US 3835439 A
A grounded surface distribution apparatus and system is provided including elastomer encapsulated cable terminals, joints, taps, load-break switches, current limiting fuses and surge protectors, each enclosed completely within a metal sheath combined in various arrangements to perform operational functions required in loop and radial underground distribution systems. The cable terminals include a soft dielectric filler making a void-free interfacial engagement with the surface of a hard dielectric filler of a mating component. To provide for breaking a coupling under load, an arc-quenching follower is retractable into an axial cavity in the coupling components of the system and projectable therethrough upon breaking of the circuit and disconnecting of the components to provide an improved arc-quenching function. Thus, there is provided an underground system having security, operational safety and convenience.
Claims available in
Description (OCR text may contain errors)
United States Patent [191 Yonkers [111 3,835,439 [451 Sept. 10,1974
[ GROUNDED SURFACE DISTRIBUTION APPARATUS  Inventor: Edward II. Yonkers, Wilmette, Ill.
 Assignee: Joslyn Mfg. and Supply Co.,
 Filed: Mar. 15, 1972  Appl. No.: 234,864
Related US. Application Data  Continuation of Ser. No. 871,105, June 30, 1969, abandoned, which is a division of Ser. No. 660,748, Aug. 15, 1967, abandoned.
FOREIGN PATENTS OR APPLICATIONS 957,032 5/ 1964 Great Britain 339/19 Primary Examiner-Joseph H. McGlynn Attorney, Agent, or Firm-Mason, Kolehmainen, Rathbum & Wyss [571 I ABSTRACT I A grounded surface distribution apparatus and system is provided including elastomer encapsulated cable terminals, joints, taps, load-break switches, current limiting fuses and surge protectors, each enclosed completely within a metal sheath combined in various arrangements to perform operational functions required in loop and radial underground distribution systerns. The cable terminals include a soft dielectric filler making a void-free interfacial engagement with the surface of a hard dielectric filler of a mating component. To provide for breaking a coupling under load, an arc-quenching follower is retractable into an axial cavity in the coupling components of the system and projectable therethrough upon breaking of the circuit and disconnecting of the components to provide an improved arc-quenching function. Thus, there is provided an undergroundsystem having security, operational safety and convenience.
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EDWARD H. YONKERS,
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GROUNDED SURFACE DISTRIBUTION APPARATUS The present application is a continuation of application Ser. No. 871,105, filed June 30, 1969 and now abandoned, and, which is a division of application Ser. No. 660,748, filed Aug. 15, 1967, now abandoned.
The present invention relates to a new and improved grounded-surface distribution apparatus and system for underground installation such as required in loop and radial underground distribution systems. More particularly, there is provided unique cable-terminal loadbreak switch elements which make possible hot-stick disconnecting, switching, sectionalizing and the like without moving the cable or the cable terminals and providing visible separation between grounded-surface circuit elements. I
The present strong trend toward underground distribution of electricity brings with it the need for new kinds of associated apparatus to provide the necessary system functions including switches, fuses, surge arrestors, cable terminals, taps and joints. The new aspect of such apparatus is that it must be able to carry on its functions underground in contact with and at times under water. This means that every part of the circuit which is maintained at system potential must be surrounded by a continuous sheath of impervious, voidfree insulation within a continuous conductive grounded housing.
Commercial apparatus attempting to fulfill these difficult requirements is still in the early stages of development. Prior known apparatus has not been entirely successful. In fact, the trend toward such underground distribution systems is so new that standard nomenclature has not been established by the electrical industry. The term submersible is sometimes applied to these devices for want of a more appropriate term. Groundedsurface distribution apparatus is a more appropriate and more truly descriptive term for this class of equipment since a conductive grounded-outside surface is a function requirement for operational and safety reasons.
The essential and main ingredient in underground distribution of electricity is obviously cable which must carry distribution current and voltage underground with trouble-free long life performance. Recent developments in synthetic dielectric materials have made possible the production of solid polymer insulated cable with high performance and low cost. However, the advantages of the new cable cannot be realized fully without effective, safe and convenient means for connecting the cable to various devices required in underground distribution systems. By employing voltage grading and interfacial sealing techniques, it has been possible to provide grounded-surface submersible devices to perform functions of cable joining and terminating, load-break switching, sectionalizing, and fusing.
The term grounded-surface may be taken literally in that apparatus in this category does in fact have a grounded external surface preferably of metal thick enough to provide mechanical support and to carry fault current if it occurs. Conductive plastic coatings will perform part of the function of grounding the surface but they may not provide safety under fault conditions.
Thus, it is an object of the present invention to provide a new and improved grounded-surface distribution system.
A further object of the present invention is the provision of a new and improved distribution system suitable for underground and submersible installation.
A further object of the present invention is the provision of a new and improved cable terminal for a groundedsurface distribution system.
A further object of the present invention is the provision of a new and improved coupler for a distribution cable.
A further object of the present invention is the provision of a new and improved load-break coupling suitable for grounded-surface distribution system application.
Yet a further object of the present invention is the provision of a new and improved arrangement of taps and connecting units for an underground distribution system.
A further object of the present invention is a new and improved surge arrestor for a grounded-surface distribution system.
Another object of the present invention is the provision of a new and improved fuse structure for a groundedsurface distribution system.
The difficult design problem in grounded-surface distribution apparatus is to put the entire high potential circuit inside the grounded housings and still provide means for carrying out switching and sealing-off functions. In accordance with the present invention there is provided a system which employs a combination of soft and hard dielectrics cast into place around the high voltage elements with compression springs at appropriate locations to maintain all critical interfaces void-free and under pressure over all ambient variations expected in operation.
In accordance with one aspect of the invention each circuit is maintained separately in its own grounded sheath with interfltting components available to set up various functions such as load-break disconnect. [n this case the two cable terminals are supported by a rigid clamp mounted on a ground rod. The load-break features are present in both cable terminals independent of each other. The switch blade is a groundedsurface inverted U-coupling which may be removed with a hot stick from above. The operator moves only the coupling piece. The cables and terminals are not moved or disturbed in the operation. The energized circuits are never exposed since loadbreak followers fill the connector openings when the switch is open. The open circuits are visibly separated and metallic grounds are between them. Insulated or grounded caps can be secured or latched over the elements of the open switch, if desired. Thus, the switch whether open with separate caps or closed with the U-coupling, is completely safe and without hazard to operating personnel working in close proximity to it.
In accordance with another aspect of the present invention, the more complicated arrangements carry the same features of system security, operating convenience and safety. For example, a three terminal'tap switch arrangement according to the present invention is very effective in loop systems where sectionalizing is needed.
In accordance with the present invention a groundedsurface current-limiting fuse provides system security when used in the tap circuits.
An improved surge arrestor provides convenient means for surge protection of the open position in loop circuits. Such a surge arrestor is also equipped for installation or removal with a hot stick.
The basic element of the present grounded-surface distribution apparatus is the cable terminal. It performs several important functions: (1) connection to the cable conductor, (2) grading of the field and provision of a permanent seal over the cable insulation, (3) pro vision of a disconnect and load-break element, (4) provision of a standard conical sealing surface to mate with various elements such as couplers, fuses, insulating and grounding covers, and (5) to provide interfitting of various elements having high versatility in meeting circuit requirements by means of a rigid cylindrical housing of stainless steel with locating means in precise bracket structures. All of the interfltting elements employ the same standardized conical sealing surface and latch spring geometry. The grounded cover of the cable terminal is latched into place providing the standardized conical seal which is waterproof due to the void-free interface held under permanent pressure by the latch springs.
In accordance with one aspect of the invention wherein a U-coupler is latched in place between two cable terminals, the U-coupler may readily be removed with a hot stick to provide load-break disconnecting. The U-coupler and associated load-break terminals easily meet the usual requirement encountered with single phase distribution systems. The concentric neutral wires of the cable are connected directly to the cable terminal housing and serve to hold the cable in place by means of split bolt connectors, then continue on to be connected together and to ground. This firm connection is particularly important where system fault currents are high.
The present devices are particularly well adapted for sub-surface switching points or control centers. In such control center arrangements the loop can be separated and part of it temporarily grounded with a grounding cover and also it may be sealed off in the open position with an insulating cover or a surge arrestor. Versatile components thus provide means for safely controlling, protecting and servicing underground single phase loop or radial systems. Maximum safety is afforded to operating personnel by virtue of the continuous grounded sheath which covers all energized elements with rugged stainless steel which can carry the high fault currents which sometimes occur in distribution systems.
Another safety feature which is inherent in the grounded-surface system is that open circuit positions always provide visible separation with solidly grounded elements between the separate circuit terminals. Thus, when all circuit terminals are sealed and latched with couplers, fuses, arrestors, covers or the like as required, the sub-surface control centers provide the maximum in circuit reliability, the minimum in customer outages,
and maximum in safety and convenience for servicing.
For a better understanding of the present invention, reference may be had to the accompanying drawings wherein:
FIG. 1 is an isometric view of a cable terminal with a grounding cap in place according to the present invention;
FIG. 2 is a cross sectional view of the cable terminal of FIG. 1, and illustrating the electrical coupling components within the cable terminal;
FIG. 3 is a cross sectional view of the cable terminal of FIG. 1, taken along line 3-3 of FIG. 2, and illustrating the plug-in connector components within the cable terminal;
FIG. 4 is a cross sectional view of the connector coupling components of FIG. 3, illustrated to a larger scale;
FIG. 5 is an exploded view of the coupling components of FIGS. 3 and 4;
FIG. 6 is an isometric drawing illustrating a groundedsurface load-break switch employing two standard load-break cable terminals and a standard U-coupler.
FIG. 7 is a cross sectional view of a U-coupling unit taken along line 7-7 of FIG. 6;
FIG. 8 is a cross sectional view of the U-coupling unit of FIG. 7, taken along line 88 of FIG. 7, assuming that FIG. 7 illustrates the entire structure;
FIG. 9 is a top view of a single tap arrangement employing three load-break cable terminals, and a tap manifold or bus in accordance with the present invention;
FIG. 10 is an elevational view of the structure of FIG. 9 and further illustrating U-couplers in phantom;
FIG. 11 is an elevational view of a three-point manifold or bus of the type illustrated in FIGS. 9 and 10, illustrated in broken away section;
FIG. 12 is an elevational view of a surge protector for use with a cable terminal according to the present invention and illustrated partially in broken away section;
FIG. 14 is a cross sectional view of a current limiting fuse for use with terminals according to the present invention;
FIG. 15 is an alternate structure of a fuse connector for use with terminal taps according to the present invention and illustrating a removable fuse arrangement;
FIG. 16 is an end view of the fuse structure of FIG. 15;
FIGS. 17 and 18 illustrate an alternate control center arrangement including a connecting unit having multilevel terminals to provide desired economy of space and apparatus;
FIGS. 19 and 20 illustrate the isolating or grounding of one of the lines in the control center of FIG. 17;
FIG. 21 illustrates in cross section a primary cable terminal for the grounded surface submersible system according to the present invention;
FIG. 22 illustrates in broken away section a cable joint according to the present invention;
FIG. 23 is an end or bottom view of the cable joint of FIG. 22 taken along line 23-23 of FIG. 22;
FIG. 24 is a cross sectional view of the cable joint of FIG. 22, taken along line 24-24 of FIG. 22;
FIGS. 25 and 26 illustrate a switching point assembly employing an improved T-terminal; and
FIG. 27 illustrates a sub-surface switching point assembly.
FIG. 13 is a top view of the surge protector of FIG.
Referring now to the drawings and particularly to the embodiment of FIGS. 1, 2 and 3, there is shown the details of a cable terminal with a grounding cover 32 latched in sealed position. The cable terminal 30 includes a conducting housing 34 of suitable material such as stainless steel, and cylindrical in cross section. A cover 35 also of conducting material such as stainless steel engages two side pins 36 in the housing 34 in a spiral bayonnet action to compress an inner thrust spring 37 to be compressed in the latched position as shown so as to exert an axial thrust on a soft elastomer dielectric filler 38 confined at its lower end by a piston-like cup retainer 39.
The soft dielectric filler 38 is cast within the housing 34 to interfit with a hard dielectric filler 40 which is firmly cast and locked into the housing 34 but which projects from the end of the housing to provide a standardized conical sealing surface 41 having a connector entrance 42. Although the hard dielectric filler 40 is illustrated as formed of two parts 40a and 40b, it may be made of one piece if desired.
As used herein, the soft dielectric filler may be of any void-free dielectric soft enough to conform to the adjacent surfaces in void-free interfacial engagement under the loading of the selected thrust spring. It has been found that a soft poly-urethaneor other limited cross linked polymer, preferably castable, with a Shore A hardness of 20 to 40, worked satisfactorily. As used herein, the hard dielectric filler may be of any void-free dielectric hard enough to provide mechanical strength to position the components. Castable synthetic polymers such as epoxy resins having a Shore A of 100 or higher were found satisfactory. v
The soft dielectric filler 38 is designed to receive a power cable 45 of the type having a basic insulation 46 and a sheath 47 as customized dimensions. In addition to the sheath 47, the cable 45 may contain a plurality of strands of grounding wire 48. The end thrust spring 37 permits a reasonable range in diameter variation and still maintains a permanent void-free interfacial seal between the insulation 46 and the soft elastomer 38 even under submerged conditions.
The cable terminal 30 includes a connector 50 for terminating the end of the cable 45 and defining a cable connector 50a at one end. The cable connector 50a has an elongated body of conducting material, such as copper and the like, and defines a receptacle 51. A conducting pin or plug 52 is adapted for insertion into an elongated axially aligned pin cavity 53 of the receptacle 51 to establish a low resistance connection capable of carrying rated current as well as momentary high currents. The pin 52 is connected to the short exposed end 450, FIG. 2, of the cable 45, and the pin 52 is-formed with an elongated axially aligned socket 54 extending inwardly from the lower end of the connector. After the central conductor 45a is inserted into the socket 54, a compression tool or the like is used to compress the walls of the socket inwardly into tight engagement with conductor 45a and thus firmly secure and electrically connect the pin 52 to the upper end of the cable 45. The pin 52 includes a cylindrical pin portion 55 of reduced diameter adapted to be inserted into the pin cavity 53 of the receptacle 51 to establish electrical connection therewith.
The receptacle 51 around the pin cavity 53 thereof is square or pa'ragonal in cross section, FIG. 3, and includes a plurality of planar outer faces 58 which angularly intersect one another, forming a plurality of longitudinally extending parallel upper ridges 59. Preferably, the ridges are provided with narrow, flattened upper faces 59a, FIG. 4, which are tangent to a circle having its center on the longitudinal center axis of the receptacle 51. Each planar face 59a of the receptacle 51 is bisected by a longitudinally extending slot 60 extending upwardly from the lower end of the connector and terminated adjacent the inner end of the pin cavity 53. The slots 60 bisect the faces 59a into pairs of segments of approximately equal area, and thereby form a plurality of movable fingers 62, each including one of the ridges 59 and a pair of segments on its outer surface and a curved segmented, cylindrical interface forming a wall portion of the pin cavity 53. The free ends of the fingers 62 are movable inwardly and outwardly with respect to the longitudinal central axis of the receptacle 51 and form the lower end portion thereof surrounding the pin cavity 53.
In order to establish a relatively high contact pressure between the fingers 62 and the pin 52 and thereby further reduce the resistance of the connection and in crease the current carrying capacity thereof, the fingers 62 are biased inwardly by a circular tension ring 63 which is slipped over the body of the receptacle 51 and bears against the flattened surfaces 59a on the ridges 59. Preferably, the ring 63 is formed of a thin band of high strength material, such as beryllium-copper alloy and is dimensioned so that the inner diameter of the' ring is slightly less than the distance between the flattened surfaces on the ridges 59 on the diametrically opposite fingers. Accordingly, the ring 63 is under tension and is force fitted over the lower end of the body and moved upwardly thereon toward the blind end of the pin cavity 53.
The amount of inwardly biasing force exerted on the fingers 62 by the ring 63 is selectively adjustable by movement of the ring 63 around the fingers of the receptacle 51. For example, the fingers 62 are more easily deflected near the outer or free ends, and when a ring of given internal diameter is positioned adjacent the free end, the fingers 62 have less inward deflection of the free ends than when the ring 63 is moved upward toward the blind end of the pin cavity 53. The flattened surfaces of the ridges 59 permit easier movement of the ring 63 thereon without gouging of the ridges.
From the foregoing, it should be noted that the cable connector 50a provides a large contact surface between the connecting members thereof and additionally provides for an adjustable contact pressure over the large contact surface. It is not necessary to tighten any bolts or clamps for assembling the cable connector once the connecting members are engaged since ample holding force is achieved by the contact pressure between the connecting members. While the receptacle 51 is illustrated as having a square cross section, it is to be understood that other configurations, such as triangular, etc., could be used as well. The fingers 62 are constructed to have a cross section that is symmetrical on opposite sides of longitudinally bisecting planes extending between the ridges 59 and the longitudinal axis of the cable connector 50. Accordingly, the inward force applied by the ring 63 to the flattened ridge surfaces is distributed fairly uniformly on both sides of the bisecting plane to the inner contact surface of the fingers 62.
The upper end of the tubular housing 34 carries a conical skirt 65, FIG. 2, so that a pair of spring latches 66 carried on the grounding cover 32 can engage with the conical skirt 65 in any radial direction. The spring latches 66 include latch loops 67 designed to be engaged by standard hot line tools for latching or unlatching the various devices which carry the standardized mating surfaces and latching elements. Suitable latch springs 68 maintain the spring latches 66 in tight assembled relation.
The connector 50 also includes a switch connector 50b for interrupting a circuit under load. The switch connector 50b includes the same components as the cable connector 50a but additionally has arcextinguishing components. Specifically, the switch connector 50b includes a switch receptacle 51a defining a switch cavity 53a formed by the fingers 62. The tension ring 63 affords inward pressure to the fingers 62 in like manner as in the cable connector 50a. The switch connector 50b will accommodate a coupling conductor or switch member to provide an excellent electrical connection.
To provide for load-break features, the upper connector opening carries a liner 72 of arc-extinguishing material which co-functions with a follower 73 of arc extinguishing material within the switch cavity 53a of the switch receptacle 51a and which is backed up by a projection spring 74 to provide load-break effects when an associated coupling conductor is removed from the switch receptacle. The material of the liner 72 and follower 73 possesses desired arc-quench properties and may be of synthetic polymer material carrying a suitable amount of arc-quenching material such as molybdenum sulfide or alumina.
In operation the follower 73 moves into the opening in the liner 72 when a coupling conductor 77 of the grounding cover 32 is removed from the associated switch cavity 53a. The cooperation of the arcquenching elements 72 and 73 extinguishes any arc that may be formed as the coupling conductor 77 leaves the end of the switch connector 50 by deionization of the plasma. Since the arc is interrupted in the narrow space between the follower 73 and the liner 72 and since the follower 73 remains in the opening, there is no significant amount of ionized gas between the separated circuit elements. That is, the ionized gases associated with the receptacle side of the circuit remain inside and those associated with the connector side of the circuit are dissipated on the outside.
The connector 50 is in a receptacle chamber 80 in the relatively high potential field associated with the cable conductor. This region would therefore be subject to corona problems unless all the air spaces around the receptacle are eliminated. This is accomplished according to the present invention by applying a conductive layer or member 81 to the inside wall of the chamber 80. If desired, the conductive layer 81 may be a conductive paint or coating.
.The inside wall of the receptacle chamber 80 includes two peripheral grooves 82 and 83 of semicircular cross section, one 82 at the cable entrance end which serves to reduce the voltage gradient at the end of the conductive layer 81 because of the enlarged radius of curvature provided by the conductive surface of the groove, and one 83 generally centrally of the receptacle chamber 80 which serves to lock the connector 50in proper position in the chamber by means of a metallic spring ring 84. This ring 84 also serves to connect electrically the conductive layer 81 to the connector 50.
The outer surface of the hard dielectric filler 40 is also provided with a conductive layer or member, shown in the form of a conductive coating 85 in the regions where it is normally in contact with the metal housing 34. This is to prevent ionization of air in the small gap between the inside surface of the housing 34 and the outside surface of the filler 40 which may occur due to differences in the thermal expansion coefficients of the two materials. This problem of differing thermal coefficients of expansions also occurs between the soft dielectric filler 38 and the metal housings 34 andretainer 39. However, in these locations the action of the latch springs 68 and the thrust spring 37 on the soft elastomer keeps all of the critical interfacial surfaces in void-free contact throughout the ranges of expected ambient temperatures and operating conditions.
The grounding cover 32 serves to provide a positive ground to a cable terminal 30 when it is desired to work in the area of a disconnected terminator. To this end, the coupling conductor 77 of the grounding cover is electrically connected to a metal grounding housing or cap 88 which in turn is grounded to the spring latches 66 and the conical skirt 65 to the grounded conducting housing 34 of the cable terminal. However, an additional ground connection is recommended to the grounding cap housing by means of a flexible ground wire connected to the terminal 88b. A soft dielectric filler 90 fills the grounding cap around the coupling conductor 77 and forms a void-free interfacial engagement with the conical sealing surface 41 of the cable terminal. As heretofore described, the latch springs 68 serve to maintain a permanent void-free interfacial seal between the critical interfacial surfaces in a manner similar to the thrust spring 37. Thus, there is provided the standard conical sealing assembly with the hard dielectric filler 40 having the convex sealing surface 41, while mating soft dielectric filler 90 has a concave mating surface 91, which, in the illustrated embodiment, are both conical in shape.
The structure shown in FIGS. 1, 2 and 3 is particularly adapted to receive the co-axial cable 45 which employs the plurality of wires 48 arranged in symmetrical spirals over the outside surface of the cable. These wires serve as the neutral conductor of the circuit as well as a grounded protective sheath. Since these wires 48 are part of the power circuit, they must provide a high conductivity path throughout the circuit. For this reason, the lower cover 35 is provided with extension members 92 which receive split bolt connectors 93 for holding the strands 48 of the neutral conductor so as to make connection and at the same time hold the cable firmly in place. The neutral wires 48 can then continue on to be grounded to ground or other neutral wires as hereinafter described. The extension member 92 also serves as means for rotating the cover 35 into the closed and latched position.
FIGS. 6, 7 and 8 illustrate a simple typical switch connection between two cable terminals of the type heretofore described. As therein illustrated, a pair of cable terminals 30 identical to that heretofore described, are supported in spaced relation from a grounding rod 95 by a suitable mounting clamp 96. The mounting clamp 96 is precisely machined to match the diameter of the terminal housing 34 and includes a groove 97 accommodating a rib 98, FIGS. 1 and 2, which isprecisely located on all of the terminal housings 34. The mounting clamps 96 are slotted with grooves 97 so as to fit the rib 98 whereby all of the terminals 30 are rigidly held in place at the proper level with respect to the mounting clamp 96. Thus, all terminals 30 in a single mounting clamp will be normal to the plane of the bracket, at a standard distance apart and at a standard level permitting complete interchange of removable components.
As best illustrated in FIG. 6, the neutral wires 48 of the cables 45 are divided into two parts, one half going to one extension member 92 and the other half to the other extension member 92 of a respective terminal 30. This is done in order to balance theforces holding the cable in place and also to keep all of the neutral wires tight and uniformly covering as much of the cable sheath as is possible. A grounding clamp 99 on the grounding rod 95 serves to join all neutral wires together and to connect them to ground.
The pair of cable terminals 30 in FIG. 6 are connected by a U-shaped switch coupler 100, also illustrated in FIGS. 7 and 8, and provided with a loop 101 for engagement with a linemans hot stick. The switch coupler 100 includes a central conducting assembly made up of two switch couplings or pins 104 serving as switch blades and braised or otherwise secured to a crossbar 105 formed of electrically conducting materials such as copper. The switch couplings are silverplated and carry a switch tip 104a which is controlled in size so as to fit the switch cavity 53a in the mating cable terminal. The horizontal portion of the central conducting member carries a cylindrical molding of conductive plastic or other suitable material 106 to enlarge the radius of the conductive portions and reduce the potential gradient. This cylindrical molding of conductive material 106 eliminatescorona problems from air gaps in high gradient regions which could develop due to differences in thermal coefficients of expansion between plastics and metals. With this construction the field starts at the outer surface of the conductive material 106 which is surrounded in bonded, voidfree relationship with a hard dielectric filler 107 of the same expansion coefiicient as the conductive material 106 so as to remain sealed at all temperatures. The entire assembly is enclosed within a conductive housing here illustrated as a stainless steel housing 108, formed of mating housing portions 108a and 108b, so that the filler assembly including the contact plugs 104, crossbar 105, conductive material 106, and hard dielectric filler 107 may be prefabricated and then assembled within the housing. The housing portions 108a and l08b may be gripped in place together such as by the overlaps 108C. The housing 108 is closed by end caps 109 which may be spot welded into position as shown.
The standardized conical sealing surface 41 of the cable terminal 30 must be mated with a soft dielectric in order to establish the void-free interface under the spring forces of the standard latch system. This is accomplished by providing conical cavities 110 around the switch coupling 104 in the dielectric filler 107 which are larger than the standardized conical sealing surface 41. A soft dielectric molding 111 is preformed with the exact geometry of the space between the conical cavities 110 and the conical sealing surfaces 41 to provide the standard conical sealing surface 91. The
soft dielectric fillers are formed of double cones bonded to the hard dielectric filler 107 on the coupler 100 to provide a permanent void-free interface between the hard and soft dielectrics in the coupler 100. Each of the downwardly depending portions of the coupler housing are provided with a pair of latch springs 66 at the ends of latch loops 67 and adapted to be loaded through latch springs 68 in the manner described in embodiment of FIGS. 1, 2 and 3.
By the proper selection and arrangement of grounded surface elements, a variety of important distribution system functions can be performed according to the present invention. FIGS. 9, 10 and 11 illustrate, for example, an assembly of standard elements ar ranged so as to provide a single fuse tap, illustrated in phantom at 114, on an underground distribution loop circuit. Sectionalizing functions are provided by means of two switch couplers 100 of the type illustrated in FIGS. 6 to 8. The necessary interconnections are established by means of a three terminal manifold or bus 115 and three cable terminals 30. Each cable terminal 30 is identical with that of FIGS. 1, 2 and 3. In addition, the manifold 115, as illustrated, is provided with three vertical risers or cable terminals 116 each containing similar load-break features. Thus, each riser 116 is an exact replica in form and function as the upper end of the standard cable terminal. Each riser housing includes a locating rib 117, FIG. 11, and latching cone 118 so that all removable components will interfit. Thus, one of the risers 116 and one of the cable terminals 30 are tied together by the mounting clamp 96 onto the grounding clamp 95. The remaining two vertical risers 116 and cable terminals 30 are connected by a 4-place mounting clamp 122 secured to a grounding rod 123. Each of the clamping portions of the mounting clamp 122 is provided with a circumferential groove 124, FIG. 10, receiving one of the locating ribs 98 and 117 to vertically position the respective terminals.
The design details of the multi-terminal manifold 115 will be more clearly understood by reference to FIG. 11. As therein illustrated, the manifold 115 includes a central conductor 128 which may be of copper or other suitable material. Standard switch connectors 50b, identical with the switch connectors 50b of the connector 50 illustrated in the embodiment of FIGS. 1, 2 and 3, are braised to the central conductor 128. Briefly, therefore, the switch connectors 50b each include the switch receptacle 51a provided with the switch cavity 53a for receiving a mating connector rod. As heretofore described, the switch receptacle 51a is similar to the switch receptacle 51a illustrated in FIGS. 4 and 5 and include the plurality of fingers 62 encircled by the tension ring 63. The liner 72 of arc-quenching material leads into the switch cavity 53a, and the projectable follower 73 is biased into the liner 72 by the projection spring 74 when connecting components are not in place. It is understood that the load-break components including the sleeve 72, follower 73, and projecting spring 74 may be omitted where it is not desired to provide for breaking of the circuit under load.
In like manner as with the switch coupler 100 illustrated in FIGS. 7 and 8, a conductive material 130 is cast around the middle connecting circuit components thereby enlarging the radius of the conducting portion and reducing the potential gradient. Thus, there is eliminated the corona problems from air gaps in high gradient regions which could develop due to differences in thermal coefficients of expansion between the metal parts and the dielectric fillers. With this construction, the field starts at the outer surface of the conductive material 130. However, since the upper ends of the switch receptacle 51a in the region of the follower 73 must be movable, a soft cover 131 of plastic or other suitable material covers the free end of the switch receptacle 51a. A hard dielectric filler 132 is molded over the entire conducting system with the outside surfaces conforming to a housing 133 of stainless steel or other suitable material and with the standard conical sealing surface 41 of each riser'position. The entire manifold assembly 115 may be preformed and inserted into an upper housing portion 1330 with a lower housing portion 133b slipped into position and with end caps 134 spot welded into place. As in previous compo nents, the outside surface of the hard dielectric filler 132 is covered with a conductive layer 135 expect on the conical sealing surfaces.
The risers 116 may be provided in any number; however, most circuit requirements can be met with three or four terminal manifolds. It should be noted that the risers are arranged in line and spaced the standard distance apart. Also, the vertical sleeve portions of the I housing 133 are fully standardized to fit brackets and to mate with removable components. Thus, two four terminal manifolds can be combined to provide sectionalized switches and four fused taps in a single control center.
Surge production is frequently desired at the open end of a loop circuit or other suitable locations when it is to remain in this condition for a long period of time. FIG. 12 illustrates in partial cross section a surge arrestor 140 which may be connected to any of the standard terminals in a cluster or control center. The surge arrestor 140 includes a grounding housing 141 of stainless steel or other suitable material and includes a lower portion 141a which is standardized with the conical sealing surface 91 to the fit cable terminals and multiterminal manifolds of the grounded surface distribution system. According to the present invention, the functional parts of the surge arrestor 140 include a system of quench gaps 142 in series with valve blocks 143 of suitable material such as silicon carbide. These elements are arranged in dielectric tube 144 under compression of a compression spring 145. The housing includes a top cover 146 locked to the remainder of the housing through side pins in like manner as cover 35 in the embodiment of FIGS. 1, 2 and 3. The space between the dielectric tube 144 and the metal housing 141 is filled with a soft dielectric filler 147 which is maintained in void-free interfacial contact by means of the inner thrust spring 37 acting between the end cover 146 and the retainer 39. A connector pin 148 extends from the lower end of the surge arrestor 140 for mating within the switch cavity 530 of a collaborating member. A cone of soft dielectric material 149 is placed around the upper end of the contact plug 148 in order to control the gradient in this region. It is understood that the connecting components of the lower housing 141a are identical to those heretofore described, including the spring latches 66, the latch loops 67, and the latch springs 68 which serve the dual function of biasing the spring latches 66 and applying a positive pressure to the dielectric filler 147.
To provide for fusing of the grounded surface distribution system, one of the interchangeable elements may consist of a current limiting fuse, such as the current limiting fuse 152, illustrated in FIG. 14. As therein illustrated, the current limiting fuse 152 is housed within an assembly similar to the switch coupler more fully described in the discussion of FIGS. 7 and 8. More specifically, there is provided the fuse unit 153 enclosed within a metal housing 154, similar to housing 108 heretofore described, and cast in the center of a hard dielectric filler 155. A pair of conically shaped soft dielectric fillers 156 are provided having the standard conical sealing surfaces 91 for engaging the conical sealing surface 41 of cable terminals or manifolds, and the fuse 152 is provided with the standardized latches to interfit with the other components.
Referring now to the fuse unit 153, the operation thereof is known and depends upon the melting and vaporization of a silver fuse wire 157 and the subsequent deposition of the silver over the surfaces of sand grains 158 which surround it. This takes place so rapidly under high fault conditions that the current is cut off before it reaches the full value of the available fault current. The silver metal becomes so diffused in the sand grain matrix that it no longer carries significant current. In such fuses it is necessary to maintain sufficient distance between the turns of the silver wire to prevent hot ionized gas from shorting out turns. In the illustrated design, in order to minimize the length of the fuse for a given rating, a wide flange surrounding the spiral core 159 is used to separate the turns of the silver fuse wire 157. As previously mentioned, this space around the wire between the spiral flanges is filled with refractory granulars such as alumina or silica. The granular matrix may be bonded with a minimum of refractory cement in order to permit the assembly of the parts within an insulating tube 160. The tube 160 may be of organic or inorganic material, but preferably it is of high strength and refractory at least in its lining in order to minimize internal pressures which may develop during operation. This fuse has no outlet for gaseous discharge since its entire envelope must be capable of withstanding system voltages within the grounded housing. The respective ends of the silver fuse wire 157 is soldered to the center of opposed cylindrical ferrules 161 fitted over the ends of the surrounding spirals 159 and insulating tube 160. Thus, the silver fuse wire 157 may be of maximum length. A pair of contact rods or plugs 162 extend concentrically through the soft dielectric filler for engagement within a plug receiving cavity 153 of a conductor assembly 50.
In order to control the potential gradient around the turns of the fuse wire in the sand and thus prevent corona in this region, a conductive film is applied to the outer surface of the fuse tube 160. A terminal to terminal resistance in the range of 50 to 150 megohms provides satisfactory operation of the fuse.
In the above fuse design, the active fuse wire 157 is not removable in the field from the matrix of the hard dielectric filler 155. When blown, the fuse 152 will have some salvage value for factory rebuilding, but cannot be rebuilt in the field. FIGS. 15 and 16 illustrate a current limiting fuse 165 which, although somewhat more expensive initially than the fuse 152, may have the active element replaced by the user in the field, and the fuse unit 165 could go back into service immediately.
The principle of operation of the fuse 165 is similar to that of fuse 152 and includes the silver fuse wire 157