Patent Publication Number: US-6903277-B2

Title: Conduit for use in the transmission of electrical power

Description:
FIELD OF THE INVENTION 
   This invention relates generally to the transmission of electrical power, and in particular, to a conduit for transmitting three-phase electrical power from a power source to a target that significantly minimizes the leakage of common mode noise, the associated phenomenon and the associated currents created by such transmission that may stray into the physical earth and elsewhere. 
   BACKGROUND AND SUMMARY OF THE INVENTION 
   Electrical power is supplied to rural America using three-phase electrical power transmitted over three conductors. In order to minimize the cost of supplying electrical power to these rural areas, the physical earth is used as a return path for the imbalances in electrical power. While functional for its intended purpose, the use of the physical earth as the return path for the three-phase electrical power has resulted in certain unforeseen effects on livestock. More specifically, the energy flowing through physical earth has been found to have a detrimental effect on the feeding habits and milking of livestock, as well as, pregnant livestock and their young. 
   Compounding the problems associated with the use of physical earth as a return path for the imbalances in electrical power, in order to save costs and conserve energy, farmers have begun utilizing variable frequency drives to power the various motors and equipment utilized on their farms. These variable frequency drives allow a farmer to vary the electrical power supplied to the motors and equipment utilized on the farm, thereby resulting in a significant amount of energy savings for both the farmer and the electrical co-generation facility. However, it has been found that the phase waveforms supplied by the variable frequency drive are not identical at any given time. By transmitting these phase waveforms, common mode noise, and associated phenomenon over the conductors, additional stray currents flow through the physical earth. As heretofore described, these stray currents flowing through the physical earth may cause adverse effects on the livestock maintained on the farm. In view of the foregoing, it can be appreciated that it is highly desirable to minimize the flow of stray currents through the physical earth. 
   Therefore, it is a primary object and feature of the present invention to provide a conduit that may be used for transmitting three-phase electrical power from a power source to a target. 
   It is a further object and feature of the present invention to provide a conduit that minimizes the leakage of common mode noise, associated phenomenon, and associated stray currents created by the transmission of electrical power. 
   It is a still further object and feature of the present invention to provide a conduit that is simple to manufacture and to utilize. 
   It is a still further primary object and feature of the present invention to provide a conduit that inhibits all cross talk between the conduit and adjacent conduits. 
   In accordance with the present invention, a conduit is provided for use in the transmission of electrical power. The conduit includes a plurality of conductors for electrically connecting a power source and a component. Each conductor has a predetermined length and includes a wire having insulation wrapped thereabout. A flexible inner jacket has an inner surface defining a passageway for housing the conductors and an outer surface. A tubular core extends about the outer surface of the inner jacket. Braiding is wound about the outer surface of the core. The braiding has first and second opposite ends. A flexible outer jacket extends about the braiding. 
   The conduit further includes a ground wire extending within the inner jacket. The ground wire may be wrapped around the insulation of at least one of the conductors or extend along the length of at least one of the conductors. The braiding includes first and second end portions. Each end portion of the braiding extends through the outer jacket of the conduit. The outer jacket includes first and second ends. First and second connectors may be mounted on corresponding ends of the outer jacket. 
   In accordance with a further aspect of the present invention, a conduit is provided for carrying electrical power from a power source to a target. The power source and the target have terminals and neutral points. The conduit includes a conductor operatively connecting the terminal of the power source and the terminal of the target. Braiding extends about the conductor for operatively connecting the neutral point of the power source and the neutral point of the target. 
   The conduit may include a ground wire having first and second ends. The ground wire is positioned adjacent to and extends along the length of the conductor. The first end of the ground wire is operatively connectable to a first end of a braiding and the second end of the ground wire is operatively connectable to the second end of the braiding. The conduit may include a hollow core that defines a passageway for the conductor to pass therethrough. In addition, the conduit may include a flexible inner jacket positioned between the conductor and the core, and a flexible outer jacket extending about the braiding. As such, the braiding separates the outer jacket from the core. The braiding may include first and second end portions. Each end portion extends through the outer jacket of the conduit. The ground wire may extend along the length of the conductor or be wrapped about the conductor. 
   In accordance with a still further aspect of the present invention, a conduit is provided for carrying three-phase electrical power from a power source to a target. The power source has terminals corresponding to each phase of the electrical power, a neutral point and a ground terminal. The target has terminals corresponding to each phase of the electrical power and a ground terminal. The conduit includes a first conductor having a first end connectable to a first terminal of the power source and a second end connectable to a first terminal of the target. A second conductor has a first end connectable to a second terminal of the power source and a second end connectable to a second terminal of the target. A third conductor has a first end connectable to a third terminal of the power source and a second end connectable to a third terminal of the target. A shield extends about the conductors for preventing electromagnetic and radio frequency interference from passing therethrough. Braiding extends about the shield. The braiding has a first end portion connectable to the neutral point of the power source and a second end portion connectable to the ground terminal of the target. 
   The conduit may also include a first ground wire positioned adjacent the first conductor. The first ground wire has a first end connectable to the ground terminal of the power source and a second end connectable to the ground terminal of the target. A second ground wire is positioned adjacent the second conductor. The second ground wire has a first end connectable to the ground terminal of the power source and a second end connectable to the ground terminal of the target. A third ground wire is positioned adjacent the third conductor. The third ground wire has a first end connectable to the ground terminal of the power source and a second end connectable to the ground terminal of the target. 
   It is contemplated to provide a flexible inner jacket between the conductors and the shield, and a flexible outer jacket about the braiding. The first and second end portions of the braiding extend through the outer jacket of the conduit. The shield of the conduit includes first and second ends. It is contemplated to mount connectors on corresponding ends of the shield. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The drawings furnished herewith illustrate a preferred construction of the present invention in which the above advantages and features are clearly disclosed as well as others which will be readily understood from the following description of the illustrated embodiment. 
     In the drawings: 
       FIG. 1  is an isometric view of a portion of a first configuration of a conduit in accordance with the present invention; 
       FIG. 2  is an isometric view of a portion of a second configuration of a conduit in accordance with the present invention; 
       FIG. 3  is an isometric view of a portion of a third configuration of a conduit in accordance with the present invention; 
       FIG. 4  is an isometric view of a conduit in accordance with the present invention; 
       FIG. 5  is a cross-sectional view of the conduit of the present invention taken along line  5 — 5  of  FIG. 4 ; 
       FIG. 6  is a side elevational view, partially in section, showing connection of first and second conduits within a variable frequency drive housing; 
       FIG. 7  is an enlarged, cross-sectional view of the housing for the variable frequency drive housing taken along line  7 — 7  of  FIG. 6 ; 
       FIG. 8  is a side elevational view, partially in section, showing connection of first and second conduits within a junction box; and 
       FIG. 9  is a schematic view of an electric circuit utilizing a plurality of conduits in accordance with the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIG. 4 , a conduit in accordance with the present invention is generally designated by the reference numeral  10 . As hereinafter described, it is intended that conduit  10  be used to carry three-phase electrical power from an isolation source transformer  62  to a motor  64 , FIG.  9 . It can be appreciated that conduit  10  may carry electrical power between other components without deviating from the scope of the present invention, and that the number of phases of electrical power carried by conduit  10  may be varied, by merely varying the number of conductors  12  provided in conduit  10 . 
   Conduit  10  includes a plurality of conductors  12  corresponding in number to the number of phases of the electrical power transmitted thereon. Each conductor  12  includes a plurality of conducting wires  14  positioned adjacent to each other and insulation  16  molded about the grouping of adjacent conducting wires  14 . Insulation  16  maintains conducting wires  14  of corresponding conductors  12  adjacent to one another so as to isolate conducting wires  14  of one conductor  12  from the conducting wires  14  of the other conductors  12  in conduit  10 . 
   Conduit  10  further includes a plurality of ground wires  18  corresponding to the number of phases of the electrical power transmitted by conduit  10 .  FIGS. 1-3  disclose alternate configurations of ground wires  18  for use in conduit  10  of the present invention. Referring to  FIG. 1 , a first configuration of ground wires  18  for conduit  10  is depicted. Each ground wire  18  includes a plurality of ground wire strands  24  grouped together. Ground wires  18  are positioned longitudinally adjacent to outer surfaces  16   a  of insulation  16  of corresponding pairs of conductors  12 . Referring to  FIG. 2 , a second alternate configuration of ground wires  18  for conduit  10  is depicted. The plurality of ground wire strands  24  of ground wire  18  are wrapped about corresponding outer surfaces  16   a  of insulation  16  of conductors  12  in order to maintain wire strands  24  in close proximity to conducting wires  14  of corresponding conductors  12 . Referring to  FIG. 3 , a third alternate configuration of ground wires  18  of conduit  10  is depicted. In the third configuration, ground wire strands  24  of ground wires  18  take the form of metallic tape  19  constructed from heavy copper or the like. Tape  19  is spirally wrapped about outer surfaces  16   a  of insulation  16  of conductors  12  such that tape  19  is close as possible to conducting wires  14  of corresponding conductors  12 . 
   Inner jacket  26  is provided in order to maintain conductors  16  and corresponding ground wires  18  in close proximity. As best seen in  FIG. 5 , inner jacket  26  includes an inner surface  28  defining passageway  30  for receiving conductors  12  and ground wires  18  therein, and an outer surface  31 . It is contemplated that inner jacket  26  be formed from a flexible material. Conduit  10  further includes a metallic core  32  constructed from galvanized steel, bronze or the like. Core  32  includes an inner surface  34  defining passageway  36  therethrough for receiving inner jacket  26 , and an outer surface  38 . Wire braid  40  is wrapped about outer surface  38  of core  32 . It is intended that wire braid  40  and core  32  shield conductors  12  by preventing electromagnetic interference and radio frequency interference from passing therethrough and that wire braid  40  provide a low impedence path for high frequency associated phenomenon to pass. Conduit  10  further includes an outer jacket  42  wrapped about wire braid  40 . Outer jacket  42  includes an inner surface  44  which engages wire braid  40  and an outer surface  46 . It is intended for outer jacket  42  to be formed from PVC or a similar material so as to discourage oils, acids, alkalines, ozone and ultraviolet light from passing therethrough. 
   As best seen in  FIGS. 6-7 , inner jacket  26 , conductors  12  and ground wires  18  extend beyond ends  32   a  of core  32 . In addition, ends  32   a  of core  32  project through wire braid  40  such that end portions  40   a  of wire braid  40  adjacent corresponding ends  32   a  of core  32  bunch together to facilitate the connection of wire braid  40  to targets such as terminals, wires or the like. End portions  40   a  of metal braid  40  project through outer jacket  42  to further facilitate connection of end portions  40   a  of metal braid  40  to targets. Alternatively, portions of outer jacket  42  adjacent corresponding ends  32   a  of core  32  may be removed to expose end portions  40   a  of metal braiding  40 . It can be appreciated that electrical tape or the like may be used to retain the position and configuration of end portions  40   a  of metal braid  40 . Connectors  48  are mounted on corresponding ends  32   a  of core  32  to allow conduit  10  to be interconnected to a mounting bracket, junction box or the like. Each connector  48  includes a ferrule  50  threaded onto a corresponding end  32   a  of core  32  and a back nut  52 . 
   Referring to  FIG. 9 , an electrical circuit utilizing first, second and third conduits  10   a ,  10   b  and  10   c , respectively, is generally designated by the reference numeral  60 . First, second and third conduits  10   a ,  10   b  and  10   c  are identical in structure to conduit  10 , heretofore described, and as such, the prior description of conduit  10  is understood to describe first, second and third conduits  10   a ,  10   b  and  10   c , respectively, as if fully described herein with common reference characteristics being used. Conduits  10   a ,  10   b  and  10   c  are used to interconnect isolation source transformer  62 , variable frequency drive  72 , and motor  64  so as to minimize the leakage of common mode noise, to contain associated phenomenon and to inhibit associated currents that may stray into the physical earth as a consequence of the transmission of electrical power therebetween. As is conventional, isolation source transformer  62  provides three-phase electrical power and includes terminals  64  corresponding to each phase of the electrical power supplied and a neutral point X 0 . Isolation source transformer  62  is housed in a housing  66  that includes a grounding bus  68  operatively connected to the physical earth  70  by line  69 . The first ends of conducting wires  14  of each conductor  12  are operatively connected to corresponding terminals  64  of isolation source transformer  62 . The first ends of ground wires  18  are joined together and operatively connected to end portion  40   a  on a first end of wire braid  40 ; to neutral point X 0  of isolation source transformer  62 ; and to grounding bus  68  of housing  66 . A first end  32   a  of core  32  of conduit  10  is rigidly connected to housing  66  utilizing connector  48 , as heretofore described. 
   The second, opposite end of first conduit  10   a  is operatively connected to variable frequency drive  72 . As is conventional, variable frequency drive  72  converts three-phase, 60 hertz input electrical power to an adjustable frequency and voltage source for controlling the speed of motor  64 . Referring to  FIGS. 6 and 7 , variable frequency drive  72  is contained within a housing  74  that is isolated from the physical earth. Housing  74  takes the form of a metallic box having an opening  78  in first sidewall  80  thereof so as to allow the second end of first conduit  10   a  to pass therethrough. Guide  81  is provided in opening  78  in first sidewall  80  of housing  74 . Guide  81  includes tubular guide member  82  having a first threaded end  84  extending through opening  78  in sidewall  80  of housing  74 . Lock nut  86  is threaded onto threaded end  84  of guide member  82  so as to capture sidewall  80  of housing  74  between shoulder  88  formed in outer surface  90  of guide member  82  and lock nut  86 . Guide  81  further includes a tubular extension  94  inserted into second end  96  of guide member  82 . Extension  94  has an outer surface  98  that abuts shoulder  99  formed in inner surface  100  of guide member  82 , and an inner surface  102  which defines a passageway  104  for allowing first conduit  10   a  to pass therethrough. As described, the second end of first conduit  10   a  passes through passageway  102  in extension  94  and through threaded end  84  of guide member  82  into interior  106  of housing  74 . 
   Mounting brackets  108  are provided for supporting the second end of first conduit  10   a  and the first end of second conduit  10   b  within housing  74 . Mounting brackets  108  are electrically connected to each other by line  109 . Mounting brackets  108  are generally L-shaped and include first legs  110  operatively connected to insulated spacers  112  by bolts  114 . Spacers  112  are interconnected to sidewall  116  of housing  74  by bolts  118 . As described, spacers  112  electrically isolate mounting brackets  108  from housing  74 . 
   Mounting brackets  108  further include second legs  120  having openings  122  therethrough. Mounting bracket connectors  54  are utilized to interconnect first and second conduits  10   a  and  10   b , respectively to corresponding mounting brackets  108 . Mounting bracket connectors  54  are generally tubular and include inner surfaces  124  defining passageways for allowing inner jacket  26 , ground wires  18 , and conductors  12  of corresponding conduits  10   a  and  10   b , respectively, to pass therethrough. Each mounting bracket connector  54  includes threaded first and second ends  125  and  126 , respectively, separated by an enlarged diameter portion  128 . In order to interconnect mounting bracket connectors  54  to corresponding second legs  120  of mounting brackets  108 , second ends  126  of mounting bracket connectors  54  are inserted through corresponding openings  122  in legs  120  of mounting brackets  108 . Locking nuts  130  are threaded onto second ends  126  of corresponding mounting bracket connectors  54  so as to capture second legs  120  of mounting brackets  108  between locking nuts  130  and enlarged diameter portions  128  of corresponding mounting bracket connectors  54 . 
   In order to interconnect first conduit  10   a  to a corresponding mounting bracket connector  54 , ferrule  50  of connector  48  mounted on second end  32   a  of core  32  of first conduit  10   a  is positioned within first end  125  of mounting bracket connector  54  and back nut  52  of connector  48  is threaded onto first end  125  of mounting bracket connector  54 . The second ends of the conducting wires  14  of conductors  12  are operatively connected to corresponding input terminals of variable frequency drive  72 . The second ends of ground wires  18  are operatively connected to each other and to grounding bus  132  of housing  74  for variable frequency drive  72 . End portion  40   a  on the second end of wire braid  40  of first conduit  10   a  is interconnected to a corresponding end portion  40   a  on a first end of wire braid  40  of a second conduit  10   b.    
   As hereinafter described, second conduit  10   b  electrically connects the outputs of variable frequency drive  72  to third conduit  10   c  within junction box  134 . First ends of conducting wires  14  of conductors  12  of second conduit  10   b  are operatively connected to corresponding outputs of variable frequency drives  72 . The first ends of ground wires  18  of second conduit  10   b  are joined together and operatively connected to the second ends of ground wires  18  of first conduit  10   a  and to grounding bus  132  of housing  74 . A first end  32   a  of core  32  of second conduit  10   b  is rigidly connected to a corresponding mounting bracket  108  within housing  74  utilizing connector  48 , as heretofore described. The first end of second conduit  10 b passes exit housing  74  through a corresponding guide  81  mounted in opening  132  in second sidewall  134  of housing  74 . 
   As heretofore described, the second, opposite end of second conduit  10   b  is operatively connected to the first end of third conduit  10   c  within junction box  134 . Referring to  FIGS. 8 and 9 , junction box  134  is electrically isolated from the physical earth and takes the form of a metallic box having openings  138  and  140  in corresponding sidewalls  142  and  144 , respectively, thereof. Guides  81  are provided in corresponding openings  138  and  140  injunction box  134  so as to allow the second end of the second conduit  10   b  to pass through opening  138  in sidewall  142  and to allow the first end of the third conduit  10   c  to pass through opening  140  in sidewall  144 . 
   Mounting brackets  108  are provided within junction box  134  for supporting corresponding ends of second and third conduits  10   b  and  10   c , respectively. Mounting bracket connectors  54  are interconnected to second legs  120  of corresponding mounting brackets  108  within junction box  134 , as heretofore described. Connector  48  on the second end of the second conduit  10   b  is interconnected to corresponding mounting bracket connector  54  to interconnect second end of the second conduit  10   b  to corresponding mounting bracket  108  within junction box  134  and connector  48  on the first end of third conduit  10   c  is interconnected to a corresponding mounting bracket connector  54  to interconnect first end of third conduit  10   c  to corresponding mounting bracket  108  within the interior of junction box  134 . 
   To electrically connect the second and third conduits  10  within junction box  134 , the second ends of conducting wires  14  of conductors  12  of second conduit  10   b  are interconnected to corresponding first ends of conducting wires  14  of conductors  12  of third conduit  10   c  by wire nuts  146  or the like. The second ends of the ground wires  18  of the second conduit  10   b  are operatively connected to each other and to the first ends of the ground wires  18  of third conduit  10   c . In addition, end portion  40   a  on the second end of wire braid  40  of second conduit  10   b  is interconnected to a corresponding end portion  40   a  on the first end of braid wire  40  of third conduit  10   b.    
   As best seen in  FIG. 9 , motor  64  is supported within housing  148  that is electrically isolated from the physical earth. Housing  148  includes grounding bus  150  operatively connected to end portion  40   a  on the second end of wire braid  40  of third conduit  10   c . The second ends of ground wires  18  of third conduit  10   c  are joined together and operatively connected to end portion  40   a  on the second end of wire braid  40  of third conduit  10   c  and to grounding bus  150 . The second ends of conducting wires  14  of each conductor  12  of third conduit  10  are operatively connected to corresponding terminals  152  of motor  64  so as to provide electrical power to motor  64 . Second end  32   a  of core  32  of third conduit  10   c  is originally connected to housing  148  utilizing connector  48 , as heretofore described. 
   In operation, isolation source transformer  62  provides three-phase electrical power at terminals  64  thereof. Conducting wires  14  of conductors  12  of first conduit  10   a  carry the three-phase electrical power to the inputs of variable frequency drive  72 . Variable frequency drive  72  generates three-phase electrical power with an adjustable frequency and voltage at the outputs thereof. The outputs of variable frequency drive  72  are electrically coupled to the terminals  152  of motor  64  through conducting wires  14  of conductors  12  of second and third conduits  10   b  and  10   c , respectively, as heretofore described. Cores  32  and wire braids  40  of first, second and third conduits prevent electromagnetic and radio frequency interference from passing therethrough. In addition, ground wires  18  and cores  32  of conduits  10   a ,  10   b  and  10   c  act as a low impedance conductor to provide a path for the low frequency common mode noise and the associated stray currents generated by the transmission of electrical power on conducting wires  14  of conductors  12  of first, second and third conduits  10   a ,  10   b  and  10   c , respectively. In addition, wire braid  40  of first, second and third conduits  10   a ,  10   b  and  10   c , respectively, provides an uninterrupted, very low impedance path for both high frequency electromagnetic and radio frequency noise, and associated waveform phenomenon. As such, the electromagnetic and radio frequency common mode noise, associated waveform phenomenon and associated stray currents are routed with minimized leakage to their point of origin, namely, the neutral point X 0  of isolation source transformer  62 . It can be appreciated that by isolating housing  66 ,  72  and  148 , as well as, junction box  134  from the physical earth, the common mode noise and currents associated with the transmission of electrical power are unable to stray into the physical earth and elsewhere. 
   Various modes of carrying out the invention are contemplated as being within the scope of the following claims particularly pointing and distinctly claiming the subject matter which is regarded as the invention.