Branch cable structure and performance
1. Production and technical standards
Branch cables are developed on the basis of ordinary plastic cables. Due to the development of modern civilization, urban high-rise buildings are becoming more and more popular. In the electrical design of high-rise building distribution systems, power supply reliability, engineering economy and construction convenience are more and more important, and electricity is supplied by ordinary power cables. Contradictions are always difficult to be completely unified, and they can only be focused on different projects. According to the traditional method, there are three commonly used methods in floor power distribution design:
a. Radial type, the underground power distribution room directly supplies power to each floor lead cable. This method has the best reliability, but requires a large number of cables, bridges and large cable wells. The cost is high and the economy is the worst.
b. Link method, the power distribution cable is led to the bottom distribution box, and then the bottom layer is connected to the upper layer by layer. This method is economical, but the more the number of layers, the lower the security system, and the number of security systems is The stages are multiplied, so the reliability is the worst.
c. Partition trunk type, divide a high-rise building into n unit areas, each unit is powered by cable from the power distribution room, and then distributed to each floor in the unit area. This method is relatively reliable and economical and is often used.
d. Mainline cable branching method, one or several trunk cables are taken out from the power distribution room, and each floor is connected to the trunk cable. This method has the best economical efficiency and theoretically has the reliability of radial power distribution. But construction is the most troublesome. What is more troublesome is that when the floor branch is made on the main cable, the quality of the joint is uneven due to the structure of the cable, the construction conditions on site, and the quality of the personnel. The reliability of the actual operation is not satisfactory, but this method makes People thought of making joints with cables, which gave birth to a new generation of building distribution cables - branch cables.
The branch cable is a single-core power cable that has been specially processed as the main cable of the building. According to the structural characteristics and dimensions of each specific building, the branch joint is designed and manufactured together with the branch line and the trunk cable. The on-site construction and management work of the above method (4) is completed by a professional manufacturer, so that the reliability of the joint is greatly improved, and the process consistency also brings the quality consistent, and the purpose of ensuring operational reliability is achieved.
Branch cables appeared in the UK and Japan earlier. In terms of technical standards, in 1980, the Japan Wire Industry Association issued the first industry standard JCS376 (1980). With the development and advancement of technology, the standard was carried out in 1992. The revision has relaxed the requirements for product structural materials and improved the technical indicators of finished products. At present, the product standards of domestic formal branch cable manufacturers are mainly based on this standard.
2, structure
The branch cable is divided into a single core type and a multi-core stranded type. Each single-core branch cable can be divided into three parts:
(1) trunk cable;
(2) branch cable;
(3) Branch connector.
At present, due to the simple structure of the single-core branch cable, which is convenient for production and construction, it has been widely used. According to the Japanese standard, the multi-core branch cable is essentially a twisted body of a plurality of single-core cables, rather than the structure of the conventional multi-core cable. The multi-core branch cable has separate insulation and protection on the outside of each phase conductor. Set, each core has a separate branch connector. The multi-core branch cable has the performance of a general multi-core cable. Only a small number of large-scale integrated cable factories in China have production capacity, and they are already being promoted and applied.
3, performance
The branch cable is a new type of power distribution cable with two key features:
First of all, a branch cable with good quality must be a power cable with excellent performance. For domestic products, its conductor performance, insulation performance, and mechanical and physical properties of the material should meet the GB12706-91 standard. The basic indicator of the product.
Second, the performance of the branch connector is critical, which is a key feature of the branch cable. The branch connector connects the trunk cable to the conductor of the branch cable and is insulated and moisture-proof. From the appearance, it is impossible to know the quality of the internal joints. There are two important tests to test the joint performance, namely the mechanical tensile test and the electrothermal cycle test. For the mechanical tensile test, the breaking force of the branch joint (including the main line and the branch conductor) should be maintained at more than 80% before the connection. For the electrothermal cycle test, the rated load and no load at 125 time intervals. After the cycle, the temperature rise of the branch connector is not higher than the branch head temperature of 8 at 25 cycles. The key to determining the mechanical and electrical performance of the branch connector is the material and process of the branch connector. For the majority of users, should pay full attention to the cable quality of the branch cable, the material selection of the joint and the production process tooling.
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