Based on the currently power system of 35 kV and below different kinds of cable attachment type, based on the direction of development of medium voltage cable accessories "prefabricated", "simplicity", introduces the part of current in cable accessories technology development and research in the process of new materials and new technologies.
introduction
With the acceleration of urbanization and the improvement of living standards of urban and rural areas, the proportion of cable applications in urban distribution networks, especially in large and medium sized cities, has become increasingly high. Which led to the strong demand for cable accessories products, but also to promote the speed of its product development and improvement.
1 the role of cable accessories
In cable terminations and joints, due to the cable metal sheath and breaking the shielding layer, makes the field distribution over the cable body is much more complicated, in cable terminal field in the presence of an axial stress. Therefore, it is necessary to use cable accessories to achieve cable continuous and swivel, namely a can meet certain insulation and sealing requirements of a connection device.
Cable conductor, insulation, shielding and protection layer, such as four main structure layer, cable accessories as cable line part of the cable terminal head, the middle connector to the cable four layer structure respectively to get a continuation of the and conductor connection good, reliable insulation, sealing good and sufficient mechanical strength, ensure the quality of the cable terminal and cable joint, in order to ensure the cable distribution network power supply reliability.
Classification of 235kV and the following medium voltage cable accessories
At present, in accordance with the main insulation molding process, common 35kV and below cable terminal and intermediate joints can be divided into winding package type, heat shrinkable, shrinkage and prefabricated and four products commonly used type. In addition to casting and separable cable accessories for specific product ranges.
2.1 wrapped cable accessories are wrapped type cable accessories is refers to the insulation and shielding are the use of tape around the package and the cable accessories, the force control method of the stress cone or the use of high dielectric constant stress control tape, the technology level of construction personnel requirements higher, construction technology is more complex, has gradually been eliminated from the scene.
2.2 heat shrinkable cable accessories using with polymer "elastic memory effect" principle, to develop all heat shrinkable tubing, sets of branch, a rain skirt and heat shrink prefabricated parts, according to the procedure in after treatment at the end of the cable or connector, the heating, the contraction of the hoop in the desired position.
Heat shrinkable cable accessories has the advantages of simple process, low cost, easy to maintain. But it also has some problems, such as the "respiration" caused by the environmental temperature variation, which can shorten the service life of the environment, which will affect the reliability of the power supply.
2.3 and contraction cable accessories are the engineering application of cold shrinkable tube and other cold shrink prefabricated parts, with silicone rubber or EPDM rubber as the main raw material, after special formulation, pre expansion in the helix support core line and, when installed and used without any external heat source, as long as undraw the bracing wire core will shrink, and tight hoop in the desired position.
Shrinkage type cable accessories must be used in the use of the prescribed period, and the price is higher.
2.4 prefabricated cable accessories using rubber material, cable accessories enhanced insulation and semiconductive shielding layer in the factory mold made a whole or a number of components, the scene set in after treatment at the end of the cable or the middle connector cable accessories called prefabricated cable accessory. Prefabricated cable accessories can be in the factory for the corresponding factory routine test, to further improve the reliability of the operation of the cable terminal, but also greatly reduce the workload of the installation of the site. In terms of the structure, and contraction cable accessories and prefabricated cable accessories are basically the same, just some differences on the material properties and processing.
2.5 casting type cable accessories using thermosetting resin materials, on-site casting at the end of the cable after treatment or the mold or box joints in the body, after curing and forming the cable accessories. Particularly applicable to the interconnection of plastic extruded insulated cables and impregnated paper insulated cables.
2.6 separable connectors allow cables and other equipment and cable connections or disconnect all insulated cable accessories, such as terminals, connectors, and branch joints, etc.. The main object of the separable connector is a fully sealed switch cabinet, an inflatable ring net unit and a cable branch box, which can be regarded as a new type of cable terminal. And more use of prefabricated terminal structure. From the classification of the cable accessories products is not difficult to see, can simplify the site requires the installation of prefabricated and cold technology is already in the cable accessories development occupies important position.
3 new technology for cable accessories shall be
3.1 conductor is connected on the conductor connecting the basic technology requirement is: a good conductor connection: for the terminal, cable guide wire and wire rod, a connecting end between well connected; for intermediate connector, cable conductor and connecting tube between to well connected. The contact resistance of the connection point is small and stable. Compared with the same length with the resistance wire section, the new ratio should be less than 1.
At present, the use of compression technology, the need for a certain professional equipment. And using bolt connection technology, the field construction only need a torque wrench, can achieve the basic requirements of the conductor connection technology. Thus simplifying the professional requirements of the installation equipment. And the need to remove the oxide layer of aluminum cable connection, no need to carry out special treatment in advance of the oxide layer.
3.2 insulation materials ternary ethylene propylene rubber and silicone rubber material in the prefabricated cable accessories have been widely used, in the field of high voltage cable accessories, can be divided into using silicone rubber as substrate of the Euclidean structure and ternary ethylene propylene rubber as the substrate of the Japanese structure. In the field of medium voltage, after improvement of ternary ethylene propylene rubber cable accessories than similar products in the silicon rubber has better mechanical strength and tear resistance.
3.3 site pre expansion field pre expansion and shrinkage cable accessories for an installation, namely within a few hours before installation using simple disposable tools in the field of the shrinkage joint pre expansion. It avoids the conventional shrink due to product in the transportation and long-term storage of some loss in performance, thus providing a more constant reliable radial pressure. As the system is especially suitable for spare parts.
In short, to facilitate the installation and installation of the site to ensure the quality, reduce the level of on-site installation personnel are too high. Prefabrication, concise will become a main development direction of the future technology of cable accessory, to products manufactured test the shrink prefabricated cable attachment will become the scene of the mainstream in the factory, to further ensure the safe and reliable operation of the power system, and to achieve the optimal combination of the technical and economical.
