As China's urbanization accelerates and the living standards of both urban and rural areas rise, the proportion of cable applications in distribution networks in cities, especially in large and medium-sized cities, is getting higher and higher. Which led to the strong demand for cable accessories products, but also contributed to the improvement of product development speed.
First, the role of power cable accessories
At the power cable terminations and joints, the distribution of the electric field is much more complex than the cable body due to the disconnection of the metal sheath and the shield of the cable, and there is axial stress in the electric field at the cable terminations, thus requiring the use of cable accessories for cable continuity and barging Then, that is to meet a certain insulation and sealing requirements of the connection device.
The cable has four main structural layers of conductors, insulation, shielding and sheathing. The cable terminal ends and intermediate connectors of the cable accessories which are part of the cable line must be respectively extended for the four structural layers of the cable and the conductor connection is good , Reliable insulation, good sealing and sufficient mechanical strength, to ensure the quality of the cable terminal and cable connector, in order to ensure the reliability of the power distribution network of the entire cable.
Second, 35kV and below the classification of medium voltage cable accessories
At present, according to the main insulation molding process, commonly used 35kV and below the cable terminal and the middle connector can be divided into four types of commonly used products: wrap around, heat shrinkable, shrinkage and prefabricated. There are also cast and detachable cable accessories for a specific product range.
2.1 Wrapped Cable Accessories Wrapped cable accessories refers to the use of cable insulation and shielding are wrapped around the cable accessories, the stress control method using stress cones or high dielectric constant stress control band, the construction staff High level of technology, construction technology is more complex, has gradually been eliminated on the scene.
2.2 shrinking cable accessories Polymer polymers have the "elastic memory" effect of the principle of the development of a variety of heat-shrink tubing, jacket, rain skirts and other heat-shrinkable prefabricated parts, according to the program installed in the treated cable ends or Joint Department, its heating, make it shrink tight in the desired position.
Heat shrinkable cable accessories process is simple, inexpensive, easy to maintain. However, there are also problems such as the shortened service life due to the inevitable "respiration" due to the change of the ambient temperature, which affects the reliability of the power supply.
2.3 Cold Shrink Cable Accessories At present, the cold shrink tube and other cold shrink precast parts are made of silicon rubber or EPDM rubber as the main raw material. After being specially formulated, pre-expansion is performed on the spiral supporting core wire , Installation and use, without any external heat source, just pull the support wire will shrink, and tightly hoop in the desired location.
Cold shrink cable accessories must be used within the stipulated period of use, and the price is higher.
2.4 Prefabricated cable accessories The use of rubber materials, the cable accessories within the reinforced insulation and semi-conductive shielding layer molded in the factory into a whole or several parts, the site set at the end of the treated cable or intermediate joints formed cable accessories Called prefabricated cable accessories. Prefabricated cable accessories factory in the appropriate factory routine test to further improve the operational reliability of the cable terminal, but also greatly reduce the on-site installation workload. From the structural point of view, shrink cable accessories and prefabricated cable accessories are basically the same, only the material performance and handling some differences.
2.5 Cast Cable Assemblies Thermoset resin materials are cast on-site in the mold or case at the end of the treated cable or connector to form a cable attachment. It is especially suitable for the interconnection of plastic extruded insulated cables and impregnated insulated cables.
2.6 Separable connectors All-insulated cable accessories, such as terminals, connectors, and branch connectors that allow cables to be connected or disconnected from other equipment and cables. Detachable connector The main object of use is a fully enclosed switchgear, inflatable ring unit, cable branch box and other equipment, can be regarded as a new type of cable terminal. And more use of prefabricated terminal structure. It is not difficult to see from the product classification of the above cable accessories that the prefabrication and shrinking technologies that simplify the field installation have played an important role in the development of cable accessories.
Third, the application of new technology cable accessories products
3.1 Conductor connection The basic technical requirements for conductor connection are: good conductor connection: for the terminal, the cable conductor core and the outgoing rod, the connection between the terminals should be good; for the intermediate connector, the cable conductor and the connection between the tubes to be well connected. That requires the contact point of the contact resistance of small and stable. Compared with the same length with the wire cross-section of the resistance, the new ratio should not be greater than.
At present the site more use of crimping technology, requires a certain degree of professional equipment. The use of bolting technology, on-site construction requires only a torque wrench, you can achieve the basic technical requirements of the conductor connection. This simplifies the professional requirements for mounting equipment. And for the need to remove the non-conductive oxide layer aluminum cable connection, prior to the need for special de-oxidation treatment.
3.2 Insulation EPDM rubber and silicone rubber materials in the prefabricated cable accessories have been widely used in the field of high voltage cable accessories, in comparison, can be divided into silicone rubber as the substrate of the European-style structure and ternary Ethylene-propylene rubber substrate for the Japanese-style structure. In the field of medium pressure, the improved EPDM cable accessories have better mechanical strength and tear resistance than the similar products of silicone rubber.
3.3 Site Pre-Expansion Site pre-expansion technology is also a way of installing shrink-fit cable accessories that pre-expand the expansion joint at the site with easy disposable tools within a few hours of installation. It avoids the conventional shrinking products due to part of the performance of the transport and long-term storage losses, thus providing a more constant and durable radial pressure. Particularly suitable as a spare part of the system.
In short, in order to facilitate on-site installation and ensure the installation quality, reduce the on-site installation of high technical requirements. Prefabrication and simplification will become the main development direction of cable accessories technology in the future. Cold-drawn prefabricated cable accessories capable of leaving the factory for product ex-works will become the mainstream in the field, thereby further ensuring the safe and reliable operation of the power system and realizing its technology The best combination of economy.
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