Power cables are cables used to transmit and distribute electrical energy. Power cables are often used in urban underground power grids, power station outlets, internal power supply for industrial and mining enterprises, and under-sea water transmission lines.
In power lines, the proportion of cables is gradually increasing. Power cable is a cable product used to transmit and distribute high-power electrical energy in the trunk line of the power system, including 1-500KV and above various voltage levels and various insulated power cables.
The basic structure of a power cable consists of a core (conductor), an insulation layer, a shield layer, and a protective layer.
The core is the conductive part of the power cable and is used to transport electrical energy. It is the main part of the power cable.
Insulation layer is to electrically isolate the core from the ground and cores of different phases from each other to ensure the transmission of electrical energy. It is an indispensable part of the power cable structure.
15KV and above power cables generally have conductor shields and insulation shields.
The protective layer
The role of the protective layer is to protect the power cable from the intrusion of foreign impurities and moisture, and to prevent the power cable from directly damaging the power cable.
Divided by voltage level
According to the voltage level, it can be divided into medium and low voltage power cables (35 kV and below), high voltage cables (110 kV and above), ultra high voltage cables (275 to 800 kV) and ultra high voltage cables (1000 kV and above). In addition, it can be divided into AC cable and DC cable according to the current system.
Divided by insulation material
1. Oil-impregnated paper-insulated power cables Power cables with oil-impregnated paper as insulation. It has the longest application history. It is safe and reliable, has a long service life, and is inexpensive. The main disadvantage is that the laying is limited by the drop. Since the development of non-drip impregnated paper insulation, the problem of limit drop has been solved, and oil-impregnated paper insulated cables have continued to be widely used.
2. Plastic insulated power cable The insulation layer is a power cable extruded from plastic. Commonly used plastics are polyvinyl chloride, polyethylene, and cross-linked polyethylene. The plastic cable has a simple structure, convenient manufacturing and processing, light weight, convenient installation and installation, and is not restricted by the installation drop. Therefore, it is widely used as medium and low voltage cables, and has a tendency to replace viscous impregnated oil-paper cables. Its biggest drawback is the existence of branching breakdown, which limits its use at higher voltages.
3. Rubber insulation power cable: The insulation layer is made of rubber plus various additives, and after being fully mixed, it is extruded and wrapped on a conductive wire core and vulcanized by heating. It is soft and flexible, suitable for occasions with frequent movements and small bending radius.
Divided by voltage level
1. Low-voltage cable: suitable for fixed laying on power transmission and distribution lines with AC 50Hz and rated voltage 3kv and below for power transmission.
2. Medium and low voltage cables: (generally 35KV and below): PVC insulated cables, polyethylene insulated cables, XLPE insulated cables, etc.
3. High-voltage cables: (generally 110KV and above): polyethylene cables and XLPE insulated cables.
4. Extra-high voltage cable: (275 to 800 kV).
5. UHV cables: (1000 kV and above).
1. Occupies less land. It is usually buried in the soil or laid indoors. In trenches and tunnels, the insulation distance between the lines is small, no towers are used, it occupies less land, and basically does not occupy space on the ground.
2. High reliability. Affected by climatic conditions and surrounding environment, transmission performance is stable and reliability is high.
3. It has more favorable conditions for the development of ultra-high voltage and large capacity, such as low temperature and ultra-conductive cables.
4. Large distributed capacitance.
5, less maintenance workload.
6, the possibility of electric shock is small.
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