The Reasons Why High-Voltage Cables cannot be Buried Underground

Ultra-high voltage transmission refers to the use of 500 kV-1000 kV voltage levels to transmit electricity. 

If the 220 kV transmission index is 100%, the relative investment per kilometer of UHV transmission, the relative cost per kilowatt-hour electricity transmission hundred kilometers, and the consumption of metal materials, etc., have been significantly reduced, and the line corridor utilization rate has been significantly improved. 

In our daily life, we can often see the overhead ultra-high voltage transmission project, whether we have thought about such a question. 

Why can not be like the city underground cable, high-voltage power lines are buried underground?

The current underground cables are generally of lower voltage level. The transmission of lines with high voltage levels is often overhead, which is mainly a factor of cost and technology.

Underground cables are more complex than overhead lines in structure and have high technical requirements. 

Manufacturing, and construction difficulties, coupled with the cable buried underground, not easy to find faults, overhaul, and maintenance are also more difficult. 

And in terms of cost, generally, the same voltage level of the underground cable costs 3 to 5 times higher than the overhead lines.

In particular, we commonly high voltage level lines, often used for long-distance transmission. 

If underground cables are used, especially for long-distance transmission often through complex terrain, the cost and technical requirements will be even more skyrocketing.

On the other hand, it is also the inherent "hard" underground cable itself. 

Overhead lines in the air in good thermal conditions, while the air around the underground cable does not flow, difficult to dissipate heat, which largely limits the level of power underground cables can transmit. 

The important thing is that ultra-high voltage transmission has not been able to find an effective insulation material to do the outer skin insulation layer of the wire. 

Therefore, ultra-high voltage wires are bare and cannot be buried by underground. 

There are distributed capacitances around the wires, through which the current can leak out, increasing the consumption on the one hand. 

On the other hand, if there are any animals close by, there will also be the risk of electric shock.

Air is an insulator, but the Earth is a conductor. In the air, as long as the wire is direct there can be, but in the underground, to add a layer of insulation shell outside the wire. 

Otherwise, the electricity in the wire did not go far, and the leakage of electricity will leak all that is left. Underground cables are more complex than the structure of overhead lines, high technical requirements, manufacturing, and construction difficulties, coupled with the cable buried underground, not easy to find faults, overhaul, and maintenance are also more difficult. 

Generally speaking, the cost of underground cables of the same voltage level will be several times or even tens of times that of aerial high-voltage lines.

Ultra-high voltage cables buried underground have both safety and economic problems. 

If a fault occurs, the inspection and repair of the cable is a very large project, and cannot afford to toss and turn. Therefore, the current UHV cables should be hung high in the air.

Underground cable conductors outsourced insulation and protective layer manufacturing are very strict. 

There is no danger of the human body touching the outer sheath of the cable normally. 

The laying of cables is also very careful, and most of the cables are buried in special cable trenches, cable drains, or cable tunnels, which are well isolated and protected by safety. 

The depth is generally less than half a meter, and the higher the voltage level, the deeper the cable is buried. 

Moreover, there will be a cable work well or a cable marker stake as a marker every few dozen meters on the ground where the cable is buried to remind people of safety. 

Therefore, underground cables generally do not cause danger to residents.

Advantages of Using High-Voltage Overhead Lines

The advantages of overhead lines are simple structure, convenient erection, low investment, large transmission capacity, high voltage, good heat dissipation conditions, and easy maintenance.
Compared with overhead lines, cable lines have the following advantages:
(1) Not easily affected by the surrounding environment and pollution, high reliability of power delivery.
(2) The insulation distance between the lines is small, occupying less space, with no interference waves.
(3) Underground laying, does not occupy the ground and space, is both safe and reliable, and is not easy to expose the target.