Patent Publication Number: US-7215299-B2

Title: Antenna protected from dielectric breakdown and sensor or switchgear apparatus including the same

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention pertains generally to antennas and, more particularly, to antennas for application in an environment subjected to a voltage potential where breakdown can occur. The invention also pertains to such antennas for application with sensors or switchgear devices. 
   2. Background Information 
   Diagnostic sensors that are located on the line or “high” voltage side of switchgear devices, such as circuit breakers, and/or on the bus structure of such devices must survive impulse voltage tests (e.g., rated lightning impulse voltage; BIL (Basic Impulse Level)) to prove that arcing between conductive surfaces does not occur. Survival of these tests is dependent upon the distance between the conductive surfaces, the rated breakdown of the material between those surfaces, the geometry of those surfaces and the applied voltage potential. 
   If such a diagnostic sensor might implement, for example, communications employing an antenna, then such antenna, if located outside of the package of the diagnostic sensor, may likely be subjected to arcing during the impulse voltage tests. 
   U.S. Pat. No. 4,725,449 discloses that problems have been encountered with radio frequency (RF) ion source antenna coils. When the antenna coil is made of bare metal, such as copper, sparking or arcing may occur in a vacuum chamber, both between the turns of the coil, and also between the coil and various electrodes which may be employed in the ion source. When the antenna coil is operated at high power levels, the RF voltage between different portions of the coil may be quite high. This patent further discloses an RF ion source antenna coil coated with a thin impervious layer or coating of glass which is fused to a metal conductor and is strongly adherent thereto. The glass coating covers the entire surface of the antenna conductor, but not including the terminal portions or contacts, which are left bare. The glass coating is thin, continuous, impervious and substantially uniform in thickness. The continuous, impervious glass coating is an excellent electrical insulator and is resistant to voltage breakdown. The patent also discloses that the glass coating will withstand a voltage of five kV. 
   There is room for improvement in antennas. There is also room for improvement in sensors and switchgear devices employing an antenna. 
   SUMMARY OF THE INVENTION 
   These needs and others are met by the present invention, which provides an antenna element including an antenna member that is encapsulated by a suitable high voltage breakdown material, in order to suppress dielectric breakdown through the material to the encapsulated antenna member from an electrical voltage potential. In one embodiment, the antenna is physically located outside of the corona discharge shield or conductive housing of a sensor. 
   The suitably high voltage breakdown material may be, for example, Cycloaliphatic epoxy, which has a dielectric strength of about 17 MV/m to about 18 MV/m as compared to air, which has a dielectric strength of about 3 MV/m. 
   The sensor including the encapsulated antenna member may be resident within a circuit interrupter and may communicate to, for example, another internal circuit without suffering the effects of severe radio signal attenuation, because the antenna member is not within the corona discharge shield or conductive housing of the diagnostic sensor and, yet, is able to withstand impulse voltage tests as a result of the encapsulated antenna member. 
   In accordance with one aspect of the invention, an antenna protected from external dielectric breakdown comprises: an antenna element comprising an antenna member and at least one antenna lead; and a material encapsulating the antenna member, the material being adapted to suppress dielectric breakdown through the material to the encapsulated antenna member from an external voltage potential. 
   The antenna element may include at least one square corner or square edge. The material encapsulating the antenna member may define a surface which encapsulates the antenna member, the surface including a first planar surface and a second surface, the second surface excluding any square corner, excluding any square edge, and including a plurality of rounded corners and a plurality of rounded edges. 
   As another aspect of the invention, a sensor comprises: an antenna element comprising an antenna member and at least one antenna lead; a material encapsulating the antenna member, the material being adapted to suppress dielectric breakdown through the material to the encapsulated antenna member from an external voltage potential; a conductive housing including an opening receiving the at least one antenna lead; and a sensor circuit disposed in the conductive housing, the sensor circuit adapted to output a radio frequency signal to the at least one antenna lead or to input a radio frequency signal from the at least one antenna lead. 
   The material encapsulating the antenna member may include a surface which is substantially larger than the opening. The surface of the material may be mounted on the conductive housing and may cover the opening thereof. 
   As another aspect of the invention, a switchgear apparatus comprises: a switchgear device comprising a power bus; an antenna element comprising an antenna member and at least one antenna lead; a material encapsulating the antenna member, the material being adapted to suppress dielectric breakdown through the material to the encapsulated antenna member from the power bus; a conductive housing including an opening receiving the at least one antenna lead, the conductive housing being mounted on or proximate to the power bus; and a sensor circuit disposed in the conductive housing, the sensor circuit adapted to output a radio frequency signal to the at least one antenna lead or to input a radio frequency signal from the at least one antenna lead. 
   The switchgear device may be a circuit breaker. The circuit breaker may include an internal wireless circuit adapted to communicate with the sensor circuit through the antenna element. 
   The switchgear device may be a bus structure adapted to be electrically connected to a circuit breaker. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A full understanding of the invention can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which: 
       FIG. 1  is an isometric view of a diagnostic sensor including an antenna in accordance with the present invention. 
       FIG. 2  is a vertical elevation view of a portion of a circuit breaker vacuum bottle and power bus including the diagnostic sensor and antenna of  FIG. 1 . 
       FIG. 3  is a plan view of an antenna in accordance with another embodiment of the invention. 
       FIG. 4  is a vertical elevation view of another antenna in accordance with another embodiment of the invention. 
       FIG. 5  is an isometric view of a bus structure including the diagnostic sensor and antenna of  FIG. 1 . 
       FIG. 6  is an isometric view of another antenna in accordance with another embodiment of the invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   As employed herein the term “antenna” shall expressly include, but not be limited by, any structure adapted to radiate and/or to receive electromagnetic waves, such as, for example, radio frequency signals. 
   As employed herein the term “switchgear device” shall expressly include, but not be limited by, a circuit interrupter, such as a circuit breaker; a bus structure for a circuit interrupter; a vacuum interrupter; a vacuum bottle; and/or other switchgear devices that are subjected to one or more voltage potentials where breakdown can occur. 
   As employed herein the term “encapsulated” or “encapsulating” shall expressly include, but not be limited by, embedded or embedding; surrounded by another material; and/or insert molded in another material. 
   As employed herein, the statement that two or more parts are “connected” or “coupled” together shall mean that the parts are joined together either directly or joined through one or more intermediate parts. Further, as employed herein, the statement that two or more parts are “attached” shall mean that the parts are joined together directly. 
   The present invention is described in association with an antenna for a diagnostic sensor of a circuit breaker, although the invention is applicable to a wide range of sensor and/or antenna applications in an environment including a voltage potential where breakdown can occur. 
   Referring to  FIG. 1 , a diagnostic sensor  2  includes an external antenna  4 . The antenna  4 , which is protected from dielectric breakdown, includes an antenna element  6  having an antenna member  8  and at least one antenna lead  10  (as best shown in  FIG. 2  with the one antenna lead  10 ). The antenna  4  also includes a material  12  encapsulating the antenna member  8 . The material  12  is adapted to suppress dielectric breakdown through such material to the encapsulated antenna member  8  from an external voltage potential. 
   EXAMPLE 1  
   The material  12  may be a suitable casting and potting material, such as a Cycloaliphatic epoxy, having a dielectric strength of about 17 MV/m to about 18 MV/m, although a wide range of different dielectric strengths may be employed. 
   EXAMPLE 2 
   The antenna element  6  and the antenna member  8  may be adapted to communicate in a low-rate wireless network (not shown), such as a low-rate wireless local area network (LR-WLAN). Alternatively, any suitable communication protocol may be employed. 
   EXAMPLE 3 
   The dielectric strength of an insulating material is the maximum electric field strength that it can withstand intrinsically without breaking down and experiencing failure of its insulating properties (e.g., a dielectric breakdown through the material). The higher the dielectric strength (expressed as volts per unit thickness) of a material the better its quality as an insulator. Knowing the breakdown or dielectric strength of the material  12  being employed in, for example, MV/m, and the voltage (e.g., of a power bus structure, such as power bus  14  or  18  of  FIG. 2 ) of interest, the worst-case required thickness of the material  12  employed around the antenna member  8  may be calculated. For example, if the desired protection is a voltage of 100 kV (as applied, for example, to the surface of the material  12  as a worst case scenario), and if the dielectric strength of the material  12  is for example, 17 MV/m, then 0.0059 meters (=1/17 MV/m/100 kV) or 5.9 mm of the material  12  is employed around the antenna member  8 . 
   EXAMPLE 4 
   The dielectric constant, ε r , is the ratio of the permittivity of a substance, ε, to the permittivity of free space, ε o . The dielectric constant is an expression of the extent to which a material concentrates electric flux, and is the electrical equivalent of relative magnetic permeability. As the dielectric constant increases, the electric flux density increases, if all other factors remain unchanged. A high dielectric constant, in and of itself, is not necessarily desirable. Generally, substances with high dielectric constants breakdown more easily when subjected to intense electric fields, than do materials with low dielectric constants. For example, dry air has a low dielectric constant, but it makes an excellent dielectric material for capacitors used in high-power radio-frequency (RF) transmitters. Even if air does undergo dielectric breakdown (a condition in which the dielectric suddenly begins to conduct current), the breakdown is not permanent. When the excessive electric field is removed, air returns to its normal dielectric state. Solid dielectric substances, such as polyethylene or glass, however, can sustain permanent damage. 
   For example, the material  12  of  FIG. 1  may employ a dielectric constant of about 3.5 to about 4.72. 
   EXAMPLE 5 
   As another example of the material  12 , a casting and potting material, such as Stycast 2651-40 Catalyst-9 Epoxy having a dielectric strength of 17.7 MV/m, a dielectric constant of about 3.90 at 25° C., and being marketed by Emerson &amp; Cuming of Canton, Mass., may be employed. 
   EXAMPLE 6 
   As another example of the material  12 , a casting and potting material, such as EPON Resin 828/NMA/EMI-24—Anhydride Cure having a dielectric strength of 17.7 MV/m, a dielectric constant of about 3.26 at 25° C., and being marketed by Resolution Performance Products of Houston, Tex. may be employed. 
   EXAMPLE 7 
   As another example of the material  12 , a casting and potting material, such as EPON Resin 828/PACM—Cycloaliphatic Cure having a dielectric strength of 17.7 MV/m, a dielectric constant of about 3.50 at 25° C., and being marketed by Resolution Performance Products of Houston, Tex. may be employed. 
   EXAMPLE 8 
   As an alternative to Examples 1 and 3–7, a wide range of other suitable materials may be employed depending upon the desired level of breakdown protection. 
   Referring to  FIG. 2 , the diagnostic sensor  2  and antenna  4  are shown in combination with a vacuum bottle  16  and the power bus  14  (e.g., flexible shunt or laminated conductor of a power bus) of a switchgear apparatus such as, for example, a circuit breaker  17  or other switchgear device including such a power bus  14 . An example of a vacuum circuit breaker is disclosed in U.S. Pat. No. 6,373,358, which is incorporated by reference herein. For example, the vacuum bottle  16  includes separable contacts (not shown) of which a fixed contact (not shown) is electrically connected, for example, to a line bus (not shown) and, also, includes a moveable contact (not shown), which is electrically connected by the power bus  14  to, for example, a load conductor  18 . 
   The diagnostic sensor  2  includes a suitable housing  20  (e.g., without limitation, a corona discharge shield; a conductive housing) including an opening  22  receiving the one or more antenna leads  10  (only one antenna lead  10  is shown in  FIG. 2 ) therethrough. The housing  20  is mounted (e.g., without limitation, bolted to; strapped on; mechanically fixed to; or otherwise coupled to) proximate to or on a power bus, such as the load conductor  18 . Alternatively, the housing  20  may be mounted proximate to or on any suitable power bus, such as a line bus (not shown). A suitable sensor circuit  24  is disposed in the housing  20 . The sensor circuit  24  is adapted to output a radio frequency signal  26  to the antenna leads  10  or to input a radio frequency signal  28  from the antenna leads  10 . 
   The circuit breaker  17  includes an internal wireless circuit  29  adapted to communicate with the sensor circuit  24  through the antenna element  6 . 
   As shown in  FIG. 2 , the material  12  of the antenna  4  includes a surface  30 , which is substantially larger than the opening  22  of the housing  20 . The surface  30  is preferably suitably mounted on (e.g., coupled to; adhesively coupled; by flanging (not shown) the surface  30  and clipping (not shown) it to the housing  20 ; retained by employing suitably rigid antenna lead(s)  10 ) the housing  20 , thereby covering the opening  22  thereof. 
   EXAMPLE 9 
     FIG. 3  shows another antenna  32  including a patch antenna element  34 . The patch antenna element  34  includes a radiating element  36  spaced suitably close to a parallel ground plane  38 . One example of the patch antenna element  34  is a consumer-grade GPS antenna. Often, the implementation uses printed circuit board techniques, usually with a fiberglass dielectric. The driven element is sometimes circular, although square, rectangular (as shown in  FIG. 3  with radiating element  36 ) and linear shapes may be employed. The radiating element  36  is usually fed at the edge, or a little way in from the edge, as shown, for example, at lead  40  through feed portion  42 . The patch antenna element  34  functions as two slot dipoles side by side or as a resonant cavity with open sides that radiate. 
   In accordance with the invention, the antenna  32  also includes a material  44  substantially encapsulating the patch antenna element  34 . Similar to the material  12  of  FIGS. 1 and 2 , the material  44  is adapted to suppress dielectric breakdown through such material to the encapsulated patch antenna element  34  from an external voltage potential. 
   The material  44  includes six surfaces  46 , 48 , 50 , 52 , 54 , 56  of which surface  46  is opposite and generally parallel to surface  48 , surface  50  is opposite and generally parallel to surface  52 , and surface  54  is opposite and generally parallel to surface  56  (shown in hidden line drawing). The encapsulated patch antenna element  34  may be disposed substantially intermediate the opposing surfaces  46 , 48 ,  50 , 52  and  54 , 56 . The lead  40  protrudes through the surface  56 , which may be disposed adjacent the housing  20  of  FIG. 2 . The lead  40  and another lead (not shown) for the ground plane  38  may enter the opening  22  of  FIG. 2 . 
   EXAMPLE 10 
   As an alternative to the spacing of  FIG. 3 , as shown in  FIGS. 1 and 2 , the surface  30  of the material  12  is a first planar surface and such material  12  includes a second planar surface  58  opposite the first planar surface  30 . The antenna element  6  is generally disposed a first distance  60  from the first planar surface  30  and a second greater distance  62  from the second planar surface  58 . 
   EXAMPLE 11 
     FIG. 4  shows another antenna  64  including a planar inverted-F antenna (PIFA) element  66 , which is, in general, achieved by short-circuiting its radiating patch or wire  67  to the antenna&#39;s ground plane  68  with a shorting pin  70 . The PIFA element  66  can resonate at a relatively much smaller antenna size for a fixed operating frequency. Such PIFA designs usually occupy a compact volume. 
   In accordance with the invention, the antenna  64  also includes a material  72  substantially encapsulating the PIFA element  66 . Similar to the material  12  of  FIGS. 1 and 2 , the material  72  is adapted to suppress dielectric breakdown through such material to the encapsulated PIFA element  66  from an external voltage potential. Leads  74  and  76  from the radiating patch or wire  67  and the ground plane  68 , respectively, penetrate the material  72 . 
   The region  78  between the radiating patch or wire  67  and the ground plane  68  may or may not employ an air substrate. For example, as shown in  FIG. 4 , the material  72  is disposed in the region  78 . 
   EXAMPLE 12 
   Although the antenna elements  6 ,  34  and  66  of  FIGS. 2 ,  3  and  4 , respectively, include at least one square corner or square edge, as best shown in  FIG. 1 , the material  12  defines a surface which encapsulates the antenna member  8 , the surface distal (i.e., any surface other than the surface  30 ) from the housing  20  excluding any square corner, excluding any square edge, and including a plurality of rounded corners  80 , 82 , 84 , 86  and a plurality of rounded edges  88 , 90 , 92 , 94  ( FIG. 1 ). 
   Alternatively, the surface  30  may include rounded corners and rounded edges (not shown) having a suitable radius (as measured from inside the material  12 ) like the surface  58 . Alternatively, the surface  30  may be slightly larger than the surface  58  and include a tapered edge (not shown) having a suitable radius (as measured from outside the material  12 ). 
   The external surfaces of the housing  20  and the antenna  4  preferably have a suitable minimal surface texture, in order to minimize or eliminate sharp points. 
   The housing  20  may include a cover mounted to a base using a number of suitable methods (e.g., non-conductive fasteners, such as plastic screws). Preferably, the housing  20  employs rounded corners and rounded edges, as shown. 
     FIG. 5  shows a power bus structure  96  including the diagnostic sensor  2  of  FIG. 1 . The bus structure  96  is adapted to be electrically connected to a circuit breaker (CB), such as CB  98 . 
   EXAMPLE 13 
     FIG. 6  shows an antenna  100 , which is protected from dielectric breakdown, including a wire loop antenna element  102  having a loop antenna member  104  and two antenna leads  106 ,  108 . The antenna  100  also includes a material  112  encapsulating the loop antenna member  104 . Similar to the material  12  of  FIG. 1 , the material  112  is adapted to suppress dielectric breakdown through such material to the encapsulated loop antenna member  104  from an external voltage potential. 
   EXAMPLE 14 
   Although Examples 2 and 9–13 disclose different antenna examples, the invention is applicable to a wide range of antennas. As further non-limiting examples, a dipole antenna or a monopole antenna may be employed. 
   While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the claims appended and any and all equivalents thereof.