FI86929C - Spiral dressings - Google Patents

Description

86929

The present invention relates to a threaded connection for attaching a conductor, in particular a coated open conductor, to an insulator, comprising a helically biased threaded portion having an inner diameter at most equal to the outer diameter of the conductor and a loop adjustable around the neck of the insulator.

The high-frequency conductor vibration 10 caused by the wind causes a dynamic alternating voltage at the conductor attachment points, which, when summed with other stresses, can cause conductor damage. Fatigue cracking progresses slowly in the microstructure of the conductor metal and the rupture may not follow until years after installation.

15 Conductor vibration can be prevented or damped using vibration dampers. The use of vibration dampers in transmission lines is systematic in certain places due to the high risk of vibration and the inconvenience caused by cable breakage. Medium voltage distribution network-20 sa, which in Finland is built almost entirely of overhead lines, does not normally use vibration dampers, as the risk of vibration is lower (smaller conductors, shorter spans, lower clamping stresses, wires low often under shelter or building protection).

25 The introduction of PAS conductors (plastic-coated medium voltage overhead lines) has changed the situation in the medium voltage network. PAS conductors vibrate more sensitively than uncoated open conductors of the same diameter. The vibration sensitivity of the PAS conductor is due to the lightening effect of the plastic layer compared to the bare conductor of the same diameter, the increased wind surface, the cylindricalness of the conductor (surface not helical as with a stranded metal conductor), and the internal damping factors of the conductor.

In the solutions according to patents FI 79915, 69537 and 80546, the vibration of the coated overhead line is not damped per se, but the mounting end of the conductor is designed in such a way that stresses are minimized and no damage occurs during the use of the conductor.

5 Preventing vibration damage to the PAS conductor is difficult, especially when using standard medium voltage insulators. In the method of fixing the conductor according to patent FI 80546, an elongate vibration shield stiffening the structure is placed under the bond. The vibration shield modifies the stress-10 field at the point of attachment of the conductor, whereby the service life is extended as the stresses decrease.

Another approach to the vibration problem is the use of vibration dampers. However, separate vibration dampers are difficult to attach to the plastic-coated conductor 15 and may further provide a potential arc damage point to the conductor.

It is an object of the present invention to solve the above-mentioned problem, especially when a threaded bandage is used to tie the conductor to the insulator. This solution to the problem according to the invention is characterized in that at least one end of the helical section is associated with a second helically prestressed helical section with an inner diameter larger than the outer diameter of the conductor.

In order to maximize the vibration damping effect of the helical bandage according to the invention, it is preferred that the second helical portion extends at least from the point of attachment of the stationary stationary wave conductor in the case of oscillations typical of the conductor to the maximum amplitude point of the first half wave.

The threaded bandage according to the invention will now be described in more detail with reference to the accompanying drawing, which shows the attachment of a conductor to the neck of an insulator using a threaded bandage according to the invention.

Figure 1 shows a situation in which the conductor 1 is attached to the neck of the insulator 2 by means of a threaded I: 3 86929 reset according to the invention. This helical bandage comprises a portion 3 corresponding to a conventional helical bandage, which is thus biased into a helical thread having an inner diameter not exceeding the outer diameter of the conductor 1. With this ta-5, by fitting the threaded portion 3 around the conductor, a good mechanical grip on the conductor 1 is obtained. The threaded bandage further comprises a portion 5 which forms a loop around the neck of the insulator 2. In order to obtain a conductor vibration damping property for the helical bond, a prestressed portion 4 with an inner diameter larger than the outer diameter of the conductor 1 is connected to both ends of the portion 3 10 as a helical thread. In practice, this difference in diameter is of the order of a few millimeters. In order to make the vibration damping property as good as possible, the part 4 extends to the conductor 1 in the vibration situation from the point of attachment of the typical standing wave conductor to the point of maximum amplitude of the first half-wave. For a typical PAS conductor, the half-wavelength of the standing wave motion is about 3 m, so the end of the section 4 should be at least 20 to 1.5 m from the insulator 2. Naturally, the length of the section 4 is determined by the characteristics of the conductor to be protected. in connection with the above-mentioned structures, the optimal total length of the threaded tie will be slightly different from the above-2 5 va.

As the material of the first helical portion 3 of the spiral bandage as well as the helical thread portion 4 integral therewith, an insulating weather-resistant plastic such as hard PVC or PE can be most preferably used. If necessary, the properties of these materials can be improved with various fiber reinforcements. Plasticized steel wire can also be used as the material of the spiral bandage according to the invention.

The threaded bandage according to the invention has been described above by means of only one exemplary embodiment, in which the actual threaded bandage and its associated vibration damping portions form a unitary assembly with a loop 5 in the middle of the threaded bandage binding portion 3 for placing the insulator on the neck. In another conventionally used type of helical bandage 5, the helical bandage forms a U-shaped loop in the bottom of which the neck of the insulator is placed and the threaded portions of which then overlap partly on the conductor and partly on top of each other. This type of helical bandage is also suitable for modification in accordance with the invention by attaching a conductor vibration damping portion to one end of this U-shaped helical bandage 10. Since two such U-shaped helices are conventionally used in connection with each conductor attachment point, an installation solution is created in which the conductor vibration damping portions associated with different threads will be located on different sides of the attachment point, as in the design alternative shown in the figure.

Claims (3)

A spiral joint for attaching a conductor, especially a coated blank lead (1), to an insulator (2) comprising a helical biased helical portion (3), the inside diameter of which corresponds to the outer diameter of the conductor at most, and a neck around the insulator (2) Applicable loop (5), characterized in that at least one helical section (3) is connected to at least one helical biased helical section (4), the inside diameter of which is larger than the outer diameter of the conductor (1). 2. A spiral joint according to claim 1, characterized in that the second spiral joint (4) extends at least over the maximum amplitude point of a first conductor attachment point calculated from the leading position of a swivel state for the conductor (1). Spiral joints according to claim 1 or 2, characterized in that at least the material of the second spiral section (4) is plastic, especially fiber-reinforced plastic, or plastic-coated frame.