Overhead cable is the main part of overhead power line. Its function is to transmit current and power. It is divided into overhead conductor and overhead insulated cable. Overhead conductors include AAC conductors, which are commonly used in distribution lines below 35KV; AAAC conductor, commonly used in distribution lines above 110kV; ACSR conductor is widely used in high voltage lines. Overhead insulated cables usually use multi strand conductors. It can be used for medium voltage and low voltage power lines. Depending on the type of insulation, it can be PE, PVC or XLPE insulated cables.
This kind of cable hanging on the pole at a certain height from the ground is called overhead cable, which is fully called overhead insulated cable. It is an overhead wire with insulating layer and protective skin. It adopts a special cable similar to the production process of cross-linked cable. It is a new transmission mode between overhead wire and underground cable.
The main characteristics of overhead cable are high power supply reliability, good power supply safety, convenient installation and maintenance, economy and rationality. Its main technical parameters include weather resistance, insulation grade, internal and external semi-conductive shielding layer. Compared with underground cables, although overhead cables are more vulnerable to external influence, unsafe and unsightly, overhead cables are easier to erect, and have the main characteristics of high power supply reliability, good power supply stability, convenient erection and maintenance and reasonable economy. Therefore, they are far away from the signal tower, and the number of users is small and changes greatly, It is still widely used where it is difficult to lay underground cables.
Overhead cables are generally single core cables. According to their structure, they can be divided into hard aluminum wire structure, hard drawn copper wire structure, aluminum alloy wire structure, steel core or aluminum alloy core support structure and self-supporting three core grain structure (the wire core can be hard aluminum or hard copper wire), etc.
Seeing the above, many people may ask: Why are the conductors of overhead cables aluminum? The reason is also due to the characteristics of aluminum wire, including its conductivity, density, insulation, cost, etc. the specific explanations are as follows:
1. The conductivity of aluminum is second only to copper, and its conductivity is only two-thirds of that of copper, but its density is only one-third of that of copper. The density of copper is greater than that of aluminum, that is, it is heavier, which will increase the difficulty of overhead. Therefore, the quality of aluminum wire is only half that of copper wire, which is more suitable for high-altitude use.
2. The oxide film on the surface of aluminum not only has corrosion resistance, but also has certain insulation. Therefore, aluminum is widely used in electrical manufacturing, wire and cable industry and radio industry.
3. The cost of aluminum is cheaper than copper, and the technical economy of overhead lines is better than copper.
4. Connection between indoor copper wire and aluminum wire. The connection between copper wire and aluminum wire will have electrochemical reaction. After the aluminum wire is oxidized, a layer of gray white material will be generated on it, which is prone to line failure. Therefore, try to connect with the copper slot terminal. The cable erected at high altitude is different. It will not cause line failure. Therefore, only aluminum wire is needed.
To sum up, high-altitude cables are the cables we see on high-altitude poles. The reason why aluminum wire is used instead of copper wire is that compared with copper wire, aluminum wire has its uniqueness and is more suitable for high-altitude. I hope you know more.