This invention reiates primarily to devices for spacing and dampening vibrations in suspended elongate objects such as. e.g., electrical conductors or fiber optic cables. The invention is described below with reference to spacing electrical conductors but is not limited thereto.

Overhead conductors, particularly those forming extra-high voltage (EHV) transmission lines, are often "bundled" into groups for traversing the distance between adjacent transmission towers. To reduce discharges and adverse field effects caused by contact (or near contact) between conductors in a bundled group, rigid metallic spacers for the conductors have sometimes been used. These spacers are generally incapable of dampening many wind-induced vibrations in the spaced conductors, however. Should such vibrations reach certain levels, considerable damage to the conductors or transmission towers may result.

US-A-4,242,537 discloses alternative spacers for use with overhead conductors. Unlike the rigid metallic spacers referenced above, those of US-A-4,242,537 also operate to dampen certain oscillations to which the conductors are subjected. These spacer dampers comprise a substantially planar frame of rigid, one-piece construction, typically of an aluminum alloy. Clamping arms are connected to the conductors via clamps and are pivotally connected to the planar frame by bolts passing through resilient, energy-absorbing elastomeric bushes. The clamping aims may pivot only in or parallel to the plane of the frame (i.e. only about parallel axes of rotation normal to the plane of the planar frame) and as a result can accommodate only limited differential longitudinal conductor motion. Degradation of some existing spacer dampers additionally may occur as the dampening elastomeric bushes are exposed to. for example, ultraviolet radiation, ozone, or electric fields. T e elastomeric bushes, in turn, may promote corrosion in the adjacent aluminum castings.

US-A-4.159,393 details another type of vibration damper. The "Stockbridge '-type damper of US-A-4.159,393 comprises a length of resilient cable having a clamp intermediate its ends for securing it to a conductor. At each end of the cable is a weight whose center of gravity is disposed away from the cable axis. As shown in US-A-4, 159,393 a bolt secures the clamp to the conductor, and set screws or other suitable means attach each weight to the length of cable. Unlike those of US-A-4.242.537 however, the dampers of US-A-4, 159,393 do not function to space bundled conductors.

The present invention provides yet alternative devices for both spacing conductors and dampening vibrations to which such conductors may be subjected in use. In contrast to known spacer dampers such as described in US-A-4.242,537 the present invention provides a damper which is flexible about at least two non-parallel axes so allowing the damper to dampen vibrations in. and relative movement between, conductors or other elongate objects both transversely and longitudinally. Rather than using elastomeric bushes to dampen vibrations, the spacer dampers of the present invention are preferably composed of multiple lengths of stranded metal cable.

In use. flexing of the cable lengths causes interstrand friction as the strands move relative to each other, mechanically dissipating the energy imparted to the devices by the vibrations. As a result, the devices of the present invention avoid the deleterious effects sometimes associated with use of elastomeric bushes, concomitantly increasing their service life. The lengths of cable also function to space conductors in a bundle, providing a light weight, metallic spacer damper with a semi-flexible or semi-resilient frame.

Attached to the lengths of stranded cable are metallic bumpers. These bumpers, preferably made of aluminum cast or crimped onto the cable lengths, help secure the spacer dampers to their associated conductors. Formed in the bumpers are apertures through which one or more generally helical wire rods may be threaded to secure each bumper to a conductor. Using formed wire rods to attach the spacer dampers of the present invention to conductors permits them to be twisted into engagement with the conductors (effectively "snapping" them into place ), requiring no special toois and thereby facilitating installation. Omitting the internal bolts of many existing dampers also avoids disadvantageous results of their use. particularly as the bolts loosen over time and then fail properly to participate in dissipating wind-induced vibrations.

Increased multi-direcrionai flexibility additionally results from use of the spacer dampers of the present invention. Although many existing products are suitably flexible horizontally and vertically, as noted above they typically accommodate only limited motion aiong the axes of the conductors. Those of the present invention, by contrast, are not so restricted, but rather flex longitudinally as well. Consequently, they are designed to provide enhanced performance when such motion occurs, as. for example, when transmission lines experience heavy ice loading.

The nature of the present invention further facilitates manufacturing devices of differing flexibility. Merely by substituting different-sized cables for those

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nominally employed, the rigidity of the resulting product-and its frequency response-can be altered. The rigidity of conventional spacer dampers is not so easily modified, instead requiring changes to any or all of the elastomer formulation, elastomer geometry, and castings.

Other features, and advantages, of the present invention will become apparent with reference to the remainder of the written portion and the drawings of this application.

In the drawings:-

FIG. 1 is an elevational view of a two-conductor spacer damper of the present invention.

FIG. 1 A is a cross-sectional view of the two-conductor spacer damper taken along lines A-A of FIG. 1.

FIG. IB is a cross-sectional view of the two-conductor spacer damper taken along lines B-B of FIG. 1.

FIG. 2 is an elevational view of a three-conductor spacer damper of the present invention.

FIG. 2 A is a cross-sectional view of the three-conductor spacer damper taken along lines A-A of FIG. 2.

FIG. 3 is an elevational view of a four-conductor spacer damper of the present invention.

FIG. 3 A is a cross-sectionai view of the four-conductor spacer damper taken along lines A-A of FIG. 3.

Fig. 4 is an elevational view of a second embodiment of a three-conductor spacer damper of the present invention.

Fig. 5 is an elevational view of a second embodiment of a four-conductor spacer damper of the present invention.

FIG. 1 illustrates device 10 of the present invention. Designed both to space conductors 14 and 18 and to dampen vibrations induced in them, device 10 thus ftmctions as an alternative spacer damper to those currently in use. Unlike many existing spacer dampers, however, device 10 includes neither a rigid frame nor vibration-dissipating elastomeric bushes.

Instead, as shown in FIG. 1. device 10 includes a relatively flexible frame 22 formed of semi-rieid cables 26. 30, and 34. In some embodiments of the invention

cables 26, 30, and 34 comprise lengths of stranded metal, typically (but not necessarily) nineteen-strand galvanized steel commonly called "messenger cable." As cables 26, 30. and 34 flex due to vibrations, for example, friction between the individual strands functions to dissipate the vibrational energy. Cables 26. 30. and 34. moreover, permit frame 22 to flex m three dimensions, effectively dampening overhead transmission line vibrations with not only horizontal and vertical components but those with components along the transmission line axes as well. By using cables 26. 30. and 34 to dissipate vibration energy, device 10 avoids the need for elastomeric bushes or other non-metallic absorptive or dampening elements.

Attached to ends 36 and 38 of cable 26 are bumpers 40 and 42. Usually comprised of aluminum or aluminum alloy, bumpers 40 and 42 may be crimped or cast directly onto or otherwise attached to the respective ends 36 and 38 of cable 26 to ensure a suitable connection. Likewise attached to bumper 40 is end 44 of cable 30. while bumper 42 additionally is attached to end 46 of cable 34. Weight 50 (see also FIG. IB), by contrast, may be connected to ends 54 and 58 of, respectively, cables 30 and 34. FIG. 1 details these connections, with ends 54 and 58 penetrating and thus secured within weight 50.

In some embodiments of device 10. weight 50 is a spherical zinc mass cast onto ends 54 and 58. Although those skilled in the art will recognize that weights 50 of other shapes and compositions may be employed, the presence of weight 50 enhances the performance of device 10. particularly for low frequency vibrations, by adding additional mass to frame 22. Conventional twin-bundle spacer dampers usually lack such additional mass, causing the entire spacer damper itself to vibrate with the spaced conductors (rather than dissipate the vibrations) under certain conditions. Weights 50 of different masses may be substituted for those nominally shown in FIG. 1, moreover, to optimize the vibration-dissipation capability of device 10 for the varying resonant frequencies of smaller- and larger-diameter conductors. Similarly, cables of other diameters may replace cables 26, 30, and 34 if necessary or desired.

Although bumpers 40 and 42 help secure device 10 to conductors 14 and 18. they differ from conventional clamps. Rather than using jaws or a bolt to attach device 10 to conductors 14 and 18. bumpers 40 and 42 include semi-cylindrical recesses 62 and 66 into which the conductors are fitted. Each bumper 40 and 42 additionally includes apertures 70 and 74. through which formed wire or other generally heiical rods 78 and 82 (FIG. 1 A) may be threaded. Combined, recesses 62 and 66 and rods 78 and 82 permit device 10 to be twisted into secure engagement with conductors 14 and 18 without bolts, jaws, or special installation

tools. Omitting use of bolts as connection elements concomitantly avoids their loosening over time, in rum avoiding vibration-induced damage that may occur as a resuit of such loosening.

FIG. 1 illustrates an embodiment of device 10 in a standard, or normal, position. As shown in FIG. 1. the length of cable 26 may be selected so that it curves downward toward an imaginary center point P, of frame 22. assuming approximately the shape of a catenary curve absent wind-induced motion. Cables 30 and 34 similarly curve inward toward point P,. Should conductors 14 and 18 move or begin to vibrate, however, the shape of cable 26 may change as device 10 seeks to dampen the vibrations or maintain suitable spacing. Because cables 26. 30. and 34 are not rigid, frame 22 can flex in the horizontal ("x"), vertical ("y"), and longitudinal ("z") directions and thereby accommodate differential movement of conductors 14 and 18 in each.

Embodiments of device 10 consistent with FIG. 1 may function to retain the spacing of dual conductors 14 and 18 nominally eighteen inches (45.7 centimetres) apart, with recesses 62 and 66 abutting approximately three and one-quarter inch lengths ( 8.26 centimetres) of the conductors (FIG. 1A). Device 10 is not so limited, however, and may be employed under other circumstances as well. In particular, the invention embodied in device 10 is capable not only of use with a wide variety of transmission lines, but also in other circumstances where spacing and energy dissipation is desired.

Detailed in FIGS. 2 and 2 A is a three-conductor spacer damper 86 of the present invention. Unlike device 10. spacer damper 86 lacks weight 50. substituting instead a third bumper 90 abutting the third conductor 94. The triangular spacing of conductors 14. 18. and 94 and commensurate symmetry of frame 22 about point P. stabilizes spacer damper 86 sufficiently that no additional weight is required.

FIGS. 3 and 3 A illustrate device 98. an embodiment of the present invention designed to space and dampen vibrations induced in four-conductor bundles. Device 98 includes third and fourth bumpers 100 and 102. with a fourth cable 106 incorporated into frame 110. Ends 54 and 118 are attached to third bumper 100. and ends 58 and 126 are connected to fourth bumper 102. each by suitable means. As illustrated in FIG. 3. cables 26. 30. 34. and 106 are designed to curve inwardly (symmetric about center point P,), enhancing the stability of frame 1 10 in use.

The spacer dampers of Figs.2 and 3. under compressive loads between conductors, distort and then spring back to shape when the load is removed. If it is

required that there should be little or no distortion under compressive load then the embodiments of Figs.4 and 5 may be used.

Fig.4 shows a three-conductor spacer damper 150 similar to that of Fig. 2 but comprising additional elements to restrict distortion under compressive load. Spacer damper 150 comprises a central hub 151 linked with rigid rods 152, 153, 154 to respective bumpers 90.40. and 42. Rod 152 is fixed in relation to hub 151 but rods 153 and 154 are pivotally mounted to hub 151 for limited rotation about two non-parallel axes (i.e. both in the plane of and out of the plane of the drawing . This arrangement allows the spacer damper to flex both within the plane of the drawing and transverse to the plane of the drawing but limits such flexing so that conductors are kept spaced at roughly the same separation throughout the entire range of flexing of the spacer damper. Typically, for an application where the nominal spacing between conductors 14 and 18 is about eighteen inches (45.7 centimetres) this dimension may vary +/- 1 inch (2.54 centimetres). The rods 153 and 154 may move in towards the hub 151 by up to about 1/4 inch (0.64 centimetres) and outwardly by about 1 inch (2.54 centimetres ). The bumpers 40 and 42 can move transversely of the plane of the spacer damper (i.e. out of the plane of the drawing) by about +/- 1 inch (2.54 centimetres).

Fig. 5 shows a four-conductor spacer damper 160 of similar construction in which hub 161 is fixed to rod 162 and rods 163. 164. and 165 are pivotally mounted for limited rotation.

Both of the embodiments of Fig.4 and Fig.5 in essence comprise limiting means to restrict the extent or amplitude of relative movement of suspended elongate objects. The limiting means may compπse a framework of rigid members mounted for limited relative movement and serving to limit the approach of the suspended elongate objects under compressive loads. The limited relative movement may be provided by pivotally mounting a plurality of rods for limited relative rotation about two non-parallel axes. It will be appreciated by the person skilled in the art that other members capable of other limited relative motions (such as sliding motions) and non-rigid members having a limited extent of movement (such as strong springs) may be used to achieve the same effect.

The foregoing is provided for purposes of illustrating, explaining, and descπbing embodiments of the present mvention. Modifications and adaptations to these embodiments will be apparent to those skilled in the art and may be made without departing from the scope of the invention.