18. What are the requirements for the mechanical strength of cable conductor connection points?
Answer: The mechanical strength of the connection point is generally lower than the tensile strength of the cable conductor itself. For fixedly laid power cables, the tensile strength of the connection point is required to be no less than 60% of the tensile strength of the conductor itself.
19. What are the main properties of the insulation layer material of power cables?
Answer: It should have the following main properties:
(1) High breakdown strength;
(2) Low dielectric loss;
(3) Quite high insulation resistance;
(4) Excellent discharge resistance;
(5) Has certain softness and mechanical strength;
(6) The insulation performance is long-term and stable.
20. The applications of wires and cables are mainly divided into three categories:
(1), power system
The wire and cable products used in the power system mainly include overhead bare wires, busbars (busbars), power cables (plastic cables, oil-paper power cables (basically replaced by plastic power cables), rubber sheathed cables, overhead insulated cables), branch cables (replacing some busbars), electromagnetic wires, and electrical equipment wires and cables for power equipment, etc.
(2), Information transmission system
The wires and cables used in information transmission systems mainly include local telephone cables, television cables, electronic cables, radio frequency cables, optical fiber cables, data cables, electromagnetic wires, power communication or other composite cables, etc.
(3), mechanical equipment, instrumentation systems
In addition to overhead bare wires, almost all other products in this section are applied, but mainly power cables, electromagnetic wires, data cables, instrumentation cables, etc.
21. Wire and cable products are mainly divided into five categories:
(1), Bare wires and bare conductor products
The main characteristics of this type of product are: pure conductor metal, without insulation and sheath layers, such as steel core aluminum stranded wire, copper aluminum busbar, electric locomotive wire, etc.; the processing technology is mainly pressure processing, such as smelting, rolling, drawing system, stranding/compression stranding, etc.; the products are mainly used in suburban areas, rural areas, user main lines, switch cabinets, etc.
(2), power cable
The main features of this type of product are: extruding (winding) the insulation layer on the conductor, such as overhead insulated cables, or twisting several cores (corresponding to the phase line, neutral line and ground wire of the power system), such as overhead insulated cables with more than two cores , or add a sheath layer, such as plastic/rubber sheathed wire and cable. The main process technologies include drawing, stranding, insulation extrusion (wrapping), cabling, armoring, sheath extrusion, etc. There are certain differences in the different process combinations of various products.
The products are mainly used in the transmission of strong electric energy in generation, distribution, transmission, transformation and power supply lines, with large currents (tens of tens of amps to thousands of amps) and high voltages (220V to 500kV and above).
(3) Wires and cables for electrical equipment
The main features of this type of products are: a wide range of varieties and specifications, a wide range of applications, most of the operating voltages are 1kV and below, and new products are constantly derived for special occasions, such as fire-resistant cables, flame-retardant cables, low-smoke halogen-free/low-smoke Smoke-resistant low-halogen cables, termite-proof, mouse-proof cables, oil-resistant/cold-resistant/temperature-resistant/wear-resistant cables, medical/agricultural/mining cables, thin-walled wires, etc.
(4), communication cables and optical fibers (brief introduction)
With the rapid development of the communications industry in the past two decades, products have also developed at an alarming rate. From the simple telephone and telegraph cables in the past, it has developed into thousands of pairs of voice cables, coaxial cables, optical cables, data cables, and even combined communication cables.
The structural dimensions of such products are usually small and uniform, and require high manufacturing precision.
(5), electromagnetic wire (winding wire)
Mainly used in various motors, instruments, etc.
Derivatives/new products of wires and cables are mainly due to different application situations, application requirements, convenience of equipment, and reduction of equipment costs. They use new materials, special materials, or change the product structure, or improve process requirements, or will be different. A variety of products are produced by combining them.
Use different materials such as flame-retardant cables, low-smoke halogen-free/low-smoke low-halogen cables, termite-proof, mouse-proof cables, oil-resistant/cold-resistant/temperature-resistant cables, etc.; change the product structure such as: fire-resistant cables, etc.; improve technology Requirements such as: medical cables, etc.; combined products such as: OPGW, etc.; convenient installation and reduced equipment costs, such as: prefabricated branch cables, etc.
22. What requirements should be met when laying cables?
Answer: The following requirements should be met:
(1) In terms of safe operation, try to avoid all kinds of external damage and improve the power supply reliability of cable lines;
(2) Economically, consider the aspect of saving the most investment;
(3) In terms of construction, the path of the cable line must be convenient for work and maintenance after operation.
