Overhead power lines generally are devided into low voltage and high voltage, low voltage overhead line is generally four wires, showed glyph arrangement, high pressure is three roots, is tasted glyph arrangement, tower must be high tension line, is generally two a total of six. Low-voltage wire generally used to flex, seldom used now, replaced by cable, high-voltage lines are bare, the core is steel wire, the appearance is aluminum wire, commonly known as steel core aluminum stranded wire. The overhead cable is also called the cable, not the overhead line.
The overhead line set up in the air by wire tower and cement tower, usually bare wire. Overhead line is low cost, but it occupies a large channel area, and is the main line type. Overhead lines by wire, shielding wire, towers, insulators and fittings such as forming the wire: power transmission can lightning line: the lightning current into the earth to protect power lines from lightning Tower: support insulator of conductor and ground wire: the conductors and tower keep insulating fittings: support, splice, to protect the wire and grounding wire, connection and protect the insulator.
In general high-voltage lines use overhead cable, high-voltage lines because of very high above the ground, in order to reduce the cost. Therefore, the use of bare conductor, if it is in underground or near buildings, must choose the insulated cable. The electric voltage through the high voltage line is high in the current large, easy to heat insulation, can burn the skin, even skin breakdown.
Under high pressure, some of the materials, such as rubber, plastic, dry wood, and so on will also become a conductor, it can not afford the insulation effect. If you are still in the high voltage line package insulation, it is to spend more money, wasted money and material.
The surface of the high voltage wire is not covered with insulation, it is hung on the high tower, it may be due to contact with the tower and leakage. In order to prevent this phenomenon, high voltage wires are always hanging below long string good insulation insulator, making high tension line and tower insulation.