The design principle of cross-linked cable head:
First of all, the design principle of all cross-linked cable heads should follow the principle of restoring the cable body structure. Therefore, the design idea of the joint should conform to the electrical standards of China's GB 12706-4 and IEC60502-4:1997, and must meet its electrical, physical and chemical properties to ensure the long-term normal operation of the cable head and electrical equipment. Safe operation.
Second, the principles and differences:
The design principle of the cable head should meet and meet the requirements: to 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 factors, which are also four important issues to solve the cable head.
1 Since most of the cable heads are installed in outdoor overhead and direct burial environments, waterproof and moisture-proof gas are one of the keys to ensure the safe operation of the cable head. It is also necessary to consider the sealing performance and method.
At present, there are usually two methods of sealing: one is a method of potting with asphalt or epoxy resin, which is complicated in process, difficult to control, and not conducive to maintenance; another new method is also domestic and foreign professional. The preferred method of the manufacturer is to use a highly elastic sealant, which is simple in process, reliable in performance, convenient in maintenance and installation, and these unique advantages also make it the mainstream of use. With this new method, 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, choose a glue that can adhere to the surface of the cable body and the surface of the accessory material, and also meet the requirements of different temperature changes. The glue that can be used is very important.
2 The fully cold-shrinkable power cable accessory is actually an elastic cable accessory; that is to say, the elasticity of the liquid or solid silicone rubber itself is pre-expanded in the factory to put the plastic and the support bar. Set to the specified position on the site, and take off the support bar to make it shrink naturally. This kind of technology is the cold shrinking technology. This kind of accessory is the shrinkable cable accessory. Therefore, this cold shrinkable accessory has good "elasticity", which can avoid the thermal expansion and contraction of the cable due to the atmospheric environment and the load in the cable operation. . That is, the gap between the insulation generated by "cable breathing" causes a breakdown accident. The biggest drawback of heat shrinkable attachments is that they are not elastic. Do not breathe with the cable. Therefore, the fully cold-shrinkable attachment is the best choice for use in hell with large temperature difference and high environmental impact.
The insulation requirements of the cable head are to meet the insulation between the phase and phase and the relative insulation between the phases. Requirements:
1 The insulation of the opposite phase is made of silicone rubber type and heat-shrinkable material. Generally, the insulation performance should meet the requirements according to the unit insulation index of the material and the thickness of the material. The company's full cold shrink attachment is the use of Dow Corning's liquid laurel rubber as raw material, its performance index is 24kV / mm design running thickness should meet 12mm thick, can withstand lightning shock and overvoltage test. The heat shrinkable attachment is a mixture of a variety of composite materials, which are heat-shrinkable after irradiation and processing. Its unit insulation index is 1.8-2.0kV/mm, so the design thickness is 3-4mm thicker than the silicone rubber material, namely: 15-16mm thick to meet the operational requirements.
2 Relatively insulated is to prevent the charge from climbing from a high potential to a low potential for a safe distance. The cold shrinkable silicone rubber material has good elasticity, and as long as the design is reasonable, its strong resilience has sufficient holding force. Regardless of the thermal expansion or contraction of the environment, the cold-shrinking attachment ensures that the cable is held tightly. 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-shrinkable cable head is theoretically as long as 70mm, which is more safe and still designed and operated. The distance is 90MM. The shrinkage temperature of the heat-shrinkable cable head is 100 ° C - 140 ° C, and the temperature can only meet its shrinkage condition when installed. When the temperature is low, since the coefficient of thermal expansion of the cable is different from the coefficient of expansion of the heat-shrinkable material, it is entirely possible to cause delamination in an environment below 80 o C, and thus cracks occur. This will allow water and moisture to enter under the influence of breathing, thereby damaging the insulation of the system. However, when the environmental conditions change, there is no elasticity like silicone rubber, so it also has an impact on safety. This is the disadvantage of heat-shrinkable materials.
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