CONNECTOR CONSTRUCTION FOR HIGH VOLTAGE SHIELDED CABLES
United States Patent 3656084
In an electrical connector having component parts capable of being assembled in the field, a pair of housing members each having an inner portion of electrically insulating elastomer and an outer portion of electrically conductive elastomer with a generally continuous and void-free juncture between the inner and outer portions, the junctures being routed around potential voids and following a continuous contour in the vicinity of the assembled ends of the housing members to avoid deleterious and concentrated electrical stresses in that vicinity.
Application Number:
05/052425
Publication Date:
04/11/1972
Filing Date:
07/06/1970
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Export Citation:
Assignee:
Amerace Esna Corporation (New York, NY)
Primary Class:
Other Classes:
439/521
International Classes:
H02G15/103; H02G15/10; H01R13/52
Field of Search:
339/59-61,94
Primary Examiner:
Mcglynn, Joseph H.
Claims:
I claim
1. In an electrical connector having component parts capable of being assembled in the field at the terminus of high voltage shielded electrical cables for providing a connection between first and second such cables, said cables each having a conductor surrounded by an insulating jacket within a conductive shield:
2. The invention of claim 1 wherein the contour of the juncture in said one of the housing members includes a portion having a diameter smaller than the external diameter of the plug at the root thereof and extending axially along a portion of the plug to intersect the surface of the plug a short distance beyond the root thereof such that the outer portion of said one of the housing members will overlap a corresponding portion of the receptacle adjacent the open end thereof.
3. The invention of claim 1 wherein the contour of the juncture in said other of the housing members intersects the surface of the receptacle a short distance from the open end thereof such that the outer portion of said other of the housing members will overlap and be contiguous with a corresponding portion of the plug adjacent the root thereof.
4. In an electrical connector having component parts capable of being assembled in the field at the terminus of a high voltage shielded electrical cable, said cable having a conductor surrounded by an insulating jacket within a conductive shield:
5. The invention of claim 4 wherein the contour of the juncture includes a portion having a diameter smaller than the external diameter of the plug at the root thereof and extending axially along a portion of the plug to intersect the surface of the plug a short distance beyond the root thereof.
6. In an electrical connector having component parts capable of being assembled in the field at the terminus of a high voltage shielded electrical cable, said cable having a conductor surrounded by an insulating jacket within a conductive shield:
7. The invention of claim 6 wherein the contour of the juncture intersects the surface of the receptacle a short distance from the open end thereof.
1. In an electrical connector having component parts capable of being assembled in the field at the terminus of high voltage shielded electrical cables for providing a connection between first and second such cables, said cables each having a conductor surrounded by an insulating jacket within a conductive shield:
2. The invention of claim 1 wherein the contour of the juncture in said one of the housing members includes a portion having a diameter smaller than the external diameter of the plug at the root thereof and extending axially along a portion of the plug to intersect the surface of the plug a short distance beyond the root thereof such that the outer portion of said one of the housing members will overlap a corresponding portion of the receptacle adjacent the open end thereof.
3. The invention of claim 1 wherein the contour of the juncture in said other of the housing members intersects the surface of the receptacle a short distance from the open end thereof such that the outer portion of said other of the housing members will overlap and be contiguous with a corresponding portion of the plug adjacent the root thereof.
4. In an electrical connector having component parts capable of being assembled in the field at the terminus of a high voltage shielded electrical cable, said cable having a conductor surrounded by an insulating jacket within a conductive shield:
5. The invention of claim 4 wherein the contour of the juncture includes a portion having a diameter smaller than the external diameter of the plug at the root thereof and extending axially along a portion of the plug to intersect the surface of the plug a short distance beyond the root thereof.
6. In an electrical connector having component parts capable of being assembled in the field at the terminus of a high voltage shielded electrical cable, said cable having a conductor surrounded by an insulating jacket within a conductive shield:
7. The invention of claim 6 wherein the contour of the juncture intersects the surface of the receptacle a short distance from the open end thereof.
Description:
The present invention relates generally to electrical connections and pertains, more specifically, to an electrical connector for providing a connection, in the field, between high voltage shielded electrical cables or between such a cable and other apparatus in power distribution systems.
In recent years, heavy emphasis has been placed upon the development of underground electrical power distribution systems, especially in light industrial, commercial and residential areas. Various power distribution components, such as shielded electrical cables, transformers and electrical connectors have been evolved for use in such systems.
Among these components, shielded electrical connectors have been developed which are easily assembled in the field at the terminal ends of electrical cables so as to facilitate the construction and installation of underground power distribution systems. The numerous advantages of such connectors have given rise to the demand for connectors of the same type which will operate successfully under even higher voltages than those voltages already accommodated by earlier connectors.
It is therefore an important object of the invention to provide an electrical connector having component parts capable of ready assembly in the field to establish a reliable connection between electrical cables or between such a cable and other apparatus carrying relatively high voltage.
Another object of the invention is to provide a connection which can be assembled readily in the field without the necessity of performing tedious operations such as taping, molding, potting or like procedures.
A further object of the invention is to provide a construction in a composite elastomeric housing member which includes a portion of insulating elastomeric material, a portion of conductive elastomeric material and an essentially void-free juncture between these portions, which routes the juncture over a continuous contour and around potential voids in he vicinity of the assembled ends of assembled housing members of a connection to avoid deleterious and concentrated electrical stresses in that vicinity.
Still another object of the invention is to provide a connector for electrical power distribution cables and other apparatus which is relatively simple and inexpensive to manufacture.
The above objects, as well as still further objects and advantages are attained by the invention which may be described briefly as providing in an electrical connector having component parts capable of being assembled in the field at the terminus of high voltage shielded electrical cables for providing a connection between first and second such cables, the cables each having a conductor surrounded by an insulating jacket within a conductive shield, a pair of housing members of elastomeric material, the housing members each having an inner portion of electrically insulating elastomer and an outer portion of electrically conductive elastomer, the inner and outer portions of each housing member being joined along a generally continuous and void-free juncture, the housing members having corresponding portions at corresponding ends thereof for cooperating with one another in watertight relationship, the corresponding portions including an axially extending plug at one end of the inner portion of one of the pair of housing members, the plug having a root and a generally cylindrical surface with an external diameter different from the overall diameter of the outside surface of the remainder of the one housing member such that a generally laterally extending surface extending between the root of the plug and the outside surface, an axially extending receptacle at the corresponding end of the inner portion of the other of the pair of housing members, the receptacle having an open end and a generally cylindrical surface with an internal diameter of the plug, the internal diameter being smaller than the overall diameter of the outside surface of the remainder of the other housing member such that a generally laterally extending surface extending between the end of the receptacle and outside surface of the other housing member, the juncture between the inner and outer portions of each respective housing member following a continuous contour which extends essentially to the generally cylindrical surface of the plug and the receptacle, respectively, such that the pattern of electrical stress across the confronting corresponding ends of the joined housing members is generally continuous and the voltage gradient along the corresponding laterally extending surfaces of the housing members is reduced to a minimum.
The invention will be more fully understood, while still further objects and advantages will become apparent, by reference to the following detailed description of an embodiment of the invention illustrated in the accompanying drawing, in which:
FIGS. 1 through 3 are diagrammatic views illustrating the assembly of a splice connection utilizing a splice connector constructed in accordance with the invention;
FIG. 4 is a longitudinal cross-sectional view of an adaptor sleeve of the connector;
FIG. 5 is a longitudinal cross-sectional view of the adaptor sleeve installed upon a cable;
FIG. 6 is a cross-sectional view taken along line 6--6 of FIG. 5;
FIG. 7 is a longitudinal cross-sectional view showing a housing member being assembled into place upon the adaptor sleeve;
FIG. 8 is a cross-sectional view of the fully assembled splice connection;
FIG. 9 is a plan view of the heat conductive member of the splice connection; and
FIG. 10 is an end view of the heat conductive member.
Referring now to the drawing, and especially to FIGS. 1 through 3 thereof, a splice connection is to be made in accordance with the invention between a pair of high voltage shielded electrical cables 10 and 12 in a power distribution system. Each of the cables 10 and 12 has a central conductor 14 surrounded by an insulating jacket 16 which itself lies within an external shield 18. In order to effect a splice connection between the terminal ends of the cables, a first, or plug, housing member 20 is slipped over the terminus 22 of cable 10 and is moved along the cable away from the terminus thereof. Such movement of the housing member 20 along the cable 10 is accomplished with little or no resistance since the housing member is provided with an axially extending internal bore 24 (see FIG. 7) having an internal diameter considerably larger than the overall external diameter of the cable. Likewise, a second, or receptacle, housing member 26 is slipped over the terminus 28 of cable 12 and is advanced along the cable in a direction away from the terminus thereof.
A portion 30 of each shield 18 is removed so as to expose a portion 31 of the insulating jacket 16 between each terminus and the termination 32 of the shield. While the portion 30 of the shield 18 may be removed either prior to or subsequent to slipping the housing members 20 and 26 onto the cables 10 and 12, it is preferable to remove the shield portion 30 after the housing members have been slipped onto the cables, as shown in FIG. 1.
As best seen in FIG. 2, a pair of sleeves 34 are subsequently slipped over the terminal ends of the cables, one sleeve 34 upon each cable, and each sleeve is moved along its respective cable in a direction away from the terminus thereof. The sleeves 34 are preferably fabricated of an elastomeric material and include a first sleeve portion 36 of an electrically insulating elastomer, and a second sleeve portion 38 of an electrically conductive elastomer axially related to and integral with the first sleeve portion 36. The sleeve portions 36 and 38 are preferably molded together so that the sleeve portions are contiguous and joined together in a single assembly (also see FIG. 4), the juncture 40 between the sleeve portions being continuous and void-free. Preferably, the compounds of the sleeve portions are based upon the same polymer to assure strong bonding. An ethylene-propylene terpolymer, available under Du Pont's trademark NORDEL, is an example of a polymer which has been successully used for this purpose. Insulating NORDEL is used for the first sleeve portion 36 and conductive NORDEL is used for the second sleeve portion 38. At least portions of the second sleeve portion 38 can be in the form of a conductive coating, especially in locations of relatively thin cross-section, applied to the first sleeve portion 36. For the purposes of the instant description, the term "elastomer" is meant to include such coatings.
Each sleeve 34 has an internal bore 42 (see FIG. 4) which extends axially from end 44 to end 46 of the sleeve 34 through both the first and second sleeve portions, the bore 42 being resiliently dilatable by virtue of the resilient nature of the sleeve material. The internal bore 42 has a first internal surface 50 of a first diameter adjacent end 44 of the sleeve and extending through the first sleeve portion 36 and a part of the second sleeve portion 38 to a shoulder 52 which is located between the first internal surface 50 and a second internal surface 54 adjacent the other end 46 of the sleeve and having a diameter slightly larger than the diameter of the first internal surface. The relative dimensions of the first internal surface 50 and the diameter of the external surface of insulating jacket 16 are such that the insulating jacket 16 may be inserted into the sleeve 34 by hand, the resilient property of the sleeve permitting the sleeve to be radially expansible thereby allowing a slight dilation of the internal bore 42 to admit the insulating jacket (also see FIG. 5). Thus, the internal bore 42, along the first surface 50 thereof, will grip the exposed length 31 of the insulating jacket 16 in a tight fit. The tight fit along the exposed length of the insulating jacket increases the dielectric strength of the creep path along the outer surface of the insulating jacket between the end 44 of the sleeve and the termination 32 of the shield 18 to assure that current will not pass between the conductor 14 and the shield 18 along the insulating jacket 16. Movement of the sleeve 34 along the cable is continued until the shoulder 52 abuts the termination 32 of the shield 18 (as shown in FIG. 5). At this position of the sleeve, the internal bore 42 is resiliently dilated along the second internal surface 54 thereof to grip the shield 18 in electrical contact therewith. Each sleeve has an external surface 56 common to both portions 36 and 38.
Because there is a tendency for electrical stresses to be concentrated along the juncture 40 between the first and second sleeve portions 36 and 38, and, while the relative dimensions of the internal bore 42 and the external surface of the insulating jacket tend to eliminate voids between the sleeve 34 and the insulating jacket 16, there is a possibility that voids will be present between the sleeve 34 and the insulating jacket 16 once the sleeve is installed (due to irregularities in the external surface of the insulating jacket), the internal bore 42 of each sleeve is provided with a portion 58 of reduced internal diameter along the junction 60 of the internal bore with juncture 40 (see FIG. 4). The portion 58 of normally reduced diameter assures that upon resilient dilation of the internal bore of the sleeve, the internal bore will grip the insulating jacket in intimate, essentially void-free contact at least at the junction 60. The increased pressure of the sleeve upon the insulating jacket established by the reduced diameter at the junction has been found to insure that minor irregularities which might otherwise affect the ionization level of the interface between the sleeve and the insulating jacket will essentially be eliminated. While the reduced diameter at the junction 60 will increase the resistance to movement of the sleeve 34 along the insulating jacket 16, this resistance is minimized by localizing the reduced diameter portion 56 to the area of the junction. In order to further facilitate movement of the sleeve on the insulating jacket while at the same time assuring that air is expelled from the vicinity of the junction 60 so that intimate, essentially void-free contact is attained, the portion 58 of reduced internal diameter is provided with a profile contour which tapers by gradually increasing in diameter from the junction 60 itself toward both ends 62 of the portion 58. Preferably, the profile contour is primarily arcuate. Thus, electrical stresses at the junction 60 are controlled.
Once the sleeves 34 are in proper position upon their respective cables, a retainer shown in the form of retaining ring 66 is slipped over the terminus of each cable, as seen in FIG. 2, and affixed to the insulating jacket 16 in abutting relationship with the end 44 of each sleeve, as shown in FIG. 3. Each retaining ring 66 is preferably anchored to the insulating jacket 16 by fastener means shown in the form of set screws 68 (see FIGS. 5 and 6) which positively engage the insulating jacket 16 to anchor the ring 66 in place. The set screws 68 are threaded radially through each ring 66 to radially enter the jacket 16 and may, but need not necessarily contact the conductor 14 of the cable. Each sleeve 34 is thus positively retained against movement toward the cable terminus by a retaining ring 66. Movement in the opposite direction is restrained by abutment of the shoulder 52 with the termination 32 of a shield 18. Thus, each sleeve 34 presents an external surface 56 of prescribed external diameter common to both the first and second sleeve portions and the termination 32 of the shield 18 is encased and protected by the second sleeve portion 38 while the shield 18 is electrically connected with the external surface 56 of prescribed diameter.
A portion 70 of the insulating jacket 16 adjacent the terminus of each cable is removed to expose a length 72 of conductor 14 between each terminus 22 and 28 and the termination 74 of the insulating jacket (see FIGS. 3 and 5). While these portions 70 may be removed either before or after the installation of the sleeves 34 and the retaining rings 66, removal is preferably effected subsequent to the installation of the retaining rings so that the retaining rings may serve as guides for the location of the termination 74 of the insulating jacket 16.
The bared ends 76 of the conductors 14 are then electrically connected by means of an electrical connector element shown in the form of a tubular metallic contact 80 having a longitudinal aperture 82 divided by a transverse wall 84 to establish a pair of ferrules 86. Each conductor 14 is inserted into its respective ferrule 86 and the contact 80 is crimped at 88 and 89 (see FIG. 5) to affix the contact 80 to the conductors 14 in a well-known manner.
Turning now to FIG. 7, the first housing member 20 is seen to have a composite construction fabricated of an elastomeric material. The composite structure includes an inner portion 90 of an electrically insulating elastomer and an outer portion 92 of an electrically conductive elastomer. The inner and outer portions 90 and 92 are preferably molded together, such as by molding the inner portion first and then molding the outer portion around the inner portion to form the composite housing member, so that the housing member 20 is an integral structure having contiguous inner and outer portions joined in a single assembly, the juncture 94 between the inner and outer portions 90 and 92 being continuous and void-free to enable electrical stresses to be kept within control along the length of the housing member. Both housing members 20 and 26 are preferably fabricated of the same materials employed in the fabrication of the sleeves 34.
The internal bore 24 of the first housing member 20 has a first portion 96 common with and extending axially through the inner and outer portions 90 and 92 adjacent one end 98 of the housing member. The relative dimensions of the first portion 96 of the internal bore 24 and the external surface 56 of the corresponding sleeve 34 are such that as the housing member 20 is moved toward the cable terminus 22 and over the sleeve 34, the internal bore portion 96 is resiliently dilated to grip the external surface 56 in watertight relationship therewith.
As best seen in FIG. 8, the second housing member 26 is also a composite structure including an inner portion 100 and an outer portion 102, and the internal bore 104 thereof is likewise common to both the inner portion 100 and the outer portion 102, the relative dimensions of the first portion 106 of the internal bore 104 and its corresponding sleeve 34 bearing the same relationship as described above in connection with the first housing member 20 and its corresponding sleeve 34. The housing members 20 and 26 are provided with corresponding portions for cooperating with one another in watertight relationship, such portions being shown in the form of a plug extension 107 of the first housing member 20 and a corresponding receptacle 108 in the second housing member 26. As the housing members are both pulled toward each respective terminus 22 and 28 and thus toward one another, the plug 107 will enter the receptacle 108 to establish a watertight seal between the housing members, as well as to make electrical contact between the outer portions 92 and 102 of the housing members by the engagement of plug portion 110 with receptacle portion 112. The tight fit between the housing members 20 and 26 and their respective sleeves 34 assures that the outer portions 92 and 102 grip the respective second sleeve portions 38 to make electrical contact therewith and thus assure electrical continuity of the shield 18 across the completed splice connection 114. At the same time, the tight fit increases the dielectric strength of the creep path along the portion 116 of the external surface 56 of the sleeve which is contiguous with the inner portion of each housing member.
The internal bores 24 and 104, respectively, of the housing members 20 and 26 each have a second bore portion 120 and 122, respectively, which, when the housing members are assembled in an integral housing assembly 118 over the sleeves 34 as seen in FIG. 8, establish a closed chamber 124 within which the contact 80 is housed and sealed. An electrically conductive and heat conductive metallic tube 126 (see FIGS. 7 and 8) is located within the second bore portion 120 of the first housing member 20 and enters the second bore portion 122 of the second housing member 26 upon assembly of the housing members. Tube 126 is relatively rigid and provides an internal support for plug 107 to assure a tight seal between plug 107 and receptacle 108 and is preferably fabricated of aluminum. The first housing member is provided with a bridging portion 130 of electrically conductive elastomeric material which extends between one end 132 of the metallic tube 126 and a part 134 of the first bore portion 96. Likewise, the second housing member 26 includes a bridging portion 136 of electrically conductive elastomeric material extending between the other end 137 of the metallic tube 126 and a part 138 of the first bore portion 106 of the internal bore 104 of that housing member. Thus, when the housing members are assembled in the integral housing assembly 118, as seen in FIG. 8, the closed chamber 124 is surrounded by a wall of electrically conductive and heat conductive material extending coaxially with the contact 80 and the conductors 14 and spaced radially from the outer surface 140 of the contact. While it is contemplated that the housing assembly 118 may be supplied in the form of a unitary housing, it has been found preferably to assemble the housing in the field from a pair of housing members, as described above.
Prior to the assembly of the two housing members 20 and 26 and the consequent closing of the chamber 124, a member of heat conductive material, illustrated in FIGS. 8 through 10 in the form of metallic member 142, is placed upon the outer surface 140 of the contact 80 such that upon assembly of the housing members and the closing of the chamber the conductive member 142 will contact both the electrical contact 80 and the metallic tube 126 to provide a path for the conduction of heat across the gap between the contact and the tube thereby enabling dissipation of excessive heat from the contact 80 and increasing the effective capacity of the splice connection 114. At the same time, the conductive member 142 is electrically conductive and thus eliminates any deleterious potential difference between the wall of the chamber 124 and the contact 80 and conductors 14. Bridging portion 136 of the second housing member 26 is also continued around the bottom 143 of the receptacle 108 at 144 so as to eliminate deleterious electrical stresses across any gap between the end of the plug 107 and the bottom of the receptacle 108. The bridging portions 130 and 136 are preferably integrally molded with the inner portions 90 and 100 of the respective housing members 20 and 26 so as to provide a contiguous and void-free juncture 146 between each bridging portion and its respective inner portion.
As best seen in FIGS. 8, 9 and 10, the conductive member 142 is preferably in the form of a resilient arcuate band 150 of metal having a radius which is normally greater than the radius of the cylindrical outer surface 140 of the contact 80 and greater than the inner cylindrical surface of the metallic tube 126. A plurality of resilient fingers 152 project from both ends 154 of the metallic band 150, and are unitary therewith, each finger 152 extending axially from the end of the band to terminate at a free tip 156. The free tips 156 of the fingers 152 lie along an arc having a circumferential length smaller than the circumferential length of the arc of the band 150 and extend axially parallel to one another such that the metallic member 142 may be wrapped around the outer surface 140 of the contact 80 with the tips 156 of the fingers 152 contacting the outer surface of the contact 80 and with the band 150 in position to contact the metallic tube 126. The finger tips 156 are preferably positively affixed to the contact 80 by means of a relatively short length of wire or tape wrapped around the finger tips at 158, as seen in FIG. 8. Thus, upon assembling the housing members 20 and 26 over the conductive member 140, an effective heat conducting path is provided between the contact 80 and the tube 126 within the assembled housing 118. In this manner, heat from the contact may be conducted directly to the tube and thereby dissipated to the surrounding housing.
The combination of the housing 118 with the corresponding sleeves 34 enables ready assembly in the field since the sleeves 34, which incorporate thin wall sections relative to the corresponding wall sections of the housing, are easily placed in proper position upon the cables by hand without damage to the cable and especially to the shield. The greater forces needed to pull the housing or housing members over the sleeves are easily applied to the larger diameter housing or housing members. The sleeves 34, being secured against movement in response to such pulling forces by virtue of the retaining rings 66, can withstand such pulling forces and the pulling forces need not be applied directly to the more delicate shield 18. In addition, cables of different diameters may be accommodated without changing the size or configuration of the housing by merely providing sleeves 34 having internal bores of various diameters while maintaining the external surfaces 56 of the sleeves at the same diameter. In certain instances, it may be desirable to have cable 10 differ in size from cable 12 and such a difference is easily accommodated by employing sleeves 34 of different diameter internal bores. Thus, by selecting the proper sleeves 34 the splice connector may be adapted to accommodate a wide variety of cable sizes.
In order to assure that the connection completed by the assembly of the housing members 20 and 26 with one another is capable of withstanding the high voltages present between the conductor 22 and the shield 18 of the connected cables, the electrical stresses within the connection should be controlled and any concentration of electrical stress at one particular location or another should be avoided. One such location where there is a tendency for electrical stresses to become concentrated is in the vicinity of the junction 160 of the housing members 20 and 26. The tendency exists at this location in view of the presence of laterally extending surfaces on each of the housing members, the laterally extending surfaces defining the confronting end surfaces of the assembled housing members.
Thus, as best seen in FIGS. 7 and 8, a laterally extending surface 162 extends between the root 164 of the axially extending plug 107 and the outside surface 166 of the remainder of the housing member 20, since the generally cylindrical surface of the plug 107 has a diameter smaller than the overall diameter of the outside surface 166. Likewise, a laterally extending surface 170 extends between the end 172 of the axially extending receptacle 108 and the outside surface 174 of the remainder of the housing member 26, since the generally cylindrical surface of the receptacle 108 has a diameter smaller than the overall diameter of the outside surface 174. Because there is a tendency for air to be trapped in voids present between these laterally extending surfaces 162 and 170 when the housing members 20 and 26 are assembled with one another, these voids become potential points of stress concentration, leading to the eventual breakdown of the insulation at these points with concomitant failure of the connection.
In order to avoid such a concentration of electrical stresses, the juncture 94 between the inner portion 90 and the outer portion 92 of the housing member 20 is made to follow a continuous contour which extends essentially to the surface of the plug 107 adjacent the root 164 thereof. Likewise, the juncture 176 between the inner portion 100 and the outer portion 102 of the housing member 26 follows a continuous contour which extends essentially to the surface of the receptacle 108, adjacent the end 172 thereof. In this manner, the electrical stresses within the insulating portions 90 and 100 of the housing members 20 and 26, respectively, are made to follow a generally continuous pattern with no abrupt changes in pattern to cause deleterious concentration of stresses. The term "continuous," as employed herein in connection with the contour of the junctures 94 and 176 and in connection with the patterns of electrical stress, is employed in a mathematical sense; that is, changes in direction are smooth and gradual rather than abrupt and angular.
Thus, the contour of the junctures 94 and 176 in the vicinity of the laterally extending surface 162 and 170, respectively, not only attain an advantageous pattern of electrical stress across the junction of the housing members 20 and 26, but also reduces to a minimum the voltage gradient along these laterally extending surfaces, thus tending to eliminate the establishment of corona within voids located between these surfaces and the deleterious effects associated with corona.
While such undesirable effects can be reduced or essentially eliminated by bringing the junctures 94 and 176 practically to the surfaces of the plug 107 and the receptacle 108, respectively, it has been found advantageous to extend the juncture 94 into the plug 107 such that the juncture will intersect the surface of the plug at 178, a short distance along the plug from the root 164 thereof. In this manner the outer portion 92 will overlap the surface of the receptacle 108 when the housing members 20 and 26 are assembled to assure that all voids between the confronting laterally extending surfaces 162 and 170 are bounded by electrically conductive material. Likewise, juncture 176 preferably is made to intersect the surface of the receptacle 108 a short distance from the open end 172 thereof so that the outer portion 102 will overlap the plug 107 adjacent the root 164 thereof.
In a like manner, any voids which could occur along the length of tube 126 between the tube 126 and the inner portion of housing member 20 may be surrounded by conductive material by extending bridging portion 130 in the form of a thin layer 180 of conductive material to extend the void-free juncture 146 to the end 182 of the housing member 20.
The above detailed description of a preferred embodiment of the invention is provided by way of example only. Various details of design and construction may be modified without departing from the true spirit and scope of the invention as defined in the appended claims.
In recent years, heavy emphasis has been placed upon the development of underground electrical power distribution systems, especially in light industrial, commercial and residential areas. Various power distribution components, such as shielded electrical cables, transformers and electrical connectors have been evolved for use in such systems.
Among these components, shielded electrical connectors have been developed which are easily assembled in the field at the terminal ends of electrical cables so as to facilitate the construction and installation of underground power distribution systems. The numerous advantages of such connectors have given rise to the demand for connectors of the same type which will operate successfully under even higher voltages than those voltages already accommodated by earlier connectors.
It is therefore an important object of the invention to provide an electrical connector having component parts capable of ready assembly in the field to establish a reliable connection between electrical cables or between such a cable and other apparatus carrying relatively high voltage.
Another object of the invention is to provide a connection which can be assembled readily in the field without the necessity of performing tedious operations such as taping, molding, potting or like procedures.
A further object of the invention is to provide a construction in a composite elastomeric housing member which includes a portion of insulating elastomeric material, a portion of conductive elastomeric material and an essentially void-free juncture between these portions, which routes the juncture over a continuous contour and around potential voids in he vicinity of the assembled ends of assembled housing members of a connection to avoid deleterious and concentrated electrical stresses in that vicinity.
Still another object of the invention is to provide a connector for electrical power distribution cables and other apparatus which is relatively simple and inexpensive to manufacture.
The above objects, as well as still further objects and advantages are attained by the invention which may be described briefly as providing in an electrical connector having component parts capable of being assembled in the field at the terminus of high voltage shielded electrical cables for providing a connection between first and second such cables, the cables each having a conductor surrounded by an insulating jacket within a conductive shield, a pair of housing members of elastomeric material, the housing members each having an inner portion of electrically insulating elastomer and an outer portion of electrically conductive elastomer, the inner and outer portions of each housing member being joined along a generally continuous and void-free juncture, the housing members having corresponding portions at corresponding ends thereof for cooperating with one another in watertight relationship, the corresponding portions including an axially extending plug at one end of the inner portion of one of the pair of housing members, the plug having a root and a generally cylindrical surface with an external diameter different from the overall diameter of the outside surface of the remainder of the one housing member such that a generally laterally extending surface extending between the root of the plug and the outside surface, an axially extending receptacle at the corresponding end of the inner portion of the other of the pair of housing members, the receptacle having an open end and a generally cylindrical surface with an internal diameter of the plug, the internal diameter being smaller than the overall diameter of the outside surface of the remainder of the other housing member such that a generally laterally extending surface extending between the end of the receptacle and outside surface of the other housing member, the juncture between the inner and outer portions of each respective housing member following a continuous contour which extends essentially to the generally cylindrical surface of the plug and the receptacle, respectively, such that the pattern of electrical stress across the confronting corresponding ends of the joined housing members is generally continuous and the voltage gradient along the corresponding laterally extending surfaces of the housing members is reduced to a minimum.
The invention will be more fully understood, while still further objects and advantages will become apparent, by reference to the following detailed description of an embodiment of the invention illustrated in the accompanying drawing, in which:
FIGS. 1 through 3 are diagrammatic views illustrating the assembly of a splice connection utilizing a splice connector constructed in accordance with the invention;
FIG. 4 is a longitudinal cross-sectional view of an adaptor sleeve of the connector;
FIG. 5 is a longitudinal cross-sectional view of the adaptor sleeve installed upon a cable;
FIG. 6 is a cross-sectional view taken along line 6--6 of FIG. 5;
FIG. 7 is a longitudinal cross-sectional view showing a housing member being assembled into place upon the adaptor sleeve;
FIG. 8 is a cross-sectional view of the fully assembled splice connection;
FIG. 9 is a plan view of the heat conductive member of the splice connection; and
FIG. 10 is an end view of the heat conductive member.
Referring now to the drawing, and especially to FIGS. 1 through 3 thereof, a splice connection is to be made in accordance with the invention between a pair of high voltage shielded electrical cables 10 and 12 in a power distribution system. Each of the cables 10 and 12 has a central conductor 14 surrounded by an insulating jacket 16 which itself lies within an external shield 18. In order to effect a splice connection between the terminal ends of the cables, a first, or plug, housing member 20 is slipped over the terminus 22 of cable 10 and is moved along the cable away from the terminus thereof. Such movement of the housing member 20 along the cable 10 is accomplished with little or no resistance since the housing member is provided with an axially extending internal bore 24 (see FIG. 7) having an internal diameter considerably larger than the overall external diameter of the cable. Likewise, a second, or receptacle, housing member 26 is slipped over the terminus 28 of cable 12 and is advanced along the cable in a direction away from the terminus thereof.
A portion 30 of each shield 18 is removed so as to expose a portion 31 of the insulating jacket 16 between each terminus and the termination 32 of the shield. While the portion 30 of the shield 18 may be removed either prior to or subsequent to slipping the housing members 20 and 26 onto the cables 10 and 12, it is preferable to remove the shield portion 30 after the housing members have been slipped onto the cables, as shown in FIG. 1.
As best seen in FIG. 2, a pair of sleeves 34 are subsequently slipped over the terminal ends of the cables, one sleeve 34 upon each cable, and each sleeve is moved along its respective cable in a direction away from the terminus thereof. The sleeves 34 are preferably fabricated of an elastomeric material and include a first sleeve portion 36 of an electrically insulating elastomer, and a second sleeve portion 38 of an electrically conductive elastomer axially related to and integral with the first sleeve portion 36. The sleeve portions 36 and 38 are preferably molded together so that the sleeve portions are contiguous and joined together in a single assembly (also see FIG. 4), the juncture 40 between the sleeve portions being continuous and void-free. Preferably, the compounds of the sleeve portions are based upon the same polymer to assure strong bonding. An ethylene-propylene terpolymer, available under Du Pont's trademark NORDEL, is an example of a polymer which has been successully used for this purpose. Insulating NORDEL is used for the first sleeve portion 36 and conductive NORDEL is used for the second sleeve portion 38. At least portions of the second sleeve portion 38 can be in the form of a conductive coating, especially in locations of relatively thin cross-section, applied to the first sleeve portion 36. For the purposes of the instant description, the term "elastomer" is meant to include such coatings.
Each sleeve 34 has an internal bore 42 (see FIG. 4) which extends axially from end 44 to end 46 of the sleeve 34 through both the first and second sleeve portions, the bore 42 being resiliently dilatable by virtue of the resilient nature of the sleeve material. The internal bore 42 has a first internal surface 50 of a first diameter adjacent end 44 of the sleeve and extending through the first sleeve portion 36 and a part of the second sleeve portion 38 to a shoulder 52 which is located between the first internal surface 50 and a second internal surface 54 adjacent the other end 46 of the sleeve and having a diameter slightly larger than the diameter of the first internal surface. The relative dimensions of the first internal surface 50 and the diameter of the external surface of insulating jacket 16 are such that the insulating jacket 16 may be inserted into the sleeve 34 by hand, the resilient property of the sleeve permitting the sleeve to be radially expansible thereby allowing a slight dilation of the internal bore 42 to admit the insulating jacket (also see FIG. 5). Thus, the internal bore 42, along the first surface 50 thereof, will grip the exposed length 31 of the insulating jacket 16 in a tight fit. The tight fit along the exposed length of the insulating jacket increases the dielectric strength of the creep path along the outer surface of the insulating jacket between the end 44 of the sleeve and the termination 32 of the shield 18 to assure that current will not pass between the conductor 14 and the shield 18 along the insulating jacket 16. Movement of the sleeve 34 along the cable is continued until the shoulder 52 abuts the termination 32 of the shield 18 (as shown in FIG. 5). At this position of the sleeve, the internal bore 42 is resiliently dilated along the second internal surface 54 thereof to grip the shield 18 in electrical contact therewith. Each sleeve has an external surface 56 common to both portions 36 and 38.
Because there is a tendency for electrical stresses to be concentrated along the juncture 40 between the first and second sleeve portions 36 and 38, and, while the relative dimensions of the internal bore 42 and the external surface of the insulating jacket tend to eliminate voids between the sleeve 34 and the insulating jacket 16, there is a possibility that voids will be present between the sleeve 34 and the insulating jacket 16 once the sleeve is installed (due to irregularities in the external surface of the insulating jacket), the internal bore 42 of each sleeve is provided with a portion 58 of reduced internal diameter along the junction 60 of the internal bore with juncture 40 (see FIG. 4). The portion 58 of normally reduced diameter assures that upon resilient dilation of the internal bore of the sleeve, the internal bore will grip the insulating jacket in intimate, essentially void-free contact at least at the junction 60. The increased pressure of the sleeve upon the insulating jacket established by the reduced diameter at the junction has been found to insure that minor irregularities which might otherwise affect the ionization level of the interface between the sleeve and the insulating jacket will essentially be eliminated. While the reduced diameter at the junction 60 will increase the resistance to movement of the sleeve 34 along the insulating jacket 16, this resistance is minimized by localizing the reduced diameter portion 56 to the area of the junction. In order to further facilitate movement of the sleeve on the insulating jacket while at the same time assuring that air is expelled from the vicinity of the junction 60 so that intimate, essentially void-free contact is attained, the portion 58 of reduced internal diameter is provided with a profile contour which tapers by gradually increasing in diameter from the junction 60 itself toward both ends 62 of the portion 58. Preferably, the profile contour is primarily arcuate. Thus, electrical stresses at the junction 60 are controlled.
Once the sleeves 34 are in proper position upon their respective cables, a retainer shown in the form of retaining ring 66 is slipped over the terminus of each cable, as seen in FIG. 2, and affixed to the insulating jacket 16 in abutting relationship with the end 44 of each sleeve, as shown in FIG. 3. Each retaining ring 66 is preferably anchored to the insulating jacket 16 by fastener means shown in the form of set screws 68 (see FIGS. 5 and 6) which positively engage the insulating jacket 16 to anchor the ring 66 in place. The set screws 68 are threaded radially through each ring 66 to radially enter the jacket 16 and may, but need not necessarily contact the conductor 14 of the cable. Each sleeve 34 is thus positively retained against movement toward the cable terminus by a retaining ring 66. Movement in the opposite direction is restrained by abutment of the shoulder 52 with the termination 32 of a shield 18. Thus, each sleeve 34 presents an external surface 56 of prescribed external diameter common to both the first and second sleeve portions and the termination 32 of the shield 18 is encased and protected by the second sleeve portion 38 while the shield 18 is electrically connected with the external surface 56 of prescribed diameter.
A portion 70 of the insulating jacket 16 adjacent the terminus of each cable is removed to expose a length 72 of conductor 14 between each terminus 22 and 28 and the termination 74 of the insulating jacket (see FIGS. 3 and 5). While these portions 70 may be removed either before or after the installation of the sleeves 34 and the retaining rings 66, removal is preferably effected subsequent to the installation of the retaining rings so that the retaining rings may serve as guides for the location of the termination 74 of the insulating jacket 16.
The bared ends 76 of the conductors 14 are then electrically connected by means of an electrical connector element shown in the form of a tubular metallic contact 80 having a longitudinal aperture 82 divided by a transverse wall 84 to establish a pair of ferrules 86. Each conductor 14 is inserted into its respective ferrule 86 and the contact 80 is crimped at 88 and 89 (see FIG. 5) to affix the contact 80 to the conductors 14 in a well-known manner.
Turning now to FIG. 7, the first housing member 20 is seen to have a composite construction fabricated of an elastomeric material. The composite structure includes an inner portion 90 of an electrically insulating elastomer and an outer portion 92 of an electrically conductive elastomer. The inner and outer portions 90 and 92 are preferably molded together, such as by molding the inner portion first and then molding the outer portion around the inner portion to form the composite housing member, so that the housing member 20 is an integral structure having contiguous inner and outer portions joined in a single assembly, the juncture 94 between the inner and outer portions 90 and 92 being continuous and void-free to enable electrical stresses to be kept within control along the length of the housing member. Both housing members 20 and 26 are preferably fabricated of the same materials employed in the fabrication of the sleeves 34.
The internal bore 24 of the first housing member 20 has a first portion 96 common with and extending axially through the inner and outer portions 90 and 92 adjacent one end 98 of the housing member. The relative dimensions of the first portion 96 of the internal bore 24 and the external surface 56 of the corresponding sleeve 34 are such that as the housing member 20 is moved toward the cable terminus 22 and over the sleeve 34, the internal bore portion 96 is resiliently dilated to grip the external surface 56 in watertight relationship therewith.
As best seen in FIG. 8, the second housing member 26 is also a composite structure including an inner portion 100 and an outer portion 102, and the internal bore 104 thereof is likewise common to both the inner portion 100 and the outer portion 102, the relative dimensions of the first portion 106 of the internal bore 104 and its corresponding sleeve 34 bearing the same relationship as described above in connection with the first housing member 20 and its corresponding sleeve 34. The housing members 20 and 26 are provided with corresponding portions for cooperating with one another in watertight relationship, such portions being shown in the form of a plug extension 107 of the first housing member 20 and a corresponding receptacle 108 in the second housing member 26. As the housing members are both pulled toward each respective terminus 22 and 28 and thus toward one another, the plug 107 will enter the receptacle 108 to establish a watertight seal between the housing members, as well as to make electrical contact between the outer portions 92 and 102 of the housing members by the engagement of plug portion 110 with receptacle portion 112. The tight fit between the housing members 20 and 26 and their respective sleeves 34 assures that the outer portions 92 and 102 grip the respective second sleeve portions 38 to make electrical contact therewith and thus assure electrical continuity of the shield 18 across the completed splice connection 114. At the same time, the tight fit increases the dielectric strength of the creep path along the portion 116 of the external surface 56 of the sleeve which is contiguous with the inner portion of each housing member.
The internal bores 24 and 104, respectively, of the housing members 20 and 26 each have a second bore portion 120 and 122, respectively, which, when the housing members are assembled in an integral housing assembly 118 over the sleeves 34 as seen in FIG. 8, establish a closed chamber 124 within which the contact 80 is housed and sealed. An electrically conductive and heat conductive metallic tube 126 (see FIGS. 7 and 8) is located within the second bore portion 120 of the first housing member 20 and enters the second bore portion 122 of the second housing member 26 upon assembly of the housing members. Tube 126 is relatively rigid and provides an internal support for plug 107 to assure a tight seal between plug 107 and receptacle 108 and is preferably fabricated of aluminum. The first housing member is provided with a bridging portion 130 of electrically conductive elastomeric material which extends between one end 132 of the metallic tube 126 and a part 134 of the first bore portion 96. Likewise, the second housing member 26 includes a bridging portion 136 of electrically conductive elastomeric material extending between the other end 137 of the metallic tube 126 and a part 138 of the first bore portion 106 of the internal bore 104 of that housing member. Thus, when the housing members are assembled in the integral housing assembly 118, as seen in FIG. 8, the closed chamber 124 is surrounded by a wall of electrically conductive and heat conductive material extending coaxially with the contact 80 and the conductors 14 and spaced radially from the outer surface 140 of the contact. While it is contemplated that the housing assembly 118 may be supplied in the form of a unitary housing, it has been found preferably to assemble the housing in the field from a pair of housing members, as described above.
Prior to the assembly of the two housing members 20 and 26 and the consequent closing of the chamber 124, a member of heat conductive material, illustrated in FIGS. 8 through 10 in the form of metallic member 142, is placed upon the outer surface 140 of the contact 80 such that upon assembly of the housing members and the closing of the chamber the conductive member 142 will contact both the electrical contact 80 and the metallic tube 126 to provide a path for the conduction of heat across the gap between the contact and the tube thereby enabling dissipation of excessive heat from the contact 80 and increasing the effective capacity of the splice connection 114. At the same time, the conductive member 142 is electrically conductive and thus eliminates any deleterious potential difference between the wall of the chamber 124 and the contact 80 and conductors 14. Bridging portion 136 of the second housing member 26 is also continued around the bottom 143 of the receptacle 108 at 144 so as to eliminate deleterious electrical stresses across any gap between the end of the plug 107 and the bottom of the receptacle 108. The bridging portions 130 and 136 are preferably integrally molded with the inner portions 90 and 100 of the respective housing members 20 and 26 so as to provide a contiguous and void-free juncture 146 between each bridging portion and its respective inner portion.
As best seen in FIGS. 8, 9 and 10, the conductive member 142 is preferably in the form of a resilient arcuate band 150 of metal having a radius which is normally greater than the radius of the cylindrical outer surface 140 of the contact 80 and greater than the inner cylindrical surface of the metallic tube 126. A plurality of resilient fingers 152 project from both ends 154 of the metallic band 150, and are unitary therewith, each finger 152 extending axially from the end of the band to terminate at a free tip 156. The free tips 156 of the fingers 152 lie along an arc having a circumferential length smaller than the circumferential length of the arc of the band 150 and extend axially parallel to one another such that the metallic member 142 may be wrapped around the outer surface 140 of the contact 80 with the tips 156 of the fingers 152 contacting the outer surface of the contact 80 and with the band 150 in position to contact the metallic tube 126. The finger tips 156 are preferably positively affixed to the contact 80 by means of a relatively short length of wire or tape wrapped around the finger tips at 158, as seen in FIG. 8. Thus, upon assembling the housing members 20 and 26 over the conductive member 140, an effective heat conducting path is provided between the contact 80 and the tube 126 within the assembled housing 118. In this manner, heat from the contact may be conducted directly to the tube and thereby dissipated to the surrounding housing.
The combination of the housing 118 with the corresponding sleeves 34 enables ready assembly in the field since the sleeves 34, which incorporate thin wall sections relative to the corresponding wall sections of the housing, are easily placed in proper position upon the cables by hand without damage to the cable and especially to the shield. The greater forces needed to pull the housing or housing members over the sleeves are easily applied to the larger diameter housing or housing members. The sleeves 34, being secured against movement in response to such pulling forces by virtue of the retaining rings 66, can withstand such pulling forces and the pulling forces need not be applied directly to the more delicate shield 18. In addition, cables of different diameters may be accommodated without changing the size or configuration of the housing by merely providing sleeves 34 having internal bores of various diameters while maintaining the external surfaces 56 of the sleeves at the same diameter. In certain instances, it may be desirable to have cable 10 differ in size from cable 12 and such a difference is easily accommodated by employing sleeves 34 of different diameter internal bores. Thus, by selecting the proper sleeves 34 the splice connector may be adapted to accommodate a wide variety of cable sizes.
In order to assure that the connection completed by the assembly of the housing members 20 and 26 with one another is capable of withstanding the high voltages present between the conductor 22 and the shield 18 of the connected cables, the electrical stresses within the connection should be controlled and any concentration of electrical stress at one particular location or another should be avoided. One such location where there is a tendency for electrical stresses to become concentrated is in the vicinity of the junction 160 of the housing members 20 and 26. The tendency exists at this location in view of the presence of laterally extending surfaces on each of the housing members, the laterally extending surfaces defining the confronting end surfaces of the assembled housing members.
Thus, as best seen in FIGS. 7 and 8, a laterally extending surface 162 extends between the root 164 of the axially extending plug 107 and the outside surface 166 of the remainder of the housing member 20, since the generally cylindrical surface of the plug 107 has a diameter smaller than the overall diameter of the outside surface 166. Likewise, a laterally extending surface 170 extends between the end 172 of the axially extending receptacle 108 and the outside surface 174 of the remainder of the housing member 26, since the generally cylindrical surface of the receptacle 108 has a diameter smaller than the overall diameter of the outside surface 174. Because there is a tendency for air to be trapped in voids present between these laterally extending surfaces 162 and 170 when the housing members 20 and 26 are assembled with one another, these voids become potential points of stress concentration, leading to the eventual breakdown of the insulation at these points with concomitant failure of the connection.
In order to avoid such a concentration of electrical stresses, the juncture 94 between the inner portion 90 and the outer portion 92 of the housing member 20 is made to follow a continuous contour which extends essentially to the surface of the plug 107 adjacent the root 164 thereof. Likewise, the juncture 176 between the inner portion 100 and the outer portion 102 of the housing member 26 follows a continuous contour which extends essentially to the surface of the receptacle 108, adjacent the end 172 thereof. In this manner, the electrical stresses within the insulating portions 90 and 100 of the housing members 20 and 26, respectively, are made to follow a generally continuous pattern with no abrupt changes in pattern to cause deleterious concentration of stresses. The term "continuous," as employed herein in connection with the contour of the junctures 94 and 176 and in connection with the patterns of electrical stress, is employed in a mathematical sense; that is, changes in direction are smooth and gradual rather than abrupt and angular.
Thus, the contour of the junctures 94 and 176 in the vicinity of the laterally extending surface 162 and 170, respectively, not only attain an advantageous pattern of electrical stress across the junction of the housing members 20 and 26, but also reduces to a minimum the voltage gradient along these laterally extending surfaces, thus tending to eliminate the establishment of corona within voids located between these surfaces and the deleterious effects associated with corona.
While such undesirable effects can be reduced or essentially eliminated by bringing the junctures 94 and 176 practically to the surfaces of the plug 107 and the receptacle 108, respectively, it has been found advantageous to extend the juncture 94 into the plug 107 such that the juncture will intersect the surface of the plug at 178, a short distance along the plug from the root 164 thereof. In this manner the outer portion 92 will overlap the surface of the receptacle 108 when the housing members 20 and 26 are assembled to assure that all voids between the confronting laterally extending surfaces 162 and 170 are bounded by electrically conductive material. Likewise, juncture 176 preferably is made to intersect the surface of the receptacle 108 a short distance from the open end 172 thereof so that the outer portion 102 will overlap the plug 107 adjacent the root 164 thereof.
In a like manner, any voids which could occur along the length of tube 126 between the tube 126 and the inner portion of housing member 20 may be surrounded by conductive material by extending bridging portion 130 in the form of a thin layer 180 of conductive material to extend the void-free juncture 146 to the end 182 of the housing member 20.
The above detailed description of a preferred embodiment of the invention is provided by way of example only. Various details of design and construction may be modified without departing from the true spirit and scope of the invention as defined in the appended claims.