EP0218719A1

EP0218719A1 - Vibration damper for a conductor on an overhead electric line

Info

Publication number: EP0218719A1
Application number: EP86903290A
Authority: EP
Inventors: Oscar Traini
Original assignee: RIGANTI SpA
Current assignee: RIGANTI SpA
Priority date: 1985-04-22
Filing date: 1986-04-09
Publication date: 1987-04-22
Also published as: IT8520435A0; IT1208531B; ZA862609B; CN86102654A; WO1986006560A1; AU5900886A

Abstract

Un amortisseur de vibrations pour un conducteur d'une ligne électrique aérienne comprend un serre-câble (3), pour se fixer à un conducteur (2), et un corps creux (6) à l'épreuve des agents atmosphériques, contenant un fluide incompressible (13) et une tige sensiblement verticale (9) dont l'axe rencontre l'axe du conducteur, et un élément solide ayant un trou au travers duquel ladite tige (9) peut passer de telle manière que l'élément solide (11) peut osciller le long de ladite tige; l'élément solide (11) est maintenu dans une position intermédiaire le long de la tige (9) au moyen de deux ressorts hélicoïdaux (10, 12), l'un au-dessus et l'autre au-dessous de l'élément solide (11).A vibration damper for a conductor of an overhead power line comprises a cable tie (3), for attaching to a conductor (2), and a hollow body (6) resistant to atmospheric agents, containing a fluid incompressible (13) and a substantially vertical rod (9) whose axis meets the axis of the conductor, and a solid element having a hole through which said rod (9) can pass in such a way that the solid element (11 ) can oscillate along said rod; the solid element (11) is held in an intermediate position along the rod (9) by means of two coil springs (10, 12), one above and the other below the element solid (11).

Description

Vibration damper for a conductor on an overhead electric line.

The present invention concerns a vibration damper for a con ductor on an overhead electric line.

The conductor on the overhead electric line will hereinafter be simply referred to as a conductor. For over sixty years a damper, called a Stockbridge damper, has been known, so named after its inventor, consisting of an element at the top of which is a clamp for connection to a conductor and having at its lower end a base for fixing on to a cable composed of steel elementary wires, which cable lies parallel to the conductor and has two equal weights, placed symmetrically in relation to the centre line of the clamp, at its two ends. Recently the two weights have been varied so that, while those of the original Stockbridge dam per had two modes of vibrating, in the recent version the weights have four modes of vibrating. The steel cable constitutes the elastic element which dissipates energy. Another well-known damper consists of weights placed one upon the other, separated by free elastic elements in the form of rubber pads, the weights and elastic elements haying a central hole through which passes a shaft at whose lower end is a stopping means for weights and at whose upper end there is a clamp for clamping to a conductor. Lastly, patent application No. 20412 A/84, whose inventor is the applicant in the present application, describes a damper comprising a base for holding elastic elements bearing weights wherein each elastic element is placed so that its main axis is perpendicular to the axis of the conductor, having one end fixed to said base and the other end fixed to a weight enabling it to vibrate normally to the axis of the conductor.

The above already known dampers possess drawbacks common to them all since they comprise damping elements, exposed to the external environment, whose damping characteristics will lessen over a period of time, due both to their perhaps inevitable design limitations and to adverse climatic conditions. For example, in the case of the Stockbridge damper, aggressive atmospheric agents attack the elastic elements consisting of the messenger cables, even though they are pro tected by galvanization; in dampers whose elastic elements are made of elastomers, super heating, or even physiological heating only, will in time alter their rigidity. Further examples of drawbacks are: snow and ice which can cover the dampers for more or less long periods preventing movement of the elastic elements; dust, desert sand or aggressive agents can also prevent articulation of these dampers.

The damper, subject of this present invention, overcomes all the above drawbacks as well as others left unmentioned.

Said damper comprises a clamp by which it can be clamped on to a conductor, fixed to a hollow body below the conductor, weatherproof, and containing an incompressible fluid and a solid element free to oscillate in said incompressible fluid in a direction substantially vertical when the hollow body vibrates with the conductor. The hollow body and the solid, element are so related that, when the solid element moves towards the top of the hollow body, part of the fluid above the solid element passes below the solid element through passages and, when the solid element moves towards the bottom of the hollow body, part of the fluid below the solid element passes above the solid element through the passages.

A spacing means is placed between the bottom of the hollow body and the lower part of the solid element to keep this latter separated from the bottom of the hollow body. Said spacing means may be rigid or elastic.

The shape of the hollow body is substantially that of a cy linder whose axis meets the axis of the conductor and is substantially perpendicular to the axis of the conductor.

The solid element is shaped like a cylinder whose axis coin cides with the axis of the cylinder of the hollow body and comprises at least one passage that crosses it from one end of the cylinder to the other. Alternatively, the hollow bo dy comprises a shaft whose axis coincides with the axis of the cylinder of the hollow body and the solid element compri ses a hole through which said shaft passes to allow the solid element to oscillate along said shaft. The solid element is held in an intermediate position along said shaft by two elastic means, one placed between the bot torn of the hollow body and the lower surface of the solid element and the other placed between the top of the hollow body and the upper surface of the solid element. The above elastic means are helical springs placed around the above shaft.

Alternatively said elastic means are two elastomer bushings placed around the above shaft.

The sum of hydraulic resistances in the above passages for the incompressible fluid is sufficient to produce the desired range of frequencies of oscillation of the solid element and of strengths of hydraulic reaction when, due to inertia, said solid element oscillates within the hollow bo dy vibrating together with the length of conductor on which the damper is mounted.

If there is only one rigid or elastic means below the solid element the damper's own vibration frequency is a function of the viscosity of the incompressible fluid only; in that case the damper concerned is technically known as 'untuned' and such a damper can be designed and made for damping all foreseeable frequencies of disturbance. If the solid element is held by two elastic means, one above and one below said element, the damper concerned is technically known as 'tuned' and its own vibration frequency is a function of the viscosity of the incompressible fluid, of the rigidity of the two elastic means and of the weight of the solid ele ment. One of the chief advantages of the damper here invented is the ability to maintain its efficiency at varying atmospheric temperatures; if atmospheric temperature is high, the range of dangerous vibration frequencies in a conductor is in fact lessened and, generally, the energy conferred upon the conductor by the wind is reduced, and vice versa if atmospheric temperature is low. Consequently, since the incompressible fluid inside the hollow body, if carefully cho sen, is sensitive to temperature variations, what happens is that, at high atmospheric temperatures, the viscosity of said fluid decreases and, together with it, the damper's own vibration frequency. Contrarywise, if atmospheric temperatures are low the viscosity of said fluid increases and, together with it, the damper's own vibration frequency. Another advantage offered by the damper here invented is that the entire damping system is enclosed in the hollow bo dy sheltered from all harmful effects upon it from outside agents. Further, the substantially oval shape of the hollow body considerably reduces the corona effect and radio interference.

A more detailed description of the invention is given here below aided by drawings which show an example of its embodi ment, wherein: Fig. 1 is a partially cutaway view of a tuned damper; Fig. 2 is a view of Fig. 1 cut through at I - I; Fig. 3 is a view given a 90° turn, compared with Fig.1, around the axis II - II; Fig. 4 is a partially cutaway view of an untuned damper; Fig. 5 is a partially cutaway view of another untuned damper; Fig. 6 is a view of Fig. 5 cut through at V - V.

The damper 1 seen in Figs. 1, 2 and 3 is fixed to an alumi nium-steel conductor 2, diameter of which is 31.5 mm and weight 2.00 kg/m, by means of a clamp 3 held firm by a bolt

4. The upper part 5 of the hollow body 6 is in one piece with the clamp 3, the lower part 5' being forced into the upper part. Clamp 3 and hollow body 6 are of aluminium alloy.

In two opposite seats 7, 8 of the hollow body 6, a shaft 9 is mounted around which there is a lower helical steel spring 10, a cylindrical steel element 11, weighing 1.5 kg. and an upper helical steel spring 12. Axis II-II is common to the shaft 9 and to the element 11, and coincides with the longitudinal axis of the damper. Axis II-II lies in a vertical plane and is perpendicular to axis III-III of the conductor 2. The entire cavity of the hollow body 6, not occupied by parts 9, 10, 11, 12, is filled with a mineral oil 13 whose viscosity is 5° Engler. The screw cap H closes the aperture 15 through which the mineral oil 13 is poured into the above cavity. The difference between the internal diameter of the hollow body 6 and that of the element 11, Ø₁- Ø₂, is 6 mm.

It will be clear that when the conductor 2 vibrates in a ver tical plane, it draws the hollow body 6 into the same vibrations along with it; element 11 then oscillates by inertia moving along the shaft 9, meeting the hydraulic resistance set up by the quantity of mineral oil 13 which passes through the passage 16, alternatingly, in both directions and meeting the elastic reaction of spring 10 and, alternatingly, of spring 12.

Axis III-III of conductor 2 is not horizontal and, even so, axis II-II of the damper is left perpendicular to axis III-III. Axis II-II will therefore not be vertical but allowance is made for this and any trouble is avoidable. The damper 1A illustrated in Fig. 4 shows the following differences compared with the damper illustrated in Figs. 1, 2 and 3: there is no spring above element 11; axis II-II of the hollow body 6 is inclined compared with axis IV-IV of the clamp substantially at the same angle as that between axis III-III and horizontal. In this way axis II-II is substantially vertical. The damper 1B illustrated in Figs. 5, 6 also has a hollow bo dy 6 composed of the two parts 5, 5', with aperture 15 and cap 14, but it differs from the two previous dampers because shaft 9 is missing and the solid element 11A is a cylinder placed inside the hollow body, with a certain degree of tolerance and containing four ducts 17,parallel to axis II-II, to allow the mineral oil 13 to pass from the upper part to the lower part of the solid element 11A, and vice versa. A certain amount of mineral oil 13 will also pass through the pas sage 16. Prom the bottom of the cavity of the hollow body 6 a rigid spacing means 18 rises up and keeps the solid element 11A from touching the bottom of the hollow body 6.

Corresponding parts in the Figures illustrating the three dampers 1, 1A and 1B are indicated bearing the same reference numbers.

Claims

1. Vibration damper in a conductor on an overhead electric line comprising a clamp (3), for clamping onto a conductor (2), characterized in that the clamp is fixed to a hollow body (6) below the conductor, proof against atmospheric agents, containing an incompressible fluid (13) and a solid element (11) free to oscillate in the incompressible fluid (13) in a direction substantially vertical when the hollow body (6) vibrates with the conductor.

2. Vibration damper according to claim 1 characterized in that the hollow body (6) and the solid element (11) are so related that, when the solid element moves towards the top of the hollow body, some fluid above the solid element passes below the solid element through passages (16,17), and when the solid element moves towards the bottom of the hollow body, some fluid below the solid element passes above the solid element along passages (16,17).

3. Vibration damper according to claims 1 and 2 characterized in that a spacing means (18) is placed between the bottom of the hollow body (6) and the lower part of the solid element (11) to keep this latter from touching the bottom of the hollow body.

4. Vibration damper according to claims 1,2,3, characterized in that the hollow body (6) has substantially the form of a cylinder whose axis encounters the axis of the conductor and is substantially perpendicular to the axis of the conductor.

5. Vibration damper according to the preceding claims characterized in that the solid element (11) is shaped like a cylinder whose axis coincides with the axis of the cylinder of the hollow body and comprises at least one duct (17) passing through it from one end of the cylinder to the other.

6. Vibration damper according to claims from 1 to 4 characterized in that in the hollow body (6) there is a shaft (9) whose axis coincides with the axis of the cylinder of the hollow body, and in the solid elemunt (11) there is a hole through which said shaft passes to allow the solid element to oscillate along said shaft.

7. Vibration damper according to claim 6 characterized in that the solid element (11) is held in an intermediate posi tion along said shaft (9) by means of two elastic elements (10,12), one placed between the bottom of the hollow body (6) and the lower surface of the solid element (11) and the other placed between the top of the hollow body and the upper surface of the solid element (11).

8. Vibration damper according to claim 7 characterized in that each of the above elastic elements (10,12) is a helical spring placed around the above shaft (9).

9. Vibration damper according to claim 7 characterized in that each of the above elastic elements is an elastomer bu shing placed around the above shaft (9).