The difference between the cold shrink tube and the heat shrinkable tube for cable head protection
For outdoor cables, joints and other protection from heat shrinkable tubes to cold shrink tubes, in order to adapt to the development of the industry and reduce the failure rate of the cable. The cold-shrinkable product runs reliably and has a short construction time, which greatly shortens the processing time of the accident.
Let us understand the main differences between cold shrinkage and heat shrinkage during construction.
First, the cross-linked cable is composed of an outer sheath of the cable, a metal armor, an inner sheath, a filler, a copper mask layer, an outer semi-conductive layer, an insulating layer, an inner semi-conductive layer, a wire, and the like. Therefore, what kind of cable structure requires the kind of materials and the cable accessories of the process and his one-to-one correspondence and matching, so that the cable can operate safely in any natural environment. Among the four factors that need attention: sealing, insulation, electric field, and process.
Let's take a look at the main differences between cold-shrink and heat-shrink products during construction.
The sub-cables are installed in an outdoor overhead, direct burial environment, etc., and therefore waterproof. Moisture resistance is one of the keys to ensuring the safe operation of the cable head, and its sealing performance and methods need to be considered. At present, the preferred method at home and abroad is to use a highly elastic sealant, and its simple process and reliable performance also make him the mainstream of use, but the use of this glue should especially consider the performance of the glue, because the performance of the sealant directly affects The sealing performance at the joint, it is difficult to choose a glue that can adhere to the surface of the cable body and the surface of the accessory material, and also to meet the requirements of different temperature change environments. important.
The cold-shrinking product is actually an elastic cable accessory, that is to say, the elasticity of the rubber itself is pre-expanded into the support bar at the factory. Nest to the site at the specified location and remove the support bar to naturally contract. This end is the cold shrink technique. This kind of accessory is a cold-shrinkable cable accessory, so the cold-shrinkable accessory has good "elasticity", which can avoid the gap generated by the thermal expansion and contraction of the cable due to the atmospheric environment and the load in the cable operation, resulting in breakdown. Accidents, and the biggest disadvantage of heat-shrinking products is that their elasticity cannot fully satisfy the same breathing with cables. Therefore, cold-shrinking products are used for areas with large temperature difference and are affected by climate and environment.
The insulation requirement of the cable head is to satisfy the two major insulations between the phase-to-phase insulation box and the ground.
Two kinds of insulating materials of insulating rubber and heat-shrinkable materials of opposite phase generally have insulation properties according to the unit insulation index of the material and the thickness of the material. The performance index of the fully cold-shrinkable accessory is 24kv/mm. The design running thickness should meet 12mm, which can withstand the test of lightning impulse and overvoltage. The heat shrinkable accessory is a mixture of a variety of composite materials. It has a heat shrinkage function after irradiation, and its unit insulation index is fed 1.8~2.0kv/mm. Therefore, the design thickness is 3~4mm thicker than the rubber material, namely: 15~ 16mm, can meet the operational requirements.
Relative insulation is a safe distance to prevent the charge from climbing to a low potential due to high potential. The cold-shrinkable tube rubber material has good elasticity. As long as the design is reasonable, its strong resilience has sufficient holding force, and no matter the thermal expansion and contraction of the environment, it is ensured that the cable is wrapped tightly. This prevents the inhalation of water and moisture, and the safe internal creep distance is well guaranteed. The heat shrinkable attachment is only suitable for the shrinkage condition when it is installed. When the temperature is low, since the thermal expansion coefficient of the cable is different from the expansion coefficient of the heat shrinkable material, delamination may occur, so cracks occur, so that water and The moisture will enter under the breath, thus destroying the insulation of the system. Because there is no elasticity like enamel rubber, it will also have an impact on safety. This is the weakness of the heat shrinkable product relative to the shrinking product.
 Electric field
The cold shrink attachment is applied in the electric field processing. The electric field distribution is changed by the stress cone. It is solved by a certain geometry and an accurate R angle. This method is easier to control and test. It can be ensured and realized at the factory. The power treatment method of the heat shrinkable attachment is to change the distribution of the electric field with linear parameters, and must rely on two important parameters: a volume resistance, b dielectric constant, due to the complicated production process, large changes due to environmental factors, so it is difficult to control the parameters. Stable, so it will have an impact on the stability of quality.
More than the above analysis, the cold shrink tube and the heat shrink tube are essentially different. However, as long as it is operated under normal conditions, it can meet the safety requirements, but as the environment changes, the cold-shrink tubing has incomparable differences and advantages compared with the heat-shrink tubing; in addition, the cold-shrink tubing is made of a special mold. The shape after installation is very beautiful, the installation speed is fast; save time; anti-pollution and other advantages.
DWH high-rate 矽 rubber cold-shrink tubing is made of special enamel rubber material, which has the advantages of large shrinkage ratio, excellent physical and mechanical properties, and resistance to puncturing. It is suitable for waterproof and moisture-proof sealing of communication and cable connection connectors, insulation and sealing of wire and cable connection, and insulation protection of other types of connectors. Its continuous use temperature: -60 ° C ~ 200 ° C, expansion ratio of about 4 times, suitable for connection seals of different diameters
Today, we are in a fast-developing society. The continuous development of the company's power system often needs to face environmental tests such as high load, high temperature, low temperature, and thunderstorms along the coast. Only stable operation can ensure the stable development of the enterprise. Therefore, it is very important to select high-performance cable accessories in the power system. The appearance of cold-shrink tubing meets this requirement, which makes the cold-shrink tubing more widely used.