- Jun 28, 2020-
Power cables generally consist of three parts: core, insulating layer and protective layer. The core is used to conduct electricity; the insulation layer is to isolate the core conductor and the protective layer to prevent leakage; the protective layer is used to prevent the cable insulation layer from being injured and damp, and to prevent the outflow of liquid insulation (insulating oil).
There are two types of core cables: copper core and aluminum core. The cross-sectional shape of the core is round, semi-circular and sector. Three-core and four-core low-voltage cables use fan-shaped cores. According to the different types and specifications of the cable, the core can be made into a single entity or a stranded core. The stranded core is formed by twisting round single wires and shaped single wires.
Features of various insulation structures:
(1) Oil-paper insulated cables are mainly divided into viscous impregnated paper insulation and non-drip, which are generally used in 3-35KV systems. Viscous impregnated paper insulated cable: simple structure, convenient manufacturing, low price, easy to install and maintain, and long life; it is not suitable for high-drop laying, and the insulating oil is easy to flow. Non-drip impregnated paper insulated cable; the cost is slightly higher than that of viscous paper insulation, the working life is longer, and it can be laid with high drop.
(2) Plastic insulated cables commonly include polyvinyl chloride, polyethylene and cross-linked polyethylene cables.
1) PVC insulated cable. The installation process is simple, the installation and maintenance are convenient, and it can be adapted to high-drop installation and is non-combustible; the working temperature has a significant impact on its mechanical properties. Generally used in 6KV and below systems.
2) Polyethylene insulated cable. It is suitable for high-drop laying, has good process performance and is easy to process, but it is easy to prolong combustion, easy to deform when heated, and easy to cause stress cracking. Used less frequently.
3) Cross-linked polyethylene cable. The cross-linked polyethylene cable has a higher allowable temperature rise, so it has a larger allowable current carrying capacity and good heat resistance. It is suitable for high-drop laying, easy to install and maintain, and has poor anti-corona and free discharge performance. Cross-linked polyethylene cables are now more and more widely used, suitable for various voltages.
(3) Rubber insulated cable
Rubber insulated cables are flexible, easy to bend, and flexible. They are suitable for multiple disassembly and assembly lines, but they have poor corona resistance, ozone resistance, heat resistance and oil resistance, so they can only be used as low voltage cables. Protective layer structure In order to prevent mechanical damage, electrochemical corrosion and moisture intrusion, the cable core and insulation layer of the power cable have a strict protective layer. Take XLPE insulated and PVC sheathed power cables as examples to illustrate the protective layer structure of power cables.
The conductor is covered with a layer of semiconductor shielding layer, called the inner semiconductor shielding layer, which is used to prevent the electric field decomposition and corrosion caused by the long-term effect of the conductor electric field on the cross-linked polyethylene insulation 3. A layer of semiconductor shielding is also covered outside the cross-linked polyethylene insulation 3, which is called an outer semiconductor shielding layer.
There is a layer of copper tape shielding outside the outer semiconductor shielding layer. Their role is to weaken the effect of the external electric field on the cross-linked polyethylene to ensure good insulation performance. The copper tape shield is also used as a welding point for cable protective grounding. Outside the copper tape shielding, fillers are filled between the three cores, and the outermost layer is a three-phase turnkey steel ladle tape and a PVC outer protective sleeve.