US2087876A - Annular strand - Google Patents

Description

July 20, 1937. T. F. PETERSON 2,087,876

ANNULAR STRAND Filed Oct. 19, 1955 2 Sheets-Sheet l [Egi bweiwr:

WON/=75 PETE/Q6 ON) Patented July 20, 1937 UNITED STATES PATENT OFFICE ANNULAR STRAND Application October 19, 1933, Serial No. 694,310

7 Claims.

This invention relates to flexible tubular, or annular strands. Although there are numerous specific applications, depending on its properties as flexible tubing with good longitudinal conduction and tensile strength, or large surface area for a given weight per foot, for purposes of disclosure its use as a hollow conductor intended for high voltage transmission of electric energy is considered.

Electric conductors of annular construction offer numerous advantages to justify their use under widely diifering conditions. In case of large cross-sectional areas, such a disposition of metal insures maximum efliciency in its use since skin effect tends to cause the current to flow in outer fibers. Then, too, the increased area improves radiation of heat from surface, or conduction of heat through surrounding insulation. Furthermore, by increasing the outside diameter the electrical stress in adjacent dielectric is reduced, thus reducing the tendency for corona formation, or insulation breakdown. Standard stranding to the desired diameter frequently entails the use of more metal than is required for carrying capacity or voltage regulation; Annular conductors are then used. These may be hollow, or rope core.

In the former class are those consisting of wires laid around supporting members, such as twisted strips, cylindrical pieces, braided structures, helical strips and tubes.

The object of this invention is to provide an annular strand without internal supporting members, and in which the elements are used to best advantage for conduction'and tension. Another object is to provide a tubular conductor which is self-locking, non-collapsible, light in weight, and which may be laid up in a conventional stranding machine using wire of simple shape.

According to this invention, a strand is made of strips longitudinally arranged edge-to-edge helically to form a tubular-structure, and key wires are interposed between the edges of these strips which are longitudinally recessed to en-. gage the same. The strips are not locked to these wires in any manner but are free to laterally separate sufiiciently to provide flexibility when the strand is flexed. These wires and recesses are respectively proportioned. to space the edges of the strips while allowing substantial portions of the latter to overlie the wires.

When subjected to tension, bridging of the wires occurs and prevents separation of the strips, the key wires acting as principal bearings between the recessed strips and allowing for laterally pivotal and separating action and longitudinal slippage of adjacent strips. The strand here contemplated is completely hollow in the sense that it contains no internal supporting means whereby it may be considered as being self-supporting. These elements may be made of'copper, the strips being preferably hardened to provide the strength required to withstand the tensions caused by long spans.

Some of the strips may be made of metals having much higher tensile strength. Such a composite structure has characteristics far superior to usual composite strands, such as aluminum and steel for example since, regardless of the physical properties of the metals, the pressure between the strips requires that they all operate in unison. If the strips are locked to the key wires such a composite structure is inoperative because unequal thermal expansion of the parts cannot be accommodated and the strand is subjected tostructural stresses that cause it to stifien.

One of the advantages of the above is that, although the parts are held against radial disengagement, the strips may laterally separate, pivot or swing on the wires when the conductor is flexed. I-Ieretofore, conductors of this general character were made of strips having tongueand-groove or laterally interlocked connections which prevented this pivoting and separating and made the conductor rather rigid.

Another advantage is freedom for longitudinal slippage of strips with respect to one another, and with respect to the key wires. Such movement takes place in the act of bending. The flexibility thus developed improves vibration and fatigue characteristics.

surfaces are eliminated, this reducing dangers of corona discharge. By the use of thin key wires ample strip material may be aflorded to allow for rounding the corners. An additional feature which I have embodied involves making the radius of the curvature of the outside surface of a strip less than one-half the outside diameter of cable. The scalloped efiect resulting acts to shield the valleys and reduce dangers of any corona formation at the edges.

It is to be understood that the lateral separation of the strips during flexing of the strand is not a complete separation from the key wires, the portions of the strips which overlie the wires being proportioned to prevent such'action. This applies to all service conditions encountered by strands of the character being discussed.

A still further advantage is that sharp edges or corners on the outside 1y when the strand is bent, such separation tak-- ing place on the longer side of the bent strand. If the strips did not so separate the strand would be relatively inflexible.

Figure 3 is an enlargement more clearly showing that the edges of the strips are spaced. This allows the lateral pivoting and separating action which makes the conductor more flexible. It should be noted that the wires are rather thinner than the strips, this permitting substantial portions of the latter to overlie the former. Thus, radial disengagement is prevented unless the conductor is flexed beyond the limits intended and which would ordinarily be encountered inshipping it on drums or in'service.

The helical arrangement of the strips causes them to grip the wires and thus maintain the tubular structure. The strips may be preformed or in some other way be set so that there is little tendency for the conductor to collapse or open even when broken. Tests have shown that when the conductor is ruptured it will collapse only limited distances. Its ends may be wrapped during shipment and installation, to'maintain its form. Once installed the conductor cannot come apart. Service tensions only cause the strips to grip the pivoting wires more firmly.

Figure 4 shows the use of wires 2 which are somewhat flattened or elliptical. Their sides present round surfaces to the adjacent strips to enable them to pivot thereon. Such a modification might be desirable where greater flexibility without danger of collapse is desired, as it'enables the use of deeper recesses without letting the strips edges butt. These flattened wires are ar ranged in the strips cylindrical plane.

Figure 5 is another modification, wherein the strips are centrally reduced throughout their length. This provides the required edge thickness so that the wires on which the strips bear or pivot may be properly engaged. At the same time, the conductor will be materially lightened. The reduced portions are indicated by I.

Figure 6 is a modification in which the radius of curvature of the outside surface of a strip, defined by a plane at right angles to the conductor axis, is less than one-half the outside diameter of the cable. The corners are carefully rounded so that there will be little tendency for corona formation, even if the strips should become twisted out of place. The strips are numeraled l their rounded corners I and the bearing wires function as bearings between the strips on which the latter pivot laterally. Also, these wires function to prevent radial separation of the strips. But never do they function to prevent the lateral separation of the strips that is required to provide strand flexibility. The reason for these functions is because of the previously described construction.

I claim:

1. A self-supporting flexible annular strand including a plurality of strips helically arranged in edge-to-edge relationship to form a tubular structure and wires interposed between and separating the edges of said strips, said edges being recessed to partially receive said wires and the interengaging surfaces of the two being shaped to permit lateral separation of said strips during flexing of said strand and to permit said strips to pivot on said wires.

2. A self-supporting flexible annular strand including a plurality of strips helically arranged in edge-to-edge relationship to form a tubular structure, and wires interposed between and separating the edges of said strips, said wires being of substantially less thickness than said edges and the latter being recessed to partially receive the former while providing substantial portions which overlie the same, said recesses providing entrances that are as wide as the thickest parts of the portions of said wires that are received thereby, 1

whereby said strips may separate laterally when said strand is flexed.

3. A self-supporting flexible annular strand including a plurality of strips helically arranged in edge-to-edge relationship to form a tubular 1 structure and wires interposed between and separating the edges of said strips,'said wires being of substantially less thickness than said edges and the latter being recessed to partially receive the former while providing substantial portions which overlie the same, the interengaging surface of said edges and said wires being shaped to permit lateral separation of said strips and to permit said strips to pivot on said wires during flexing of said strand.

4. A self-supporting flexible annular strand including a plurality of strips helically arranged in edge-to-edge relationship to form a tubular structure and flat wires interposed between and separating the edges of saidstrips, said wires being arranged in the cylindrical plane of said structure and said edges being recessed to par-. tially receive the edge portions of said wires, the interengaging surfaces of said edges and said edge portions of said wires being shaped to permit lateral separation of said strips and to permit said strips to pivot on said wires during flexing of said strand.

5. A self-supporting flexible annular strand including a plurality of strips helically arranged in ,edge-to-edge relationship to form a tubular structure and flat wires interposed between and separating the edges of said strips, said wires being progressively reduced from their longitudinal centers to their longitudinal edge portions and being of substantially less thickness than said strips, the edges of the latter being recessed and at least partially receiving said edge portions of said wires and the interengaging surfaces of the two being shaped to permit lateral separation of said strips and to permit said strips to pivot on said wires during flexing. of said strand.

6. A self-supporting flexible annular strand including a plurality of strips helically arranged in edge-to-edge relationship to form a tubular struc- 1 flexing of said strand, said strips being permanently set in helical shapes which coincide with the shapes they possess when helically arranged edge-to-edge to form said structure.

7. A self-supporting flexible annular strand including a plurality of strips helically arranged in edge-to-edge relationship to form a tubular structure and wires interposed between and separating the edges of said strips, said edges being recessed to partially receive said wires and the interengaging surfaces of the two being shaped to permit lateral separation of said strips and to 1 permit said strips to pivot on said wires during flexing of said strand, said strips being per- 10 manently set in their helical arrangement.

THOMAS F. PETERSON.

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