Although silver is the best conductor, its cost limits its use to special circuits. Silver is used where a substance with high conductivity or low resistivity is needed. The two most commonly used conductors are copper and aluminum. Each has positive and negative characteristics that affect its use under varying circumstances. A comparison of some of the characteristics of copper and aluminum is given in below table. Comparative Characteristics of Copper and Aluminum
Tensile strength (lb/in2).
Tensile strength for same conductivity (lb).
Weight for same conductivity (lb).
Cross section for same conductivity (C.M.).
Specific resistance (W/mil ft).
Copper has a higher conductivity than aluminum. It is more ductile (can be drawn out). Copper has relatively high tensile strength (the greatest stress a substance can bear along its length without tearing apart). It can also be easily soldered. However, copper is more expensive and heavier than aluminum.
Although aluminum has only about 60 percent of the conductivity of copper, its lightness makes long spans possible. Its relatively large diameter for a given conductivity reduces corona. Corona is the discharge of electricity from the wire when it has a high potential. The discharge is greater when smaller diameter wire is used than when larger diameter wire is used. However, the relatively large size of aluminum for a given conductance does not permit the economical use of an insulation covering.
The resistance of pure metals,such as silver, copper, and aluminum, increases as the temperature increases. However, the resistance of some alloys, such as constantan and manganin, changes very little as the temperature changes. Measuring instruments use these alloys because the resistance of the circuits must remain constant to get accurate measurements.
In table 1-1, the resistance of a circular-mil-foot of wire (the specific resistance) is given at a specific temperature, 20°C in this case. It is necessary to establish a standard temperature. As we stated earlier, the resistance of pure metals increases with an increase in temperature. Therefore, a true basis of comparison cannot be made unless the resistances of all the substances being compared are measured at the same temperature. The amount of increase in the resistance of a 1-ohm sample of the conductor per degree rise in temperature above 0°C is called the temperature coefficient of resistance. For copper, the value is approximately 0.00427 ohm. A length of copper wire having a resistance of 50 ohms at an initial temperature of 0°C will have an increase in resistance of 50 X 0.00427, or 0.214 ohms. This applies to the entire length of wire and for each degree of temperature rise above 0°C. A 20°C increase in resistance is approximately 20 X 0.214, or 4.28 ohms. The total resistance at 20°C is 50 + 4.28, or 54.28 ohms.
6061 is a precipitation hardening aluminium alloy, containing magnesium and silicon as its major alloying elements. Originally called "Alloy 61S," it was developed in 1935. It has good mechanical properties and exhibits good weldability. It is one of the most common alloys of aluminium for general purpose use.
It is commonly available in pre-tempered grades such as 6061-O (annealed) and tempered grades such as 6061-T6 (solutionized and artificially aged) and 6061-T651 (solutionized, stress-relieved stretched and artificially aged).
T6 temper 6061 has an ultimate tensile strength of at least 42,000 psi (300 MPa) and yield strength of at least 35,000 psi (241 MPa). More typical values are 45,000 psi (310 MPa) and 40,000 psi (275 MPa), respectively. In thicknesses of 0.250 inch (6.35 mm) or less, it has elongation of 8% or more; in thicker sections, it has elongation of 10%. T651 temper has similar mechanical properties. The typical value for thermal conductivity for 6061-T6 at 80°C is around 152 W/m K. A material data sheet defines the fatigue limit under cyclic load as 14,000 psi (100 MPa) for 500,000,000 completely reversed cycles using a standard RR Moore test machine and specimen. Note that aluminum does not exhibit a well defined "knee" on its S-n graph, so there is some debate as to how many cycles equates to "infinite life". Also note the actual value of fatigue limit for an application can be dramatically affected by the conventional de-rating factors of loading, gradient, and surface finish.
6061-T6 is used for:
· The construction of bicycle frames and components.
· Many fly fishing reels.
· The famous Pioneer plaque was made of this particular alloy.
· The secondary chambers and baffle systems in firearm sound suppressors (primarily pistol suppressors for reduced weight and functionality), while the primary expansion chambers usually require 17-4PH or 303 stainless steel or titanium.
· The upper and lower receivers of many AR-15 variants.
· Many aluminum docks and gangways are constructed with 6061-T6 extrusions, and welded into place.
An overhead power line, also known as a "pylon" in some areas, is a structure used in electric power transmission and distribution to transmit electrical energy along large distances. It consists of one or more conductors (most often three or four) suspended by towers or utility poles. Since most of the insulation is provided by air, overhead power lines are generally the lowest-cost method of power transmission for large quantities of electric energy.
Towers for support of the lines are made of wood (as-grown or laminated), steel (either lattice structures or tubular poles), concrete, aluminum, and occasionally reinforced plastics. The bare wire conductors on the line are generally made of aluminum (either plain or reinforced with steel, or composite materials such as carbon and glass fiber), though some copper wires are used in medium-voltage distribution and low-voltage connections to customer premises. A major goal of overhead power line design is to maintain adequate clearance between energized conductors and the ground so as to prevent dangerous contact with the line, and to provide reliable support for the conductors, resilient to storms, ice load, earthquakes and other potential causes of damage. Today overhead lines are routinely operated at voltages exceeding 765,000 volts between conductors, with even higher voltages possible in some cases.
Structures for overhead lines take a variety of shapes depending on the type of line. Structures may be as simple as wood poles directly set in the earth, carrying one or more cross-arm beams to support conductors, or "armless" construction with conductors supported on insulators attached to the side of the pole. Tubular steel poles are typically used in urban areas. High-voltage lines are often carried on lattice-type steel towers or pylons. For remote areas, aluminum towers may be placed by helicopters. Concrete poles have also been used. Poles made of reinforced plastics are also available, but their high cost restricts application.
Each structure must be designed for the loads imposed on it by the conductors. The weight of the conductor must be supported, as well as dynamic loads due to wind and ice accumulation, and effects of vibration. Where conductors are in a straight line, towers need only resist the weight since the tension in the conductors approximately balances with no resultant force on the structure. Flexible conductors supported at their ends approximate the form of a catenary, and much of the analysis for construction of transmission lines relies on the properties of this form.
A large transmission line project may have several types of towers, with "tangent" ("suspension" or "line" towers, UK) towers intended for most positions and more heavily constructed towers used for turning the line through an angle, dead-ending (terminating) a line, or for important river or road crossings. Depending on the design criteria for a particular line, semi-flexible type structures may rely on the weight of the conductors to be balanced on both sides of each tower. More rigid structures may be intended to remain standing even if one or more conductors is broken. Such structures may be installed at intervals in power lines to limit the scale of cascading tower failures.
Foundations for tower structures may be large and costly, particularly if the ground conditions are poor, such as in wetlands. Each structure may be stabilized considerably by the use of guy wires to counteract some of the forces applied by the conductors.
Power lines and supporting structures can be a form of visual pollution. In some cases the lines are buried to avoid this, but this "undergrounding" is more expensive and therefore not common.
For a single wood utility pole structure, a pole is placed in the ground, then three crossarms extend from this, either staggered or all to one side. The insulators are attached to the crossarms. For an "H"-type wood pole structure, two poles are placed in the ground, then a crossbar is placed on top of these, extending to both sides. The insulators are attached at the ends and in the middle. Lattice tower structures have two common forms. One has a pyramidal base, then a vertical section, where three crossarms extend out, typically staggered. The strain insulators are attached to the crossarms. Another has a pyramidal base, which extends to four support points. On top of this a horizontal truss-like structure is placed.
Connectors for longitudinally splicing two lengths of cable or other electrical connectors together, commonly referred to as “automatic splices,” have long been known. Such devices are typically used by power utility linemen to quickly splice lengths of overhead or otherwise suspended high voltage cable together and have become a mainstay in the electrical utility industry. Originally developed for emergency restoration, theautomatic splicehas evolved into a nominal construction component for overhead power lines, and has been extensively used in the industry for over seventy years.
An early version of theautomatic spliceis disclosed in U.S. Pat. No. 3,205,300 to Becker. The opposed ends of Becker's device each contain a set of tapered jaws. The lineman inserts the cable ends through apertures provided in each of the opposed ends of the device. After inserting suitable lengths of each cable into the device, the lineman draws the cables longitudinally away from the device. This action pulls the jaws into the tapered ends of the device's casing, thereby securely clamping the jaws on to the cable.
However, even modernautomatic spliceconnectors still have numerous components, which require careful assembly and installation. Additionally, the cost of the raw materials of theseautomatic spliceconnectors remains high.
Accordingly, it would be desirable to provide a low costautomatic splicemade with less raw material, fewer components and reduced assembly steps.
SUMMARY OF THE INVENTION The present invention provides anautomatic spliceconnector with an outer casing formed from a solid piece of conductive alloy. Thus, theautomatic spliceconnector of the present invention generally includes a unitary casing having a longitudinal axis along which first and second ends of the casing taper conically toward the axis. The first end of the casing terminates at a first aperture and the second end of the casing terminates at a second aperture. The casing has an internal integral wall formed perpendicular to the longitudinal axis midway along the axial length of the casing, wherein the wall and the casing are contiguously formed as one piece.
The connector further includes a first cable gripping device disposed within the first end of the casing, a second cable gripping device disposed within the second end of the casing, a first biasing element disposed in the casing between the casing integral wall and an inner end of the first cable gripping device for urging the first cable gripping device along the axis towards the first aperture and a second biasing element disposed in the casing between the casing integral wall and an inner end of the second cable gripping device for urging the second cable gripping device along the axis towards the second aperture. A first plug is preferably secured in the first aperture and a second plug is preferably secured in the second aperture.
In a preferred embodiment, the casing is made of aluminum and the integral wall is formed with an axial through-hole to permit water flow between the first and second ends of the casing. Also, each of the first and second plugs preferably includes a tapered funnel guide fitted within a respective aperture and a pilot cup disposed within the funnel guide for receiving an end of a cable. The first and second plugs respectively temporarily prevent the first and second springs from advancing the first and second set of jaws towards the first and second apertures.
In addition, each of the first and second cable gripping devices are preferably in the form of a cooperating set of cable gripping jaws having a conically tapered outer surface conforming to the conically shaped first and second ends of the casing. Each of the first and second set of cable gripping jaws further preferably defines a semi-cylindrical inner surface bearing serrated teeth for gripping a cable.
The present invention further involves a method for manufacturing anautomatic splice, which utilizes cold forming, or other similar process, to eliminate the need for seamless tube and improve manufacturability. Thus, the method according to the present invention generally includes the step of forming a unitary casing from a solid slug of metallic material, wherein the casing has a longitudinal axis, a first end terminating at a first aperture, a second end terminating at a second aperture longitudinally opposite the first aperture and an internal integral wall formed perpendicular to the longitudinal axis midway along the axial length of the casing, and wherein the wall and the casing are contiguously formed as one piece.
The method according to the present invention further includes the step of inserting a first biasing element within the first end of the casing, inserting a first cable gripping device within the first end of the casing such that the first biasing element is disposed between the casing integral wall and an inner end of the first cable gripping device for urging the first cable gripping device along the axis towards the first aperture. A second biasing element is then inserted within the second end of the casing and a second cable gripping device is inserted within the second end of the casing such that the second biasing element is disposed between the casing integral wall and an inner end of the second cable gripping device for urging the second cable gripping device along the axis towards the second aperture. The first and second ends of the casing are then mechanically deformed to form first and second ends that taper conically toward the longitudinal axis. The assembly is complete by securing first and second plugs in the respective first and second apertures.
The casing is preferably formed from a solid slug of aluminum, or other electrically conducting material, using a cold-forming process. The method for forming the casing further preferably includes the step of forming an axial through-hole in the integral wall to permit water flow between the first and second ends of the casing.
In a preferred embodiment, the unitary casing is formed by providing an elongate solid slug of metallic material, inserting a tool along the longitudinal axis in opposite axial ends of the slug to form the casing having respective axial bores formed in opposite ends thereof and stopping the tool short of forming a continuous axial bore in the casing, thereby leaving the internal integral wall in the casing.
A preferred form of the automatic splice, as well as other embodiments, objects, features and advantages of this invention, will be apparent from the following detailed description of illustrative embodiments thereof, which is to be read in conjunction with the accompanying drawings.