Question: What are the common problems that transmission towers often encounter during use? I'm referring to structural issues, such as the failure of certain components. Additionally, for tall towers with long spans, is there a widespread phenomenon of component fatigue failure in the parts where the conductors are supported? I'm referring to the fatigue failure caused by vibrations resulting from conductor swaying. The reason why I thought of this issue was that I read a piece of literature last year, which stated that the conductor support limbs of the large-span transmission towers in North America often suffered damage. However, such content is rarely mentioned in domestic literature, and I haven't found it either now.
Viewpoint One:
In actual engineering projects, what often occurs is that the fatigue failure causing tower collapse has not been observed yet. This might be related to the fact that there are relatively few large-span structures in China and the history is relatively short. The accidents are usually caused by design flaws, improper layout of guy wires during construction, theft of components, and incorrect material selection during processing. The vibration caused by the wire swaying has to pass through the fittings, porcelain insulators, fittings, and then reach the tower. So, when the wire sways, after going through such a long string of porcelain insulators, how much impact can it have? I'm not familiar with the situation in North America. It's speculated that it's a low-voltage crossing, and the string of porcelain insulators might be shorter. In China, large crossings are often high-voltage, and low-voltage crossings are costly and not cost-effective. The "low voltage" I'm referring to is below 110KV. In addition, the connection of iron towers and porcelain bottles is first done with fittings (U-shaped bolts), then the hanging plate, and finally the angle steel. Fatigue failure may not occur for the fittings because they can rotate. The hanging plate is more likely to have such a problem. In actual engineering design, the hanging plates are usually thick and large, with ample safety reserves. The possibility of fatigue failure for the angle steel is also low because it is connected by bolts. To cause damage, it would have to start from the bolts and the gaps between them, and the positions are not fixed. Therefore, the possibility of such a failure is also not high.
Our country is different from foreign countries. The maintenance department regularly inspects the porcelain bottles. Even if there are any problems, they can be detected. Unlike foreign countries where inspections are rarely conducted from the towers.
In the early foreign-style towers, were there any welded components at the ends of the crossbars? If so, fatigue might occur.
Furthermore, the design in North America is highly dependent on the experience of engineers. It is not ruled out that there might be issues with the selection of conductor tension. In our country, there are restrictions on the conductor tension under the annual average temperature, which is also a powerful measure against fatigue failure.
If the tension of the wire is improperly selected, it may cause the wire to suffer fatigue damage at the outlet of the clamp. In engineering, this can be prevented by implementing measures such as installing shock absorbers, pre-wound wires, special clamps, and limiting the outlet angle. There have also been many studies on this topic in China.
Viewpoint Two:
The above-mentioned "vibration caused by the swinging of the conductors can be prevented in engineering by measures such as installing shock absorbers, pre-wound wires, special line clamps, and limiting the outlet angle". I have doubts about the effectiveness of these passive control measures.
The large-span high-voltage transmission tower line system (such as the transmission tower line structure system in Jiangyin, 500kv) will experience intensified vibration of the transmission tower's upper structure due to the coupling vibration between the conductors and the transmission tower when subjected to dynamic loads such as strong winds and earthquakes. If the conductor sway is severe enough to cause the fatigue failure of the conductor support limbs as described by Jieyun, then the conductor's sway will further intensify the vibration of the upper structure of the transmission tower. Conversely, the intense vibration of the upper structure of the transmission tower will also have an adverse effect on the conductor sway. The complex coupling vibration effect between the two is difficult to ensure safety solely through the aforementioned preventive measures. Regarding how to solve these problems, Wang Zaimin, a doctoral student from Tongji University, has relevant control methods in his thesis. However, they are only theoretical and the methods do not have significant breakthroughs. Source: Power Transmission and Distribution Equipment Network
I also want to conduct research in this area. On one hand, I haven't done much design work in this field and only have a superficial understanding of it in theory. On the other hand, the transmission tower line structure system is characterized by its unique complexity and nonlinearity, making system identification difficult (there are too many general model assumptions and the accuracy is not high).
However, I have an idea: In a certain area near the connection of the transmission tower lines, parallel conductors should be connected with rigid rods at regular intervals to enhance the overall stiffness of the conductors. Then, conductors and the transmission tower should be symmetrically connected with ropes of appropriate size and initial stress, just like the design principle of the mast in the design of the mast structure (because the vibration control of the transmission tower is much easier, such as TMD, AHD, and semi-active control based on MR dampers, etc.). The transmission tower is regarded as a larger rigid foundation (because the vibration control of the transmission tower is much easier, for example, TMD, AHD, and semi-active control based on MR dampers, etc.).
Furthermore, can the MR damper control device be equivalent to a cable with a certain initial stress? By utilizing the relative displacement between the conductor and the transmission tower to fully dissipate the vibration energy, it can minimize the coupling vibration between the two, thereby reducing the stress burden on the insulator, lowering the possibility of fatigue failure of the insulator during repeated vibrations, and increasing its service life. On the one hand, it can control the large-scale swaying of the conductor, avoiding unrestricted swaying of the conductor that causes large vibrations of the transmission tower, ensuring the overall stability of the transmission tower, and also reducing the possibility of fatigue failure of the transmission tower.
Since it is unknown whether the aforementioned methods can be implemented in the specific design, and whether the assumption that the transmission tower is regarded as a rigid foundation is reasonable is worthy of discussion and analysis, I wonder if you could offer some guidance to help me figure out the issue. Would it be possible to further proceed with the research based on the aforementioned approach? Of course, for the systematic identification of the transmission tower's line structure system, the identification technology based on intelligent theories (such as neural networks, genetic algorithms, etc.) can be considered. It can be solved by learning first and then applying.