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High voltage overhead transmission lines and high-voltage cables, what's the difference?

Information Source:Henan Huadong Cable Co., Ltd Release date:2014-02-27

The transmission line has two kinds, one is the overhead line the most common, it generally use the bare wire insulation, through the tower stands on the ground as support, the conductor insulator suspension in the tower; the other is the power cable, the cable which uses a special processing manufacturing and become, buried in the underground or laid in cable tunnel.

The transmission capacity and transmission distance power transmission line and voltage. Line voltage higher transport distance farther. According to the transmission distance and capacity to determine the voltage circuit and system required.

1 overhead transmission line routing overhead line tower transmission lines, conductors, insulators, set up above the ground.

Overhead transmission line

Overhead transmission line

Good by the conductive metal wires are made, thick enough cross section (to maintain proper flow density) and large radius of curvature (to reduce corona discharge). EHV transmission is to use more split conductor. Overhead ground wire (also known as the lightning line) is arranged above the transmission line, used to protect the lines from lightning strikes. Transmission line important usually use two overhead ground wire. By a single suspension insulator string (or rod) insulators which are connected in series, to meet the insulation strength and mechanical strength requirements. The number of each string insulator is determined by the voltage level of transmission. The tower is made of steel or reinforced concrete, is the main supporting structure of overhead transmission line. Erection of overhead lines and convenient repair, low cost. Effect of overhead transmission lines to consider the temperature change, it is the strong storms, lightning, Yu Lin, ice, floods, wet fog and other natural conditions at design time. Overhead transmission line path also have enough ground corridor width and clearance.

The maximum transmission power transmission lines in the comprehensive consideration of technical, economic and other factors are identified, called the transmission capacity of the line. Transmission capacity in general and the transmission voltage is proportional to the square of the. Therefore, to improve the transmission voltage is the main technical means to realize large capacity and long distance transmission, but also a symbol of the development level of transmission technology. The current global (including the developed countries in Europe and America) is widely used in overhead lines as the main means of conveyance of electricity.

2 power cable line

Power cable by wire, insulation layer and protective layer with a single core, dual core and three core cable.

Underground lines used for overhead line construction difficult areas, such as transmission city or special cross section. At present, the cable transmission, mainly from the point of view of city landscape and the line security. But the cable line fault finding time and repair time is very long, to the normal operation of power grid reliability and electricity brings the serious influence. So in power grid construction, cable lines to replace all the overhead line or unable to realize.

Cable line features:
(1) power supply reliability.
(2) does not occupy the ground and space
(3) do not use the pole, saving wood, steel, cement
(4) the operation and maintenance are simple, save repair cost line.
(5) cable price expensive, hard line branch, cable construction process joint is complex, difficult to find the fault point, not timely processing of the accident.

3The power frequency electric field, magnetic field overhead lines and cable lines

3.1 power frequency electric field voltage electric field, voltage, and the population size and line overhead line power frequency electric field intensity of the distance from the. According to HJ_T_24-1998 "500kV EHV power transmission and transformation project electromagnetic radiation environmental impact assessment of technical specifications", residential power frequency electric field intensity of the implementation of 4kV/m standard, power grid construction project only by the environmental impact assessment, in full compliance with the standards to the construction.

The underground tunnel and cable buried deep in the 7-10 meters, the tunnel reinforced concrete and surface soil layer, the power frequency electric field on the ground surface is very small, and tend to the environment background value. Therefore, the power frequency electric field intensity of cable line can be ignored.

3.2 power frequency magnetic field

An electric current produces a magnetic field, the current size, and population size and line overhead line power frequency magnetic induction intensity of distance and other relevant. According to HJ_T_24-1998 "500kV EHV power transmission and transformation project electromagnetic radiation environmental impact assessment of technical specifications", residential power frequency magnetic field strength of the implementation of 0.1mT standard. The cable lines due to shield tunnel reinforced structure, and away from the larger reason and the surface, the surface of the power frequency magnetic field intensity is generally not more than 0.003mT. Along with the increase of distance and cable tunnel level, power frequency magnetic field intensity decay rapidly, more environmental background value.

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