The basic structure of the cable
2019-06-24
The basic structure of the cable is mainly composed of three parts: the conductive core for the transmission of electrical energy; insulation to ensure that the power along the core transmission, the electrical wire and the outer core isolation; protective layer from the role of protective seal, so that the insulation is not immersed in moisture , Without external damage, to maintain insulation performance.
Power cables are generally made according to a certain voltage level, the voltage levels were 0.5kV, 1,3,6,10,20,35,60,110,220,330kV. One of the 1kV voltage level power cable used the most. 3 ~ 35kV voltage level of power cables in large and medium-sized buildings within the main power supply lines are often used. 60 ~ 330kV voltage level of the power cable used in the use of overhead lines should not be used as the transmission lines and over the river, submarine laying and other occasions. According to the voltage can be divided into low-voltage cable (less than 1kV) and high-voltage cable (greater than 1kV). It is also divided into low voltage power cable, medium voltage power cable (1 ~ 10kV) and high voltage power cable from the aspects of construction technical requirements, cable connector, cable terminal structure and operation and maintenance.
2. Cable according to the wire core cross-sectional area classification
The conductive cable of the power cable is made according to a nominal cross-sectional area of a certain grade, making it easy to manufacture and design and construction. China's power cable nominal cross-sectional area of 2.5,4,6,10,16,25,35,50,70,95,120,150,185,240,300,400,500,600 mm2, a total of 19 species. High-pressure oil-filled cable nominal cross-sectional series of specifications for the 100,240,400,600,700,845 mm2 a total of six kinds. Multi-core cable is the largest cross-section of the phase prevail.
3. Sort by the number of cores
Power cable conductive core line with 1 to 5 core 5 kinds. Single-core cable for single-phase AC, DC and special occasions (high-voltage motor leads). 60kV and above voltage level of oil-filled, inflatable high-voltage cable for single-core. Two-core cable is used to transmit single-phase alternating current or direct current. Three-core cable for three-phase AC power grid, widely used in 35kV below the cable line. Four-core cable for low-voltage distribution lines, neutral point of the TT way and TN-C way power supply system. Five-wire cable for low-voltage distribution lines, neutral grounding TN-S way power supply system. Both the core and the four core are low voltage 1kV below the cable.
4. Classification by insulation
Oil-immersed paper insulated power cable: it is the oldest, most widely used and most commonly used cable, its low cost, long life, heat resistance, electrical stability and stability. In a variety of low-voltage power cables have a wide range of applications. It is usually made of paper as the main insulation, impregnated with insulating impregnation made of full. According to the situation of impregnation and insulation structure is different, divided into the following. Ordinary viscous impregnated paper insulated cable, the impregnant is composed of low-pressure cable oil and rosin mixed viscous impregnant. According to the different structure, but also divided into uniform package, split lead (aluminum) package and split phase shield type. Plastic insulated cable: plastic insulated cable manufacturing is simple, light weight, terminal head and middle head easy to manufacture, bending radius is small, laying simple, easy maintenance, a certain resistance to chemical corrosion and water resistance, the use of high drop and vertical laying occasions. Plastic insulated cables are PVC insulated cables and XLPE insulated cables. The former for 1kv below the cable line, which is used for more than 10kV to high-voltage cable lines. Rubber insulated cable: because the rubber is flexible, stable performance, have better electrical, mechanical, chemical properties, a large number of cables for the following 1kV. Flame-retardant PVC insulated cable: The common drawback of the three cables in front is that the material is flammable. When an accident occurs in the line or at the joint, the cable may burn due to local overheating and expand the range of accidents. Flame-retardant cable is in the PVC with the addition of flame retardants, even if the fire barbecue will not burn. Belonging to a kind of plastic cable, for 10kV below the cable line.
Insulated wire and hanging insulated wire strand design safety factor should not be less than 3. The self-weight load of the stranded wire with the insulated wire shall include the insulation wire, the strand, the quality of the insulation support and the 200 kg construction load. The minimum cross section of the strand shall not be less than 50 mm2. Different metals, different specifications, different twisted wire and non-bearing line of the bundling line is strictly prohibited in the range from the connection. Within a range, each conductor should not exceed a bearing joint. The fixing point of the joint from the wire shall not be less than 500mm. Insulation bracket safety factor should not be less than 5, the insulation pull rod damage is not less than 90% of the wire to calculate the pull force. And the insulation support and insulation rod damage stress should meet the maximum short-circuit electric power requirements.
