Patent Application
20140027153
RF transceivers have traditionally been located on the ground and RF signals transmitted to/received from antennas mounted atop radio towers interconnected with the RF transceivers by RF coaxial cables. A move towards remote radio head (RRH) installations, wherein the RF transceivers are themselves located atop radio towers proximate the antennas, has reduced the need for RF coaxial cables to transmit the RF signals between the transceiver and the antenna, but has also increased the demand for electrical power at the top of the radio tower.
Traditional electrical power cables comprise large gauge copper conductors with a circular cross section. However, such power cables are heavy, difficult to bend and have a high material cost directly related to the rising cost of copper metal.
Cost and weight efficient aluminum power cables are known. However, to deliver the same current capacity an aluminum power cable requires an increased cross-sectional area. Also, a differential in the thermal expansion coefficient of aluminum material cables and that of the various metals comprising connections/connectors is a cause of aluminum cable electrical interconnection reliability issues, which increase as the diameter of the clamped portion of the aluminum conductor increases.
As the diameter of a power cable increases with increasing power capacity, the bend radius of the power cable increases.
Competition within the electrical power transmission cable and in particular the Remote Radio Head systems market has focused attention upon reducing materials and manufacturing costs, providing radio tower electrical power delivery and overall improved manufacturing quality control.
Therefore, it is an object of the invention to provide an electrical power cable and method of manufacture that overcomes deficiencies in such prior art.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given above, and the detailed description of the embodiments given below, serve to explain the principles of the invention.
The inventor has recognized that the prior accepted circular cross section power cable design paradigm results in unnecessarily large power cables with reduced bend radius, excess metal material costs and/or significant additional manufacturing process requirements.
An exemplary flexible aluminum power cable 1 is demonstrated in
The flattened characteristic of the cable 1 has inherent bend radius advantages. When the bending moment is applied across the narrow dimension of a rectangular conductor 1, the bending radius may be dramatically reduced. For a circular cross section, the bending moment is proportional to radiuŝ4 (any direction). However, along the thin dimension of a rectangular cross section, the bending moment is significantly smaller. As best shown in
A tighter bend radius also improves warehousing and transport aspects of the cable 1, as the cable 1 may be packaged more efficiently, for example provided coiled upon smaller diameter spool cores which require less overall space.
The bend radius may be further improved by enabling the several conductors of the stack to move with respect to one another as a bend is applied to the cable 1. Application of a lubrication layer 25 between at least two of the conductors 5 facilitates the movement of the conductors 5 with respect to one another as a bend is applied to the cable 1. Thereby, conductors 1 closest to the bend radius may establish a shorter path than conductors at the periphery of the bend radius, without applying additional stress to the individual conductors 5 of the cable 1, overall.
The lubrication layer 25 may be applied as any material and/or coating which reduces the frictional coefficient between conductors 5 to below the frictional coefficient of a bare conductor 5 against another bare conductor 5. The lubrication layer 25 by be applied as a layer/coating of, for example, synthetic hydrocarbons, solvent based vanishing lubricants, molybdenum disulfide, tungsten disulfide, other dry lubricants like mica powder or talc, waxes, primary branched alcohol and ester based additives, primary linear alcohols and lauric acid based additives, soap and non-soap based greases, polymer based lubricant, ester based lubricant, mineral oil based protective coating fluid, blends of mineral and synthetic oils. Further, the selected lubrication layer 25 may be semisynthetic emulsifiable.
The jacket 15 may be formed with, for example, polymer materials such as polyethylene, polyvinyl chloride, polyurethane and/or rubbers applied to the outer circumference of the stack 10. The jacket 15 may comprise laminated multiple jacket layers to improve toughness, strippability, burn resistance, the reduction of smoke generation, ultraviolet and weatherability resistance, protection against rodent gnaw through, strength resistance, chemical resistance and/or cut-through resistance.
The edges of the stack 15 may present a sharp corner edge prone to snagging and/or tearing. To apply a smoother radius to the corner edges of the cable 1, the top conductor 30 and bottom conductor 35 may be provided with a width that is less than a width of a middle conductor 40 proximate the middle of the stack 10, for example as shown in
The shortest bend radius will be applied to the top conductor 30 or bottom conductor 40 (depending upon the desired direction of bend) of the stack 10. As shown for example in
Multiple conductor stacks 10 may be applied to form a multiple conductor flexible power cable 1, for example as shown in
One skilled in the art will appreciate that the cable 1 has numerous advantages over a conventional circular cross section copper power cable. Because the desired cross sectional area may be obtained without applying a circular cross section, an improved bend radius may be obtained. If desired, the significant improvements to the bend radius enables configuration of the cable 1 with increased cross sectional area. This increased total cross sectional area, without a corresponding increase in the minimum bend radius characteristic, may also enable substitution of aluminum for traditional copper material, resulting in materials cost and weight savings. Where aluminum conductors 5 are applied, a termination characteristic, for example by soldering, and/or corrosion resistance of the aluminum conductors 5 may be improved by coating at least one side of one of the individual aluminum conductors 5 with a coating 55, such as copper.
One skilled in the art will appreciate that in addition to the aluminum versus copper material cost savings, a weight savings for an electrical cable with aluminum conductors installed upon a radio tower is especially significant, as an overall weight savings enables a corresponding reduction in the overall design load of the antenna/transceiver systems installed upon the radio tower/support structure. Further, the improved bending characteristics of the flexible electrical power cable may simplify installation in close quarters and/or in remote locations such as atop radio towers where conventional bending tools may not be readily available and/or easily applied. Finally, because complex stranding structures which attempt to substitute the solid cylindrical conductor with a woven multi-strand conductor structure to improve the bend radius of conventional circular cross section electrical power cables may be eliminated, required manufacturing process steps may be reduced and quality control simplified.
The inventor has also recognized a further benefit of the invention with respect to handling the effects of a differential in the thermal coefficient of expansion encountered, for example, when aluminum conductors are terminated in steel or copper interconnection/termination structures. One skilled in the art will appreciate that when the cable 1 is terminated by clamping the stack 10 between the top and bottom, that is along the thin dimension of the flat cable, the thickness of the aluminum cable material across which a differential in thermal expansion coefficient relative to the interconnection/termination structure material will apply is reduced dramatically, compared to, for example, a conventional circular cross section cable.
Where in the foregoing description reference has been made to ratios, integers or components having known equivalents then such equivalents are herein incorporated as if individually set forth.
While the present invention has been illustrated by the description of the embodiments thereof, and while the embodiments have been described in considerable detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details, representative apparatus, methods, and illustrative examples shown and described. Accordingly, departures may be made from such details without departure from the spirit or scope of applicant's general inventive concept. Further, it is to be appreciated that improvements and/or modifications may be made thereto without departing from the scope or spirit of the present invention as defined by the following claims.
