Abstract:
A device for attaching to an electric power line conductor includes a housing with an opening for accepting the power line conductor and a first jaw assembly and a second jaw assembly. The first jaw assembly and the second jaw assembly are located within the housing and are configured to engage the power line conductor. The first jaw assembly is fixed relative to the housing and the second jaw assembly is movable relative to the housing. A first magnetic core is movable relative to the first jaw assembly and a second magnetic core is fixed to the second jaw assembly. The first magnetic core and the second magnetic core are configured to surround the power line. An actuator is connected to the second jaw assembly and is configured to move the second jaw assembly relative to the first jaw assembly.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The application claims priority to U.S. Provisional Application No. 61/740,517 which was filed on Dec. 21, 2012. 
    
    
     BACKGROUND 
     The present disclosure relates to a multiple parameter sensor-transmitter/receiver unit which may be installed on or removed from an energized electric power line, such as an overhead power line. With the advent of Smart-Grid applications for electric power systems, there is an ever increasing need for a device that measures electric, mechanical, and environmental parameters of the power line. 
     In order to address the increasing need for monitoring power lines, devices have been developed that attach directly to the power line. These devices generally require a power source, such as batteries or solar panels. When utilizing batteries, regular maintenance must be performed to replace the batteries, which can become costly. When solar panels are used, the device may only be powered during sunny weather conditions and during daylight hours. Therefore, there is a need for a device which is low maintenance and can be constantly powered independent of weather conditions. 
     SUMMARY 
     A device for attaching to an electric power line conductor includes a housing with an opening for accepting the power line conductor and a first jaw assembly and a second jaw assembly. The first jaw assembly and the second jaw assembly are located within the housing and are configured to engage the power line conductor. The first jaw assembly is fixed relative to the housing and the second jaw assembly is movable relative to the housing. A first magnetic core is movable relative to the first jaw assembly and a second magnetic core is fixed to the second jaw assembly. The first magnetic core and the second magnetic core are configured to surround the power line. An actuator is connected to the second jaw assembly and is configured to move the second jaw assembly relative to the first jaw assembly. 
     A method of attaching a device to a power line conductor includes resting a first jaw assembly on a power line conductor with the first jaw assembly fixed relative to a housing. A second jaw assembly is moved toward the first jaw assembly with an actuator. A second magnetic core is moved toward a first magnetic core with the actuator. The second magnetic core is fixed relative to the second jaw assembly and the first magnetic core is moveable relative to the first jaw assembly. The first magnetic core and the second magnetic core move relative to the first jaw assembly. 
     These and other features of the disclosed examples can be understood from the following description and the accompanying drawings, which can be briefly described as follows. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a right side view of an example sensor transmitter receiver unit (“STR unit”). 
         FIG. 2  illustrates a front view of the STR unit of  FIG. 1 . 
         FIG. 3  illustrates a cross-sectional view taken along line A-A of  FIG. 2 . 
         FIG. 4  illustrates a cross-sectional view taken along line A-A of  FIG. 2  with an example hotstick. 
         FIG. 5  illustrates another cross-sectional view taken along line A-A of  FIG. 2  with the example hotstick. 
         FIG. 5   a  illustrates an enlarged view of a keyhole slot. 
         FIG. 6  illustrates another cross-sectional view taken along line A-A of  FIG. 2  engaging a conductor. 
         FIG. 7  illustrates an example upper magnetic core subassembly. 
         FIG. 8  illustrates an expanded view of an example upper magnetic core and an example lower magnetic core surrounding the conductor and an example power supply transformer. 
         FIG. 9  illustrates a schematic view of the line mounted power supply, electronics and transmitter-receiver of the STR unit. 
         FIG. 10  illustrates an expanded view of the lower magnetic core, example lead screw assembly, and an example hotstick guide tube. 
         FIG. 11  illustrates the collapsed view of the lower magnetic core, the lead screw assembly, and the hotstick guide tube. 
         FIG. 12  illustrates a cross-sectional view taken along line B-B of  FIG. 2 . 
         FIG. 13  illustrates a cross-sectional view taken along line C-C of  FIG. 1 . 
         FIG. 14  illustrates an exploded view of example support blocks mounting the upper magnetic core subassembly and example upper and lower jaws. 
         FIG. 15  illustrates an exploded view of an upper magnetic core mount and the upper and lower jaws. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1 and 2  illustrate an example sensor transmitter receiver unit (“STR unit”)  1  installed on a power line conductor C for measuring and monitoring various parameters of the power line conductor C and its environment. The STR unit  1  is formed from a one piece upper housing  2  and a one piece lower housing  3 . The lower housing  3  is accepted into a bead  4  formed on a distal end of the upper housing  2 . In this example, the bead  4  which is an integral part of the upper housing  2  is formed by machining a portion of the upper housing  2  to form a groove on the inside of the bead  4 . The lower housing  3  is secured to the bead  4  and the upper housing  2  by a collar  5 . The collar  5  attaches to a hotstick guide tube  13  ( FIG. 3 ) that is secured to the upper housing  2  and extends through the lower housing  3 . 
     In one example, the upper housing  2  and the lower housing  3  are made of aluminum or other suitable electrically conductive material. The material chosen should accommodate subassembly installation without the use of external surface fasteners which could generate corona discharges due to high voltage being applied to the upper housing  2  and the lower housing  3 . The upper housing  2  has the advantage of reducing the number of mating surfaces and eliminating mismatches between multiple cast parts which can generate corona discharges and audible noise due to slightly offset sharp edges of the mating surfaces of the adjacent castings. 
     Referring to  FIGS. 3 and 4 , before the STR unit  1  is clamped onto the conductor C, a lower jaw  7  is moved to its fully lowered position spaced from upper jaws  6 . This allows the conductor C to pass from position “A” of  FIG. 3  through a throat T on the left side of the upper housing  2  and onto the upper jaws  6  in position “B” as shown in  FIG. 5 . 
     With the lower jaw  7  of the STR unit  1  in its fully lowered position, a specially designed hotstick  10  is inserted into the bottom of the STR unit  1  and inside the hotstick guide tube  13 . In this example, the hotstick  10  is made of an electrically insulated material such as fiberglass. The hotstick  10  includes a hotstick driver assembly  9  ( FIG. 4 ) attached to the hotstick  10  with a pin  36 . The hotstick  10  provides the required electrical insulation between the hands of the linemen and the energized conductor C. A flexible stirrup assembly  11  ( FIG. 4 ) contains a flexible braided conductor  12  which bends out of the way to allow the hotstick driver assembly  9  to enter a hole in the collar  5 . As mentioned earlier, the collar  5  secures the lower housing  3  to the bead  4  on the upper housing  2 . The collar  5  is fastened to the hotstick guide tube  13  using the set screw  5   a  which is screwed into the collar  5  and into a hole in the hotstick guide tube  13 . 
     With the hotstick  10  and the hotstick driver assembly  9  fully engaged inside the hotstick guide tube  13 , the STR unit  1  can be lifted by the lineman with the hotstick  10  onto the conductor C while maintaining the STR unit  1  securely attached to the hotstick  10 . 
     The upper housing  2  includes two jaw inserts  8 , shown in  FIGS. 5 and 14 , located adjacent the throat T and the upper jaws  6 . The two jaw inserts  8  include inclined surfaces  8   a  and the upper jaws  6  include inclined surfaces  6   a . The angle of incline of the inclined surfaces  8   a  matches the angle of the incline of an inclined surface  2   a  on the upper housing  2 . 
     The angle of the inclined surfaces  6   a  is steeper than the angle of the inclined surfaces  8   a  and the inclined surface  2   a  to aid in installing the STR Unit  1  on the conductor C. As the conductor C slides across the inclined surfaces  2   a  and  8   a  and reaches the steeper incline of the inclined surface  6   a , the STR unit  1  will bounce slightly upward and land in a circular notch  6   b  of the upper jaws  6  (See  FIG. 4 ). This allows a conductor temperature sensor to be mounted vertically and in the middle inside the upper jaws  6  and initially extends slightly below the circular notch  6   b  for the upper portion of the conductor C. The two different inclined surfaces  6   a  and  8   a  of the jaw inserts  8  and upper jaws  6  prevent the conductor temperature sensor S, shown in  FIGS. 3 and 4 , from becoming damaged since the conductor C firmly lands vertically in the circular notch  6   b  of the upper jaws  6  and pushes the conductor temperature sensor S up to the inside surface of the circular notch  6   b.    
     In  FIG. 3 , the lower jaw  7  is located in a pocket P between two legs of a lower magnetic core  14 . The lower jaw  7  is held in place with two spring pins  132  and  133  ( FIG. 15 ) located in the lower jaw  7  that snap into two holes  15  in a lower jaw holder  16  ( FIGS. 10 and 11 ) which is attached to a bottom block  19  using two screws  20  ( FIG. 3 ). The bottom block  19  is located adjacent the base of the upper housing  2 . 
     Two identical electrically conductive lower core covers  17  partially surround the two legs of the lower magnetic core  14 . The lower core covers  17  are attached to the bottom block  19  on each side of the lower jaw holder  16  using screws  18  of  FIG. 3  on the front right side and one set of the screws  18  on the back left side (not shown). The front and back lower jaw holders  16  are both held in place by the four screws  20 , two in the front and two in the back. The two legs of the lower magnetic core  14  are totally encased by the two lower core covers  17  and the front and back lower jaw holders  16 . Therefore, the lower magnetic core  14  is not exposed to any moisture, such as from rain, snow, and ice that could enter through the throat T of the upper housing  2  ( FIG. 3 ). 
     The bottom block  19  contains a conical hole  21  in the center which provides a very low friction bearing surface for the semi-circular top of a lead screw  22  ( FIG. 3 ). The lead screw  22  is held in the conical hole  21  with a retainer plate  23  which has a hole in the middle the size of the lead screw  22  diameter and is fastened to the bottom block  19 . The lead screw  22  is threaded into the center of a threaded bushing  25 . The threaded bushing  25  has a reduced diameter cylindrical lower portion which fits inside the hotstick guide tube  13  and a larger diameter cylindrical top portion of the threaded bushing  25  is supported on the upper end of the hotstick guide tube  13 . Both the threaded bushing  25  and the hotstick guide tube  13  are attached to a hotstick guide support  26  using two large through bolts  27  and nuts which are placed through the holes in a bottom support  28 . 
     Referring to  FIG. 2 , the upper jaws  6  include two spaced apart jaws and the lower jaw  7  includes a single jaw aligned between the two spaced apart upper jaws  6 . When lower jaw  7  is clamped onto the conductor C, the conductor C is bent slightly upward as the lower jaw  7  extends upward between the upper jaws  6  creating a bending moment in the conductor C. The bending moment in the conductor C prevents the STR unit  1  from sliding down the conductor C, especially when the STR unit  1  is mounted at the point of attachment adjacent a utility pole or tower where the slope of the conductor C is at its maximum value. Preventing the upper jaws  6  and the lower jaw  7  from sliding down the conductor C at the point of attachment is necessary when the STR unit is being used to measure sag of the power line conductor. 
     Referring to  FIGS. 5 and 5   a , the bottom support  28  includes an upside down “U” shaped cross member and is fastened at each end to the upper housing with two large threaded screws  29  on each side. The threaded bushing  25  has two small vertical holes  25   a  drilled through the threaded bushing  25  on each side of the threaded hole in the middle for the lead screw  22 . The vertical holes  25   a  are countersunk on the top and provide drainage paths for fluid, such as rain water, that can accumulate underneath the bottom block  19  and on top of the bottom support  28  ( FIG. 5   a ). The water then drains through the two vertical holes  25   a  in the threaded bushing  25  and drops on the inside of the hotstick guide tube  13  and out the bottom of the STR unit  1 . Therefore, water will not leak into the lower housing  3 . 
     Referring to  FIG. 6 , the lead screw  22  has a small diameter hotstick guide  30  which is threaded on the inside and is screwed on the bottom of the lead screw  22 . A pin  31  keeps the hotstick guide  30  from turning on the lead screw  22 . The hotstick guide  30  prevents the inside of a hotstick lead screw driver  33  from coming into contact with the threads on the lead screw  22  and damaging the internal bore of the lead screw driver  33 . It also guides the lead screw driver  33  onto the lead screw  22 . When the pin  31  engages the lead screw driver  33  the STR unit  1  is ready for installation on the conductor C. 
     The hotstick driver assembly  9  includes the lead screw driver  33 , a hotstick driver coupling  32 , a rivet  34 , a hotstick sleeve  35 , the pin  36 , and the hotstick  10 . The hotstick  10  of  FIG. 4  rests on the rounded portion of the hotstick driver coupling  32  and the rounded inside bottom of the hotstick guide tube  13 . This prevents the lead screw driver  33  from applying pressure to the threaded bushing  25  upon installation of the STR unit  1  on the conductor C. The lead screw driver  33  and the hotstick driver coupling  32  are each fastened to the hotstick sleeve  35  by the rivet  34  and the hotstick sleeve  35  is attached to the hotstick  10  with the pin  36 . A long narrow vertical slot in the lead screw driver  33  allows the pin  31  of the lead screw  22  to be engaged with the lead screw driver  33  and is free to slide up or down in the vertical slot  37  as the lead screw is turned to tighten the lower jaw  7  on the conductor C or to loosen the lower jaw  7  from the conductor C to remove the STR unit  1 . 
     When the hotstick driver assembly  9  is engaged with the lead screw  22  as shown in in  FIG. 4 , the STR unit  1  is raised to position “A” relative to the height of the conductor C. The STR unit  1  is then moved toward the conductor C so that the conductor C passes through the throat T of the upper housing  2  and into position “B” as shown in  FIG. 5 . Once the STR unit  1  is fully supported by the conductor C in position “B”, the hotstick driver assembly  9  is turned clockwise by the installer with the hotstick  10  and allowed to drop down from its position in  FIG. 4  to a lower position as in  FIG. 5 . A horizontal keyhole slot  38  of the lead screw driver  33  is now engaged with the pin  31  of the lead screw  22 . With the pin  31  in the horizontal keyhole slot  38 , the hotstick driver assembly  9  and the hotstick  10  are secured to the STR unit  1 . 
     In this example, an opening and closing mechanism  39  of  FIG. 6  extends the lower jaw  7  upward to secure the STR unit  1  on the conductor C. Additionally, the opening and closing mechanism  39  can also retract the lower jaw  7  to remove the STR unit  1  from the conductor C. The opening and closing mechanism  39  includes the lower magnetic core  14 , the lower core covers  17 , the lower jaw holders  16 , the lower jaw  7 , spring pins  132  and  133 , the bottom block  19 , the retainer plate  23 , two fasteners  24 , the lead screw  22 , the hotstick guide  30 , and the pin  31 . 
       FIG. 6  illustrates the keyhole slot  38  on the lead screw driver  33  engaged with the pin  31  on the lead screw  22 . As the lead screw  22  is turned clockwise, the opening and closing mechanism  39  moves the lower magnetic core  14  toward an upper magnetic core  40 . The upper magnetic core  40  has two large compression springs  41  to bias the upper magnetic core  40  downward. The compression springs  44  provide pressure to hold both the upper magnetic core  40  and the lower magnetic core  14  together to reduce the magnetic reluctance caused by air gaps  54  ( FIG. 8 ) between the upper magnetic core  40  and the lower magnetic core  14 . 
     The hotstick driver assembly  9  can continue to be turned clockwise even after the lower magnetic core  14  begins to mate with the upper magnetic core  40  because the compression springs  41  compress at the top of the upper magnetic core  40 . The clockwise motion of the hotstick driver assembly  9  can be achieved either manually or with a battery powered drill or another rotating device, until the lower jaw  7  is tightened onto the conductor C. After the STR unit  1  is mounted on the conductor C, the hotstick  10  is turned slightly to the left, or counterclockwise, and the pin  31  will become disengaged from the horizontal portion of the keyhole slot  38 . The hotstick  10  is then free to be removed when the pin  31  aligns with the vertical slot  37 . 
       FIGS. 7 and 8  illustrate the bottom of the compression springs  41  are held in alignment in two cylindrical pockets  42  of two identical horizontal upper core blocks  43  which are each used to clamp the upper magnetic core  40  to two identical magnetic horizontal lower core blocks  44 . The top of the compression springs  41  are held in place with two projections  49  extending downward on the inside of the upper housing  2 . The compression springs  41  are totally enclosed by the upper housing  2  and are protected from the adverse weather which can cause corrosion. The air gaps  54  between the upper and lower magnetic cores  40  and  14  are totally enclosed by the upper housing  2  which prevents the air gaps  54  from becoming corroded due to moisture from the environment. The horizontal upper core blocks  43  and the horizontal lower core blocks  44  are clamped around the upper magnetic core  40  on each side using two through bolts  45  and two nuts  46  in the front and two through bolts  45  and two nuts  46  located in the back of the upper horizontal core blocks  43  and horizontal lower core blocks  44 . 
     When the two large compression springs  41  push the upper core blocks  43  down, the upper magnetic core  40  is prevented from falling out of a left core shoe  50  and a right core shoe  51 , by a step  52  located at the bottom of the right core shoe  51  and a step  53  located at the bottom of the left core shoe  50 . 
     When the lower magnetic core  14  mates with the upper magnetic core  40 , the lead screw  22  can be turned further clockwise to move the two upper core blocks  43  away from the steps  52  and  53  and further compress the compression springs  41 . The lead screw  22  can continue to be turned clockwise and compress the compression springs  41  until the lower jaw  7  and the upper jaws  6  are tight on the conductor C. 
     Electrical insulating spools  47  are inserted over each of the through bolts  45  and electrical insulating washers  48  are inserted under the head of each through bolt  45  and under each nut  46 . The insulating spools  47  and the insulating washers  48  on each of the through bolts  45  prevent shorted electrically conductive paths around the upper magnetic core  40  which is comprised of the four through bolts  45 , four nuts  46 , the two electrically conductive upper core blocks  43  and the two lower core blocks  44 . 
     When the upper jaws  6  and the lower jaw  7  are firmly tightened on the conductor C, the compression springs  41  are compressed to their maximum distance, and thus the maximum compressive force is also applied to the lower magnetic core  14  and the upper magnetic core  40 . This decreases the size of the air gaps  54  between the lower magnetic core  14  and the upper magnetic core  40  and the magnetic reluctance between the lower magnetic core  14  and the upper magnetic core  40 . Depending on the size of the conductor C, varying amounts torque can be applied to the hotstick driver assembly  9  to tighten the opening and closing mechanism  39  on the conductor C. 
     The physical size and shape of the upper jaws  6  and the lower jaw  7  are designed such that approximately the same compressive force is applied to the upper magnetic core  40  and the lower magnetic core  14 . In one example, there are five different sets of upper and lower jaws  6  and  7  that can fit different conductor sizes and types ranging from 0.162 inches in diameter and up to 1.17 inches in diameter. The opening and closing mechanism  39  allows the STR unit  1  to be installed on a wide range of conductor diameters without changing the upper jaws  6  and the lower jaws  7  while maintaining sufficient contact between the upper magnetic core  40  and the lower magnetic core  14  to complete the magnetic circuit of the power supply transformer  55  of the STR unit  1  which derives its power from the current flowing through the conductor C to power a power supply module  60  of  FIG. 9 . Because the STR unit  1  derives power from the conductor C, batteries or solar cells are not required to power the STR unit  1 . The STR unit  1  is powered at all times when current is flowing in the conductor C, even at current levels as low as 6.8 amperes and still process data and transmit data at 1 watt power levels because of the low threshold of the power supply module  60 . 
     Maintaining a minimum magnetic reluctance insures that a power supply transformer  55  ( FIGS. 8 and 9 ) will provide the needed secondary voltage V 2  and secondary current I 2  to operate the power supply transformer  55 , sensor electronics module  63 , and transmitter/receiver  64 . The power supply transformer  55  includes the upper magnetic core  40 , the lower magnetic core  14 , and a coil winding  56 . The upper magnetic core and the lower magnetic core form a window W for accepting the conductor C. 
     The number of secondary turns N 2  of wire on the coil winding  56  are optimized to produce the required secondary voltage V 2  and secondary current I 2  with a minimum of current I 1  in the conductor C. The coil winding  56  is held in place by two coil bobbins  57  which are supported laterally by the two upper core blocks  43  and the two lower core blocks  44 . Secondary leads  58   a  and  59   a  of coil windings  58  and  59 , respectively, are connected to the power supply module  60  which maintains the same level of secondary voltage across leads  61  and  62  for the sensor electronics module  63  and the transmitter/receiver  64  even though the primary current may range from 34 amperes up to 1000 amperes. Lower primary currents of 6.8 amperes are achievable with the low threshold current power supply module  60 . The power supply module  60  contains an energy storage device  256  ( FIG. 13 ) which can power the transmitter/receiver  64  when the conductor C current ceases to flow. A transmitting and receiving antenna  81  for the on-board transmitter/receiver  64  is mounted on the upper housing  2  ( FIG. 12 ). 
     Locating the coil winding  56 ,  58 , and  59  on the upper magnetic core  40  allows the heat from the coil winding  56 ,  58 , and  59  to escape through a vent  65  ( FIG. 1 ) in the upper housing  2 . When the conductor sensor S located within the STR unit  1  measures the temperature of the conductor C, it is important that the heat from the coil windings  56 ,  58 , and  59  does not affect the temperature of the conductor C or the conductor temperature sensor S, which is in electrical communication with the sensor electronics module  63 . As shown in  FIG. 6 , a thermally insulating barrier  66  located below the coil windings  56 ,  58 , and  59 , allows for a more accurate temperature reading of the conductor temperature by blocking heat from the coil windings  56 ,  58 , and  59 . 
       FIGS. 10-12  and  13  illustrate the lower magnetic core  14  with the lower core covers  17 , the lead screw  22 , the hotstick guide tube  13 , and other related parts in both exploded and collapsed views. The hotstick guide tube  13  is anchored at the top with the through bolts  27  that extend through the bottom support  28  and the hotstick guide support  26 . A round cylindrical milled slot  67  is located along opposing sides of the top of the hotstick guide tube  13  to accept the through bolts  27  that support the hotstick guide tube  13 . 
     A central hole  70  extends through a base plate support  68  and a base plate  69  for accepting a bottom portion of the hotstick guide tube  13 . The base plate support  68  and the base plate  69  are connected to each other with four identical threaded screws  71 . The hotstick guide tube  13  is attached to the base plate support  68  and the base plate  69  with set screws  72  and  73 . Left and right side panels  76  of  FIG. 12  are attached to the base plate support  68  and the bottom support  28  for the lower core  14  with the use of two identical screws  74  extending through the bottom support  28  and the side panel  76  and at the bottom with two identical screws  75  extending through the side panel  76  and the base plate support  68 . 
     The threaded bushing  25  rests on top of the hotstick guide tube  13  and is prevented from turning relative to the hotstick guide tube  13  using a set screw  77 . The left and right side panels  76  not only provide added strength, but also provide the physical space to mount the power supply module  60 , the transmitter/receiver  64 , the sensor electronics  63 , and support left and right lower core guides  78  and  79 . 
     The left lower core guide  78  and a right lower core guide  79  are “U” shaped and guide the opening and closing mechanism  39  such that the lower magnetic core  14  is aligned with the upper magnetic core  40 . Each of the left and right lower core guides  78  and  79  are attached to the left and right side panels  76  with four threaded screws  80 . The lower housing  3  is placed over the hotstick guide tube  13  at the bottom and fitted up to the base plate  69  and held in place with the collar  5 . This means that once the collar  5  is removed, the lower housing  3  can be removed thus allowing access to the power supply module  60 , sensor electronics module  63 , and the transmitter/receiver  64  of  FIG. 9  mounted inside and on the left and right side panels  76  for easy maintenance and repair. 
     FIGS.  7  and  12 - 15  illustrate an upper magnetic core subassembly  40   a  mounted to the upper housing  2 . The left and right core shoes  50  and  51  support the upper magnetic core  40  such that the upper magnetic core  40  can move freely up and down inside the left and right shoes  50  and  51 . The left and right core shoes  50  and  51  are attached to the upper housing  2  using four support blocks  86  and  87  of  FIG. 14 , right and left upper core guides  90  and  93 , and four vertical through bolts  94 ,  95 ,  96 , and  97 . 
     The upper magnetic core subassembly  40   a  can be inserted through the throat T and fastened to the inside of the upper housing  2 . A top portion of the upper housing  2  is “C” shaped which provides a surface on the inside for mounting a current sensing device  156  for measuring the power line frequency current (60 Hz or 50 Hz) and a loop coil  157  for measuring lightning stroke current ( FIGS. 13 and 16 ). 
     The right core shoe  51  has two identical threaded holes  82  and  83  on the front and back for a total of four, and left core shoe  50  has two identical threaded holes  84  and  85  on the front and back for a total of four as shown in  FIGS. 7 and 14 . As shown in  FIG. 14 , two identical support blocks  86  on the right side are placed on the front and back of the right core shoe  51  and two identical support blocks  87  are placed on the front and back of the left core shoe  50 . 
     To align the two right side support blocks  86  with the two sets of threaded holes  82  and  83  on the right side of the right core shoe  51 , threaded screws  88  and  89  are first inserted into the upper and lower holes in the right side upper core guide  90  and then through the two holes in the right support block  86  and screwed into the accommodating threaded holes  82  and  83  of the right core shoe  51 . The two left side support blocks  87  are held in alignment with the left core shoe  50  by first inserting two threaded screws  91  and  92  through the other end of the right side upper core guide  90  and then through the holes in the left side support block  87  and screwed into the threaded holes  84  and  85  of the left core shoe  50 . The same process is repeated on the back side by connecting support blocks  86  and  87  to the left upper core guide  93  with the backside of the right core shoe  51  and the back side of the left core shoe  50 . 
     The purpose of the upper core guides  90  and  93  is to insure the two long vertical through bolts  94  and  95  placed through the vertical holes in the two right side support blocks  86  and two long vertical through bolts  96  and  97  placed through the vertical holes in the two left side support blocks  87  line up with the four threaded holes in four threaded inserts  98 ,  99 ,  100 , and  101 , which are embedded in the casting of the upper housing  2 . The two right side support blocks  86  are prevented from falling down by inserting the back of a right side upper jaw holder  102  and the back of the left side upper jaw holder  103  over the vertical through bolts  94  and  95  and threading nuts  104  and  105  onto the two vertical through bolts  94  and  95  and tightening them down, respectively. The two left side support blocks  87  are held in place by inserting the vertical through bolts  96  and  97  through the front hole in the right side upper jaw holder  102  and the front hole in the left side upper jaw holder  103  and threading two nuts  106  and  107  on the vertical through bolts  96  and  97  and tightening them down, respectively. 
     Four threaded through standoffs  108 ,  109 ,  110 , and  111  are screwed onto the four vertical through bolts  94 ,  95 ,  96 , and  97 , respectively. The thermal barrier  66  is placed over the four bottom holes of the standoffs  108 ,  109 ,  110 , and  111  and screwed to the standoffs  110  and  111  on the front left side with two flat head screws  112  as shown in  FIG. 15 . 
       FIGS. 2 and 15  illustrate casting fillers  113  and  114  located on the back left and back right sides of the STR unit  1  and secured with round head screws  115  which are first inserted through holes in the casting fillers  113  and  114  and then through the two back holes on the right and left side of the thermal barrier  66  and into the standoffs  108  and  109 , respectively. 
     After the upper magnetic core subassembly  40   a  is mounted, the left and right lower core guides  78  and  79  including the opening and closing mechanism subassembly  39  and the left and right side panels  76  are inserted through the bottom of the upper housing  2  (See  FIG. 12 ). Four screws  29  are inserted through the two holes on the left and the two holes on the right of the bottom support  28  and screwed into the threaded holes of the upper housing  2 . It should be noted that during the insertion process, the right lower core guide  79 , shown in  FIG. 12 , slides around the outside surface of the right core shoe  51  and underneath a tab  116  at the top as a weldment on the right upper side of the right core shoe  51 . 
     As shown in  FIG. 12 , the tab  116  insures that the right lower core guide  79  fits precisely around the outside of the right core shoe  51  to provide a near perfect alignment of the lower magnetic core  14  with the upper magnetic core  40 . The precise alignment between the upper magnetic core  40  and the lower magnetic core  14  reduces magnetic reluctance by decreasing the air gaps  54 . This results in a decrease in the threshold current for the operation of the power supply module  60 . 
     Referring to  FIGS. 14 and 15 , the right side upper jaw holder  102  and the left side upper jaw holder  103  support the two upper jaws  6  and the jaw inserts  8 . The long vertical through bolts  96  and  97  which are screwed into the threaded inserts  100  and  101  at the top and on the inside of the upper housing  2  fit through top holes  117  and  118  on the back and front of the right side upper jaw holder  102  on the right side. Also, flush mount screws  119  and  120  are inserted on the back and through corresponding holes in the right side upper jaw holder  102  and are screwed into the upper housing. The flush mount screws  119  and  120  are installed before the upper jaws  6  and inserts  8  are mounted to the right side upper jaw holder  102 . The same arrangement for mounting the left side upper jaw holder  103  is followed using screws  121  and  122 . 
     Right and left upper jaw keepers  123  and  124  prevent the upper jaws  6  from dropping down on the inside, because spring pins  126  and  127  are located on the outside and when depressed snap into the holes  128  and  129  of the right side upper jaw holder  102 . The same procedure is followed with the left upper jaw keeper  124 . 
     The jaw inserts  8  on the right and left sides of the STR unit  1  and in front of the upper jaws  6  are held in place by inserting threaded bolts  130  and  131  into each insert  8  and through the right and left keepers  123  and  124  and screwing into the upper jaw holders  102  and  103 . The spring pins  132  and  133  are included in the lower jaw  7  which when depressed snap into the two holes  15  in the lower jaw holder  16 . 
     The transmitting and receiving antenna  81  for the on-board transmitter and receiver  64  shown in  FIG. 9  is mounted on the housing  2 . The antenna  81  is displayed in  FIGS. 1 and 2  and is installed on the top left side in  FIG. 1 . The solar sensor assembly  134  is located at the top of this housing and on its vertical centerline ( FIG. 13 ). The small hole  140  located directly to the right of the conductor  1  allows access and adjustment of the electric power line sag sensor  140  ( FIG. 1 ). 
     The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this disclosure. The scope of legal protection given to this disclosure can only be determined by studying the following claims.