What is an overhead cable？
Aerial cables have the main advantages of high power supply reliability, good power supply security, convenient erection and maintenance, and reasonable economy. The use of overhead cables greatly reduces the occurrence of various dangerous accidents, ensures personal safety, and reduces the maintenance and repair work of the line. What is the difference between overhead cables and buried cables? Let Zhengzhou Jinshui Cable Group take everyone to understand.
一、Overhead Cable Definition
Overhead cable (full name overhead insulated cable) is an overhead wire equipped with an insulating layer and a protective sheath. It uses cross-linked polyethylene as insulation and is a new way of transmitting circuits.
1. It can simplify the structure of line poles and towers, and can even be laid along the wall, which not only saves line materials, but also beautifies the city streets.
2. It is conducive to improving and enhancing the safety and reliability of the power distribution system. It not only greatly reduces the risk of personal electric shock casualties, avoids short circuits caused by foreign objects, reduces the workload of maintenance, but also greatly improves the power consumption of cable lines. Take advantage of.
3. Save the line power loss and reduce the voltage loss, the line reactance is only 1/3 of the ordinary bare wire line reactance.
4. Go deep into the high-voltage load center to improve voltage quality and reduce power loss.
5. Reduce the gravity requirements of the line, reduce the investment of fittings, and reduce the labor intensity of workers when setting up the wire.
6. Reduce the space and land area occupied by the path of overhead transmission lines, making it more convenient for lines to shuttle in narrow areas. Compared with overhead bare lines, the line corridor can be reduced by 1/2.
7. Reduce wire corrosion, thereby improving the service life of the line and the reliability of power distribution.
8. The technical upgrade of the line prolongs the maintenance cycle of overhead cables and reduces the maintenance workload.
1. The allowable current carrying capacity of high-voltage insulated overhead wires is smaller than that of bare wires, because after the plastic layer is added, the heat dissipation of the wires is poor, and the shape of overhead insulated wires should be higher than usual. Matched to 95mm2.
2. The wire diameter of the high-voltage insulated overhead wire is larger, and with the addition of plastic sheath, the wire diameter is one grade larger than that of the steel-cored aluminum stranded wire with the same cross-section. Although insulated wires have many advantages, the unit cost is higher than that of bare wires, about twice as high for medium-voltage lines, and about 25% higher for low-voltage lines.
Environmental requirements for laying overhead insulated cables
1. When laying cables, the ambient temperature should not be lower than -20°C. When laying below -20°C, the cables must be heated in advance.
2. When laying overhead cables, the bending radius of rated voltage 1kV overhead insulated cables should not be less than 6 times the outer diameter of the cable, and the bending radius of overhead insulated cables with rated voltages of 101kV and 35KV should not be less than 15 times the outer diameter.
3. The erection method of the cable is the same as that of the overhead bare conductor, and it still needs to be fixed on the insulator of the cross arm, but the distance can be appropriately reduced.
4. The cable should be used in conjunction with specially designed metal appliances for overhead insulated cables.
5. During laying construction and storage, attention should be paid to the sealing of the cable end to prevent the cable from entering water and reducing its performance.
6. The long-term operating temperature of overhead cables (that is, the long-term allowable operating temperature of the cable conductive core), XLPE insulation should not exceed 90 ° C, high-density polyethylene insulation should not exceed 75 ° C; polyethylene, polyvinyl chloride insulation should not exceed 70°C; cross-linked polyethylene insulation should not exceed 250°C during short circuit; high-density polyethylene, polyvinyl chloride insulation should not exceed 150°C, and the longest duration should not exceed 5 seconds.
Use of overhead insulated cables
Overhead insulated wire and cable is a new type of overhead transmission line for electric energy transmission, and it has become a preferred product for power grid construction and transformation of 10kV transmission lines.
二、The difference between overhead cables and buried cables
1. Different meanings
Overhead cables mainly refer to overhead open wires, erected above the ground, and are transmission lines that use insulators to fix the transmission wires on the towers standing on the ground to transmit electric energy.
Underground cables are different from overhead lines. Underground cables are usually laid in underground cable trenches, tunnels, or pipelines, so they are also called buried cables.
2. Different materials
Aerial cables generally use steel-cored aluminum strands as conductors. Steel has high strength and is not easy to break. Aluminum has a low specific gravity and is easy to install. It can also be used for overhead interception. If the distance is not long, the steel core can also be used. Use aluminum wire directly. If there is insulation, it is generally weather-resistant black polyethylene or cross-linked polyethylene, generally without a sheath.
Underground cables generally use aluminum as the conductor, polyethylene as the insulation, and polyvinyl chloride or polyethylene as the sheath layer.