What are medium and low voltage cable accessories?
The most commonly used product varieties of medium and low-voltage cable accessories currently include heat shrinkable accessories, prefabricated accessories, and cold shrinkable accessories.
The materials used in heat shrink accessories are generally composed of blends of various material components such as polyethylene, ethylene-vinyl acetate (EVA), and ethylene-propylene rubber. This type of product mainly uses stress tubes to solve the problem of electrical stress concentration. That is to say, the parameter control method is used to alleviate the electric field stress concentration. The main advantages are that it is lightweight, easy to install, has good functions, and is cheap.
The stress tube is a heat shrinkable tube with special electrical parameters with moderate volume resistivity (1010-1012Ωcm) and large dielectric constant (20--25). The electrical parameters are used to force the stress at the cable insulation shielding fracture to be distributed evenly along the stress tube. This technology is generally used in cable accessories of 35kV and below. Because the stress tube will heat up when the voltage level is high and cannot work reliably.
To ensure that the electrical parameters of the stress tube must reach the values specified in the above standards, it can work reliably. In addition, attention should be paid to using silicone grease to fill the air gap at the fracture of the cable insulation semi-conductive layer to remove gas and achieve the purpose of reducing partial discharge. Cross-linked cables will shrink greatly during operation due to poor internal stress management. Therefore, when installing accessories, pay attention to the overlap between the stress tube and the insulation shield by no less than 20mm to prevent the stress tube from separating from the insulation shield during shrinkage. Due to the small elasticity of heat-shrunk accessories, thermal expansion and contraction during operation may cause air gaps at the interface, so sealing skills are very important to prevent moisture from infiltrating.
The material used in prefabricated accessories is generally silicone rubber or ethylene-propylene rubber. The geometric structure method, that is, the stress cone, is mainly used to solve the stress concentration problem. Its main advantages are excellent material performance, simpler and faster installation, installation without heating, and good flexibility, which greatly improves the interface function. It is the main form of medium, low voltage and high voltage cable selection in recent years. The shortcoming is that the outer diameter of the cable insulation layer is required to be high. The general interference is 2 to 5 mm. If the interference is too small, the cable accessories will malfunction; if the interference is too large, it will be very difficult to install the cable accessories. Particularly, problems arise with the intermediate joints, which are inconvenient to install and often become fault points. In addition, the price is more expensive.
Hengyuan Technology cable joint series includes: European cable joints, American cable joints, cold shrink cable heads, cold shrink cable joints, cable plug-in heads
The size of the accessory and the size of the cable to be installed must meet the specified requirements. In addition, silicone grease must be used to lubricate the interface to facilitate installation and fill the air gap in the interface. Prefabricated accessories generally rely on their own rubber elasticity to achieve a sealing effect, and sometimes sealant and elastic clamps can be used to enhance the sealing.
Like prefabricated accessories, it has excellent material properties, can be installed without heating, and has good elasticity, which greatly improves the interface function. Compared with prefabricated accessories, its advantage is that it is more convenient to install. You only need to pull out the inner lining core tube of the cable accessory at the correct position to complete the installation. The materials used are better in terms of mechanical strength than prefabricated accessories, and the requirements for the outer diameter of the cable insulation layer are not very high. As long as the inner diameter of the cable accessories is 2 mm smaller than the outer diameter of the cable insulation, the requirements can be met. Therefore, the construction installation of cold shrinkable accessories is more convenient.
