Abstract:
Apparatus for reducing the risk of flashover during loadbreak operations of insulated separable connectors. A substantial airtight seal is prevented between the collar of the bushing insert and the cuff of the mating component. The connection is vented to break any adhesion between the bushing insert and the mating component cuff and to provide a chamfered airway for atmospheric airflow during removal of the mating component. A latch ring is reformed to include at least one raised edge about its outer diameter. Each raised edge has the shape of a sharply angled ramp and extends outward. There may be four or six raised edges.

Description:
TECHNICAL FIELD  
         [0001]    This invention relates to loadbreak separable electrical connectors, and more particularly, to venting of these connectors to break the adhesion between the bushing insert and the overlapping cuff of the mating component.  
         BACKGROUND  
         [0002]    High-voltage separable connectors interconnect transformers and other electrical equipment to distribution networks or the like. Frequently, it is necessary to connect and disconnect the electrical connectors. These connectors typically feature an elbow component, which contains a male connector, and a bushing component, which contains a female connector. When the components are connected, elastomeric O-rings seal the connection.  
           [0003]    Disconnecting energized connectors is an operation known as a loadbreak. A problem known as “flashover” has been known to occur while switching or separating loadbreak separable connectors. The male connector probe is typically maintained within the elbow, and the female connector contact is contained within the bushing. During a loadbreak operation, the elbow is pulled from the bushing using a hotstick to separate the components. This, in effect, creates an open circuit. During separation, flashover may occur when an arc from the energized connector extends rapidly to a nearby ground.  
           [0004]    Existing connector designs contain a number of arc extinguishing components so that the devices can have loadbreak operations performed under energized conditions with no flashover to ground occurring. The object of caution is to control the arc and gases generated during loadmake and loadbreak operations. Even with these precautions, however, flashovers have occurred on rare occasions.  
           [0005]    Flashovers commonly occur during the initial approximate one-inch of separation of the connectors from each other. The separation of the elbow from the bushing causes a partial vacuum to surround the energized components of the connector assembly. Because a partial vacuum presents a lower dielectric strength than that of air at atmospheric pressure, a flashover is more likely to occur at the moment that the elastomeric seal between the components is broken and before atmospheric pressure is reestablished around the energized portions of the components. Also, after being connected over a long period of time, the elbow may adhere to the bushing interface so that the connectors cannot be easily disengaged. This is known as a stuck condition, and greater force is required to separate the elbow, which may result in a more rapid change in pressure and dielectric strength in the air surrounding the energized components.  
           [0006]    During a flashover, an electrical arc between the energized components and ground may result, which may cause damage to the equipment and possibly create a power outage. The problem of flashovers involves principally 25 KV and 35 KV loadbreak connectors but also may include 15 KV connectors.  
           [0007]    Variations in the design of electrical connectors have been attempted to prevent flashovers. One adaptation has been to provide a groove or channel in the bushing insert shoulder. Another adaptation is to provide ribs on the transition shoulder of the bushing insert to prevent flashover. The plurality of ribs are circumferentially spaced along the transition shoulder portion of the bushing insert. Another design variation employs ribs that are spaced apart on the circumference of the outer surface of an indicator band.  
         SUMMARY  
         [0008]    Techniques are provided to reduce the risk of flashover during loadbreak operations.  
           [0009]    Generally, when removing the mating component from the bushing insert, the connection is vented to break any adhesion between the bushing insert and the mating component cuff and to prevent flashover. A chamfered airway for atmospheric airflow is provided by the raised edges on the latch ring lifting the cuff away from the collar during removal of the mating component. A chamfered corner creates an opening larger than a groove, which reduces a problem associated with the use of a groove in that the groove could be clogged by lubricating grease.  
           [0010]    A latch ring of a separable electrical connector is disposed over a forward portion of a collar of a bushing insert and over a shoulder of the bushing insert. The latch ring includes at least one raised edge extending outward beyond the circumference of the latch ring. Each raised edge has the shape of a sharply angled ramp and has dimensions of approximately 0.02 inches (height), 0.2 inches (width), and 0.5 inches (length). The at least one raised edge is formed on the latch ring during insulation-molding. Additionally, the at least one raised edge may be multiple raised edges evenly distributed along the circumference of the latch ring. In alternative implementations, there may be four or six raised edges, evenly distributed about the circumference of the latch ring. The latch ring may be part of a connector assembly including a bushing insert and a mating component. When the bushing insert and the mating component are assembled together, a cuff portion of the mating component overlaps the latch ring and a forward portion of the collar, and, as the mating component is removed from the bushing insert, the at least one raised edge pushes the cuff away from the latch ring and creates venting passages at the sides of the at least one raised edge.  
           [0011]    The described techniques have particular application for electrical connections in the 15-35 KV voltage range. However, they also may be applied to other connections at other voltages.  
           [0012]    The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features and advantages will be apparent from the description and drawings, and from the claims. 
       
    
    
     DESCRIPTION OF DRAWINGS  
       [0013]    [0013]FIG. 1 is a cross-sectional view of an exemplary elbow shaped male connector.  
         [0014]    [0014]FIG. 2 is a cross-sectional view of an exemplary bushing-type female connector configured to receive the male connector of FIG. 1.  
         [0015]    [0015]FIG. 3 is a cross-sectional view of a bushing insert of the connector of FIG. 2.  
         [0016]    [0016]FIG. 4A is an enlarged view of the bushing insert, a collar, and a latch ring of FIG. 3.  
         [0017]    [0017]FIG. 4B is an enlarged view of the bushing insert, the collar, the latch ring, a mating component cuff, and an air cavity in an assembled form.  
         [0018]    [0018]FIG. 5 is a view of an exemplary latch ring.  
         [0019]    [0019]FIG. 6 is a view of the latch ring of FIG. 5 with multiple raised edges.  
         [0020]    [0020]FIG. 7 is a view of a connector assembly using an implementation of a latch ring with multiple raised edges. 
     
    
       [0021]    Like reference symbols in the various drawings indicate like elements.  
       DETAILED DESCRIPTION  
       [0022]    The construction and operation of conventional electrical connector assemblies, which are in many respects similar to the connectors described below, are well known and have been in widespread use commercially for many years. Reference is made, for example, to U.S. Pat. No. 5,221,220, which is incorporated by reference.  
         [0023]    Referring to FIGS. 1 and 2, an electrical connector assembly  10  includes a male contact connector  20  (FIG. 1), such as an elbow connector, electrically connected to a portion of a high-voltage circuit (not shown), and a female contact connector  100  (FIG. 2), such as, for example, a bushing insert or connector, connected to another portion of the high-voltage circuit. As shown, the male contact connector  20  is in the form of a cable termination device, such as an elbow. Male and female contact connectors  20  and  100  are reversibly connectable and respectively interfit to achieve electrical connection. In one implementation, the connector assembly  10  is a 200 A, 25 KV class connector assembly. The construction and operation of electrical connector assemblies is well known in the art. Therefore, only relevant major components are described here.  
         [0024]    The male connector  20  includes an elastomeric and electrically-resistive housing  22  constructed from a material such as EPDM (ethylene-propylene-dienemonomer) rubber, which is provided on its outer surface with a semiconductive shield layer  24  that may be grounded by a perforated grounding tab  26 . The male connector  20  is generally elbow-shaped, with an upper horizontal portion  28  and a lower vertical portion  30  connected at a central portion  32 . A pulling eye  34  extends horizontally from the central portion  32 . An optional test point  36  is located along the lower portion  30 . In addition, an annular band  37  surrounds the lower portion  30  to identify the male connector  20  as a loadbreak rated device.  
         [0025]    A horizontally-oriented and generally conical bore  38  is disposed within the housing  22 . A semiconductive insert  40  is contained within the housing  22  such that vertical portions  42  of the insert  40  extend into the lower portion  30  of the connector  20 . A horizontally-disposed portion  44  of the insert  40  extends into the upper portion  28  of the connector  20  and presents an inner radial surface  46 , which defines a conically-shaped recess  48 . The insert  40  also presents an annular locking ring  50 , which is inwardly directed within the recess  48  from the inner radial surface  46  of the insert  40 . The locking ring  50  divides the inner radial surface  46  into a recessed area  47  and an extended area  49 .  
         [0026]    An insulative layer  52  of electrically-resistive material is disposed within the recess  48  of the insert  40 . The insulative layer  52  is preferably also made of EPDM and may be unitarily molded with portions of the housing  22  during manufacture. The insulative layer  52  extends from the inner surface of the bore  38  along the inner surface  46  of the insert  40  to the locking ring  50  so that the extended area  49  of the inner surface  46  is insulated. Additionally, the recessed area  47  of the insert  40  may be insulated.  
         [0027]    A male contact  54 , which also is referred to as a probe assembly, is largely contained within the housing  22  and is aligned down the axis of the conical bore  38  of the insert  40 . A conductor contact  56  is applied to a cable conductor (not shown) to make electrical contact with the cable conductor and is disposed within the lower portion of the male connector  20 . The probe assembly  54  threadedly engages the conductor contact  56 .  
         [0028]    The probe assembly  54  also features a male contact element or probe  58  that is formed of a material such as copper and extends horizontally from the conductor contact  56  into the bore  38  of the upper portion  28  and the recess  48  of the insert  40 . At the distal end of the probe extends an arc follower  60  of ablative material. In one implementation, the ablative material for the arc follower  60  is an acetal co-polymer resin loaded with finely divided melamine. The ablative material is typically injection molded onto a reinforcing pin (not shown). An annular junction recess  62  is disposed at the junction between the probe  58  and the arc follower  60 . A second annular, radially-reduced recessed portion  64  is provided within the surface of the probe  58  to be nearly adjacent to the position of the locking ring  50  when the probe  58  has been assembled within the male connector  20 . The recessed portion  64  is elongated along the longitudinal axis of the probe  58  and will typically measure between ½″-3″ in length.  
         [0029]    An insulative sheath  66  is disposed about the portions of the exterior of the probe  58 . The sheath  66  does not cover the entire length of the probe  58  as at least the distal end of the probe  58  proximate to the arc follower  60  must remain unsheathed so that an electrical connection may be made. The sheath  66  extends to and abuts the recessed area  47  of the inner radial surface  46  of insert  40 .  
         [0030]    [0030]FIG. 2 illustrates the female connector  100 , which is implemented as a bushing insert composed generally of an outer electrically resistive layer  102  and an inner rigid, metallic, electrically conductive tubular assembly with associated components, referred to herein as a contact assembly  104 . Though the construction and operation of female connectors of this type is well known in the art, major components will be described here. The female connector  100  is electrically and mechanically mounted to a bushing well (not shown) disposed on the enclosure of a transformer or other electrical equipment.  
         [0031]    A central passageway  106  extends through the generally cylindrical contact assembly  104  and presents a forward opening  108 . The passageway  106  is largely defined by a nosepiece  110  having a radially central portion  112  and a radially surrounding portion  114 .  
         [0032]    For purposes of description, the term “rear” shall mean the direction toward the bushing well of the electrical equipment and the term “forward” shall mean the direction toward the nose piece  110  and the male connector  20 . The central portion  112  features an insulated chamber  116  having a metallic interior, which is radially surrounded by an arc interrupter  118 . A female contact  120  is disposed toward the rear of the chamber  116  and is maintained in a radially central position by a copper knurled piston  122  through which the female contact  120  is electrically and mechanically coupled to a bushing well (not shown). The female contact  120  has forwardly extending collet fingers  124  which are fashioned to grip the probe  58  of the male connector  20 . Nosepiece  110  has an external circumferential locking groove  126 , which serves as a securing detent for a complimentary locking ring associated with the insert  40  of the male connector  20 .  
         [0033]    The forward end of the central passageway  106  includes an entrance vestibule  128  immediately rearward of opening  108 . The vestibule  128  is separated from the chamber  116  by a hinged gas trap  130  that is operable between an open position, in which gas communication is possible between the chamber  116  and the vestibule  128 , and a closed position, in which gas communication is substantially prevented between the chamber  116  and vestibule  128 . The gas trap  130  is spring-biased toward the closed position and may be moved to its open position, as the probe  58  of the male connector  20  is disposed within the central passageway  106  through the vestibule  128  and into the chamber  116 . A pair of elastomeric O-rings  132 ,  134  are located within the vestibule  128 . When the connectors  20  and  100  are fully engaged, O-ring  132  is located in the recessed portion  64  of probe  58  in an uncompressed condition to prevent distortion of the elastomeric material making up the O-ring  132 .  
         [0034]    A portion of the outer electrically resistive layer  102  forms a radially enlarged section  136  that surrounds the copper tube  112 . One or more ground tabs  138  are provided and are positioned at the radial exterior of the enlarged section  136 . The enlarged section  136  also carries an annular semi-conductive shield or collar  140  about its circumference, which presents a forward bushing shoulder  141 . In conventional electrical connector assemblies, this shield or collar  140  presents a ground plane to which an arc might tend toward during a flashover.  
         [0035]    During a loadbreak or switching operation, the male connector  20  (i.e., the elbow and the probe assembly) is separated from the female connector  100  (i.e., the bushing insert). The connectors are energized when they are electrically connected to a high voltage distribution current. During loadbreak separation, contact occurs between the probe  58  and the female contact  120 , which creates a mechanical drag between the probe  58  and the collet fingers  124  of female contact  120 . Upon disconnection, arcing occurs as the probe  58  and the fingers  124  separate. The arcing is expected to be generally extinguished within the chamber  116  through the generation of arc-quenching gases by components within the chamber. These gases are directed inwardly within the central passageway  106  of the female connector  100 . In a conventional connector assembly, arcing may unexpectedly and undesirably occur during loadbreak operation, with the arc extending from exposed conductive portions of the probe  58  or the insert  40  to a nearby available ground plane. In most cases, the ground plane is the annular semi-conductive shield  140  of the female connector  100 , which is grounded through the ground tabs  138 .  
         [0036]    [0036]FIG. 3 illustrates a cross-section of a bushing insert  100 . The bushing insert  100  includes a latch ring  160  disposed over a front portion of the collar  140  and the forward bushing shoulder  141  of the bushing insert  100 . The latch ring  160  is chamfered to provide better venting. In particular, the latch ring  160  is reshaped in at least one location during insulation-molding to create raised edges  162 , which are higher than the outer diameter of the collar  140  on the bushing insert  100 . During insulation-molding, the latch ring  160 , the collar  140 , and then the bushing insert  100  are placed in the mold, which has indentations for the raised edges, and the latch ring is reshaped to include raised edges  162 .  
         [0037]    When the bushing insert  100  is assembled with the mating component  170 , a cuff portion  180  overlaps the latch ring  160  and a portion of the collar  140 , and an air cavity  190  is created between the mating component cuff  180  and the latch ring  160 . A vacuum potentially could be created within the cavity  190  when the mating component  170  is removed from the bushing insert  100 . However, the raised edges  162  provide a way to vent the cavity  190  and to break any adhesion between the bushing insert  100  and the overlapping cuff  180  of the mating component  170 . This occurs because the raised edges  162  cause the overlapping cuff  180  to lift away from the bushing insert collar  140  so as to provide chamfered airways next to the edges  112  for atmospheric air flow to the cavity  190 . As a result, any adhesion between the mating component  170  and the bushing insert collar  140  is broken and any vacuum in the cavity  190  is relieved to atmospheric pressure.  
         [0038]    The raised edges  162  are evenly distributed about the circumference of the latch ring and each raised edge has the shape of a sharply angled ramp. In one implementation, there are four raised edges and each raised edge has dimensions of approximately 0.02 inches (height), 0.2 inches (width), and 0.5 inches (length).(see FIG. 7) Other implementations may have more (e.g., six) or fewer (e.g., two or one) raised edges, and may have edges with different dimensions.  
         [0039]    Having a sharp edge on the raised edge provides an effective way of rapidly venting the connector assembly on disassembly to prevent flashover. Also, the cuff of the mating elbow is able to both overlap the bushing insert and form a good seal with the bushing insert over the at least one raised edge.  
         [0040]    [0040]FIGS. 4A and 4B are enlarged views of the bushing insert  100 , the collar  140 , the latch ring  160  with at least one raised edge  162 , the cuff  180  of the mating component  170 , and the air cavity  190  created upon assembly of the bushing insert  100  and the mating component  170 . As is seen, the raised edge protrudes beyond the outer diameter of the latch ring to extend the cuff  180  away from the collar  140 .  
         [0041]    [0041]FIG. 5 is an exemplary latch ring  160 . FIG. 6 shows the latch ring of FIG. 5 with multiple raised edges. As is seen, the raised edges  162  are distributed along the outer circumference of the latch ring  160 . FIG. 7 (not to scale) shows an implementation of a latch ring with multiple raised edges in use with a connector assembly. The approximate dimensions of the raised edges are indicated in the figure.  
         [0042]    A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made. For example, the orientation, shape and/or size of the raised edges could be varied as long as the raised edges provided the necessary venting. Accordingly, other implementations are within the scope of the following claims.