As is well known, electrical terminal kits are the parts of a power transmission or distribution line where the insulation structure is relatively weak and prone to operational failures, and their production requirements are very strict. in this post, we are going to point out the problems that are often overlooked in the production of electrical terminal kits and middle cable joints. It describes and analyzes these problems and proposes several points to pay attention to during production and solutions.
Electrical terminal kits and middle cable joints are relatively weak insulation structures in cable lines that are prone to faults. Experience in operational management has shown that many accidents have exposed numerous problems in our engineering and quality management of cable lines. Therefore, it is necessary to carefully study the laying of cables, the production of electrical terminal kits and intermediate joints, etc., in order to ensure the long-term safe operation of cables.
Comparison of different types of electrical termination kit
1.1 Heat shrink electrical terminal kit
The heat shrink electrical terminal kit mainly relies on stress tubes to handle the problem of electrical stress concentration, that is, using parameter control methods to alleviate electric field stress concentration. Stress tube is a heat shrink tube with a special electrical parameter of moderate volume resistivity and high dielectric constant. It uses electrical parameters to force the stress at the insulation shielding fracture of the cable to disperse into a more uniform distribution along the stress tube. The key technical issue in its use is to pay attention to filling the air gap at the fracture of the cable insulation semiconducting layer with silicone grease to eliminate gas and achieve the goal of reducing partial discharge. Due to poor internal stress treatment, cross-linked cables may experience significant shrinkage during operation. Therefore, when installing accessories, it is important to ensure that the stress tube and insulation shield are not less than 20mm overlapped to prevent detachment during shrinkage. Due to its small elasticity, heat shrink attachments may create air gaps at the interface during thermal expansion and contraction during operation. Therefore, sealing technology is important to prevent moisture from entering.
1.2 Prefabricated Electrical Terminal Kit
The prefabricated electrical terminal kit mainly uses the geometric structure method, namely stress cone, to handle stress concentration problems. Its main advantages are excellent material performance, easy and fast installation, no need for heating for installation, good elasticity, which greatly improves the interface performance. It is the main form used in recent years for medium and low voltage and high voltage cables. The shortcomings lie in the high requirement for the outer diameter of the insulation layer of the cable, with a typical interference fit of 2-5mm (i.e. the outer diameter of the cable insulation should be greater than the inner hole diameter of the cable accessory by 2-5mm). If the interference fit is too small, the cable accessory will malfunction; Excessive interference makes it very difficult to install cable accessories, and in addition, the price is relatively expensive. During installation, attention should be paid to using silicone grease to lubricate the interface for easy installation, while filling the air gap at the interface. Prefabricated accessories can generally have a certain sealing effect by relying on their own rubber elasticity, and sometimes sealing can also be enhanced by using sealant and elastic fixtures.
1.3 Cold shrink electrical terminal kit
Cold shrink attachments generally use geometric structure method and parameter control method to deal with the problem of electrical stress concentration. Like prefabricated accessories, the material has excellent performance, can be installed without heating, and has good elasticity, resulting in significant improvement in interface performance. The difference is that its installation is more convenient and fast, just pull out the inner core tube of the cable accessory in the correct position to complete the installation.
2 . Construction and production precautions for electrical termination kit
2.1 Personnel engaged in homework. Many units do not have supervision measures to ensure the quality of the project during construction, and the quality of laying and installation, as well as the level of operation and maintenance technology, are relatively lagging behind. Personnel who do not understand or have only partial knowledge of cable line construction technology are employed in the production of cable heads. Their skills are all learned from the master’s “threading belt” technique, and their awareness of the construction process from cable laying to terminal and intermediate head production is insufficient. Therefore, it is necessary to provide professional training and pass exams for personnel engaged in cable operations before taking up their positions, establish cable construction process standards, and strengthen the management of cable head production processes.
2.2 Selection of Electrical Terminal Kit. During construction, it is recommended to use cold shrink cable heads as much as possible, because cold shrink silicone rubber cable accessories are easy to make and do not require spray lamps or soldering. And the silicone rubber cable accessories are elastic and tightly adhere to the cable, overcoming the shortcomings of heat shrink materials.
2.3 Electrical terminal kit production issues. When making terminal heads, some may not need to cut the pencil head, but when sealing tape needs to be wrapped between the cable insulation end and the wiring tool, to ensure the sealing effect, the insulation end is usually cut into a cone to ensure that the wrapped sealing tape and insulation can be well connected.
2.4 Use of stress tubes and stress relief adhesive. The stress tube and stress relief adhesive in cable accessories are mainly used to alleviate the effect of dispersed electrical stress. The material composition of stress tube and stress relief adhesive is composed of various polymer materials mixed or copolymerized. Generally, the substrate is polar polymer, and high dielectric constant fillers are added. These materials must be used according to regulations.
2.5 Lead out of grounding wire. When making cable heads, it is recommended to separate the steel armor and copper shielding layer by welding and grounding them, which is beneficial for detecting the quality of the cable’s inner protective layer. When testing the cable sheath, a voltage is applied between the steel armor and the copper shield. If it can withstand a certain voltage, it indicates that the inner sheath is intact and undamaged. Steel armor and copper shielding layer can also be connected together for grounding, and we advocate grounding after separate leads.
3. Conclusion
With the improvement of industrial automation, the stability and reliability of power supply are receiving more and more attention from people. How to ensure the safe and reliable operation of these electrical terminal kit and middle cable joints, reduce accident rates, and improve power supply quality is also a common concern for us all at present.