Analysis of the causes of cross-linked cable connectors and precautions

First, the cross-linked cable connector intact joints and accessories for mechanical and electrical equipment safe, economical, reliable operation and power supply security is very important, and now, 6-10KV high voltage power cable in hydraulic engineering and power system is widely used, so the design Good, reasonable construction of the cable connector, the actual operation proved that in most cases can be long-term use. However, due to the cross-linked cable current carrying capacity, current density, the quality requirements of the conductor connection is more stringent. The electrical conditions required for the joints are increasingly severe, especially for 6-10KV motor cables, where the various joints will experience significant thermal stresses and short-circuit currents of higher severity and duration. Therefore, the cross-linked cable accessories are not affiliated, but not secondary components, it is with the cable is equally important and indispensable components, but also is closely related to the safe operation of key products. Cross-linked cables have been widely used in foreign countries, although the domestic widespread adoption of only 10 years, there are still some problems, but with the development of technology, accessories supporting, quality improvement, process improvement, cross-linked cables have been replaced oil paper and cable The trend has broad and far-reaching prospects for development. Second, the analysis of the reasons for the failure of cross-linked cable connector Cable accessories as a result of the type, form, specifications and more; uneven quality; builders of different levels of technology; cable connector operation mode and conditions, resulting in cross-linked cable connector failure The reasons vary. Due to the different cross-linking cable and oil-and-paper cable media, the connector failure causes are very different, oil-paper cable connector failure is mainly the impact of insulation, and cross-linked cable connector failure is mainly the conductor connection. Cross-linked cables allow high operating temperature, the cable connector on the proposed higher requirements, so that the joint fever problem becomes more prominent. Contact resistance is too large, temperature rise, fever is greater than the heat to promote the joints of the oxide film thickening, but also to greater contact resistance, temperature rise faster. Such a vicious cycle, so that the joints of the insulation damage, the formation of short-circuit, causing explosion burned. Resulting in increased contact resistance for the following reasons. 1, poor technology. Mainly refers to the cable connector construction workers before and after the conductor connection construction process. (1) connection fittings poor contact surface treatment. Regardless of the terminal or connecting pipe, due to the production or storage conditions, the tube wall often have impurities, burrs and oxide layer, which is not the people pay attention to defects, but the quality of the conductor connection, quite serious. Especially the aluminum surface is easy to generate a layer of hard and insulating aluminum oxide film, so that the connection of aluminum conductors than the copper conductor connection to increase a lot of trouble, the stringency of technology is much higher. The main cause of the heating (crimping, soldering and mechanical connections) is that the key is process technology and responsibility, with the exception of tools and material properties. Construction workers do not understand the connection mechanism, not strictly in accordance with the requirements of the operation, it will cause the connection to reach the electrical and mechanical strength. Operation Proof When the contact surface between the crimping tool and the wire is clean, the thinner the oxide film is, the smaller the contact resistance is when the temperature of the connector is increased. (2) conductor damage. Strong cross-linked insulation stripping difficult, when cutting workers with electrical workers around the left and right cut, sometimes simply cut with a hacksaw marks, tend to grasp the wire injury is not good. Although the peeling is not very serious, but the core bending and crimping peristalsis can lead to injury at the conductor damage increased or broken, crimping is not easy to find, due to reduced cross-section caused by serious fever. (3) The conductor is not in place when the conductor is connected. When the conductor is connected, the length of the insulation stripping requires that the depth of the crimping metal be increased by 5mm, but because the depth of the product is not standard, the length of the stripping is not enough, or the position of the conductor is formed by the string during crimping, Conduction, resulting in increased contact resistance, heat increases. 2, the pressure is not enough. The current information in the production of joint technology and standard diagram only refers to the number of pits at each end of the cable connection without specifying the crimping area and crimp depth. According to the requirements of construction workers press enough pit pressure, the effect of how can not be determined. No matter what kind of pressure connection, the connector resistance is mainly the contact resistance, and the size of the contact resistance depends on the contact force and the actual contact area, which is related to the output tonnage of the crimping tool. The main reason for the lack of pressure on the conductor connection is the following three points. (1) pressure equipment pressure is not enough. In recent years, more manufacturers of crimping machines, management chaos, there is no uniform standard, especially in recent years, the production of mechanical pressure clamp, pressure pit is not only narrow, and the pressure in place after the upper and lower die can not match; there are some manufacturers to buy or produce Foreign-type pressure clamp, due to the implementation of the foreign standards, and domestic cross-section of the wire is not adapted, difficult to ensure the quality of crimping. (2) connection with a large gap. The connectors used in most units of cross-linked cable joints are now terminals and crimp tubes made of fan-and-paper cable fanned conductors. In theory, the effective cross-section of the circular and fan-shaped core is the same, but from the actual operation, the crimping effect of the two differ greatly. As the cross-linked cable conductor is tightly twisted round wire core, with the larger diameter of the commonly used metal fittings after crimping not reach enough compression. The contact resistance is inversely proportional to the applied pressure and will therefore result in an increase. (3) poor quality of fake and shoddy products. Fake and shoddy fittings not only impure material, the appearance of rough, prone to cracks after pressing, and the specifications are not allowed, the effective cross-section with a great difference, simply can not meet the quality requirements of crimping, running under normal conditions, a serious fever, a slight load Volatility must fail. 3, insufficient cross-section of the cross-linked cables and oil-paper cables allow the current carrying capacity, the ambient temperature is 25 ℃, the comparison concluded that: ZQ2-3 × 240 paper copper cable available YJV22-3 × 150 cross-linked copper Core cable replacement. Because YJV22-3 × 150 cross-linked cable allows the carrying capacity of 476A; and ZQ2-3 × 240 paper and paper cables allow the flow of 420A, but also beyond the 56A. ZLQ2-3 × 240 can be replaced by YJLV22-31 × 50 because the current carrying capacity of the cross-linked 3 × 150 aluminum cable is 364A while the current carrying capacity of the oil-paper 3 × 240 aluminum cable is 320A. The cross-linked cable also exceeds 44A. If you use the allowable flow calculation, 150mm2 cross-linked cables and 240mm2 paper and paper cables are basically the same, or 150mm2 cross-linked cable application 240mm2 fittings in order to normal operation. This shows that the lack of cross-section of the connection fittings will be cross-linked cable joint fever serious an important reason. 4, heat is not good. Wrap connectors and a variety of cast connectors, not only wrapped around the cable insulation than the insulation layer is thick, and the shell also note the mixture, is the smallest type of thermal connector, the insulation and protective layer is also greater than the cable body More than doubled So no matter what type of connector there are cooling difficulties. The existing insulation materials of various joints are poor in heat resistance. The normal working temperature of J-20 rubber self-adhesive tape does not exceed 75 ° C .; the J-30 only reaches 90 ° C; and the heat-shrinkable material is used in the temperature range of -50 ° to 100 ° C. When the cable runs at normal load, the internal temperature of the joint can reach 100 ℃. When the cable is fully loaded, the core temperature of the cable reaches 90 ℃ and the temperature of the joint reaches about 140 ℃. When the temperature rises again, the temperature at the joint Membrane thickening, the contact resistance increases, the role of a certain power time, the connector of carbonization of non-insulating material insulation, resulting in failure. To sum up, increasing the pressure of the connecting fittings, reducing the operating temperature, cleaning the surface of the connecting metallic materials, improving the structural size of the connecting fittings, and selecting the high-quality standard accessories, the strict construction process is a few key factors to reduce the contact resistance. Third, to improve the quality of cross-linked cable connector solutions As the cross-linked cable connector where the environment and operation of different connected electrical equipment and location of different cable accessories in the material, structure and installation process has a lot of choice, However, the basic performance of various attachments is consistent, so the following measures should be strengthened to improve the quality of joints. (1) Must choose the advanced technology, mature technology, reliable quality, can adapt to the environment and conditions of the cable accessories. Counterfeit and shoddy products must resolutely resist, new technologies, new processes, new products should focus on testing, continue to sum up, gradually promote each year. (2) The use of high quality, specifications, cross-section meet the requirements, safe and reliable operation of the connection fittings. For the terminals, should be used as much as possible blocking oil type, because the terminal section generally larger, can reduce the heat, but also effectively solve the moisture-proof seal. The connecting pipe should be made of copper rod or 1 # aluminum car, the size should be the same with the diameter of the cross-linked cable core as well. In recent years, Changsha and Shenyang Cable Factory Annex Factory provided a cross-linked cable connector crimping pipe, the use of better. (3) Selection of crimp tonnage, good mold fit, enough pressure pit area, crimp effect to meet the technical requirements of the crimping machine. Do the pre-press interface treatment, and coated with conductive paste. (4) well-trained and skilled craftsmanship, serious and responsible work, capable of cable construction, installation and operation and maintenance of cable mechanics. Enhance the construction of the cross-linked cables to enhance awareness, enhance the understanding of the characteristics of cross-linked cable accessories, research technology, improve technology, develop construction norms, strengthen quality control and ensure safe operation. Due to the short promotion and application of cross-linked cables, cable accessories, messy varieties of construction workers, ranging from high and low technical level, coupled with the contact force and the actual contact area is with the joints in the operation of a variety of different operating conditions in the Changes, so a variety of cross-linked cable failure causes are also different, in addition to heat problems, for sealing, stress problems, connection problems, grounding problems caused by joint failures should also be taken seriously.