The insulated power source that can transmit large-capacity electricity safely and reliably for a long time is called "power cable". Power cable is a cable with high quality insulation material outside the conductor and various protective layers. It includes na2xy and its main function is to transmit and distribute large-capacity electrical energy in the power system, just like overhead wires. The difference with the overhead line is that power cable can be laid in a variety of environments, safe and concealed, not subject to the interference of external climate change; as well as can be less maintenance, durable (generally requires more than 40 years). However, the structure of the power cable wire for sale is more complex, manufacturing processes, product prices are dozens of times higher than overhead conductors; therefore, generally used in the city does not adapt to the use of overhead lines, such as power transmission and distribution lines and industrial and mining enterprises in the introduction of power and plant trunk power lines; and across rivers and railroad stations, through the underground tunnels. In fact, power lines are overhead wires and power cables together, overhead wires focus on the generation of power transmission, transformation, distribution part, while power cables focus on the use of power distribution, power end, therefore, the production of low-voltage power cables accounted for more than 98%. With the rapid improvement of China's economic level, the proportion of power cables in the power system continues to increase. Such as urban centers, low-voltage overhead lines will be gradually changed to hidden cable lines, suburban and central towns will use overhead insulated cables.
Compared to mv abc cables, power cables can withstand high or even very high working voltage for a long time. Should have very good electrical insulation properties, so power cables can be divided according to the use of voltage level: low voltage (1 kV and below), medium voltage (6 - 35 kV), high voltage (66 - 330 kV) ), ultra-high voltage (500 kilovolts and above).
Power cables such as mv armoured cable can transmit a large current (hundreds of amps or even thousands of amps), so will use a cross-sectional area of hundreds or even thousands of square millimeters of conductive wire core. At the same time, the insulation and other materials used are required to have excellent heat aging properties, while the overall structure can maintain thermal balance.
In order to adapt the cable to various laying methods and use environments (underground, underwater, trench pipe, tunnel, shaft), a variety of combinations of protective layer structure must be used.
In fact, the high-voltage insulation technology, high-current transmission technology, as well as the structural balance and sheath structure on which power cables are based represent the academic level of these aspects in the electrical discipline.