Patent Publication Number: US-11640861-B2

Title: Power cable which reduces skin effect and proximity effect

Description:
FIELD OF THE INVENTION 
     The invention is directed to a cable which has individual conductors arranged to reduce or eliminate skin effect and proximity effect. 
     BACKGROUND OF THE INVENTION 
     In standard Litz constructions, individual strands are insulated from each other and are then bundled together. The original intent was to minimize electrical skin effect in RF coils in early radio thereby increasing available signal strength. In order to use Litz wires for power, the gauge of the strands remains small (30 to 40 AWG) and the strand count is greatly increased. This creates two major deficiencies. First, the insulated strands tend to short together over time, destroying the countering effect to skin effect. Second, to terminate traditional Litz wire each and every strand mist be terminated at both ends by either butt soldering or chemically stripping the insulation and crimping. Both of the termination methods are unreliable. 
     It would, therefore, be beneficial to provide a power cable which has a plurality of individual conductors which are configured to support 100% cross sectional usage to maximize power carrying capability, to allow known termination techniques, such as soldering or crimping, to be used. In would also be beneficial to provide a power cable which has a plurality of individual conductors which are configured to reduce or eliminate the skin effect of the power cable and the proximity effect of the power cable. 
     SUMMARY OF THE INVENTION 
     The following provides a summary of certain illustrative embodiments of the present invention. This summary is not an extensive overview and is not intended to identify key or critical aspects or elements of the present invention or to delineate its scope. 
     The power cable of the present invention allows the gauge size of the conductors to be maximized to support 100% cross sectional usage for current conduction, thereby allowing conventional termination techniques, such as soldering or crimping. 
     The power cable of the present invention allows for a much more robust construction than traditional Litz construction by eliminating the delicate strand to strand insulation of the Litz construction. 
     The power cable of the present invention use of a phase interweave, coupled with an external shield and placement of a central conductor ground references allows the electrical proximity effect to be canceled. 
     An embodiment is directed to a power cable having an outer shell and a plurality of individual conductors. The plurality of individual conductors are positioned in the outer shell. The individual conductors have a cross sectional area which is optimized. The individual conductors have the same diameter and each individual conductor is configured to support 100% cross sectional usage to maximize power carrying capability. The diameter of the individual conductors is proximate to, but below, the skin effect cutoff diameter of the individual conductors. 
     An embodiment is directed to a power cable having a shield referenced to a system ground potential and multiple individual phase interweave power conductors. The multiple individual phase interweave power conductors have a phase interweave which cancels the electrical proximity effect. 
     An embodiment is directed to a power cable having a central ground conductor. Phase interweave power conductors are positioned about the central ground conductor. Individual phase interweave power conductors have the same diameter. The individual phase interweave power conductors have a cross sectional area which is optimized. Each of the individual phase interweave power conductors is configured to support 100% cross sectional usage to maximize power carrying capability. The power cable reduces the skin effect of the power cable and the proximity effect of the power cable. 
     Additional features and aspects of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the illustrative embodiments. As will be appreciated by the skilled artisan, further embodiments of the invention are possible without departing from the scope and spirit of the invention. Accordingly, the drawings and associated descriptions are to be regarded as illustrative and not restrictive in nature. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated into and form a part of the specification, schematically illustrate one or more illustrative embodiments of the invention and, together with the general description given above and detailed description given below, serve to explain the principles of the invention, and wherein: 
         FIG.  1    is a diagrammatic view of an application in which the power cable is used. 
         FIG.  2    is an enlarged cross sectional view of the cable taken along line  2 - 2  of  FIG.  1   . 
         FIG.  3    is a cross sectional view of an alternate embodiment of the cable, 
         FIG.  4    is a cross sectional view of another alternate embodiment of the cable. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The description of illustrative embodiments according to principles of the present invention is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description. In the description of embodiments of the invention disclosed herein, any reference to direction or orientation is merely intended for convenience of description and is not intended in any way to limit the scope of the present invention. Relative terms such as “lower,” “upper,” “horizontal,” “vertical,” “above,” “below,” “up,” “down,” “top” and “bottom” as well as derivative thereof (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) should be construed to refer to the orientation as then described or as shown in the drawing under discussion. These relative terms are for convenience of description only and do not require that the apparatus be constructed or operated in a particular orientation unless explicitly indicated as such. Terms such as “attached,” “affixed,” “connected,” “coupled,” “interconnected,” and similar refer to a relationship wherein structures are secured or attached to one another either directly or indirectly through intervening structures, as well as both movable or rigid attachments or relationships, unless expressly described otherwise. Moreover, the features and benefits of the invention are illustrated by reference to the preferred embodiments. Accordingly, the invention expressly should not be limited to such preferred embodiments illustrating some possible non-limiting combination of features that may exist alone or in other combinations of features, the scope of the invention being defined by the claims appended hereto. 
     Illustrative embodiments of the present invention are now described with reference to the Figures. Reference numerals are used throughout the detailed description to refer to the various elements and structures. Although the following detailed description contains many specifics for the purposes of illustration, a person of ordinary skill in the art will appreciate that many variations and alterations to the following details are within the scope of the invention. Accordingly, the following embodiments of the invention are set forth without any loss of generality to, and without imposing limitations upon, the claimed invention. 
     As shown in  FIG.  1   , a power cable  10  has connectors  12 ,  14  at either end. The power cable  10  is used to provide an electrical interconnection between to components  12 ,  14 . The configuration shown in  FIG.  1    is meant to be illustrative, as the cable  10  of the present invention can be used in many varied application. Examples include, but are not limited to: airspace industry, providing power to turbines for aircraft; rail industry, providing power from the converters to the motor; and automotive industry, providing power from the batteries in electric vehicles to the motor. 
     As shown in the cross sectional view of the cable  10  in  FIG.  2   , the cable  10  includes an external shield or shell  20 , a plurality or multiple individual phase interweave power conductors  22  and a central conductor  24 . In the illustrative embodiment shown, nine individual phase interweave power conductors  22  are positioned around the circumference of the central conductor  24 , but other configurations may be used. 
     The shell  20  includes an outer insulative sleeve  30 , an inner insulative sleeve  32  and a conductive member  34  provided between the outer insulative sleeve  30  and the inner insulative sleeve  32 . The conductive member  34  may be a braided member which is configured to be provided in electrical engagement with the system ground potential. However, other types of known shell  20  which provide a ground path may be used. 
     The central conductor  24  is an individual wire with an insulative jacket or coating. The central conductor  24  is a ground reference which is configured to be provided in electrical engagement with the system ground potential. The gauge or size of the central conductor  24  is dependent upon the size of the multiple individual phase interweave power conductors  22  and the amount of current the power cable  10  is rated to carry. 
     A filler  36  may be provided about the circumference of the central conductor  24 . The filler  36  is made from insulative material and is configured to provide the proper spacing between the central conductor  24  and the plurality or multiple individual phase interweave power conductors  22 . The filler  36  may be an extrusion over the central conductor  24 . However, other types of fillers  36  may be used. 
     The power conductors  22  are individual wires with an insulative jacket or coating. The gauge or size of each of the individual power conductors  22  is dependent upon the amount of current the power cable  10  is designed or rated to carry. Each of the individual power conductors  22  is configured to have the same size or gauge as the other individual power conductors  22 . 
     For a three phase system, there is at least one power conductor  22  per phase with the number of power conductors  22  increasing in multiples of three, to carry more current. In the illustrative embodiment shown in  FIG.  2   , the power cable  10  has nine power conductors  22  with three being fed by each phase in the system. 
     The size or gauge of the power conductors  22  is chosen such that the diameter of each of the power conductors  22  is proximate to, but just below or less than, the skin effect cutoff diameter for the maximum operating frequency of the power cable  10 . The individual power conductors  22  have a cross sectional area which is configured to support 100% cross sectional usage to maximize power carrying capability of the power conductors  22  and the power cable  10 . This allows the gauge of the power conductors  22  to be optimized to carry the desired power, while having a large enough diameter to allow for the use of existing termination techniques, such as, but not limited to, soldering or crimping. 
     The power conductors  22  are arranged to have a phase interweave. Examples of desired phase interweaves for power cable  10  with nine power conductors  22  include, but are not limited to, 1,2,3-2,3,1-3,1,2 or 1,2,3-1,2,3-1,2,3 or 1,2,1-2,3,2-3,1,3, where: 1 represents current carrying lines carrying current in the first phase; 2 represents current carrying lines carrying current in the second phase; and 3 represents current carrying lines carrying current in the third phase. The interweave allows that, for any given conductor, if the preceding phase is lagging, the subsequent phase is always leading. This allows the proximity effect in the power conductors  22  to be minimized or canceled, thereby minimizing the effective resistance of each of the power conductors  22 . 
     By maximizing the gauge size of the power conductors  22  to just support 100% cross sectional usage for current conduction, conventional termination techniques are possible by soldering or crimping. This creates a much more robust Litz construction as compared to known Litz construction, as the delicate strand to strand insulation present with known Litz construction is eliminated. In addition, the overall cross section for current carrying path associated with the power conductors  22  of the power cable  10  is reduced when compared to known Litz construction, as the bulk associated with individual strand wise insulation is eliminated. 
     By use of the power conductors  22  and the phase interweave, coupled with the grounded external shield or shell  20  and placement of the grounded central conductor  24 , the electrical proximity effect is canceled. This allows the effective resistance of the power cable  10  to be reduced compared to known power cables in which the proximity effect is not canceled or addressed. 
     For example, in a nine power conductor  22  power cable  10  with a ground central conductor  24  (10 AWG) and a grounded shell  20  (10 mil of perfluoroalkoxy (PFA) insulation) which is rated for a 3 KHz power feed, the individual conductors  22  are configured to have a nominal diameter of 0.130 inches (10 AWG) to accommodate 55 amps per conductor  22 . 
     Alternate illustrative embodiments are shown in  FIGS.  3  and  4   .  FIG.  3    is an illustrative embodiment of a power cable  110  with a triangular phase grouping of the power conductors  122  with infinite parent cable lay with the power conductors  122  laid straight along the length of the power cable  110 , with no rotation. The power cable  110  may or may not include a central ground reference conductor. 
     In this illustrative embodiment, the power cable  110  has nine power conductors  122  with three being fed by each phase in the system. The size or gauge of the power conductors  122  is chosen such that the diameter of each of the power conductors  122  is proximate to, but just below or less than, the skin effect cutoff diameter for the maximum operating frequency of the power cable  110 . The individual power conductors  122  have a cross sectional area which is configured to support 100% cross sectional usage to maximize power carrying capability of the power conductors  122  and the power cable  110 . This allows the gauge of the power conductors  122  to be optimized to carry the desired power, while having a large enough diameter to allow for the use of existing termination techniques, such as, but not limited to, soldering or crimping. 
     The power conductors  122  are arranged in a triangular arrangement with triangular groupings of power conductors  122  spaced by triangular fillers  136  positioned between. An example of a desired arrangement of the power conductors  122  for a power cable  110  with nine power conductors  122  includes, but is not limited to, phase 1 conductors include A 1 , B 3 , C 2 , phase 2 conductors include B 1 , A 2 , C 3 , and phase 3 conductors include C 1 , B 2 , A 3 . This arrangement allows the proximity effect in the power conductors  122  to be minimized, thereby minimizing the effective resistance of each of the power conductors  122 . 
       FIG.  4    is another illustrative embodiment of a power cable  210  with a triangular phase grouping of the power conductors  222  with an inner ring layer and an outer ring layer having counter rotating lays. The inner ring layer, comprising A 1 , B 1 , C 1 , has a left hand rotation. infinite parent cable lay. The outer ring layer, comprising A 2 , A 3 , B 2 , B 3 , C 2 , C 3 , has a right hand rotation. 
     In this illustrative embodiment, the power cable  210  has nine power conductors  222  with three being fed by each phase in the system. The size or gauge of the power conductors  222  is chosen such that the diameter of each of the power conductors  222  is proximate to, but just below or less than, the skin effect cutoff diameter for the maximum operating frequency of the power cable  210 . The individual power conductors  222  have a cross sectional area which is configured to support 100% cross sectional usage to maximize power carrying capability of the power conductors  222  and the power cable  210 . This allows the gauge of the power conductors  222  to be optimized to carry the desired power, while having a large enough diameter to allow for the use of existing termination techniques, such as, but not limited to, soldering or crimping. 
     The power conductors  222  are arranged in a triangular arrangement with triangular groupings of power conductors  222  spaced by round fillers  236  positioned between. An example of a desired arrangement of the power conductors  122  for a power cable  110  with nine power conductors  122  includes, but is not limited to, phase 1 conductors include A 1 , B 3 , C 2 , phase 2 conductors include B 1 , A 2 , C 3 , and phase 3 conductors include C 1 , B 2 , A 3 . As the inner layer counter rotates relative to the outer layer, the phase positions changes along the length of the power cable  10 , allowing the proximity effect in the power conductors  222  to be minimized or canceled, thereby minimizing the effective resistance of each of the power conductors  222 . 
     Other illustrative embodiments may include, but are not limited to: variations on the grouping or separation of the power conductors based on the number of power conductors used; other phase interweave patterns for each of the multiple groupings; individual shielding options for each of the groupings; and/or replacing the left or right cable twisting with conductor braid arrangements, with or without a woven in ground reference in each braid group. 
     While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the spirit and scope of the invention as defined in the accompanying claims. One skilled in the art will appreciate that the invention may be used with many modifications of structure, arrangement, proportions, sizes, materials and components and otherwise used in the practice of the invention, which are particularly adapted to specific environments and operative requirements without departing from the principles of the present invention. The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being defined by the appended claims, and not limited to the foregoing description or embodiments.