SUSPENSION CLAMP FOR HANGING THE WIRES OF HIGH-VOLTAGE OPEN CABLES ON A SUPPORT STRUCTURE

Abstract: The invention relates to a suspension clamp used for hanging the wires of high-voltage, at least 52 kV open cables, particularly to a suspension clamp for an optical ground wire, said suspension clamp comprising a hook-shaped suspension clamp body portion, including a base member whereby the suspension clamp is adapted to be secured to a support structure, and a hook portion intended for fitting therein a wire or a like to be supported. The suspension clamp further includes: a trough portion (5) mounted on a hook portion (4) and extending lengthwise of a wire (1) for supporting the wire (1), said hook portion being adapted to extend from two opposite sides of the suspension clamp, the extension having its size and the trough portion (5) having its rigidity dimensioned such that, as a result of the forces applied to the trough portion (5) by oscillations or vibrations of the wire (1), the trough portion may experience elastic resilience, a locking element (6) which is adapted at a controlled force to clamp the wire (1) against the bottom (7) of the trough portion (5) over a section of the length of the trough portion (5) and to lock the wire (1) in its longitudinal direction securely relative to the trough portion (5), and a clamping element (8) which is adapted to clamp the locking element (6) against the wire (1), said clamping element (8) being pivotably mounted relative to the suspension clamp such that the clamping element can be set in a position which allows the lowering of the wire (1) into the trough portion (5).

Description: Suspension clamp for hanging the wires of high-voltage open cables on a support structure The present invention relates to a suspension clamp used for hanging the wires of high-voltage, at least 52 kV open cables, particularly to a suspension clamp for an optical ground wire, said suspension clamp comprising a hook-shaped suspension clamp body portion, including a base member whereby the suspension clamp is adapted to be secured to a support structure, and a hook portion intended for fitting therein a wire or a like to be supported. The suspension clamp subject to the invention is intended for use particularly in connection with optical ground wires, OPGW, or in connection of other like conductors, wherein the clamping force applied by the suspension clamp to the wire must be distributed evenly without sharp discontinuities. The optical ground wire is an earth conductor used in power transmission lines with optical fibres added for telecommunications. The optical fibres are located in the centre of the cable surrounded by electrically conductive wire layers. The OPGW-system forms a part of today's vital telecommunications. Such a system must provide reliable service for at least 30 years. With respect to land installations, the most significant difference is vibration caused by wind, ice and other climatic factors and stresses caused by thunder, which may destroy an otherwise high- standard system. Vibrations may inflict two types of faults: the wire does not mechanically withstand the stresses of vibraions or the optical fibres are damaged even if the wire were mechanically in perfect order. If the wire sustains strand ruptures, those shall inevitably lead also to the increase of fibre suppressions and ultimately to fibre breakups. Traditional suspension clamps have several undesired features: - time-consuming, difficult and complicated installation, plenty of loose components, - the high and irregularly adjustable clamping force of clamping elements and the sharp point of discontinuity caused by the termination of clamping subject the wire to plastic strain and denting effect, - a rigid, inflexible, short trough which follows poorly the wire vibrations (a structure contributing to the fatigue of a wire), - the installation correctness difficult to control, - a rigid, inflexible suspension structure increases the need for vibraion dampers since there are limited capabilities of transferring vibrations between chords adjacent to the suspension clamp, - the suspension clamp and clamping element have a structure which also requires the use of protective windings in order to avoid an excessive plastic strain in the wire, this again causes a reduction in the effect of vibration dampers as the latter cannot be fitted in their ideal position or must be fitted on top of the protective winding which impairs the effect thereof. In order to eliminate these drawbacks, an object of the invention is to provide a suspension clamp of the above type, subjecting a wire to strains as low as possible, said suspension clamp striving to alleviate the effect of vibrations occurring in a wire and said suspension clamp having a structure in consideration of installation- facilitating factors. According to the invention, this object is achieved such that a suspension clamp of the invention is characterized in that the suspension clamp further includes: a trough portion mounted on a hook portion and extending lengthwise of a wire for supporting the wire, said hook portion being adapted to extend from two opposite sides of the suspension clamp, the extension having its size and the trough portion having its rigidity dimensioned such that, as a result of the forces applied to the trough portion by oscillations or vibrations of the wire, the trough portion may experience elastic resilience, a locking element which is adapted at a controlled force to clamp the wire against the bottom of the trough portion over a section of the length of the trough portion and to lock the wire in its longitudinal direction securely relative to the trough portion, and a clamping element which is adapted to clamp the locking element against the wire, said clamping element being pivotably mounted relative to the suspension clamp such that the clamping element can be set in a position which allows the lowering of the wire into the trough portion. Preferred evolutions of the invention are set forth in the subclaims. The suspension clamp is designed to include no loose components and to enable its threading into position while the suspension clamp is fixed to its point of attachment on a tower. The object of a suspension clamp is not only to support a wire but also to serve as a vibrations transmitting link between two adjacent wires. One of the' qualities of the link must be tis ability to serve as a damping element and to reduce the level of vibration. These qualities have been searched by designing the link to consist of a rigid, massive body portion and a long, flexible trough portion. The mounting of a wire is implemented by means of a saddle- shaped, elongated spline unit, clamping progressively in the direction of a line and having its keyway designed in such a manner that the spline and the trough squeeze a wire in radial direction by at least three peripheral points, whereby the wire does not collapse but the threaded strands "are vaulting" to form layers with each other. This provides as low-straining as possible, yet sufficient a clamping effect between the suspension clamp and the wire. The design of spline and trough is effected such that they gradually "loosen their grip" on a wire towards its free, chord-bound section, thus managing to minimize the sharp termination of a clamping effect provided by the spline as well as the development of an indentation effect on the point of discontinuity. Thus, the qualities of a suspension clamp structure have been brought to resenble very closely the desired properties of a protective winding, yet avoiding the outbound stiffening effect of a protective winding directed towards the chord and the point of discontinuity at the end of a winding remote from the point of support. The invention will now be described in more detail with reference made to the accompanying drawings, in which: fig. 1 shows a suspension clamp of the invention in a side view. Fig. 2 shows a suspension clamp of the invention is a plan view. Fig. 3 shows a suspension clamp of the invention in a partially sectioned plan view. Fig. 4 shows a section along the line IV-IV in fig. 3. Fig. 5 shows a section along the line V-V in fig. 1. Fig. 6 shows the suspension clamp of fig. 5 in a cable installation position. In figs. 1 - 6 a suspension clamp of the invention is depicted in views from various sides and at various stages of installation. The suspension clamp is partiaularly intended for hanging optical ground wires used in the overhead cables of a power transmission network on support towers. Naturally, the suspension clamp can also be used for hanging other aerial wires and the like. As best shown in fig. 6, the suspension clamp comprises a hook-shaped suspension clamp body portion 2, including a base member 3 whereby the suspension clamp is adapted to be secured to a support structure (not shown) by means of per se known elements, and a hook portion 4 intended for fitting therein a wire or a like to be supported. The hook portion 4 is in a per se known fashion provided with a long, flexible trough portion 5 for supporting a cable 1. An object of the trough portion 5 is to distribute as evenly as possible the load applied to the wire 1 at the suspension clamp. The trough portion 5 is preferably made of a round-bottomed element, having its bottom 7 shaped in the longitudinal direction of the element such that the element has a mid-section 9 which includes a portion curving with a high radius (radius of curvature e.g. 2000 mm) and both ends 10 include a more sharply curving and flexible portion, the bottom surface providing a substantially convex support surface for the wire 1. The trough portion 5 has a substantially constant inner width over its mid-section 9. On both sides of the mid-section 9, the inner width of the trough portion 5 increases when progressing towards the ends of the trough portion. The locking element designated by reference numeral 6 is adapted at a controlled force to press or clamp the wire 1 against the bottom 7 of said trough portion 5 over at least a section of the length of the trough portion 5 and to lock the wire 1 in its longitudinal direction securely relative to the trough portion 5. In practice, the clamping force applied by the locking element 6 against the cable 1 is adapted to be produced by means of a clamping element designated by reference numeral 8. The clamping element is adapted to force the locking element 6 against the wire 1. The clamping element 8 is pivotably mounted relative to the suspension clamp such that the clamping element 8 can be set in a position which allows the lowering of the wire 1 into the hook portion 5. This position is shown in fig. 6. The side of the locking element 6 coming against the wire 1 is designed in the shape of a trough, as best shown in figs. 5 and 6. Thus, the pressure applied to the wire 1 by the trough-shaped, preferably V-shaped groove included in the locking element 6 and coming against the wire 1 as well as by the trough portion 5 is distributed evenly and it is particularly distributed over a long section of the wire 1. The locking element 6 has an effective clamping length which preferably equal to the length of the high-radius curving portion of said mid-section 9. A gap formed by the locking element 6 and the trough portion 5 is cross-sectionally of a substantially constant size at said mid-section 9 and preferably increases in size outside said mid-section 9. The clamping element 8 is at one end thereof journalled to the free end of the hook portion 4 of a suspension clamp and at the other end thereof adapted to be secured to the section of said hook portion 4 facing the base member 3. Prior to mounting the wire 1 in its position, the clamping element 8 is fastened to the hook portion 4 merely by means of one end-mounted pivot 11, as best depicted in fig. 6. In view of articulating the clamping element 8, the free end of the hook portion 4 is fitted with a pivot 11 which, transversely to the longitudinal axis of said pivot 11, is provided with a threaded hole 12 for a clamping element attachment and set screw 13. Thus, the hook portion has its free end provided with a vertical slot in order to enable the pivoting of the screw 13 and hence the clamping element 8 to the position shown in fig. 6 for installation of the cable 1. The clamping element 8 is designed as a U-shaped component, the section of hook portion 4 facing the base member 3 being adapted to be secured between the legs of said component. Fig. 3 shows an example which uses two tubular cotters 15, which are fitted in coaxial slots made in said legs and which tubular cotters 15 are intended, after installing the wire 1 in position, to be struck into a hole 16 extending through the base member 3 of said hook portion 4 for locking the end of said clamping element 8 in position. The U-shaped component has its connecting part provided with a hole for the attachment and set screw 13 of the clamping element 8. By tightening the screw 13 to a predetermined tightness the clamping force applied by the suspension clamp to the wire 1 can be adjusted as desired. When using a suspension clamp of the invention, there may be a situation in which the wire 1 for one reason or another is broken outside the suspension clamp and, in order to control that, the locking element 6 has its surface 14 facing towards the clamping element 8 given a concave shape and preferably in such a manner that there are two such concave surfaces 14, as shown in fig. 4. In a normal situation, the legs of the clamping element 8 lean against the lowest points of the concave surfaces 14 (fig. 4). If the wire 1 is broken, the suspension clamp is no longer capable, by its normally produced clamping force, of stopping the wire 1 from sliding. In this situation, however, the wire 1 also carries along the clamping element 6 whereby, as a result of the shaping of the top surface 14 of said clamping element 6, the clamping force applied to the wire by the clamping element increases significantly and disengagement of the wire is prevented. If necessary, it is possible to wind a protective tape 15 in the region of the suspension clamp prior to fitting the wire 1 in the suspension clamp. The purpose of the protective tape is to further reduce the stresses applied to the wire 1. The protective tape 15 can be an aluminium strip, for example. In order to facilitate installation, the components of a suspension clamp of the invention are assembled together for providing a ready-to-install, integral unit. Thus, the number of loose parts can be 0 or 1 depending whether or not the locking element 6 is secured to the clamping element 8.

Claims: Claims 1. A suspension clamp used for hanging the wires of high- voltage, at least 52 kV open cables, particularly to a suspension clamp for an optical ground wire, said suspension clamp comprising a hook-shaped suspension clamp body portion, including a base member whereby the suspension clamp is adapted to be secured to a support structure, and a hook portion intended for fitting therein a wire or a like to be supported, c h a r a c t e r i z e d in that the suspension clamp further includes: a trough portion (5) mounted on a hook portion (4) and extending lengthwise of a wire (1) for supporting the wire (1), said hook portion being adapted to extend from two opposite sides of the suspension clamp, the extension having its size and the trough portion (5) having its rigidity dimensioned such that, as a result of the forces applied to the trough portion (5) by oscillations or vibrations of the wire (1), the trough portion experiences elastic resilience, a locking element (6) which is adapted at a controlled force to clamp the wire (1) against the bottom (7) of the trough portion (5) over a section of the length of the trough portion (5) and to lock the wire (1) in its longitudinal direction securely relative to the trough portion (5), and a clamping element (8) which is adapted to clamp the locking element (6) against the wire (1), said clamping element (8) being pivotably mounted relative to the suspension clamp such that the clamping element can be set in a position which allows the lowering of the wire (1) into the trough portion (5) . 2. A suspension clamp as set forth in claim 1, c h a r ¬ a c t e r i z e d in that the trough portion (5) is made of a round-bottomed element, having its bottom shaped in the longitudinal direction of the element such that the element has a mid-section (9) which includes a portion curving with a high radius and both ends (10) of the element include a more sharply curving portion, the bottom surface providing a substantially convex support surface for the wire (1). 3. A suspension clamp as set forth in claim 2, c h a r ¬ a c t e r i z e d in that The trough portion (5) has a substantially constant inner width over its mid-section (9), and that on both sides of the mid-section 9, the inner width of the trough portion increases when progressing towards the ends of the trough portion (9). 4. A suspension clamp as set forth in claim 1, c h a r - a c t e r i z e d in that The side of the locking element (6) coming against the wire (1) is designed in the shape of a trough, preferably in the shape of V. 5. A suspension clamp as set forth in claim 1, c h a r - a c t e r i z e d in that the clamping element (8) is at one end thereof journalled to the free end of the hook portion (4) of a suspension clamp and at the other end thereof adapted to be secured to the section of said hook portion (4) facing the base member (3). 6. A suspension clamp as set forth in claim 5, c a r ¬ a c t e r i z e d in that the free end of the hook portion (4) is fitted with a pivot (11) which, transversely to the longitudinal axis of said pivot (11), is provided with a threaded hole (12) for an attachment and set screw (13) of the clamping element (8). 7. A suspension clamp as set forth in claim 5 or 6, c h a r a c t e r i z e d in that the clamping element (8) is designed as a U-shaped component, the section of the hook portion (4) facing the base member (3) being adapted to be secured between the legs of said component and the U-shaped component has its connecting part provided with a hole for the attachment and set screw (13) of the clamping element (8). 8. A suspension clamp as set forth in any of claims 1 - 7, c h a r a c t e r i z e d in that the locking element (6) has its surface (14) facing the clamping element (8) given a concave shape in the region of both legs of the clamping element. 9. A suspension clamp as set forth in any of claims 1 - 8, c h a r a c t e r i z e d in that around the wire (1 ) is adapted to be wound a protective tape (15) in the region of the suspension clamp prior to fitting the wire (1) in the suspension clamp. 10. A suspension clamp as set forth in any of claims 1 - 9, c h a r a c t e r i z e d in that the suspension clamp components are assembled together for providing a ready-to- install, integral unit.

Inventors: HORELLI JOUKO, HORELLI, JOUKO
Applicants: ENVO AB OY, HORELLI JOUKO, HORELLI, JOUKO, OY ENVO AB
Application year: 1996
Main classification: H02G7
IPC codes: G02B6, H02G7