Abstract:
An electrical apparatus of an electric distribution power system includes an electrical device having a high voltage electrical terminal that may be energized, an exterior insulating housing, and an insulator. The exterior insulating housing surrounds and insulates the electrical device, and includes an opening through which the high voltage electrical terminal protrudes such that at least a portion of the high voltage electrical terminal is external to the exterior insulating housing. The insulator covers the electrical terminal and is attached to the exterior insulating housing such that no current flow path is provided through an interface between the insulator and the exterior insulating housing.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application claims priority to U.S. application Ser. No. 60/646,525, filed Jan. 25, 2005, which is incorporated herein by reference in its entirety. 

   TECHNICAL FIELD 
   This description relates to an insulator that covers an energized terminal of an electrical device in a power system. 
   BACKGROUND 
   Electrical devices used in power systems include, for example, surge arresters, terminations, and bushings. Such electrical devices typically have a high voltage or energized terminal. For example, a surge arrester may include a high voltage or energized terminal and a ground terminal. If an object comes in direct contact with or is in close proximity to the energized terminal of the surge arrester and the object simultaneously is in direct contact with or is in close proximity to a grounded area, the object can become a conducting path for current of the power system. Current flow through or over the object results in a power system outage, and, if the object is an animal, may be a fatal event. 
   SUMMARY 
   In one general aspect, an electrical apparatus of an electric distribution power system includes an electrical device having a high voltage electrical terminal that may be energized, an exterior insulating housing, and an insulator. The exterior insulating housing surrounds and insulates the electrical device, and includes an opening through which the high voltage electrical terminal protrudes such that at least a portion of the high voltage electrical terminal is external to the exterior insulating housing. The insulator covers the electrical terminal and is attached to the exterior insulating housing such that no current flow path is provided through an interface between the insulator and the exterior insulating housing. 
   Implementations may include one or more of the following features. For example, the electrical device may include a surge arrester. 
   The insulator may be formed on the electrical device such that a bond between the insulator and the exterior insulating housing is established during formation of the insulator. The insulator may be formed from silicone rubber or from an elastomeric polymer. The insulator may serve as an animal protector. 
   The exterior insulating housing may include a weather shed to which the insulator is bonded or over which the insulator fits. 
   In another general aspect, a high voltage electrical apparatus of an electric distribution power system is made. An electrical device is surrounded with an exterior insulating housing and at least a portion of a high voltage electrical terminal extends through the exterior insulating housing such that the high voltage electrical terminal portion is external to the exterior insulating housing. The high voltage electrical terminal of the electrical device is covered with an insulator. The insulator is attached to the exterior insulating housing and the high voltage terminal is covered such that no current flow path is provided through an interface between the insulator and the exterior insulating housing. 
   Implementations may include one or more of the following features. For example, the electrical device may include a surge arrester. 
   The insulator may be attached to the exterior insulating housing by bonding the insulator to a weather shed of the exterior insulating housing. The insulator may be attached to the exterior insulating housing by forming the insulator on the exterior insulating housing such that a bond between the insulator and the exterior insulating housing is established during formation of the insulator. The insulator may be attached to the exterior insulating housing by fitting the insulator over a weather shed of the exterior insulating housing. 
   The insulator may be formed from silicone rubber. The insulator may be formed from an elastomeric polymer. 
   In another general aspect, a high voltage terminal of an electrical device within an electric distribution power system is insulated. A high voltage electrical terminal that is external to an exterior insulating housing is covered with an insulator. The insulator is attached to the exterior insulating housing such that no current flow path is provided through an interface between the insulator and the exterior insulating housing. 
   Implementations may include one or more of the following features. For example, the electrical device may include a surge arrester. 
   The insulator may be attached to the exterior insulating housing by bonding the insulator to a weather shed of the exterior insulating housing. The insulator may be attached to the exterior insulating housing by forming the insulator on the exterior insulating housing such that a bond between the insulator and the exterior insulating housing is established during formation of the insulator. The insulator may be attached to the exterior insulating housing by fitting the insulator over a weather shed of the exterior insulating housing. 
   Implementations of the insulator provide effective electrical insulation of the energized areas of a surge arrester or another electrical device. The insulator may be used to prevent external influences, such as animals, tree limbs or other objects, from coming into direct contact with or coming too close to energized areas of the surge arrester. Particular implementation of the insulator provide a relatively small, inexpensive, and highly effective way for protecting wildlife, preventing costly nuisance power system outages, and improving power system reliability. Other potential advantages include improved insulation withstand performance by providing increased creep and strike distances and reduced potential for collateral damage to other power system components during the flow of power frequency fault current. 
   Other features will be apparent from the description, the drawings, and the claims. 

   
     DESCRIPTION OF DRAWINGS 
       FIG. 1  shows a side view of a surge arrester that can be used in a power system. 
       FIG. 2  shows a side view with a partial cross-sectional view of an insulator coupled to the surge arrester of  FIG. 1 . 
       FIG. 3  shows a cross-sectional view of the insulator and the surge arrester of  FIG. 2 . 
       FIG. 4  shows an illustration of another implementation of an insulator and a surge arrester. 
       FIG. 5  shows a side view with a partial cross-sectional view of another implementation of an insulator coupled to the surge arrester of  FIG. 1 . 
       FIG. 6  shows a side view with a partial cross-sectional view of another implementation of an insulator coupled to the surge arrester of  FIG. 1 . 
   

   Like reference symbols in the various drawings may indicate like elements. 
   DETAILED DESCRIPTION 
   Referring to  FIG. 1 , a surge arrester  100  includes a high voltage or energized terminal  105 , a ground terminal  110 , and an internal electrically-active conductive component such as a bonded-element stack  102  (shown in  FIG. 3 ) that is disposed within an insulating housing  115 . At least a portion of the energized terminal  105  is external to the insulating housing  115  such that a portion extends through one end of the housing  115  and connects to a first side of the bonded-element stack, and at least a portion of the ground terminal  110  extends through the opposite end of the housing  115  and connects to a second side of the bonded-element stack. The energized terminal  105  is electrically connected to one or more insulated line leads  117  for connection to other electrical components of the power system. As shown in  FIG. 1 , the housing  115  includes several weather sheds  120  that extend out from a main body  125  of the housing  115 . The housing  115  is typically made of a suitable polymeric material. An arrester of this design is shown, for example, in U.S. Pat. No. 6,279,811, issued on Aug. 28, 2001, which is incorporated herein by reference. 
   Referring to  FIGS. 2 and 3 , an electrical insulator  200  covers the energized terminal  105  of the surge arrester  100 . The insulator  200  provides electrical insulation around energized areas in proximity to the top of the surge arrester  100 . The insulator  200  prevents external objects, such as, for example, animals and tree limbs, from coming into direct contact with or coming too close to energized terminal  105  of the surge arrester  100 . 
   The insulator  200  is generally shaped like a funnel to fit over the top of the surge arrester  100  and cover the terminal  105  and at least a portion of the first shed  120 . The insulator  200  includes a circumferential internal ledge  205  that extends from a wider end  210  of a conical wall  215 , and a tube  220  that extends from a narrow end  225  of the conical wall  215 . The conical wall  215  has an opening  230  that is large enough to receive the first shed  120  and the terminal  105  of the surge arrester  100 . The tube  220  has an opening  235  that is large enough to receive the one or more insulated line leads  117  that extend from the terminal  105 . The ledge  205  is flexible, extends inward from the wider end  210 , and has an inner diameter that is smaller than an outer diameter of the first shed  120 . In this way, the ledge  205  extends below the first shed  120  to facilitate locking of the insulator  200  to the arrester  100 . 
   The insulator  200  is fabricated separately from the surge arrester  100  and then installed by placing the insulator  200  over the surge arrester  100 . The insulator  200  is pushed onto the surge arrester  100  so that the wider end  210  expands as the ledge  205  is moved outward from the first shed  120  until the ledge  205  reaches the edge of the first shed  120  and snaps back and extends below the first shed  120 . The line lead  117  is inserted through the opening  235  of the tube  220  so that the lead  117  is accessible after the insulator  200  is installed on the surge arrester  100 . 
   The insulator  200  is designed with several features that provide suitable and adequate electrical insulation. These features are the selection of material used in making the insulator  200 , the geometry of the insulator, and the fit of the insulator  200  to the associated surge arrester  100 . The insulator  200  can be made of an elastomeric insulating material, such as, for example, suitable polymers such as vinyl, silicone rubber, EPDM, EVA, or polyethylene. The elastomeric quality of the insulator  200  facilitates the installation of the insulator  200  to the surge arrester  100  because the insulator  200  is elastically deformed during installation. The insulator  200  has a geometry and a cross-sectional thickness  300  that fully covers at least a top portion of the surge arrester  100 , and in particular, the energized terminal  105 . The insulator  200  is designed to withstand power frequency voltages of up to 22 kV rms for 60 seconds while dry. Because the insulator  200  is designed with the above features, the interface  305  (that is, the region where the insulator  200  fits over the first shed  120 ) between the insulator  200  and the surge arrester  100  provides adequate dielectric strength or sufficient physical distance to prevent an electric discharge when a grounded object approaches the terminal  105 . 
   As discussed above, the insulator  200  may be retrofitted to the surge arrester  100  shown in  FIGS. 1-3 . However, the insulator can be designed to be retrofitted to other types of surge arresters or other types of electrical devices found in power systems. In other implementations, the interface  305  between the insulator  200  and the surge arrester  100  can be facilitated using external adhesives such as, for example, suitable room temperature vulcanized (RTU) silicone rubber, butyl compounds, mastic materials, or other adhesive materials. 
   For example,  FIG. 4  shows another implementation in which an insulator  400  is provided as part of an as-manufactured surge arrester  405 . The insulator  400  is made of silicone rubber and the weather shed  415  is made of silicone rubber. In this design, an interface  410  between the insulator  400  and the surge arrester  405  is formed by directly bonding the insulator  400  to a weather shed  415  of the surge arrester  405 . The bond is created during manufacture of the insulator  400  and the surge arrester  405  by casting, molding, potting, or any suitable bonding technique. Because the insulator  400  is directly bonded to the weather shed  415  of the surge arrester  405 , electrical integrity is maintained between the insulator  400  and the housing of the surge arrester  405 . 
   Like the insulator  200  described above, the insulator  400  is generally shaped like a funnel to fit over the top of the surge arrester  405  and to cover at least a portion of the first shed  415 . The insulator  400  includes a conical wall  420  that defines an opening  425  that is large enough to receive at least a portion of the first shed  415  and an opening  430  that is large enough to receive one or more insulated line leads  435  that extend from a terminal  440  of the surge arrester  405 . 
   Referring to  FIG. 5 , in another implementation, an electrical insulator  500  covers the energized terminal  105  of the surge arrester  100 . The electrical insulator  500  is designed much like the insulator  200  described above except that a wider end  510  of a conical wall  515  of the insulator  500  lacks a circumferential internal ledge (such as the ledge  205 ). Instead, the insulator  500  is designed with a circumferential lip  505  that extends from the conical wall  515 . 
   The insulator  500  is suitably locked to the arrester  100  by at least the frictional interaction between a tube  520  and the insulated line leads  117 . The insulator  500  may include ridges or notches along an inner surface of the tube  520 , the conical wall  515 , or the lip  505  to further facilitate locking of the insulator  500  to the arrester  100 . 
   Referring to  FIG. 6 , in another implementation, an electrical insulator  600  covers the energized terminal  105  of the surge arrester  100 . The electrical insulator  600  is designed much like the insulator  200  described above except that a wider end  610  of a conical wall  615  of the insulator  600  lacks a circumferential internal ledge (such as the ledge  205 ). Instead, the insulator  600  is designed such that the conical wall  615  extends an additional length to cover the first shed  120 . 
   The insulator  600  is suitably locked to the arrester  100  by at least the frictional interaction between a tube  620  and the insulated line leads  117 . The insulator  600  may include ridges or notches along an inner surface of the tube  620 , or the conical wall  615  to further facilitate locking of the insulator  600  to the arrester  100 . 
   Other implementations are within the scope of the following claims. For example, the insulator  400  can be made of vinyl, silicone rubber, EPDM, EVA, polyethylene, or other insulating materials that can be properly bonded to the material of the weather shed  415 . The insulator  200 ,  400 ,  500 , or  600  may have a geometry that minimizes the material required, and thereby reduces the cost of the insulator.