Design principle of cross-linked cable head:
First of all, the design principles of all cross-linked cable heads should follow the principle of restoring the cable body structure. Therefore, the design concept of its connector should comply with my country's GB 12706-4 and IEC60502-4:1997 electrical standards, and must meet its electrical, physical and chemical properties to ensure the long-term normal operation of the cable head and the safe operation of electrical equipment.
Secondly, the principles and differences:
Cable plugThe design principle should meet and achieve the following requirements: enable the cable to operate safely in any natural environment. In order to achieve this, we need to pay attention to four key factors, namely: sealing, insulation, electric field, process and other elements. These are also the four important issues in solving the cable head.
1. Sealing
① Since most European-style cable joints are installed outdoors in overhead or directly buried environments, waterproofing and moisture-proofing have become one of the keys to ensuring the safe operation of the cable head, and its sealing performance and method must also be considered.
There are usually two sealing methods at present: one is to use asphalt or epoxy resin potting, which is complex in process, difficult to control, and not conducive to maintenance; the other new method is also the preferred method by domestic and foreign professional manufacturers, which is the use of highly elastic sealant. Its process is simple, its performance is reliable, and it is easy to maintain and install. These unique advantages have also made it the mainstream of use. With this new approach, the first thing to consider is the performance of the sealant. Because the quality and performance of the sealant directly affects the sealing performance of the joint, it is very important to choose a glue that can bond firmly with the surface of the cable body and the surface of the accessory material, and can also be used in different temperature changing environments.
② Therefore, the fully cold shrinkable power cable accessories are actually elastic cable accessories; that is to say, the elasticity of the liquid or solid silicone rubber itself is used to pre-expand the plastic and support strips at the factory. Go to the site and put it into the designated position, and remove the support bar to allow it to shrink naturally. This technology is cold shrink technology, and this accessory is a cold shrink cable accessory. Therefore, this cold shrink accessory has good "elasticity" and can avoid thermal expansion and contraction of the cable due to the atmospheric environment and the load level during cable operation. That is, the gaps between the insulation caused by "cable breathing" cause breakdown accidents. The biggest disadvantage of heat shrink attachments is that they are not elastic. Can't breathe with cables. Therefore, fully shrinkable accessories are the best choice for use in areas with large temperature differences and large impacts from climate and environment.
2. Insulation
The insulation requirements of the cable head are to meet the two major insulation requirements: phase-to-phase insulation and phase-to-ground insulation. The requirements are:
① The relative insulation materials are silicone rubber type and heat shrinkable material. Usually the insulation performance must be based on the unit insulation index of the material and the thickness of the material to meet the requirements.
② Phase-to-ground insulation is to prevent charges from climbing a safe distance from high potential to low potential. Cold-shrinkable silicone rubber material has good elasticity. As long as the design is reasonable, its strong resilience can provide sufficient holding power. No matter thermal expansion or cold contraction occurs in the environment, the cold shrinkage attachment is guaranteed to tightly hug the part of the cable being hugged. This prevents the inhalation of water and moisture, and the safe internal creepage distance is well guaranteed. At the same time, the internal creepage distance of the fully cold-shrunk cable head is only 70mm in theory. For safer reasons, the design running distance is still 90MM. The shrinkage temperature of the heat-shrinkable cable head is 100℃-140℃. Only during installation, the temperature can meet its shrinkage conditions. When the temperature is low, since the thermal expansion coefficient of the cable is different from that of the heat shrink material, it is entirely possible for delamination to occur in an environment below 80 oC, and therefore cracks will appear. This allows water and moisture to enter through breathing, destroying the insulation of the system. However, when environmental conditions change, it will have an impact on safety because it is not as elastic as silicone rubber. This is the shortcoming of heat shrinkable materials.
3. Electric field: The geometric method is used to process the electric field of cold shrink cable joints. The electric field distribution is changed through the stress cone, which is solved with a certain geometric shape and precise R angle. This method is easier to control and inspect. This can be ensured and implemented at the factory. The electric field treatment method of heat-shrinkable cable ends is to use the linear parameter method to change the distribution of the electric field, which must rely on two important parameters: a. Volume resistance, 108-11Ω; b. Dielectric constant is 25; Due to its complex production process and large changes in environmental factors, it is difficult for the team to control the stability of the parameters, so it will have an impact on the most stable quality of the product. Based on the above analysis, there are essential differences between cold-shrinkable intermediate connectors and heat-shrinkable cable connectors. But as long as it operates under normal conditions, it can meet safety requirements; but as the environment changes, cold-shrinkable cable heads have incomparable differences and advantages compared with heat-shrinkable cable heads; in addition, full cold-shrinkable cable heads are made of special molds, and the shape after installation is very beautiful; the installation and construction speed is fast, saves time, and is anti-pollution.
High voltage arrester, arrester manufacturer, metal oxide arrester
High voltage arrester, arrester manufacturer, metal oxide arrester
