Comparison of sealing and insulation of Cold and Heat Shrinkable Cable Accessories

Power cable accessories are products that connect cables and transmission and distribution lines and related distribution devices. Generally, they refer to the intermediate connections (Joint kit) and terminal connections (Termination kit) of various cables in cable lines. Together with cables, they constitute the power transmission network. 

Cable accessories are mainly selected according to the characteristics of the cable structure. It can not only restore the performance of the cable, but also ensure the extension of the cable length and the connection of the terminal. According to the production process, it can be divided into heat shrinkage type and cold shrinkage type. So what are the differences in sealing and insulation properties between them? Let's have a look.

The Sealing Performance

At present, there are usually two sealing methods: one is the method of sealing with asphalt or epoxy resin, which is complicated, difficult to control and not conducive to maintenance. The other method is the preferred method of professional manufacturers at home and abroad - the use of high elastic sealant, its process is simple, reliable performance, convenient maintenance and installation.

Cold shrinkable cable accessories (elastic cable accessories) use the second method, that is, use the elasticity of liquid or solid silicone rubber itself, expand in advance in the factory, put plastic and support strip, set to the site to the specified position, remove the support strip to make it natural shrinkage. This technology is cold shrink technology, this attachment is cold shrinkable cable accessories.

This cold shrinkable cable accessories has good "elasticity", which can avoid the thermal expansion and cold contraction of the cable due to the atmospheric environment and the load level in the operation of the cable, that is, the gap between the insulation caused by the "cable breathing". The biggest disadvantage of heat shrinkable cable accessories is that they are not elastic and cannot "breathe" with cables.

Therefore, cold shrinkable cable accessories are the best choice for large temperature difference and large area affected by climate and environment.

The Insulation Performance

The insulation requirement of the cable termination is that it should satisfy the insulation between phase and phase and between phase and ground. The insulation between the phase and the phase has two kinds of insulation materials, silicone rubber and heat shrinkage. When choosing, it is usually necessary to meet the insulation requirements according to the unit insulation index of the material and the thickness of the material.

Cold shrinkable cable accessories (silicone rubber material), the general unit insulation index is 24kV/mm, the design operation thickness should meet 12mm thick, so that it can withstand the test of lightning shock and overvoltage.

Heat shrinkable cable accessories are made of a variety of composite materials, which have heat shrinkable function after irradiation and processing. Its unit insulation index is 1.8-2.0kV/mm, so the design thickness is relatively thicker than silicone rubber material 3-4mm.

Cold shrink silicone rubber material has good elasticity, as long as the design is reasonable, its strong resilience will have enough holding force. In any environment thermal or cold, cold cable accessories have guarantee clasped the cable corresponding parts, to prevent the inhalation of water and moisture, the safety of the creepage distance can get very good guarantee, at the same time the cold cable head creepage distance is only 70 mm is enough in theory, but for the sake of a more secure, most design its running distance is 90 mm.

The shrinkage temperature of the heat shrinkable cable termination ranges from 100 ° C to 140 ° C. Only the installed temperature can meet the contraction condition. When the temperature is low, because the thermal expansion coefficient of the cable is different from the expansion coefficient of the heat shrinkable material, it is possible to produce delamination in the environment below 80 ° C, so that the water and moisture will enter under the action of "breathing", thus destroying the insulation of the cable system, which is a disadvantage of the heat shrinkable material.

The process of cold shrinkable cable accessories and heat shrinkable cable accessories is completely different. Under normal conditions, both meet the requirements of safety, but with the change of environment, cold shrinkable is more advantageous than heat shrinkable. When choosing cable accessories, it is still necessary to take comprehensive consideration according to the use environment and product requirements.