15 there are shown output leads 15A and 15B being connected to the copper tubes at a location dia¬ metrically opposite of the connection of the above output leads 17A and 17B. In this manner all separate individual turns formed by the outer conductor sleeve which encloses each turn of the inner conductor, are connected in parallel so as to form the other winding consisting of a single turn. As will appear in particular from the cross-section through the core member 12 in Fig. 3, the conductor cross-section of the composite turn which constitutes the other winding, is thus distributed around said inner conductors which con¬ stitute the first winding, so that each turn portion of the first winding is completely surrounded by a portion of the conductor cross-section of the other winding. This compo¬ sition of the windings is very significant for attaining the particular and advantageous properties possessed by the transformer according to the invention, especially for the purpose of being employed according to the principle which appears from Fig. 1. The structure at the upper end of the magnetic circuit member 11 in Fig. 2, with the coaxial output leads in the form of copper tubes 21 and 22 the diameter of which corres¬ ponds approximately to the diameter of the toroidal cores (for example core 11A) forming the magnetic circuit members, implies a very convenient mechanical and electrical junction between the transformer windings, in particular said other winding and adjacent electrical circuits, in particular an inductive connector as referred to above. In order to keep the individual turns orderly at the top of the magnetic circuit, there is provided a top member 18 on the uppermost toroidal core in member 11. This top member 18 can for example be made of a plastic material and has a row of divicters 19 on its upper face. Between the dividers 19 there are interstices corresponding approximately to the diameter of the inner conductor so that all inner conductors can be located and kept in fixed positions around the circumference, with the associated output leads formed by the surrounding outer conductor sleeve extended upwardly for connection to the copper tubes 21 and 23 as explained above. The upper portion of Fig. 3 shows how some of the winding parts are arranged around the upper portion of the magnetic circuit member 11. It will be realized that there may be a narrow space for arranging the individual turn portions in the re- gion between the lower ends of tubes 21 and 23 and the top of the magnetic circuit. With the coaxial arrangement de¬ scribed and said top member 18 with dividers L9, it is possible, however, to obtain a convenient embodiment in practice. For obtaining the best possible electrical properties it is an advantage that the inner conductor in the region of the notches 19, i.e. between the output leads, for example said output leads 17A and 17B belonging to the turn portion or outer conductor 17, is as short as possible. Another relationship of significance is that for the interesting configurations of primary and secondary windings it is an ad¬ vantage that the cross-sectional area of the inner conductor and the cross-sectional area of the outer conductor are approximately equal, since this will result in the same current density in the windings. With a magnetic circuit composed of toroidal cores as described and based upon a ferrite material, the transformer will have small losses at signal frequencies up to 1 MHz or more. For a possible prac¬ tical application the conversion rate of the transformer can be 19 : 1 based upon galvanically separated windings. However, the winding arrangement can easily be switched so as to obtain an autotransformer having a conversion rate of 20 : 1. In the transformer there is aimed at a counteraction of current skin effect in the other (and low voltage) winding at the same time as the leakage reactance of the transformer is maintained as low as possible. Thus, there is obtained a very good current distribution in this winding. In combined utilization partly for power transmission at a moderate frequency, for example up to a few hundred Hz, at the same time as there is to be transmitted signals having a significantly higher frequency, the design has proved to be very advantageous. At the lower or moderate current supply frequency there will be a good utilization of the conductor cross-sectional area of the turns because of a small skin effect, but at higher signal frequencies the skin effect may become significant. The latter may in the first instance be taken as a disadvantage, but on the contrary involves an advantage because this skin effect will be accompanied by a reduction in the leakage field and there¬ by in the reactive voltage drop at signal frequencies. At these frequencies this is more significant than the purely ohmic voltage drop. Under no circumstances the signal trans¬ mission will lead to any undesired heating of the trans¬ former. The illustrated connection to the tubular output leads contributes to the above advantages by not introducing un¬ necessary reactance. In a manner known per se the capacity between both windings can be influenced by the choice of materials and dimensions of the winding wire, including the insulation thickness and the dielectric constant, so as to adapt or improve the transmission for the most high-frequent signals to be transmitted. Fig. 4 shows another embodiment of the windings, as seen in cross-section corresponding to the lower part of Fig. 3. In Fig. 2 there is shown a magnetic circuit having a toroidal core 32 as in the embodiment discussed above, and where the through opening accommodates a single turn in the form of a solid copper bolt 35 provided with through holes 36 in which there are inserted turn portions 34 which together constitute a winding having several turns as previously described. The turn portions 34 are of course insulated within the holes 36. Manufacturing reasons, inter alia depending upon how large numbers of such transformers which shall be manufactured, will contribute to the decision as to whether an embodiment as shown simplified in Fig. 4, can be an inte¬ resting alternative to the- embodiment according to figures 2 and 3. Also other practical embodiments may be contem¬ plated on the basis of the fundamental features of the trans¬ former according to the invention, namely that turn portions of the first winding (for example primary winding) along a major part of its length being enclosed by the magnetic circuit, are individually enclosed by that or those conduc¬ tors which constitute the other winding's turn portions which lie enclosed by the magnetic circuit. As will have appeared from the above it is also an advantage when this "coaxial" arrangement of turn portions in the form of an inner conduc¬ tor and an associated outer conductor, also continues outside the magnetic circuit in the shortest possible lengths of the turns which extend outside the magnetic circuit. In certain practical uses it can be necessary to employ relatively high conversion rates or to take care of compara¬ tively high power. Several such transformers can then be interconnected into a group by connecting in parallel said other winding (the low voltage winding) and the first windings (the primary winding) are connected in series. A simplified example of such an arrangement is shown in Fig. 5. Here there are schematically indicated three transformers of the type described, having respective magnetic circuit members 41A-41B, 42A-42B and 43A-43B. These are assembled into a star-like arrangement having a common output in the form of coaxial tubes 51 and 53 with an intermediate insula¬ tion 52 in analogy to the tubular output leads at the top of Fig. 2. Output leads from the low voltage winding, for example in the form of sleeve ends as previously described, are then connected to the tubes 51 and 52 at separate locations so that the three transformers each have a sector of about 120 of the circumference of the coaxial lead tubes 51 and 53. Moreover, there is indicated how the turns of the first winding ("primary winding") of these transformers can be connected in series so as to form a transformer arrangement having a higher conversion. rate than that of each individual transformer. It is obvious that the principles on which this inven¬ tion is based, can be realized in severalotherways inpractice, than what appears from the exemplary embodiments in the drawings. Among other things it is clear that the magnetic circuit may be composed or formed in other ways than by means of toroidal cores subdivided into two magnetic circuit members each having its tunnel-like through opening for the windings. Quite corresponding or perhaps better electrical and magnetic properties may be obtainable with a magnetic circuit consisting of one integrated unit, for example of a ferrite material, provided with two through winding openings having a relatively large length compared to the transverse dimension.

Claims: CLAIMS : 1. Connector arrangement for electrical circuits in under¬ water installations, comprising two connector parts (1A, IB) adapted for mutually separable interconnection, preferably by inductive coupling, characterized in that associated with at least one of the connector parts (1A, IB) there is pro¬ vided a transformer (2, 3) for transforming between a com¬ paratively high voltage level in an adjacent electrical cir¬ cuit, for example a transmission cable (4, 5, 9). 2. Connector according to claim 1, characterized in that the transformer(s) (2, 3) is (are) assembled with the connector (1) into an integrated unit (8) . 3. Transformer for current supply and/or signalling pur¬ poses, in particular for use in an arrangement according to claim 1 or 2, comprising a magnetic circuit (11, 12, 32), a first winding having a plurality of turns (14, 16, 34), and a second winding (15, 17, 35) having one or very few turns, whereby turn portions of both windings pass essentially in parallel through one or more openings (10,20) in the magnetic curcuit (11, 12, 32), characterized in that turn portions of the first winding (14, 16, 34) along a major part of their length which is surrounded by the magnetic circuit (11, 12, 32) are individually enclosed by that or those conductors (15, 17, 35) which constitute the turn portion(s) of the second winding being surrounded by the magnetic circuit (11, 12, 32). 4. Transformer according to claim 3, in which the second winding has a single turn, characterized in that the turn portion(s) of the second winding being surrounded by the mag¬ netic circuit (32) has the form of a solid metal bolt (35) having a cross-section which substantially fills the opening in the magnetic circuit (32) , and that the metal bolt (35) is provided with through holes for the turn portions (34, 36) of the first winding. 5. Transformer according to claim 3, characterized in that the windings are formed by a wire having an inner conductor (14, 16) an insulation layer and an outer conductor (15, 17) which coaxially encloses the inner conductor, this inner conductor forming the turns of the first winding, whereas the outer conductor (15, 17) is electrically interrupted at intervals corresponding to a number of complete turns of the inner conductor and are interconnected in groups (15A, 15B, 17A, 17B) in parallel, so as to form the second winding, possibly with an insulating sheath around the outer conductor (15, 17) . 6. Transformer according to claim 5 in which the second winding has a single turn, characterized in that the outer conductor (15, 17) is interrupted for each turn of the inner conductor (14, 16) and that all outer conductor parts are connected in parallel (15A, 15B, 17A, 17B) so as to form the second winding, and that the outer conductor pre¬ ferably has no insulating sheath. 7. Transformer according to claim 5 or 6, characterized in that the outer conductor is formed by a braided metal wire sleeve (15, 17) . 8. Transformer according to any one of claims 3-7, characterized in that the magnetic circuit is composed of toroidal cores (11A, 11B) of a ferrit material. 9. Transformer according to any one of claims 3 - 8, characterized in that the output leads (15A, 15B, 17A, 17B) from the second winding are connected as directly as pos¬ sible to coaxially arranged output conductors which preferably are in the form of mutually insulated coaxial metal tubes (21, 23) the ends of which are positioned close to said output leads.

Inventors: BOERDALEN KNUT, BOERDALEN, KNUT
Applicants: INDUSTRIFORSKNING SENTER
Application year: 1986
Main classification: H01F23
IPC codes: H01F27, H01F30, H01F38