Patent Publication Number: US-11652327-B2

Title: Insulation machining in a cable joint

Description:
TECHNICAL FIELD 
     The invention relates to electric cables, for instance in relation to high voltages. More particularly, the invention relates to a method, arrangement and computer program product for improving the properties of a joint between two cable ends. 
     BACKGROUND 
     The forming of joints between cable ends is today a more or less manual exercise where the jointing is performed in armoring or assembly machines. 
     One example of a machine that may be used in the forming of a joint is shown WO 2011/127978. In the machine described in this document a cable is received and held in a fixture. A tool is then used for removing material of the cable in order to obtain a smooth transition between a shielding layer and an insulating layer. 
     Although the document provides some improvements in the forming of a joint, it would be of interest to improve on the obtaining of the joint even further, so that the preparation time is reduced and the quality is improved. 
     Aspects of the invention are concerned with improvements in relation to the above-described interfaces. 
     SUMMARY 
     One object of the invention is therefore to improve the way a joint is obtained. 
     This is according to a first aspect achieved through a method for improving the properties of a joint between two cable ends, the method being at least partly performed by a robot controlled by robot controller and comprising: 
     obtaining two cable ends, the conductors of which are uncovered and joined in a connection zone, each cable end also comprising an uncovered insulation zone comprising uncovered insulation formed as a cone adjacent the uncovered conductor, 
     covering the joined conductors with a layer of additional insulation, 
     measuring the layer of additional insulation and the cones, 
     determining the geometry of the cones and the layer of additional insulation based on the measurements, 
     determining a deviation of the geometry from a desired geometry of the cones and the layer of additional insulation, where the desired geometry comprises a smooth transition from the uncovered insulation zones to the connection zone, 
     determining, based on the deviation determination, material to be removed from the cones and the layer of additional insulation achieving the desired geometry, and 
     removing the material from the cones and the additional layer of insulation in order to obtain a joint with improved properties. 
     The object is according to a second aspect achieved through an arrangement for improving the properties of a joint between two cable ends, the arrangement comprising: 
     a robot with a robot controller, the robot controller being configured to, 
     control the robot to obtain two cable ends, the conductors of which are uncovered and joined in a connection zone, each cable end also comprising an uncovered insulation zone comprising uncovered insulation formed as a cone adjacent the uncovered conductor, 
     control the robot to cover the joined conductors with a layer of additional insulation, 
     control the robot to measure the layer of additional insulation and the cones, 
     determine the geometry of cones and the layer of additional insulation based on the measurements, 
     determine a deviation of the geometry from a desired geometry of the cones and the layer of additional insulation, where the desired geometry comprises a smooth transition from the uncovered insulation zones to the connection zone, 
     determining, based on the deviation determination, material to be removed from the cones and the layer of additional insulation achieving the desired geometry, and 
     control the robot to remove the material from the cones and the additional layer of insulation in order to obtain a joint with improved properties. 
     The object is according to a third aspect achieved through a computer program product for improving the properties of a joint between two cable ends, the computer program product comprising computer program code which when run in a robot controller for a robot, causes the robot controller to: 
     control the robot to obtain two cable ends, the conductors of which are uncovered and joined in a connection zone, each cable end also comprising an uncovered insulation zone comprising uncovered insulation formed as a cone adjacent the uncovered conductor, 
     control the robot to cover the joined conductors with a layer of additional insulation, 
     control the robot to measure the layer of additional insulation and the cones, 
     determine the geometry of the cones and the layer of additional insulation based on the measurements, 
     determine a deviation of the geometry from a desired geometry of the cones and the layer of additional insulation, where the desired geometry comprises a smooth transition from the uncovered insulation zones to the connection zone, 
     determine, based on the deviation determination, material to be removed from the cones and the layer of additional insulation achieving the desired geometry, and 
     control the robot to remove the material from the cones and the additional layer of insulation in order to obtain a joint with improved properties. 
     The invention according to the above mentioned aspects has a number of advantages. It allows a desired geometry to be obtained in a precise way where there are smooth transitions between the cones and the layer of additional insulation. Thereby the electric fields will be smooth and the reliability of the joint increased. Moreover, the production is fast since the one and the same robot may be used for the different operations. There is thereby no need for moving the cables between differed machines. 
     In a first variation of the first and second aspects, the geometries of both cones are considered in the determining of material to be removed for obtaining a smooth transition from one uncovered insulation zone to the connection zone. 
     It is possible that the desired geometry comprises an angle between the cone surface and a longitudinal axis (A) through the conductor. 
     In a second variation of the first aspect, the removal of material is a removal that retains the angle. 
     In a corresponding second variation of the second aspect, the robot controller, when controlling the robot to remove material is further configured to control the robot to retain the angle during the removal. 
     It is furthermore possible that in the desired geometry each cone has a wall with a thickness that decreases towards the connection zone and, in an uncovered insulation zone, the thickness of the cone wall closest to the connection zone is the same as the thickness of the additional layer of insulation at the point where it is closest to said uncovered insulation zone. 
     The desired geometry comprises a smooth surface of the cones and the additional layer of insulation. 
     In a further variation of the first aspect, the removing of material may in this case be a removing of material lowering the level of the surface so that holes disappear. 
     In a corresponding further variation of the second aspect the robot controller when controlling the robot to remove material is further configured to control the robot to lower the level of the surface so that holes disappear. 
     As yet another alternative it is possible that the desired geometry comprises corrugations on the cones and/or the layer of additional insulation. 
     In yet another variation of the first aspect, the method further comprises applying secondary insulation around the additional insulation and cone to a level that is aligned with the surface of the cone where its wall is thickest. 
     In a corresponding variation of the second aspect, the robot controller is further configured to control the robot to apply secondary insulation around the additional insulation and cone to a level that is aligned with the surface of the cone where its wall is thickest. 
     In still another variation of the first aspect, the obtaining of two cable ends comprises, prior to the covering of the uncovered joined conductors with a layer of additional insulation, connecting the uncovered conductors to each other and forming the insulation cones adjacent the connection zone. 
     In a corresponding variation of the second aspect, when obtaining the two cable ends, the robot controller is further configured to control the robot to, prior to the covering of the uncovered joined conductors with a layer of additional insulation, connect the uncovered conductors to each other and form the insulation cones adjacent the connection zone. 
     It should be emphasized that the term “comprises/comprising” when used in this specification is taken to specify the presence of stated features, integers, steps or components, but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described in more detail in relation to the enclosed drawings, in which: 
         FIG.  1    schematically shows a perspective view of an end of a high voltage DC cable, 
         FIG.  2    is a schematic flow scheme of a number of method steps used in the forming of a joint between two cable ends, 
         FIG.  3    schematically shows the forming of a connection between the conductors of the joint in a connecting zone using a robot being controlled by a robot controller, 
         FIG.  4    schematically shows the forming of insulation cones around the connecting zone using the robot, 
         FIG.  5    schematically shows the forming of an additional insulation layer in the connection zone using the robot, 
         FIG.  6    schematically shows a number of measurement points on the insulation cones and the additional insulation layer in the connecting zone for measuring the cones and additional insulation layer, 
         FIG.  7    schematically shows removal of material from of a cone for obtaining a desired geometry of the cones and additional insulation layer, and 
         FIG.  8    schematically shows the adding of further insulation above the cones and additional insulation layer, and 
         FIG.  9    shows a computer program product in the form of a CD ROM disc with a computer program performing the functionality of the control unit of the remote control device. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, for purposes of explanation and not limitation, specific details are set forth such as particular architectures, interfaces, techniques, etc. in order to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention may be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known devices, circuits and methods are omitted so as not to obscure the description of the invention with unnecessary detail. 
     The invention is generally directed towards an electric cable such as a Direct Current (DC) cable like a High Voltage Direct Current (HVDC) cable, for instance operated at 100 kV and above. It should here be realized that the invention is not limited to these types of electric cables, but may also be used in relation to for instance Alternating Current (AC) cables and for cables at other voltage levels. The invention is more particularly concerned with the forming of a joint between two such cables, which joint may as an example be a so-called factory joint. 
       FIG.  1    schematically shows an end portion  24  of a first such DC cable  22  that is to be joined with a corresponding end of a similar second DC cable. The cable is an insulated electric high voltage DC cable  22  and comprises from inside and out: a high voltage DC conductor  10 , a polymer based insulation system  12 - 16 , a grounding layer  18 , and an outer covering or sheath  20 . In this example the insulating system comprises a first insulating layer inside a second insulating layer  14  and a third insulating layer  16  outside of the second insulating layer  14 . The first insulating layer  12  may be a first semiconductive insulating layer, the second insulating layer  14  may be a main insulating layer and the third insulating layer  16  may be a second semiconductive insulating layer. It should here also be realized that the third layer, i.e., the second semiconductive insulating layer may be omitted. 
     The polymer based insulation system  12 - 16  may be extruded, molded, or manufactured in any convenient manner. The main insulating layer  14  may be a crosslinked polyethylene layer, a thermoplastic layer, or a layer of other suitable material. 
     As was mentioned above the invention is concerned with forming a joint between two such cable ends. 
       FIG.  2    shows a number of method steps used in the forming of a joint between two cable ends, where at least some of the steps are being performed by a robot under the control of a robot controller in a method of improving the properties of a joint between two cable ends. 
     The operations performed on the cables by the robot are thus controlled by a robot controller, which also performs calculations in relation to at least some of these operations. This combination of robot and robot controller also forms an arrangement for improving the properties of a joint between two cable ends. 
     In order to obtain the joint it may be necessary to remove the above mentioned grounding layer  18  and sheath  20  from the cable end  24  for obtaining a connection zone in which a connection between the two conductors  10  of two cables are to be made. In order to obtain the connection zone it may also be necessary to remove the insulating system, i.e., the first and second semiconductive insulation layers  12  and  16  and the main insulating layer  14 . Such removal may be performed by the robot using a cutting tool (not shown). Here it may also be mentioned that it is possible that more of the sheath, grounding and second semiconductive insulation layers may be removed than the first semiconductive insulation layer and the main insulation layer, so that this first semiconductive insulation and main insulation layers may extend beyond the edge of the sheath, grounding layer and the second semiconductive layer. Thereby each cable may comprise a part of the connection zone, such as half of the connection zone and an uncovered insulation zone, i.e., a zone where insulation is uncovered and in this case where the second layer of insulation is uncovered. This uncovered insulation zone is also neighboring the uncovered conductor. The uncovered insulation zone may thus be placed adjacent the connection zone. The connection zone thus comprises the uncovered conductors of the two cable ends and this connection zone is surrounded by two uncovered insulation zones, which in turn transition into the non-tampered part of the cable where no layer removal has been made. 
       FIG.  3    schematically shows the robot  42  with robot controller  46  handling the jointing of the cables, where there is a connection zone CZ with the uncovered conductors  10  of two cables that are to be connected and the connection zone CZ is surrounded by a first and a second uncovered insulation zone UIZ 1  and UIZ 2  with remaining first semiconductive insulation  12  and main insulation  14  but removed second semiconductive insulation  16 , ground layer  18  and sheath  20 . In the uncovered insulation zone, the insulation has been uncovered so that it may be exposed to air. In this case it can be seen that the main insulation layer  14  is exposed to air. The first and second uncovered insulation zones UIZ 1  and UIZ 2  thereafter transitions into unaltered or non-tampered cable sections, i.e., cable sections without material being removed. 
     It may here be mentioned that the robot  42  as well as the sections and layers and are not to scale. 
     After the layers have been removed in the above described way from the uncovered insulation zones UIZ 1  and UIZ 2 , and when all material except the conductors have been removed from the connection zone CZ, i.e., only the conductors  10  remain in this zone CZ, the robot  42  connects these conductors, step  26 . This is schematically illustrated in  FIG.  3   . For this purpose the robot  42  may be equipped with a first tool  44  for connecting the conductors  10  with each other. The connecting tool may with advantage be a welding tool used to weld the two conductors to each other, where the welding may as an example be Tungsten Inert Gas (TIG) or Metal Inert Gas (MIG) welding. 
     Thereafter follows the forming of insulation cones, which cones may be truncated cones. The cones may be obtained through shaping the second insulation layer  14  in the uncovered insulation zones UIZ 1  and UIZ 2  into the shape of a cone  50 , step  28 . This shaping is schematically shown in  FIG.  4   . For this reason the robot  42  may be equipped with a second tool  48  that is used to cut and/or smooth the surface of the main insulation layer  14  into the shape of a cone  50 . This type of shaping is made in the uncovered insulation zone on both cable ends. A cone can also be seen as being provided with a wall having a thickness that diminishes or decreases towards the connection zone CZ. 
     It can thus be seen that two cable ends have been obtained where the conductors are uncovered and connected in the connection zone CZ and where the cable ends each also comprises an uncovered insulation zone UIZ 1  and UIZ 2  comprising uncovered insulation  14  formed as a cone  50  neighboring or adjacent the uncovered conductor  10  in the connection zone CZ. 
     After the above mentioned measured have been performed, it is then necessary to place additional insulation around the joined conductors in the connection zone CZ, step  30 . 
     The placing of additional insulation  52  may involve placing additional insulation of the same type as was used in the first insulating layer of the cable. This means that in the present example, the additional insulation  52  would be semiconductive insulation that is placed in the connection zone CZ around the joined conductors  10 . This is schematically shown in  FIG.  5   . The placing may be carried out through the robot  42  employing a third tool  54  that winds sheets of additional insulation around the joined conductors, such as winding sheets of cellulose or polymer paper comprising carbon black particles around the conductors-. The layer  52  of additional insulation material thereby obtained is here provided in a thickness that is roughly equivalent to the inner diameter of the cone  54 . The application may in this case not be exact. 
     Thereafter the robot  42  uses a fourth tool  56 , which may comprise an ultrasonic sensor, in order to measure the additional insulation layer and the cone, step  32 , which measuring may involve measuring the thickness of the additional insulation layer  52  in the connection zone CZ as well as thickness of the cones  50  in the uncovered insulation zones UIZ 1  and UIZ 2 , step  32 . There may because of this be defined a number of measurement points MP along the surface of the cones  50  and the surface of the additional insulation  52 . The measurement points MP may more particularly be provided radially around as well as axially along a longitudinal axis A defined by the conductors  10  of the joint. 
     A measurement point may as an example be defined on the surface of a cone  50  at an axial position along the longitudinal axis A. A number of measurement points of the cone surface surrounding the axis at the same axial position may become a set of measurement points. The points may in this case follow a curve defined by the shape of the cone, such as a circle, which curve may be provided in a plane that is perpendicular to the axis A. A number of such sets of measurement points may then be defined on the surfaces of the cones  50  along the axis A in the first and second uncovered insulation zones UIZ 1  and UIZ 2  as well as on the surface of the additional insulation layer  52  in the connection zone CZ. The surfaces are in this case the outer surfaces, i.e., the surfaces facing away from the axis A. 
     The measurements may be made through the robot  42  moving the tool  56  between measurement points. As an alternative it is possible that the robot is moved axially between the two uncovered insulation zones UIZ 1 , UIZ 2  while the cable ends  24  are being rotated by a machine. 
     Based on the measurements obtained from the measurement points MP, the robot controller  46  then forms a model of the geometry of the cones  50  in the uncovered insulation zones UIZ 1 , and UIZ 2  and the additional insulation layer in the connection zone CZ, step  33 . 
     The robot controller  46  may therefore determine the shapes of the cones and the additional insulation layer as well as the thicknesses of the cone walls and additional insulation layer. It may also detect any protrusions or holes in the outer surface of the cones and the additional insulation layer. 
     Based on the information from the measurements, the robot controller  46  thus builds a model, such as three-dimensional model of the cones and additional insulation in which models the shapes, including any surface irregularities, and thicknesses of theses element are defined. 
     The robot controller  46  may thereafter determines a deviation of the model geometry from a desired geometry of the cones and layer of additional insulation, step  34 , where the desired geometry comprises a smooth transition from the uncovered insulation zones to the connection zone. 
     A desired geometry may be a geometry where protrusions and holes have been removed from the surfaces of the cones and additional insulation layer. It may additionally be the achieving of a desired surface quality, which desired surface quality may be that the surface is smooth. As an alternative a desired surface quality may be a surface of the cones and/or the additional insulation layer having corrugations. 
     A desired cone geometry may comprise a desired cone shape and a desired shape of the additional insulation. A desired cone shape may be based on using a desired angle of inclination a of the outer surface of a cone  50  to the longitudinal axis A defined by the conductor  10 . Also the additional insulation may have a desired shape relating to an angle of inclination. However, in this case the desired angle of inclination is zero as the outer surface is parallel with the axis A. A desired shape of the additional insulating layer may be a cylinder shape with a desired thickness. A desired cone shape may comprise a smooth surface or a corrugated surface at the desired angle of inclination and a desired shape of the additional insulation may also comprise a smooth or corrugated surface. 
     A cone may have a nominal shape defined by the above-mentioned angles and the measurements being made in an uncovered insulation zone may lead to deviations of the cone surface from this shape through the occurrence of protrusions and holes. It is in the same way possible that the measurements being made of the additional insulation layer may lead to deviations of the measured insulation layer surface from the desired insulation layer surface shape through the occurrence of protrusions and holes. 
     Another possible deviation is that the desired surfaces are to comprise corrugations, while the surfaces of the model do not. 
     Thereafter the robot controller  46  determines material to be removed from the cones  50  and the additional insulating layer  52  that achieves the desired geometry based on the deviation determination, step  35 . 
     The determination may therefore involve a determination of material to be removed that achieves the desired cone shape and additional insulation shape. 
     If the desired shapes comprise smooth surfaces then this may be achieved through removing material to a level below the surface of the model where no holes remain. This removal may then also be made while retaining the same angle of inclination. The determination may thus be a determination of amount of removal of material from a cone  50  that retains the angle α while providing a smooth cone surface together with removal of material from the semiconductive insulation layer  52  that makes the radial surface of the semiconductive insulation layer smooth. 
     In another variation, holes and protrusions are still removed, while at the same time introducing corrugations. 
     Moreover as one aspect of the desired geometry is that there should be a smooth or seamless transition from the uncovered insulation zones to the connection zone, i.e., that there is a seamless transition from a cone  50  to the additional insulation layer  52 , the edge of a cone  50  adjacent the connection zone CZ has to be flush with the outer periphery of the semiconductive insulation layer  52  of the connection zone CZ. The edge of the outer surface of the cone  50  in an uncovered insulation zone UIZ 1  or UIZ 2  being closest to the connection zone CZ thus has to be flush with the outer surface of the additional insulation layer  52 . This means that the core surface at this edge, is to have the same radial distance to the longitudinal axis A as the additional insulation layer  52  This condition is required for both cones. Put differently, it can be seen that in an uncovered insulation zone the thickness of the cone wall closest to the connection zone CZ is the same as the thickness of the additional insulation layer at the point where it is closest to this uncovered insulation zone. 
     In the case of obtaining a smooth surface, this means that if the amount of material needed to be removed from a cone  50  while retaining the profile leads to the part of the outer surface of a cone that is closest to the connection zone CZ having a first distance to the axis A and the determination of the amount of material needed to be removed from the connection zone CZ leads to the outer surface of the additional insulating layer  52  having a second distance to the longitudinal axis, then more material has to be removed from the additional insulating layer  52  if the second distance is higher than the first distance, even though a material removal corresponding to the second distance is sufficient for obtaining a smooth surface. In an analogous manner more material has to be removed from the cone, while retaining the desired angle if the first distance is longer than the second distance. 
     As this consideration has to be made for both cones, the consideration made above regarding the first and second distances associated with one cone and the additional insulation layer  52  has to at the same time include a consideration of a third distance of a second cone corresponding to the first distance. The element having the lowest distance to the axis A, such as one of the cones or the additional insulation layer, is then decisive for the determination of material to be removed also from the other elements. It can thereby also be seen that the geometries of both cones are considered in the determining of material to be removed for obtaining a smooth transition from one uncovered insulation zone to the connection zone. 
     After having determined the material removal that achieves the desired geometry, the robot controller  46  then controls the robot  42  to remove the material for obtaining the desired shape, step  36 . In this case it is possible that the second tool  48  is reused, as is shown in  FIG.  7   . Here also the angle α is shown. 
     Thereafter the robot  42  applies further insulation  58  around the cones  50  and the additional insulation layer  52  in the connecting section CZ so that the insulation is aligned with insulation of the cable, step  38 . This further insulation is with advantage of the same type as the insulation used in the second insulation layer  14  of the cable, i.e., the same material as is present in the cones  50 . This may be done using the third tool  48  and winding strips of insulation round the cones and semiconductive insulation. This is schematically shown in  FIG.  8   . 
     Thereafter may follow a heat treatment of the applied insulation as well as the application of a ground layer and sheath. In all these latter steps the same robot may be used. 
     It can in this way be seen that the desired geometry is obtained in a precise way where there are smooth transitions between the cones and the additional insulation layer and smooth or corrugated surfaces. Thereby the electric fields will be smooth and the reliability of the joint increased. Moreover, the production is fast since the same robot may be used for the different operations. There is thereby no need for moving the cables between differed machines. 
     Here it may also be mentioned that although different tools were described above, it is possible to use a multipurpose tool having cutting, smoothing and winding functionality, in which case the speed may be increased even further. 
     There are a number of variations that are possible apart from those already discussed. It is for instance possible that the initial step of removing material and forming of cones are not performed using a robot, but instead are carried out in one or two dedicated machines. It is also possible that the applying of ordinary insulation above the cones and the semiconductive insulation layer is performed in a dedicated machine. 
     It is also possible that the application of the semiconductive insulation layer in the connection zone is performed in a separate machine. 
     It is thus possible that only the measuring and the removal of material in order to obtain a desired shape are actually performed by the robot. 
     Another possible variation is that the semiconductive insulation being applied is not being wound as strips. It may be applied as a number of blocks that fit into each other when being placed around the connected conductors. 
     The robot controller may be implemented as a processor with associated program memory comprising computer instructions for implementing its functionality. 
     The robot controller may therefore be provided in the form of a processor with associated program memory including computer program code for performing its functionality. It may also be provided in the form of a digital signal processor (DSP), Application Specific Integrated Circuit (ASIC) or Field-Programmable Gate Array (FPGA). 
     A computer program may also be a computer program product, for instance in the form of a computer readable storage medium or data carrier, like a CD ROM disc or a memory stick, carrying a computer program with the computer program code, which will implement the functionality of the above-described robot controller when being loaded into a processor. One such computer program product in the form of a CD ROM disc  60  with the above-mentioned computer program code  62  is schematically shown in  FIG.  9   . 
     A computer program product may also be a program provided via a server and downloaded therefrom to the robot controller. 
     While the invention has been described in connection with what is presently considered to be most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements. Therefore, the invention is only to be limited by the following claims.