Abstract:
A current measurement and voltage measurement transducer for power measurements has an upper split core attached to an upper housing and a lower split core attached to a lower housing. The upper housing and lower housing have a common hinge surface and engaging surfaces for maintaining closure and providing a magnetic circuit which surrounds a conductor placed inside the transducer, and the magnetic circuit is coupled to windings around the split core, thereby providing a measurement of current. The housings also provide one or more piercing pins which penetrate the insulation of the conductor and provide a voltage measurement.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a power sensing transducer. More particularly, the invention is directed to a device for clamp-on simultaneous measurement of voltage and current in an enclosed conductor. 
     BACKGROUND OF THE INVENTION 
     Measurement of voltage and current for estimation of power is a fundamental problem of power sensing. One prior art device uses a split-core transformer which momentarily opens to enclose a single conductor, which causes a magnetic flux to be developed in the split-core transformer. Making a magnetic flux measurement using the split core transformer, it is thereby possible to estimate the current flowing through the conductor enclosed by the split-core transformer. A voltage measurement may be combined with the current measurement to form a power measurement, such as by multiplying the current and voltage and computing a root mean square (RMS) value to generate the RMS power estimate. 
     OBJECTS OF THE INVENTION 
     A first object of the invention is a power measurement transducer having a split core transformer positioned along an axial extent of a eccentric channel for enclosing a conductor, the eccentric channel also having a first piercing pin in a first piercing pin extent and a second piercing pin in a second piercing pin extent, the first channel extent and second channel extent located on opposite sides of the split core transformer and on the conductor axis, the eccentric channel positioning a range of conductor diameters such that the conductor is an insulation piercing distance from the piercing pin. 
     A second object of the invention is a power sensing transformer having a split core transformer positioned along an axial extent for accommodating a current carrying conductor, the axial extent providing a eccentric channel for the conductor, the eccentric channel including at least one piercing pin which is in a different channel extent than the split core transformer, the split core transformers having windings coupled to a current measurement device. 
     SUMMARY OF THE INVENTION 
     A current measuring transformer for measurement of a voltage and a current in a conductor includes an eccentric channel which is surrounded by a split core transformer which couples magnetic flux generated by the conductor to windings around the split core transformer, the split core transformer having a hinge and closure for application and removal of the power sensing transducer from the conductor, the eccentric channel positioning the conductor to within a pin piercing distance from at least one piercing pin for making electrical contact with the conductor positioned by the eccentric channel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is perspective view of a clamshell wire housing. 
         FIG. 2A  is an axial cross section view of the power transducer perpendicular to the channel axis and through the transformer core and bobbin. 
         FIG. 2B  is an axial cross section view of the power transducer perpendicular to the channel axis and through the piercing pin extent. 
         FIG. 3  is a transverse section view of the power transducer through the channel axis. 
         FIG. 4  is the perspective view of another embodiment of a clamshell wire housing. 
         FIG. 5A  is an axial cross section view of a power transducer through the channel axis of the transformer core and bobbin extent. 
         FIG. 5B  is an axial cross section view of a power transducer through the channel axis of the piercing pin extent. 
         FIG. 6  is a transverse section view of the power transducer of  FIGS. 4, 5A, and 4B  through the channel axis showing the transformer core, bobbin, and piercing pins. 
         FIG. 7  is a detail view of a locking fastener of  FIG. 2B or 5B . 
         FIGS. 8A and 8B  are detail views of piercing pin embodiments. 
         FIGS. 9A, 9B, and 9C  shows the cross section view of various eccentric supports which provide electrical continuity to a piercing pin into a conductor for a range of different conductor sizes. 
         FIGS. 10A, 10B, 10A-1, 10C, 10D, 10E, 10F, 10G, 10H, 10I, and 10J  show projected section view of alternative eccentric supports and electrical isolation of the piercing pins. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a clamshell conductor housing  100  having a channel axis  101 , an upper housing  102 , lower housing  104 , conductor channel aperture  108 , and a hinge line  106  which allows the upper housing  102  to hinge open from lower housing  104  and allow a conductor (not shown) to be placed about the channel axis  101 . 
       FIG. 2A  shows a cross section view of a split core transformer upper pole piece  202  in the xy plane, showing the pole piece  202  is enclosed on five sides by upper housing  102 . Upper pole piece  202  has windings  208  which are wound around the magnetic path of the pole piece, typically using a bobbin  218  or other support for the wire windings  208 . Similarly, lower housing  104  encloses lower split core transformer pole piece  204  on five sides, the pole piece having windings  220  supported by bobbin  210 . When closed, the housings  102  and  104  place the upper pole piece  202  and lower pole piece  204  faces in contact with each other and close a magnetic circuit formed by the upper pole piece  202  and lower pole piece  204 , thereby forming the magnetic circuit for coupling flux generated by enclosed conductor  216  to windings  208  and  210 . The enclosed conductor  216  may be carrying an electric current as either alternating current (AC) or direct current (DC), although the invention is directed to AC measurements. Upper pole piece  202  and lower pole piece  204  are fabricated from a material having a high permittivity (μ) relative to the unity permittivity of air, such as any ferro-magnetic material including iron, iron powder, ferrites or other powdered iron mixtures, or laminated iron, such that the pole pieces  202  and  204  concentrate magnetic flux from conductor  216 , and couple the magnetic flux to windings  208  and  220 , thereby producing a scaled current in windings  208  and  220  which is substantially equal to the current to be measured in conductor  216  divided by the number of turns n in windings  108  and  210 . The windings  208  and  220  may thereby be coupled to an amplifier for conversion to an estimate of current flowing in conductor  216 . Central conductor  216  carrying the current to be measured is typically formed from a high electrical conductivity metal such as copper or aluminum, which is encased with an outer insulation material  217  having a high melting point, such as polyvinylchloride (PVC). 
     The clamshell conductor housing  100  has a z axis extent which includes a central bobbin and core extent as described in  FIG. 2A  and a piercing pin extent shown in  FIG. 2B  (also in the xy plane) and which is on either side of central bobbin extent of  FIG. 2A , corresponding to each piercing pin  212  and  214 , respectively. The conductor  216  and insulator  217  are supported by eccentric support  206  which offsets the conductor  216  and insulator  217  axis nearer to a lower piercing region of the conductor  216  in the x-z plane, to allow the insulation  217  to be penetrated by piercing pins  212  and  214  which are positioned in a piercing pin extent of the z axis as shown in  FIG. 2B , which is beyond the z extent of the cores  204  and  202 , bobbins  218  and  210 , and windings  208  and  220 . In one embodiment of the invention, eccentric support  206  may be split in the zx plane such that it similarly has a hinge line on an outer surface which is parallel to the z axis, and in another embodiment of the invention, support  206  may be formed as a single piece. The outer surface of support  206  may be formed from a cylindrical form for engagement with housing channel  108 . When support  206  is formed as a single piece, it is threaded over the outer insulator  217  of a conductor prior to installation of the support  206  (with the captured conductor) in channel aperture  108 . The eccentric support  206  may be formed by having the inner cylindrical aperture axis displaced from the center axis of the cylindrical solid, thereby providing preferential engagement of the supported conductor  216  with piercing pins  212  and  214 . 
       FIG. 3  shows a perpendicular view on the longitudinal axis z of  FIGS. 2A and 2B  in the yz plane. Eccentric support  206  has a z extent which includes pin extents  310  corresponding to piercing pins  212  and  214 , and optionally includes the bobbin extent  312 , with an offset in y towards the piercing pins  212  and  214 . When the upper housing  102  and lower housing  104  are snapped closed and secured with mating closure engagements  230  and  231  of  FIG. 2B , upper split core pole piece  202  and lower split core pole piece  204  are in substantial contact with each other, and piercing pins  212  and  214  penetrate insulation  217  and are in electrical contact with conductors  216 . Upper bobbin  218  winding  208  may be placed in series with lower bobbin  210  winding  220  such that leads  302  and  304  are brought out which provide a flux measurement which can easily be converted to a current estimate using the n total bobbin windings to multiply n by the measured current in windings  210  and  220 , and lead  206  is electrically connected to both piercing pins  212  and  214  provide a reliable electrical contact for voltage measurement. The current, voltage, RMS power, power factor, and other basic AC parameters may be thereby measured related to current and voltage flowing through conductor  216 . The piercing pins  212  and  214  typically have a piercing point profile which is selected to minimally spreading the insulation  217  radially at the contact point upon insertion, and the plasticity of the insulation typically causes the insulation  217  to close around the penetrating aperture when the piercing pins  212  and  214  are withdrawn. For insulators with non-plastic properties, electrical tape may be used to cover the small inclusion in the insulation which remains after the conductor is removed and the piercing pins are no longer in contact with insulation  217  which encloses conductor  216 . 
       FIGS. 4, 5A, 5B, and 6  may be examined in combination, and show another embodiment of the clamshell wire housing where upper housing  402  has a z-axis extent which is less than the lower housing  406  z extent and hinge  406  which may be formed such as by molding this feature into a single housing which forms upper housing  402  and lower housing  404 , as can also be done in  FIGS. 1   102  and  104 , respectively.  FIGS. 5A and 5B  show the similar arrangement of elements upper pole piece  202  and lower pole piece  204 . In one embodiment shown in  FIGS. 5A, 5B, and 6 , single bobbin  210  with windings  220  may be used with lower pole piece  404 , with upper pole piece  202  having no windings, but serving only to complete the magnetic circuit when housings  402  and  404  are closed and secured by closure engagements  230  and  231 . The single-coil embodiment of  FIGS. 5A, 5B, and 6  may also be used with the embodiment of  FIGS. 2A, 2B, and 3 , or with the housing shown in  FIG. 1 . 
     Housing  104  of  FIG. 2B and 404  of  FIG. 5B  have in one embodiment interlocking closure engagements  230  and  231  to ensure the required gap closure on the upper and lower pole pieces  202  and  204 , respectively. The interlocking closure engagements  230  and  231  may be placed in each of the pin extents  310 , or as a single region in bobbin extent  312 , or any combination of the pin extents  310  and bobbin extents  312 . In another embodiment of the invention which may be practiced separately or with closure engagements  230  and  231 , a countersunk screw  241  which is disposed in a recess in lower housing  104  or  404  engages with a threaded engagement  240  which is part of the upper housing  102  or  402  as shown in  FIGS. 2B and 5B , respectively. 
     In certain uses, such as utility customer power metering, it may be desired to provide a tamper evident seal on the power sensing transducer assembly.  FIG. 7  shows detail region  242  of  FIG. 2B or 5B , including, in one embodiment of the invention, a tamper-evident security lead  706  such as a wire or cable which may be threaded through apertures  704  formed into the head of screw fastener  241  and which are gathered together in seal  708 , which may be formed from metal, plastic, or any other tamper evident material. 
       FIGS. 8A and 8B  shows embodiments for the piercing pin region  324  of  FIG. 3 or 5 .  FIG. 8A  shows an embodiment for a threaded piercing pin  804  engaged with threaded nut or bushing  808 , where the piercing pin has a sharp piercing end  802  formed into a conical taper with a screw head or other engagement surface formed into actuation end  806 . When the actuation end  806  is rotated, such by using a screwdriver engaged with a slot in actuation end  806 , threads formed in shaft  804  engage with threaded nut  808  and advance the conical taper  802  through the insulation  217  and into the conductors  216 . Nut  808  is also electrically connected to lead  812  which is connected to the input of fuse  320  of  FIGS. 3 and 6 .  FIG. 8B  shows another embodiment where the piercing pin  802  is stationary, such as by attachment to housing  404 , and the closure of the housing  102  and  104  (or  402  and  404 ) results in the piercing pin  802  being forced through the insulation  217  and making contact with conductors  216 . Although the examples of  FIGS. 3 and 6  show piercing pins  212 / 214  oriented in the y axis and secured by the lower housing  104  or  404 , piercing pins  212 / 214  may be oriented for actuation from any surface of the enclosures of  FIG. 1 or 4  which provide piercing access to conductor  216 . 
     The eccentric conductor support  206  of  FIGS. 2A and 2B, and 408  of  FIGS. 5A and 5B  is shown in  FIG. 9A  in various example embodiments. The outer diameter of eccentric conductor support  408  matches the diameter of, and engages with, the upper enclosure  102 / 402  and lower enclosure  104 / 404  of  FIGS. 2A, 2B, 5A, and 5B . The eccentric support  406  inner diameter can be specific to the conductor size in use, as shown in  FIGS. 9A, 9B, and 9C  for different conductor sizes, with the eccentric offset arranged to place the conductor an insulation diameter away from the lower housing surface and piercing pins  212  and  214 , thereby allowing the same piercing pin configuration and piercing pin adjustment range to be used for a wide variety of conductor sizes and insulation thicknesses. The eccentric conductor support  408  may be fabricated as a single separate piece, or as separate halves which are secured together by circumferential force applied by upper/lower housing halves  102 / 104  or  402 / 404  when closed, or support  408  may be formed as a hinged cylindrical piece with a hinge axis oriented parallel to the Z axis. Alternatively, the eccentric support may be formed into, and integrated with, the housing  102 / 104  or  402 / 404 . 
     The power sensing transformer shown in  FIG. 3  provides current transformer leads  302  and  304 , and voltage sensing lead  306 . If the current transformer leads  302  and  304  are not terminated into a sufficiently low impedance, the voltage developed at the winding leads  302  and  304  may become large, leading to undesirable insulation breakdown and voltage arcing in the windings. This breakdown may be prevented through the use of snubber diodes or other voltage clamping devices which do not present to the circuit for low level measurement voltages, but provide a low impedance for higher voltages. Examples of voltage clamping devices include zener diodes, transzorb diodes, and positive temperature coefficient (PTC) resistors. It is generally desirable for these protective devices to have bidirectional characteristics when applied across windings  208  and  220  to prevent the generation of harmful amplitudes of positive or negative voltages. 
     Additional embodiments for the eccentric wire support and associated elements of the invention are shown in  FIGS. 10A, 10B, 10A-1, 10C, 10D, 10E, 10F, 10G, 10H, 10I , and  10 J.  FIG. 10A  shows a projected axial (xy plane) view of a slotted support  1004  which includes a piercing pin barrier in the form of elongate insulated fingers  1002  which may be formed into support  1004 , or the piercing pin barrier may be formed with lower housing  104 / 404 , or the piercing pin barrier may be provided as a bushing which is placed around or over conductor  216  and insulation  217  to isolate piercing pins  214 / 212  from inadvertent user or equipment contact. Alternatively, deformable tape (not shown) may be wrapped over conductor  216  insulation  217  to create a deformable region which insulates any exposed or accessible part of piercing pins  212 / 214 .  FIG. 10B  shows trans-axial (yz plane) view of  FIG. 10A  showing elongate insulated fingers  1002  with respect to previously described structures. When eccentric support  1004  is slotted on the bottom-facing surface as shown, elongate insulated fingers  1002  need only be present in the slotted area, although they may alternatively surround the entire wire, if desired.  FIG. 10A-1  shows a magnified view of the slotted support  1004  and elongate insulated fingers  1002 . 
       FIG. 10C  shows a projected axial section view of slotted support  1008 , which, as with support  1004  of  FIG. 10A , includes a slotted region to provide mechanical backing for the piercing pins  212 / 214  during and after penetration of the wire insulation  217 . Shim  1010  is made from an insulating material and has apertures for passage of piercing pins  212 / 214 , which also locates the shim  1010 . As with the elongate fingers  1002  previously described, shim  1010  isolates a user or other adjacent equipment from accidental contact with piercing pins  212 / 214 , thereby isolating the piercing pins from user or equipment contact.  FIG. 10D  shows a section view in the trans-axial plane indicating the relative positions of conductor  216  with insulation  217 , shim  1010 , and slotted support  1008 . Slotted support  1008  may be solid, formed with periodic support walls along the z-axis to provide backing for piercing pins  212 / 214 , or it may be formed with a shell wall thickness for engagement with upper and lower supports  102 / 402  and  104 / 404 . 
       FIG. 10F  shows an eccentric support  1012  in a trans-axial view, which may be a slotted support shown in previous figures, including horizontal breakaway tabs  1014  isolating the piercing pins as shown in  FIG. 10E   1014  detail. The tabs  1014  may be individually broken away for a particular size wire, and the breakaway tabs  1014  may be arranged above or below the conductor  216  and insulation  217 .  FIG. 10F  shows a trans-axial section view with the eccentric support  1012  and breakaway tabs  1014  positioned in regions adjacent to piercing pins  212  and  214 . 
       FIG. 10G  shows another embodiment of the eccentric support  1020  with breakaway regions  1022 , where each breakaway tab has a radius which matches a particular radius of the outer insulation  217  of conductor  216 . The breakaway tabs may be located adjacent to piercing pins  212 / 214  isolating them from equipment or user contact, or in the same plane as shown in  FIG. 10H . 
       FIG. 10I  show a slotted support  1034  with piercing pins  212 / 214  insulated by retractable insulating sleeve  1030  which slides into contact with insulation  217  of conductor  216 , with the contact force generated by associated springs  1032 .  FIG. 10J  shows the projected view in the trans-axial plane which includes piercing pins  212  and  214 , with respective insulating sleeves  1030  and  1036 , and springs  1032  and  1038  which isolate the piercing pins  212  and  214  from user or equipment contact. 
     The examples set forth are only to aid in the understanding of the invention, and are not intended to limit the scope of the invention to only the embodiments described herein. Therefore, each of the aspects and embodiments of the invention may be practiced with other aspects and embodiments of the invention without loss of generality. The scope and breadth of the invention is understood by the claims which follow.