Abstract:
An electronic watt-hour meter; a current transformer operatively coupled to the electronic watt-hour meter; a first shield on a first side of the current transformer; and a second shield on a second side of the current transformer, wherein the second side is substantially parallel to the first side, wherein the first shield and the second shield each include a substantially magnetically permeable and conductive metal.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates generally to electronic watt-hour meters and more particularly to a shield for a current transformer in an electronic watt-hour meter. 
         [0002]    Referring to  FIG. 1 , a top view, and  FIG. 2 , a perspective view, of a known electronic watt-hour meter  102  are shown. Electronic watt-hour meter  102  is used to measure usage of electricity. Electronic watt-hour meter  102  may include a meter base  103  and at least one current transformer  104  with a potential link  106  running through each current transformer  104 . Other components included in electronic watt-hour meter  102  may include, for example, a surge suppressor  105 , a current transformer cable  107 , and metrology circuitry bracket  109 . A current is measured by a metrology circuitry (not shown) in electronic watt-hour meter  102  and used in the calculation of energy usage. 
         [0003]    Referring to  FIG. 3 , a perspective view, of a known current transformer  104  and known potential link  106  are shown. A potential link current flow  122  (shown by arrow) through potential link  106  may produce a current transformer magnetic field  116  in current transformer  104 . Current transformer magnetic field  116  may moves circularly through a ferrite core (not shown) of current transformer. Current transformer magnetic field  116  may cause a current transformer current flow  117  in current transformer  104  directly proportional to the number of windings  119  in current transformer  104  and potential link current flow  122 . 
         [0004]    Referring to  FIG. 4 , a simplified top view of electronic watt-hour meter  102  is shown for illustrative purpose. If an external magnet  108  is placed in proximity to current transformer  104 , then current transformer  104  is affected by an external magnet magnetic field  115  from external magnet  108 . External magnet  108  may saturate a current transformer  104 , thereby reducing its ability to accurately induce a proportional current in the windings (not shown) of current transformer  104 . This reduction in performance results in a lower value of current flowing in the current transformer  104  and an incorrect electricity usage calculation. Use of an external magnet  108  for this purpose may result in theft of electricity. Shielding of the current transformer  104  may result in reducing the effect of the external magnet  108  on the current transformer  104 . 
       SUMMARY OF THE INVENTION 
       [0005]    A first aspect of the invention includes an electronic watt-hour meter, comprising: a current transformer operatively coupled to the electronic watt-hour meter; a first shield on a first side of the current transformer; and a second shield on a second side of the current transformer, wherein the second side is substantially parallel to the first side, wherein the first shield and the second shield each include a substantially magnetically permeable and conductive metal. 
         [0006]    A second aspect of the invention includes an electronic watt-hour meter, comprising: a current transformer operatively coupled to the electronic watt-hour meter; a first shield on a first side of the current transformer; a second shield on a second side of the current transformer, wherein the second side is substantially parallel to the first side; wherein at least one of the first shield and the second shield substantially shields up to approximately 5000 gauss from an external magnet. 
         [0007]    A third aspect of the invention includes a first magnetic shield for a current transformer, comprising; a substantially disc shape body; an aperture through approximately a center of the body; and a gap in the body, the gap extending from an edge of the body to the aperture, wherein the body includes a substantially magnetically permeable and conductive metal. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    These and other features of this invention will be more readily understood from the following detailed description of the various aspects of the invention taken in conjunction with the accompanying drawings that depict various embodiments of the invention, in which: 
           [0009]      FIG. 1  shows a top view of a known electronic watt-hour meter. 
           [0010]      FIG. 2  shows a perspective view of a known electronic watt-hour meter. 
           [0011]      FIG. 3  shows a perspective view of a known current transformer and a known potential link. 
           [0012]      FIG. 4  shows a simplified top view of a known electronic watt-hour meter. 
           [0013]      FIG. 5  shows a top view of one embodiment of an electronic watt-hour meter including a first shield and a second shield in accordance with the invention. 
           [0014]      FIG. 6  shows a perspective view of one embodiment of a first shield in accordance with the invention. 
           [0015]      FIG. 7  shows a perspective view of one embodiment of a first shield in accordance with the invention. 
           [0016]      FIG. 8  shows a perspective view of one embodiment of a first shield in accordance with the invention. 
           [0017]      FIG. 9  shows a perspective view of one embodiment of a first shield in accordance with the invention. 
           [0018]      FIG. 10  shows a side view of one embodiment of a first shield and a second shield for a current transformer in accordance with the invention. 
           [0019]      FIG. 11  shows a perspective view of one embodiment of a third shield in accordance with the invention. 
           [0020]      FIG. 12  shows a top view of one embodiment of a first shield, a second shield, and a third shield for a current transformer in accordance with the invention. 
           [0021]      FIG. 13  shows a top view of one embodiment of electronic watt-hour meter including a first shield, a second shield, and a third shield for a current transformer in accordance with the invention. 
       
    
    
       [0022]    It is noted that the drawings of the invention are not to scale. The drawings are intended to depict only typical aspects of the invention, and therefore should not be considered as limiting the scope of the invention. In the drawings, like numbering represents like elements between the drawings. 
       DETAILED DESCRIPTION 
       [0023]    Referring to  FIG. 5 , a top view of one embodiment of electronic watt-hour meter including a first shield  110  and similarly structured second shield  120  in accordance with the invention is shown. First shield  110  is illustrated closer to external magnet  108  than second shield  120 . First shield  110  or second shield  120  may be thicker than the other depending upon which of first shield  110  or second shield  120  is closest to anticipated location of external magnet  108 . First shield  110  and/or second shield  120  may be placed on current transformer  104  during manufacture of current transformer  104  or electronic watt-hour meter or both. Alternatively, first shield  110  and/or second shield  120  may be placed on current transformer  104  subsequent to manufacture of electronic watt-hour meter. In one embodiment of the invention, current transformer  104  may be substantially torodial in shape and potential link  106  may be rod-like in shape. In one embodiment, first shield  110  or second shield  120  may substantially protect current transformer  104  from external magnet magnetic field  115  of approximately 5000 gauss or less when external magnet  108  is located, for example, approximately 1.27 centimeters (0.5 inches) or more away from current transformer  104 . 
         [0024]    Referring to  FIG. 6 , a perspective view of one embodiment of a first shield  110  in accordance with the invention is shown. First shield  110  may include a substantially disc shape body  111  having an edge  112 . Current transformer  104  may be torodial in shape. Substantially disc shape body  111  may physically cover current transformer  104 . First shield  110  may include other shapes, e.g. square, triangle, or other polygonal shapes. First shield  110  may include an aperture  114  which may extend through approximately a center of body  111 . First shield  110  and second shield  120  may be placed on current transformer  104  by placing potential link  106  through aperture  114 . 
         [0025]    First shield  110  may include a substantially magnetically permeable and conductive metal. Magnetic permeability is the ability of a material to support the formation of a magnetic field within itself. It is the degree of magnetization that a material obtains in response to an applied magnetic field. Substantially magnetically permeable and conductive metal may include low carbon steel such as cold rolled steel and/or hot rolled steel. Low carbon steel may include a range of 0.05 percent to 0.26 percent carbon content such as American Iron and Steel Institute (AISI)  1005  to AISI  1026  steel. A thickness  113  of body  111  may range from, for example, approximately 0.15 centimeters to 0.64 centimeters (approximately 0.060 inches to 0.250 inches). 
         [0026]    Referring to  FIG. 7 , a perspective view of another embodiment of a first shield  210  in accordance with the invention is shown. First shield  210  may include a gap  216  extending from an edge  212  to aperture  214 . Gap  216  may include two substantially parallel straight sides  218  extending from edge  212  to aperture  214  resulting in a generally linear gap  216 . A current flowing through first shield  110  (without a gap) may produce energy losses in the form of heat and reduce the efficiency of electronic watt-hour meter  102 . Gap  216  may interrupt the current flowing through the first shield  210  reducing energy losses. Referring to  FIG. 8 , first shield  210  may include irregularities in sides  218 . For example, sides  218  may not be straight for the purpose of accommodating components in electronic watt-hour meter  102 , e.g. they may include curving sides, notches, etc. 
         [0027]    Referring to  FIG. 9 , a perspective view of another embodiment of first shield  310  in accordance with the invention is shown. In this case, a gap  316  may include two non-parallel straight sides  318  extending from an edge  312  to an aperture  314  resulting in a substantially pie-shaped gap  316 . Similarly to the embodiment shown in  FIG. 8 , sides  318  may not be straight. 
         [0028]    Referring to  FIG. 10 , a perspective view of one embodiment of a first shield  110 ,  210 ,  310  (only one reference number used hereafter for brevity) and a second shield  120 , similarly structured to first shield  110 , for current transformer  104  in accordance with the invention is shown. First shield  110  may be placed on a first side  111  of current transformer  104 . Second shield  120  may be placed on a second side  121  of current transformer  104 . Second side  121  may be substantially parallel to first side  111 . Aperture  114  accommodates potential link  106  extending through current transformer  104 . Aperture  114  is illustrated as substantially circular. A person skilled in the art will readily recognize that aperture  114  may be any shape that accommodates potential link  106 . Gap  116  may be used to accommodate components within electronic watt-hour meter, e.g., metrology circuitry (not shown) and metrology circuitry bracket  109 . 
         [0029]    Gap  116 ,  216  ( FIG. 7-9 ) in first shield  110  and/or second shield  120  may be oriented away from the anticipated location of external magnet  108 . Alternatively, gap  116  may be sufficiently wide to slide first shield  110  (and second shield  120 ) over potential link  106 . 
         [0030]    Referring to  FIG. 11 , a perspective view of one embodiment of a third shield  128  in accordance with the invention is shown. Third shield  128  may include a substantially curvilinear planar shape. In one example shown, third shield  128  has a slotted tubular shape so as to be ‘C’ shaped in cross-section. Variants of this shape may be possible, e.g. closed tubular shape and half tubular shape. Two ends  132  of third shield  128  may create a third shield gap  130 . Third shield  128  may include the same substantially magnetically permeable and conductive metal as first shield  110 , and may feature the same thickness  113  and protection of current transformer  104  from magnetic field of external magnet  108  as described herein for first shield  110 . 
         [0031]    Referring to  FIG. 12 , a perspective view of one embodiment of first shield  110 , second shield  120 , and a third shield  128  for current transformer  104  in accordance with the invention is shown. Third shield  128  may be placed on a third side  129 , e.g., an outer periphery, of current transformer  104 . Third shield  128  may be connected with at least one of first shield  110  or second shield  120 . Collectively, first shield  110 , second shield  120 , and third shield  128  may form a substantial enclosure of current transformer  104   
         [0032]    Referring to  FIG. 13 , a perspective view of one embodiment of first shield  110 , second shield  120 , and third shield  128  in electronic watt-hour meter in accordance with the invention is shown. Third shield  128  may be located on current transformer  104  in substantial proximity to the anticipated location of external magnet  108 . 
         [0033]    The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
         [0034]    This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.