What are the application characteristics of pre twisted power fittings in overhead transmission lines?

2020-01-08 09:30:59 222

1. When the line in the area of heavy icing is applied, the icing will greatly increase the vertical load and horizontal wind load of the line. When the line is not evenly covered with ice, deicing or even galloping in different periods, longitudinal tension will also occur.


In the design of overhead transmission lines in ice covered areas, it is required that the suspension clamps of pre twisted power fittings have a greater grip on the conductors to resist various adverse effects caused by ice covering. The pre twisted suspension clamp is provided with high-performance rubber pad in the inner center, which is in direct contact with the conductor. The pre twisted long conductor is wound on the surface of the rubber pad and the conductor, which has the advantages of no stress concentration point and large grip force. Taking ags5133 pre twisted suspension clamp as an example (according to the test report of China Electric Power Research Institute, the grip strength of this type of pre twisted suspension clamp reaches 65 kn, which fully meets the requirements of conductor grip strength in heavy ice area and is very suitable for heavy ice wire.


In addition, the pre twist anti galloping whip can also be applied to the icing line, which is mainly composed of clamping section, supporting section and anti galloping section. The anti galloping section of the anti galloping whip can constantly change the dynamic shape of the cable under the action of the wind, destroy the air movement of the conductor, thus preventing the conductor from galloping. In addition, because the anti galloping section is not firmly tied to the conductor, there is relative movement or even jumping between the anti galloping section and the conductor when the wind blows, which can play a certain role in deicing when the icing is shallow.


2. Large span transmission lines are characterized by large span, usually using steel or aluminum alloy wires with light weight, small cross-section and large mechanical strength. Its main disadvantage is that it is difficult to eliminate aeolian vibration. According to the operation data and the line research, the wind vibration is the main factor causing the conductor fatigue loss.


The traditional suspension clamp belongs to the bolt type clamp. Its principle is to compress the conductor through the bolt to maintain the grip strength of the hardware to the conductor. The fixture is simple in design and manufacture, low in cost and widely used. However, the statistical results at home and abroad show that almost all of the conductor fatigue damage occurs in the contact part between the conductor and the hardware. Under the action of traditional fittings, the conductor in contact area is easy to produce high dynamic stress and static stress. Although the pre twisted suspension clamp provides enough grip force for the conductor through the new structural design concept, the hardware itself does not need to act on the conductor through the bolt, so that the contact surface between the conductor and the hardware is increased, and there is no stress concentration point at the contact, so the static pressure of the hardware is effectively distributed to the area with large enough conductor. In addition, after winding a certain length of pre twisted wire on the surface of the conductor, the bending stiffness of the conductor contact area can be significantly improved and the dynamic stress can be reduced. The traditional bolt type suspension clamp and pre twisted suspension clamp are installed. Under the same condition, after tens of millions of vibration fatigue tests, the former leads are seriously broken, while the latter leads are undamaged. It can be seen that the pre twisted suspension clamp has a strong anti fatigue performance, which can effectively reduce the fatigue loss of long-span transmission lines.


3. The application of pre twisted suspension clamp in the line with large height difference can be divided into two types: single fulcrum and double fulcrum. In general, single fulcrum can meet the condition of conductor suspension angle less than 30 °, while double fulcrum can be used to 60 °. For transmission lines in mountainous areas, the pre twisted suspension clamp of pre twisted power fittings can meet the requirements of large height difference suspension angle. At the same time, due to the large vertical span and load of the suspension point, compared with the ordinary suspension clamp, the pre twisted suspension clamp can disperse the concentrated stress and provide more grip force for the conductor. Therefore, it has more advantages to use the pre twisted suspension clamp on the lines with large height difference. In addition, due to the large height difference angle of the large height difference line, the traditional fixing method of the anti vibration hammer is easy to produce the phenomenon of hammering when the wire crawls, and the pre torsional anti vibration hammer uses the pre stranded wire to connect the anti vibration hammer. For the conductor, it can not only effectively overcome the problem of slide hammer, but also play the role of anti vibration.