Want to write a paper on fault analysis of conductor joints? So how should the content of the paper be written? The following is the wire connector fault analysis paper I shared with you, hoping to help you.
In this paper, the faults of high voltage cable joints are comprehensively analyzed, and the improvement measures and preventive countermeasures are put forward for various reasons.
Keywords: cable connector; Analysis; idea
I. Introduction
The condition of cross-linked cable joints in railway power supply network is very important for power supply safety. It has been proved by actual operation that it can be equivalent to cable for a long time in most cases. Because of its strong current carrying capacity and high current density, cross-linked cables have stricter requirements on the quality of conductor connection. The mechanical and electrical requirements for joints are getting higher and higher, especially for transmission and distribution cables, and various joints will be affected by great thermal stress and short-circuit current for a long time.
Therefore, cross-linked cable accessories are not accessories, let alone secondary components. As important as cable, it is an essential component and a key product closely related to safe operation.
Second, comprehensively analyze the reasons for the failure of cross-linked cable joints.
The reasons for the failure of cross-linked cable joints show different phenomena because of the types, forms, specifications, quality of cable accessories and the technical level of construction personnel. In addition, different working modes and conditions of cable joints lead to different reasons for the failure of cross-linked cable joints. Cross-linked cables are allowed to operate at higher temperatures, and the requirements for cable joints are higher, and the problem of joint heating is more prominent. If the contact resistance is too large, the temperature rise will be accelerated. If the heat is greater than the heat dissipation, the oxide film of the joint will thicken, which will make the contact resistance larger and the temperature rise faster. This vicious circle destroys the insulation layer of the joint, forms a short circuit between phases, and causes explosion and combustion. It can be seen that the increase of contact resistance and the heating of connector are the main reasons for cable failure. The reasons for the increase in contact resistance are as follows:
1, poor workmanship. Mainly refers to the construction technology of cable joint construction personnel before and after wire connection.
2. The contact surface of the connector is not handled well. Whether it is a terminal or a connecting pipe, due to the influence of production or storage conditions, there are often impurities, burrs and oxide layers on the inner wall of the pipe, which are ignored by people and have an important impact on the quality of conductor connection. Especially, it is easy to form a hard and insulating alumina film on the aluminum surface, which makes the connection of aluminum conductors more difficult than that of copper conductors and requires much higher technology. Failure to operate strictly according to the process requirements will lead to the failure of the specified electrical and mechanical strength of the joint. The actual operation proves that the cleaner the contact surface between the crimping hardware and the conductor, the thinner the oxide film and the smaller the contact resistance Rt when the joint temperature rises.
3. The wire is damaged. The cross-linked insulating layer has high strength and is not easy to peel and cut. During ring cutting, the construction personnel peeled the skin with an electrician's knife, and sometimes cut deep marks with a hacksaw, which led to wire damage due to poor mastery. When the wire core is bent and crimped, the conductor damage at the injured part will be aggravated or broken, which is not easy to find after crimping, and the cross section will be reduced, which will cause heat in severe cases.
4. The core of the wire connecting wire is not in place. When the conductors are connected, the insulation stripping length requires that the hole depth of the crimping fittings be 5 mm However, due to the nonstandard hole depth of the parts, the stripping length is not enough, or the gap is formed at the end of the conductor due to the position of the wire rope during crimping, the contact resistance Rt only increases the wall thickness of the fittings, which leads to an increase in heat generation.
5, the pressure is not enough. At present, the relevant information only mentions the number of pressure pits at each end of cable connection in the joint manufacturing process and standard drawing, and does not specify the pressure contact area and pressure contact depth in detail. The construction workers pressed enough pits as required, and the effect was uncertain. No matter what form of crimping, the joint resistance is mainly contact resistance, which is related to the contact force and actual contact area, and also to the output tonnage of crimping tools.
6. The pressure of crimping machine is insufficient. There are many manufacturers of crimping machines and tools, with chaotic management and no unified standard. Some mechanical wire crimping pliers and crimping pits are not only narrow, but also the upper and lower dies can not cooperate after crimping. There are also some manufacturers who buy or produce foreign models of wire crimping pliers. Due to the implementation of foreign standards, it is not suitable for the nominal cross section of domestic wires, and the quality of crimping is difficult to guarantee.
7. The gap between connecting fittings is very large. At present, the connecting fittings used in most units of XLPE cable connectors are still terminals and crimping tubes produced by oil-paper cables according to sector conductors. Theoretically speaking, the effective cross sections of circular and fan-shaped cores are the same, but compared with the actual operation, the crimping effects of the two cores are far from each other. Because the conductor of the cross-linked cable is a tightly twisted round wire core, there is a big gap with the inner diameter of the commonly used hardware fittings, and the compression force after crimping is not enough. The contact resistance Tt is inversely proportional to the applied pressure, which will lead to an increase in RT. ..
8. The product quality is poor. Fake and shoddy fittings are not only impure in material, rough in appearance, prone to cracks after pressing, but also irregular in specifications, and the effective cross section is quite different from the genuine ones, which can not meet the quality requirements of pressing. Under normal circumstances, the operation is very hot, and the slight fluctuation of load will inevitably lead to failure.
9. Insufficient cross section. Taking ZQ-3×240 oil-paper copper-core cable and YJV 22-3× 150 cross-linked copper-core cable as examples, the allowable current carrying capacity of cross-linked cable and oil-paper cable is compared at 25℃, and it is concluded that YJV 22-3×1can be used for ZQ2-3× 240 oil-paper copper-core cable. Because the allowable current carrying capacity of YJV 22-3× 150 cross-linked cable is 476A；; The allowable current carrying capacity of ZQ2-3× 240 oil-paper cable is 420A, which is more than 47A. If the allowable current capacity is calculated, the150mm2 cross-linked cable is basically the same as the 240mm2 oil-paper cable, or the150mm2 cross-linked cable can only work normally if it is connected with 240mm2 hardware. It can be seen that the insufficient cross-section of the connecting hardware will be an important reason for the serious heating of the cross-linked cable joint.
10, poor heat dissipation. For wrapped connectors and various cast connectors, not only the wrapped insulation is thicker than the cable cross-linked insulation, but also the mixture is injected into the shell, which is the smallest type of heat shrinkable connector, and its insulation and protective layer are more than twice that of the cable body, so it is difficult for any type of connector to dissipate heat. At present, the insulation materials of various joints have poor heat resistance, and the normal working temperature of J-20 rubber self-adhesive tape does not exceed 75℃. J-30 only reaches 90℃; The use condition of heat shrinkable material is -50 ~ 100℃. When the cable runs under normal load, the temperature in the joint can reach100℃; When the cable is fully loaded, the core temperature will reach 90℃ and the joint temperature will reach about 140℃. When the temperature rises again, the oxide film at the joint will become thicker and the contact resistance Tt will increase accordingly. Under the action of a certain power-on time, the insulation material of the joint will carbonize into non-insulation, leading to failure.
Third, technical improvement measures
To sum up, increasing the contact pressure of connecting fittings, reducing the operating temperature, cleaning the surface of connecting metal materials, improving the structural size of connecting fittings, selecting high-quality standard accessories and strict construction technology are several key factors to reduce the contact resistance RT. Countermeasures to improve the quality of cross-linked cable joints Because the environment and operation mode of cross-linked cable joints are different, the connected electrical equipment and locations are different, cable accessories have great choices in materials, structures and installation techniques, but the basic performance of various accessories is the same. Therefore, the joint quality should be improved from the following aspects:
1. Cable accessories with advanced technology, mature technology, reliable quality and suitable for use environment and conditions shall be selected. We must resolutely resist fake and shoddy products, focus on testing new technologies, new processes and new products, constantly sum up and improve them, and gradually popularize and apply them year by year.
2. High-quality connectors whose materials, specifications and sections meet the requirements and can run safely and reliably shall be adopted. For the terminal, try to choose the oil resistance type, because this kind of terminal generally has a large cross section, which can reduce heating and effectively solve the moisture-proof seal. The connecting pipe shall be made of copper rod or 1 # aluminum lathe, and the size shall match the diameter of the cross-linked cable core.
3. Choose a crimping machine with large crimping tonnage, good mold coordination, sufficient weld area and crimping effect that can meet the technical requirements. Do a good job of cross-section treatment before crimping and coat it with conductive adhesive.
4. Cultivate cable technicians who are skilled, skilled, conscientious and responsible and can carry out cable construction, installation, operation and maintenance. Improve the construction personnel's understanding of cross-linked cables and enhance their understanding of the characteristics of cross-linked cable accessories. Study technology, improve technology, formulate construction specifications, strengthen quality control and ensure safe operation.
Four. Concluding remarks
Due to the short popularization and application time of cross-linked cable, the variety of cable accessories is messy, and the technical level of construction personnel is different, the contact force and actual contact area of the joint change with the different operating conditions of the joint in operation.
Therefore, the failure reasons of various connectors of XLPE cables are different. Besides heating problems, attention should also be paid to joint failure caused by sealing problems, stress problems, connection problems and grounding problems. If we can improve from the above aspects, the problem of joint fever will be effectively controlled.
;