Ultra-high voltage transmission refers to the use of 500 kV-1000 kV voltage levels to transmit electrical energy. If the 220kV transmission indicator is taken as 100%, the relative investment per kilometer of UHV transmission, the relative cost of 100 kilometers per kilowatt-hour of electricity transmission, and the consumption of metal materials will be greatly reduced. In this way, the utilization rate of the line corridor has been significantly improved.
In our daily life, we can often see overhead ultra-high voltage transmission projects. However, have you ever thought about this question: Why can’t all high-voltage cable be buried underground like urban underground cables?
The current underground cables are generally of lower voltage level. The transmission of lines with high voltage levels is often overhead, which is mainly due to cost and technology factors.
First, the structure of underground cables is more complicated than that of overhead lines. Second, underground cables have high technical requirements and are difficult to manufacture and construct. Third, the cables are buried underground, it is not easy to find faults, and it is difficult to repair and maintain them. In terms of cost, the cost of underground cables of the same voltage level is generally 3 to 5 times higher than that of overhead lines.
Especially our common high-voltage lines, which are often used for long-distance transmission. If underground cables are used, especially long-distance transmissions often have to pass through complex terrain, the cost and technical requirements will rise linearly.
On the other hand, it is also the congenital “mutilation” of the underground cable itself. Overhead lines have good heat dissipation conditions in the air, but the air around underground cables does not flow and it is difficult to dissipate heat. Therefore, the level of power that can be transmitted by underground cables is largely limited.
Last but not least, There is still no effective insulation material for UHV transmission as the insulation layer of the wire. Therefore, UHV wires are exposed and cannot be buried in the ground. There are distributed capacitors around the wires, and current can leak out through these capacitors, which increases consumption on the one hand. On the other hand, if any animal approaches, there is also a risk of electric shock. Air is an insulator, but the earth is a conductor. In the air, you just need to put the wires directly there, but in the underground, you need to add layers of insulating shells outside the wires, otherwise the electricity in the wires will not go far, and there will be little leakage left.
The insulation layer and protective layer of the underground cable conductor are manufactured strictly. There will be no danger to the human body in normal contact with the outer skin of the cable. The laying of cables is also very particular. Most of the cables are buried in special cable trenches, cable ducts or cable tunnels. They are well isolated and protected. The depth is generally less than half a meter. The higher the voltage level, the more the cable is buried. deep.
Moreover, every tens of meters on the ground where cables are buried, there will be a cable working well or cable marker pile as a mark to remind people to pay attention to safety. Therefore, underground cables generally do not pose a danger to residents.