Abstract:
A connector for a conductor of a power cable includes a hollow outer member configured to at least partially surround an exposed section of the conductor and configured to exert a force in an axial direction onto at least one electrically conductive inner member, and at least one electrically conductive inner member configured to be interposed between the outer member and the conductor, and configured to exert a force in a radial direction onto the conductor in response to the force in an axial direction.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the priority of British Patent Application No. 1313290.7, filed Jul. 25, 2013, the content of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to connectors for power cables, more in particular for a conductor thereof. 
     In the present description and claims, under the term “connector”, a connector for straight joints, a connector for a branch connection, a connector for breaches connections, a connector for service connections, a termination lug are encompassed as well as any other structures for connecting a conductor of a cable or the like. 
     Connectors for power cables are known in a variety of designs. Just as an example, U.S. 2002/0046865 A1 discloses some electrical connectors for a power cable. In one embodiment ( FIG. 1  thereof), the connector comprises a tubular member with a first and second hollow portions, each sized and shaped to receive an end of a conductor. Hence, a portion of the cable that has been stripped to remove the outer insulation is inserted into each hollow portion. The ends of the cables are then secured to the connector by crimping each end of the connector. 
     In another embodiment ( FIG. 11  thereof), an elongated hollow electrically conductive tubular member has a plurality of threaded openings sized to receive bolts to contact the central core of an electrical cable section when bolts are tightened. 
     The Applicant observes that the first connector has no range-taking ability and requires a special tool for connection, while in the second connector the screws may damage the strands of the conductor and only make local electrical connection. 
     EP 1837952 A2 discloses an electrical connector for corrugated coaxial cable which is installable upon an electrical cable, having a spring finger ring which can be applied to the cable by axial compression. The spring finger ring comprises a plurality of fingers with gaps between them. The fingers are jointed together at one end by the ring. The spring finger ring is located within a bore of a body coupled to the cable end. The fingers are allowed to be deflected outwards to allow the leading edge of the outer conductor to pass, and return to their steady, spaced state resting in the first corrugation behind the leading edge of the outer conductor. 
     The Applicant observes that the above connector has no range-taking ability and is only suitable for corrugated coaxial cables (i.e. cables used for communications, not for power transportation). 
     SUMMARY OF THE INVENTION 
     The Applicant found that when large size cables are to be connected, the force to be applied for fitting a connector over the conductors by crimping must be very high (e.g. a force of about 2500 N). Conductors with large sizes require a large hydraulic clamping equipment which has to be transported on the installation site. Typical compression connectors are designed to fit only specific sizes of conductors so that the operators must have many different types of connectors during installation. Sometimes the sites are very remote in cramped areas or involve connections at height which creates hard work for the fitters. 
     The Applicant, moreover, found that it is convenient to compress together the strands forming the conductor such that the lateral or radial forces applied to the strands are similar. When mechanical connectors are used, these type of connectors do not, have a full contact with the conductor as there is only a connection on the bottom surface of the connector. Further, when screws are used, they may not apply as much pressure as a compression die and do not compress all the strands together so that there is the likelihood of voltage differences between each layer of strands of the conductor. 
     In an aspect, the present invention relates to a connector for a conductor of a power cable, with an hollow outer member configured to at least partially surround an exposed section of the conductor and configured to exert a force in an axial direction onto at least one electrically conductive inner member, wherein the electrically conductive inner member is configured to be interposed between the outer member and the conductor, and it is configured to exert a force in a radial direction onto the conductor in response to the force in the axial direction. 
     In the present disclosure and in the attached claims, to exert a force in an axial direction encompasses that a force in a direction other than axial is also exerted. 
     In the present disclosure and in the attached claims, terms “outer” and “inner” are used relative to each other, not with an absolute meaning. 
     By providing for two nested members, the inner member being radially forced onto the conductor by the axial force from the outer member, the inner member may be shaped so as to have extensive contact with the conductor. Moreover, because the outer member needs only to apply an axial force instead of a compression onto the conductor, it is less sensitive to the size of the conductor and does not require special tools for assembling the connector onto the conductor. 
     Preferably, the connector further comprises a hollow counter member and the outer member is configured to engage with the counter member to exert the force in the axial direction. 
     Preferably the counter member is configured to contact an end portion of the conductor, more preferably to at least partially surround the exposed section of the conductor. 
     Preferably, the electrically conductive inner member comprises at least two shims, wherein the shims are circumferentially evenly distributed around the conductor. 
     Preferably, each shim is configured as a sector of a cylindrical element. 
     Preferably, the outer member comprises a conical inner surface and the shims comprise a conical outer surface matching the conical inner surface of the outer member. 
     Preferably, the counter member comprises a conical inner surface and the shims comprise a conical outer surface matching the conical inner surface of the counter member. 
     Preferably, the inner member is internally scored, more preferably provided with circumferentially or helically arranged grooves in an inner surface thereof. 
     Preferably, the inner member comprises at e two shims held together by a collapsible ring. 
     Preferably, the collapsible ring has bulges between adjacent ones of the shims. 
     Preferably, the connector comprises a second electrically conductive hollow outer member configured to at least partially surround an exposed section of a second conductor and configured to exert a force in an axial direction onto at least one second electrically conductive inner member, and the second electrically conductive inner member is configured to be interposed between the outer member and the second conductor, and configured to exert a force in a radial direction onto the second conductor in response to the force in the axial direction. 
     Preferably, the counter member is configured to engage with the outer member and second outer member to exert said forces in axial direction. 
     Preferably, the counter member is axially symmetric and is configured to contact end portions of the conductor and the second conductor, more preferably to at least partially surround the exposed sections of the conductor and the second conductor. 
     Preferably, the outer member(s) and the counter member have mating threads. 
     Preferably, the outer member(s) and the counter member have outer hexagonal profiles 
     Preferably, the outer member(s) is(are) electrically conductive. 
     Preferably, the outer member(s) and the counter member are held together by a pin and groove locking mechanism. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The features and advantages of the present invention will be made apparent by the following detailed description of some exemplary embodiments thereof, provided merely by way of non-limiting examples, description that will be conducted by making reference to the attached drawings, wherein: 
         FIG. 1  schematically shows an embodiment of a connector according to the present invention, in a perspective view and in a not tight condition, 
         FIG. 2  schematically shows a longitudinal section of the connector of  FIG. 1 , 
         FIG. 3  schematically shows the connector of  FIG. 1  in a partly broken away perspective view and assembled around one conductor of a cable, 
         FIG. 4  schematically shows an embodiment of a lug according to the present invention, in a perspective view, 
         FIG. 5  schematically shows another embodiment of a connector according to the present invention, in a partly sectional view, 
         FIG. 6  schematically shows another embodiment of a connector according to the present invention, in a partly sectional view, and assembled around a cable, 
         FIG. 7  schematically shows another embodiment of a connector according to the present invention, in a partly sectional view, 
         FIG. 8  schematically shows another embodiment of a connector according to the present invention, in a partly sectional view, and 
         FIG. 9  schematically shows another embodiment of a connector according to the present invention, in a partly sectional view. 
     
    
    
     Same or similar members are denoted by like numbers in the various figures. 
     DETAILED DESCRIPTION 
     A connector  1  according to a first embodiment of he invention is disclosed with reference to  FIGS. 1 to 3 . 
     Connector  1  is shown in a perspective view and in a not tight condition in  FIG. 1 , in a longitudinal section in  FIG. 2  and in a partly assembled perspective view and in a partly tight condition view in  FIG. 3 . 
     Connector  1  comprises a mid section  2 , two outer bodies  3  and a number of shims  4 . Each outer body  3  is coupled to one respective side of the mid section  2 . A threaded coupling is shown in  FIG. 1-3  by way of an example. A number of shims  4  is housed between each outer body  3  and the mid section  2 . 
     More specifically, the mid section  2  comprises a central disc wall  5 , which may be solid as shown or bored (compare  FIG. 5 ), and two collars  6  each having an outer threading  7 . The inner wall of each collar  6  is conical as shown at  8 , specifically flared, for reasons that will be clear hereinafter. 
     Each outer body  3  is an essentially cylindrical hollow body. Each outer body  3  has an inner threading  9  at a first longitudinal end  10 , matching and coupled with the outer threading  7  of the mid section. Each outer body  3  has an inner conical surface  11  at a second longitudinal end  12  opposed the first longitudinal end  10 . 
     Each shim  4  is an elongate rigid member shaped as a section of a cylindrical wall, having a first and a second, conical, specifically tapered longitudinal end  13  and  14 . Each longitudinal end  13  and  14  matches the conical surface  8  of flared collar  6  of mid section  2  and the conical surface  11  at the second longitudinal end  12  of outer body  3 , respectively. 
     In use of the connector  1 , a conductor C is axially inserted in one of the outer bodies  3  and its associated shim assembly  4 . The end portion or free end of the conductor C is preferably brought to abutment with the flared surface  8  or the disc wall  5  of mid section  2 . The mid section  2  partially surrounds the exposed section of the conductor C. 
     The outer body  3  is then axially moved towards the mid section  2  and coupled therewith, screwed thereto in the example shown. 
     Both the outer body  3  and the mid-section  2  have hexagonal profiles  15 ,  14  cut into the outer surface as shown, allowing the use of a wrench, preferably of a torque wrench to tighten the connector  1  to a specific torque. 
     The outer bodies  3  may be further locked to the mid-section  2  using a safety means to stop the connector  1  from loosening off, e.g. a pin and groove locking mechanism as disclosed below in connection with  FIG. 5 . 
     The provision of the disclosed matching conical or slanted surfaces  8 ,  13 , and  11 ,  14  allows the shims  4  to be forced radially inwards, towards axis X of connector  1 , when they are forced axially while the outer body  3  is coupled with the mid section  2  during tightening of the connector  1 . Namely, as the length of the assembly of mid section  2  and outer body  3  decreases because of threading them together, the axial compression onto the shims  4  causes a radial compression or force of the shims  4  around and towards the conductor C. The shims  4  thus close down onto the conductor C, also becoming closer to each other. 
     The tightening of the outer bodies  3  to the mid section  2  can be completed using a torque wrench up to a specified torque as said. 
     The slant of the conical surfaces  8 ,  13 , and  11 ,  14  and the length and circumferential extent of the shims  4  are properly selected so that the shims  4  may get closer to each other to clamp onto a connector C essentially all around, irrespectively of the outer diameter of the connector C within a range of outer diameters. Thus, connector  1  has range taking capability as far as the outer diameter of the conductor C is concerned. 
     Three shims  4  each extending slightly less than 120° are shown in the exemplary embodiment but they can be less or more than three, of a proper angular extent. 
     Each shim  4  preferably has a scored inner surface to promote gripping on the conductor C and also to break oxidisation of an aluminium conductor C. When aluminium reacts with oxygen in the air it develops a thin oxide film on the outer surface of the conductor C and/or on the inner surface of the shims  4 . This film can affect the conductivity and therefore it is necessary to remove it just before connection, e.g. using a wire brush. Advantageously, a scored inner surface of the connector  1  will penetrate the thin oxides and will make a clean connection without the necessity to remove it manually. 
     Preferably, the scores on the inner surface of shims  4  comprise grooves circumferentially arranged. In one version, the grooves are helically arranged. 
     In order to keep together the shims  4  that are associated with a same outer body  3  or shim assembly, in the embodiment shown a collapsible spacing ring  17  extends in a groove  18  of the shims  4 . This aids assembly of the connector  1  as well as mounting thereof to conductor C. 
     In order to preserve an equal circumferential spacing or gap between the shims  4 , collapsible spacing ring  17  advantageously has a round pin or bulge  19  between adjacent shims  4 . Bulges  19  maintain the orientation of the shims  4  and their spacing so as to aid fitting by allowing easy insertion of conductor C inside the shim assembly. Upon tightening the connector  1 , all the bulges  19  collapse together so that the gaps between shims  4  reduce together and the circumferential distribution of contact surfaces with conductor C is kept. 
     The size and resistance of the bulges  19  of collapsible spacing ring  17  is so selected that the shims  4  may clamp the conductor C but are prevented to slip around the conductor and group together at the bottom of the connector  1 , what would leave too great of a gap at the top of the connector  1 . 
     Apart from the collapsible spacing ring  17 , the connector  1  is made of metal, preferably of aluminium, brass or copper to ensure electrical conductivity between the two conductors C. 
     Collapsible spacing ring  17  is made for example of a soft rubber. 
     It is emphasised that the connector  1  of the invention provides for several advantages:
         the shims  4  ensure each conductor C is kept concentric to the outer surface of the connector  1 , and therefore also with each other in the case of a straight joint as shown;   thanks to bulged ring  17 , the shims  4  are evenly spaced around the conductor C ensuring good surface contact and, from an electrical point of view, low electrical resistance and absence of voltage differences between the layers of strands of the conductor C;   as seen above, the radial movement of the shims  4  allows for some range taking capability what allows less components to be manufactured, stored and carried at junction sites; moreover there is no need of providing a stepped connector in case two different diameter conductors C are to be jointed;   range taking capability also easily allows jointing connectors C of different diameters;   no special tool is required for installation, rather a wrench suffices;   the connector  1  is highly resistant to axial forces, in that any attempt to withdraw the conductor C from the connector  1  will only result in tightening of the shims  4 .       

     In an alternative embodiment, two or more collapsible spacing rings may be used for each shim assembly. 
     In an alternative embodiment, the shims may have bevelled end(s) and the outer body and/or the mid section may have flared surface(s). 
     In an alternative embodiment, only one or two of the ends of the outer body and the mid section may be bevelled or conical. 
     In other embodiments, interchangeable shims and/or either interchangeable outer bodies or mid sections may be provided to further extend the range take with respect to the diameter of conductor C. 
       FIG. 4  shows a termination lug  1   a  wherein instead of one symmetrical mid section  2  and two outer bodies  3  as disclosed thus far, only one outer body  3  and one lug  2   a  that plays the role of one half mid section and that is shaped to allow e.g. ground or mass connection are used. Shims (not visible in  FIG. 4 ) as discussed above are provided within the single outer body. 
     Although the threaded engagement of mid section  2  and outer bodies  3  or lug  2   a  is particularly advantageous because it allows tightening by a usual wrench, different tightening mechanisms and use of specialized tooling may be provided. A torque limiting device that indicates the connector is tight may also be provided for. 
     By way of an example,  FIG. 5  shows a connector  21  differing from connector  1  in that instead of a screw thread coupling, a pin and groove locking mechanism is used, resembling a bayonet coupling. As the connector outer body  23  is turned to lock the conductor C, a pin  26  of the mid section  22  clicks into one of a plurality of grooves  25  in the side of the outer body  23 , that are arranged at different longitudinal positions along a diagonal groove wherein the pin  26  can slide. There may be provided one groove  25  for each of a plurality of specific size conductors C. An increasing depth of engagement of the outer body  23  with the mid section  22  will again cause an increasing clamping of the shims around the conductor C. 
     Two diametrically opposed pins  26  and corresponding grooves  25 , or a larger number thereof, may also be provided to increase the axial force onto the shims. 
     As mentioned, the screw thread coupling of  FIG. 1  and the pin and groove locking mechanism of  FIG. 5  may be both provided for in a single connector, to enhance the coupling. 
       FIG. 6  shows a connector  31  that differs from that of  FIGS. 1-3  in that the mid section  32  is made longer, and comprises an internal cylindrical wall  35  adjacent a conical surface  38  at an intermediate position thereof. The outer bodies  33  having a hexagonal profile  16  are matingly threaded with the mid section  32 , internally thereto, and exert an axial force onto the shims  34  through a clamping ring  36  having a conical inner surface  37  (not visible). 
     In use, an outer layer of conductor strands S is splayed and spread outside the shims  34 , and held by clamping ring  36 , As the connector  31  is tightened the shims  34  clamp onto the inner layers of strands whilst the outer layer of strands S is held by the clamping ring  36 . This advantageously produces a great surface contact between connector  31  and conductor C for an improved electrical connection. 
     The differences highlighted above may be individually provided as a modification of the connector  1  of  FIGS. 1-3 . 
       FIG. 7  shows a connector  41  wherein again the mid section  42  is made longer, and comprises an internal cylindrical wall  45  and no conical surface. The outer bodies  43  are e.g. matingly threaded with the mid section  42  and exert an axial force onto a collapsible inner member  44 . 
     Collapsible inner member  44  is a tube shaped body comprising two end collars  46  and an intervening portion that comprises apertures  47 . 
     More specifically, apertures  47  are rhomboidal and each wall  48  between two such apertures is hourglass-shaped. Moreover each wall  48  is so slanted with respect to the collars  46  that the neck of the hourglass-shaped wall  47  lies on a smaller circumference than the collars  46 . 
     When the connector  41  is tightened, inner member  44  collapses and the hourglass-shaped walls  48  indent onto the conductor C. 
     In order to increase the grip and electrical contact, more than one series of apertures  47  and hourglass-shaped walls  48  might be provided along the length of the inner member  44 . 
       FIG. 8  shows a connector  51  wherein the two outer bodies  53  are one piece, mid section missing. Each outer body has, at its cable-side end, two or more fingers  55  having a radially inward protruding collar  56 . Conical shaped shims  54  having at least one groove  57  are forced inside the fingers  55  against the action of a spring  58  that surrounds the fingers  55 . As the shims  54  are pushed further in, they clamp the conductor C and are locked in by the radially inward protruding collars  56  of the fingers  55 . Collars  56  exert an axial force onto the shims  54  against axial displacement thereof. 
       FIG. 9  shows a connector  61  wherein again the mid section  62  is made longer, and in this case is preferably comprised of three parts  62   a,    62   b,    62   c  threaded together. Lateral parts  62   a,    62   c  preferably have female threading and intermediate part  62   b  preferably has two male threading matching therewith. Mid section  62  comprises a first internal cylindrical wall  65  having a first diameter at the cable side, and a second internal cylindrical wall  66  having a second diameter smaller than the first diameter and adjacent the first cylindrical wall  65 . 
     Each outer body  63  is matingly threaded with the mid section  62 , internally thereto, and exerts an axial force onto a collapsible inner member  64  axially forcing it towards the step formed by the second internal cylindrical wall  66 . Collapsible inner member  64  is in the form of an O ring having an olive-shaped cross section. 
     In the various embodiments, the outer body(ies) or outer member(s) exert a force in an axial direction onto the shims or inner member(s), which in turn exert(s) a force in a radial direction onto the conductor(s) C. As said terms outer and inner are used relative to each other, not with an absolute meaning. Indeed, in the embodiments of  FIGS. 6 ,  7 ,  9  the mid section  32 ,  42 ,  62  is outer with respect to the outer bodies  33 ,  43 ,  63 . 
     In the various embodiments, the mid section, where provided for, acts as a counter member configured to engage with the outer member(s) to exert the force in axial direction. 
     In the various embodiments, the mid section where provided for may be split into two or three portions connectible with each other as shown in  FIG. 9  or with flanges connected through bolts, so that each of two conductors C may first be independently coupled to a respective connector half. This may simplify the assembly operation. 
     The connectors of the invention are suitable for connecting the inner conductor of a coaxial power cable, or each conductor of a non coaxial power cable. 
     In other embodiments, the inner face of shims  4  may depart from a portion of a cylindrical wall to better adapt to shaped conductors such as lobe shaped conductors or to cables having conductors lying in a plane. 
     The collapsible spacing ring  17  of the embodiment of  FIGS. 1-3  can be provided for in the other embodiments also. 
     As said in connection with  FIG. 8 , the mid section may be missing, the two outer bodies being one piece. In other embodiments, the mid section may be missing, the two outer bodies being coupled to each other, such as by providing an outer threading of one outer body and a matching inner threading of the other outer body, or through bolted flanges. 
     It is highlighted that in the above embodiments the conductor C is held almost about its entire circumference, instead of using screws that screw inside the conductor, that might damage the strands or create voltage differences among them. 
     Experimental testing showed that the connectors of the invention perform well both in terms of resistance to traction and in electrical terms.