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Second, cross-link cable connector fault analysis due to cable accessories, types, specifications more; quality uneven; construction workers technical level varies; cable connector operating methods and conditions vary, resulting in cross-link cable connector failure The reasons vary. Because the media of the cross-linked cable and the oil-paper cable are different, the cause of the joint failure is very different. The failure of the oil-paper cable joint is mainly due to the insulation, and the breakdown of the cross-connected cable joint is mainly the conductor connection. Cross-linked cables allow for high operating temperatures and impose higher requirements on cable joints, making the joint heating problem even more pronounced. The contact resistance is too large, the temperature rise is accelerated, and the heat is greater than the heat to promote the thickening of the oxide film of the joint, which in turn makes the contact resistance larger and the temperature rise faster. In this vicious circle, the insulating layer of the joint is destroyed and a short circuit between the phases occurs, causing the explosion to burn. The cause of the increase in contact resistance is as follows.
1, poor technology. Mainly refers to the cable joint construction personnel in the conductor before and after the construction process.
(1) The contact surface of the connection hardware is not well handled. Regardless of the connection terminal or connecting pipe, due to the conditions of production or storage, there are often impurities, burrs and oxide layers on the inner wall of the pipe. This is a defect that is not taken seriously by people, but the impact on the quality of the conductor connection is rather serious. In particular, a hard and insulating aluminum oxide film is easily formed on the surface of aluminum, so that the connection of the aluminum conductor is more troublesome than the connection of the copper conductor, and the strictness of the process technology is also much higher. The main reason for the heating of the connections (crimping, welding, and mechanical connection) is, in addition to the performance factors of the implements and materials, the key is the process technology and responsibility. The construction personnel do not understand the connection mechanism and do not operate strictly according to the process requirements. This can cause the joints to fail to achieve electrical and mechanical strength. Operation proves that the cleaner the contact surface between the crimping jig and the wire is, the thinner the oxide film is and the smaller the contact resistance is when the joint temperature increases.
(2) Conductor damage. The cross-linked insulation layer is difficult to peel off, and the construction workers use an electrician's knife to cut it to the right when cutting around, and sometimes they simply cut a deep mark with a hacksaw. Although the stripping is not very serious, when the core is bent and the crimping creeps, it will cause the conductor to be damaged or broken. The crimping is not easy to find, and the cross section is reduced to cause serious fever.
(3) The core is not in place when the conductor is connected. When the conductor is connected, the length of the insulation stripping requires that the crimped metal fitting hole be deepened by 5mm. However, because the hole depth of the product is not standard, the stripping length may be insufficient, or the void may be formed at the end of the wire by crimping, and only the wall thickness of the fitting is required. Conduction leads to increased contact resistance and increased heat generation.
2, the pressure is not enough. The relevant information in the production of joints and standard drawings only refers to the number of pressing holes at each end when the cable is connected. The crimping area and the crimping depth are not described in detail. The construction personnel pressed the number of pressure pits as required, and the effect could not be determined. Regardless of the type of pressure connection, the joint resistance is mainly the contact resistance, and the size of the contact resistance is related to the size of the contact force and the actual contact area, and is related to the output tonnage of the crimping tool. There are three main reasons why the stress of the conductor connection is insufficient.
(1) The pressure of the crimping machine is insufficient. In recent years, there are many manufacturers of crimping tools, and management is chaotic. There are no uniform standards. In particular, in recent years, mechanical pressure clamps have been produced. The pressure pits are not only narrow and narrow, but they can't be matched when the pressure is received in place; there are also some manufacturers who buy or produce. The foreign types of pressure pliers, because of the implementation of foreign standards, and domestic conductors do not meet the nominal cross-section, crimping quality is difficult to guarantee.
(2) Large gaps in connecting hardware. Nowadays, the connection fittings used by most units of cross-connected cable connectors, or the terminals and crimping fittings produced by the fan-type cables according to fan-shaped conductors. Theoretically speaking, the effective cross-section of the circular and fan-shaped cores is the same, but from the actual comparison of operation, the crimping effect of the two is very different. As the cross-linked cable conductor is a tightly wound round wire core, it does not reach a sufficient compressive force after being crimped with a large gap in the inner diameter of a commonly used metal fitting. The contact resistance is inversely proportional to the applied pressure and will therefore result in an increase.
(3) The quality of fake and shoddy products is poor. The counterfeit metal fittings are not only of impure material, and have a rough appearance. They are prone to cracks after pressing, and the specifications are inaccurate. The effective cross section and the genuine product are very different. The crimp quality requirements cannot be achieved at all. Under normal circumstances, the operation is serious and the load is slight. Volatility will inevitably fail. 3. Insufficient cross section When the ambient temperature is 25°C, the allowable ampacity of the cross-linked cable and the oil-paper cable is compared. The conclusion is: ZQ2-3×240 oil-paper copper core cable can be crosslinked with YJV22-3×150 copper. Core cable replacement. Because the allowable ampacity of the YJV22-3×150 cross-over cable is 476A; and the allowable ampacity of the ZQ2-3×240 oil-fat cable is 420A, which also exceeds 56A. ZLQ2-3×240 can be replaced by YJLV22-31×50, because the cross-linked 3×150 aluminum core cable has a current-carrying capacity of 364A, while the oil-paper 3×240 aluminum core cable has a current-carrying capacity of 320A. The cross-linked cable also exceeds 44A. If the allowable ampacity calculation is used, the 150mm2 cross-linked cable is basically the same as the 240mm2 oil-paper cable, or the 150mm2 cross-connected cable can be used with the 240mm2 fixture connection to operate normally. It can be seen that the lack of cross-section of the connection fittings will be an important cause of severe heat generation in the cross-connected cable connectors. 4, heat is not good. The wrap-around joints and all kinds of cast joints are not only thicker than the cross-link insulation layer of the cable insulation, but also filled with a mixture in the housing, which is the smallest type of heat shrinkable joint, and the insulation and protection layer is also more than the cable body More than doubled. So no matter what type of joint there is difficulty in heat dissipation. The current insulation materials of various joints are poor in heat resistance, the normal operating temperature of J-20 rubber self-adhesive tapes does not exceed 75°C; J-30 also reaches 90°C; the use conditions of heat-shrinking materials are -50 to 100°C. When the cable runs at normal load, the internal temperature of the connector can reach 100°C. When the cable is fully loaded, the temperature of the cable core reaches 90°C, and the temperature of the connector reaches about 140°C. When the temperature rises again, the oxidation at the connector occurs. When the film is thickened, the contact resistance is increased. Under the action of a certain electrification time, the insulation material of the joint is carbonized into a non-insulating material, resulting in a failure. In summary, increasing the pressure of the connecting fitting contact, lowering the operating temperature, cleaning the surface of the connecting metal material, improving the structural dimensions of the connection fitting, selecting the accessories of high quality standards, and strict construction techniques are several key factors to reduce the contact resistance.
Third, to improve the quality of cross-linked cable joints due to cross-linked cable joints in the environment and the operating mode is different, the connected electrical equipment and the location is different, cable accessories in the material, structure and installation process there is a lot of choice, However, the basic performance of all types of accessories is the same, so the following points should be strengthened to improve the quality of joints. (1) Cable accessories must be selected with advanced technology, mature technology, reliable quality, and adaptability to the environment and conditions used. We must resolutely resist counterfeit and shoddy products, focus on trials of new technologies, new processes, and new products, continue to summarize and improve, and gradually promote and apply them year by year. (2) Connection hardware that can be safely and reliably operated with materials of good quality, specifications, and cross-section requirements. For the terminal block, plug oil type should be selected as far as possible, because this type of terminal generally has a large cross-section, can reduce heat, and can effectively solve the moisture-proof seal. The connecting pipe should be made of copper rod or 1# aluminum car. The size should be matched with the diameter of cross-linked cable core. In recent years, the crimping pipes for cross-connected cable joints provided by the Changsha and Shenyang Cable Plant Annex Plants have achieved good results. (3) Pressing machines with large press tonnage, good mold matching, enough pressing hole area, and crimping effect to meet the technical requirements are selected. Prepare the interface before crimping and apply a conductive paste. (4) The cable technicians who are skilled in technology, skilled in technology, and who are responsible for the work, are qualified for cable construction, installation, operation and maintenance. Improve the understanding of construction personnel on cross-linked cables, enhance understanding of the characteristics of cross-linked cable accessories, research techniques, improve processes, establish construction specifications, strengthen quality control, and ensure safe operation. Due to the short application time of cross-linked cables, the variety of cable accessories, and the level of technical level of construction workers, the contact force and the actual contact area of ​​the joints are related to various operating conditions of the joints during operation. As a result of the changes, the causes of failures in various joints of cross-linked cables are also different. In addition to heat problems, joint failures caused by sealing problems, stress problems, connection problems, and grounding problems should also be taken into account.
Renault Android Car Dvd
Cross-linked cable connector failure causes and treatment methods
I. Cross-linked cable joints Operating conditions 6-10KV high-voltage power cables are widely used in water conservancy projects and power systems. Their good joints and accessories are very important for the safe, economical, reliable operation and power supply of electromechanical equipment. Well-designed and reasonably-constructed cable connectors have proved that they can be used in the long term in most cases. However, since the cross-linked cable has a strong current carrying capacity and a large current density, the requirements for the conductor connection quality are more stringent. The mechanical electrical conditions required for joints are increasingly stricter, especially for 6-10 kV motor cables, where various joints will be subject to great thermal stresses and short circuit currents of higher severity and duration. Therefore, cross-linked cable accessories are not ancillary, more importantly, they are not secondary components. They are as important as cables and are indispensable components. They are also key products closely related to safe operation. Cross-linked cables have been widely used in foreign countries, although widely used in China, although only 10 years, there are still some problems, but with the development of technology, accessories, improve the quality, improve the process, cross-linked cables have been replaced oil-paper cable The trend has broad and far-reaching development prospects.