• Categories:Industry News
• Time of issue:2019-04-08 14:12

(Summary description) Ultra-high voltage power transmission refers to the use of 500 kV - 1000 kV voltage level to transmit electrical energy. If the 220 kV transmission index is 100%, the relative investment per kilometer of ultra-high voltage transmission, the relative cost of 100 kilometers per kilowatt-hour transmission, and the consumption of metal materials will be greatly reduced, and the utilization rate of the line corridor will be significantly reduced. improve. In daily life, we can often see overhead ultra-high voltage power transmission projects. Have you ever thought about such a question: why can't we bury all high-voltage wires underground like urban underground cables? The current underground cables are generally of low voltage level, and the line transmission with high voltage level is often overhead, which is mainly due to cost and technical factors. The structure of underground cables is more complex than that of overhead lines, the technical requirements are higher, and the manufacturing and construction are difficult. In addition, the cables are buried underground, so it is not easy to find faults, and it is also difficult to repair and maintain. 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 are often used for long-distance transmission. If underground cables are used, especially long-distance transmission often has to pass through complex terrain, the cost and technical requirements will increase linearly. On the other hand, it is also a congenital "hard injury" of the underground cable itself. Overhead lines have good heat dissipation conditions in the air, while the air around underground cables does not flow and it is difficult to dissipate heat, which limits the power level that can be transmitted by underground cables to a large extent. The important thing is For ultra-high voltage transmission, an effective insulating material has not been found to be the outer insulation layer of the wire. Therefore, the ultra-high voltage wires are exposed and cannot be buried underground. There are distributed capacitances around the wires, and current can leak out through these capacitances, which increases consumption on the one hand; on the other hand, if any animal approaches, there is also a danger of electric shock. Air is an insulator, but the earth is a conductor. In the air, as long as the wire is directly placed there, it is fine, but in the ground, a layer of insulating casing should be added to the wire, otherwise the electricity in the wire does not go far, and there will be little leakage left. The structure of underground cables is more complex than that of overhead lines, the technical requirements are higher, and the manufacturing and construction are difficult. In addition, the cables are buried underground, so it is not easy to find faults, and it is also difficult to repair and maintain. Generally speaking, the cost of underground cables of the same voltage level will be several times or even dozens of times that of high-voltage lines in the air. Burying ultra-high voltage cables into the ground has both safety and economic problems. If there is a fault, the inspection and repair of the cables is very huge and cannot stand the toss. Therefore, the current ultra-high voltage cables should be hung high. air. The insulation layer and protective layer of the underground cable conductor are very strict, and there will be no danger for the human body to touch the outer skin of the cable normally. The laying of cables is also very particular. Most of the cables are buried in special cable trenches, cable pipes or cable tunnels, which are well isolated and protected. The depth is generally less than half a meter. deep. Moreover, every tens of meters on the ground where the cables are buried, there will be a cable work well or a cable marker pile as a sign to remind people to pay attention to safety. Therefore, underground cables generally do not pose a danger to residents.