overhead cable

How many rumors do you know about wires and cables?

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The rapid development of the Internet age has not only brought convenience to everyone’s life, but also brought new challenges to our social management. In particular, we have seen the rapid spread of rumors. I believe you can distinguish many rumors, but how many rumors about wires and AAAC Cables have you heard? Can you identify it in time?


If the square of the wire is not enough, it will not be qualified?
not always! For many people, this is already a “common sense” existence, but is this really the case? With the improvement of conductor material production process and scientific and technological progress, the advanced production process of oxygen free copper has been widely used. The resistivity of copper conductor material is enough to ensure that the copper wire less than the nominal diameter can meet the requirements of DC resistance of corresponding specifications, while the conductor of wire and cable has strict requirements on the resistivity of conductor, for example, The DC resistance of 25 mm2 copper core conductor specified in the standard at 20 ° is not greater than 0.727 Ω / km (the second stranded conductor), so the conductor is qualified as long as it is not greater than this value.
Flame retardant ABC Cables will not burn?
wrong! Flame retardant of flame-retardant wire and cable refers to that when a wire and cable fire accident occurs, it can block and delay the diffusion and spread of flame along the wire and cable, and minimize the expansion of fire range of wire and cable. This type of cable has the characteristics of self extinguishing after fire. Fire resistant wire and cable refers to that in the case of wire and cable fire accident, the wire and cable product can adhere to the normal operation for a certain time under the condition that the external flame is still burning, maintain the integrity of wire and cable lines and maintain the normal operation of line equipment.
Will wires and cables have radiation?
Wires and cables do have radiation. However, the fact is that all live things have radiation. For example, 220V wires also have radiation, but the radiation is very small and basically negligible. Moreover, the radiation of wires is much lower than that of mobile phones. If you are really afraid of wire radiation, it is recommended to throw away the mobile phones first. If you are afraid of the magnetic field generated by wires and cables and think that the magnetic field will cause any harm to the human body, the geomagnetic field is even more terrible. Therefore, I think that “radiation from wires will damage health” is just groundless, and I think too much.


The thicker the cable insulation, the better?
No, too thick cable insulation will increase the difficulty of AAC Cable laying. At present, cable laying is mainly bridge or through pipe. Now many enterprises are implementing cable requirements, with tight cable requirements and small outer diameter. There can be gaps in the laying process to emit heat energy to ensure that the outer sheath of the cable is not damaged. Otherwise, it will bring some difficulties to the construction unit and cable laying. In summer, the working temperature will rise, and these temperatures will be emitted through the outer protective layer. The thickness of the sheath increases, and the heat energy is difficult to be emitted, which will affect the service life of the cable. Due to the thermal action of PVC, a series of physical and chemical changes will occur in the insulating layer, losing the original excellent performance, resulting in obvious decline in the insulating performance and even short circuit, Therefore, when selecting the cable, the thickness of the cable must be moderate.
The laying of water and electricity shall be horizontal and vertical
unnecessary! Although the water and electricity wires laid horizontally and vertically look very good, there are really many hidden dangers! Firstly, the material cost of the wire pipe is much higher than that of other laying methods. Secondly, because it is 90 degrees horizontally and vertically, it is easy to get stuck when threading the wire in the later stage! So as long as it complies with the specifications, how convenient it is to lay it!


In addition to the above, there are numerous rumors about wires and cables: wires and cables are cheap, so selling cables makes a lot of money; Wires of the same quality can certainly be bought at a cheaper price; The copper conductor used in wires and cables is not so high; Wires and cables will leak electricity in rainy days, which is unsafe.
Although some are rumors, it’s not too much to say that wires and cables are lifelines. We should be more careful when buying. Only by selecting manufacturers, products and national standard products can we use them at ease.

Advantages of high temperature superconducting cable

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Compared with traditional power cables, superconducting cables have the advantages of low loss, large transmission capacity, small ABC Cable volume and strong system security and stability. Cold insulated HTS cables have low mutual electromagnetic influence and thermal field influence, and have stable current carrying capacity. They have great development prospects in underground cable systems in densely populated big cities or specific high-capacity transmission applications. There are many underground pipe networks in big cities, various underground pipes (tunnels) are complex, and the space for cable laying is very limited. It is more and more difficult to install and lay traditional cables, and the installation and maintenance cost will be greatly increased. Using the existing pipe or cable tunnel and replacing the existing conventional cable with high temperature superconducting cable can double the transmission capacity of underground power grid and solve the contradiction between the increase of load and the limited underground space.


In terms of loss, the traditional cable transmission loss is mainly conductor loss, dielectric loss and shielding loss. Among them, for general land ACAR Cables, conductor loss accounts for about 95% of transmission loss. The loss of superconducting cable mainly includes: AC loss of cable conductor, Joule loss of cable terminal, heat leakage loss of superconducting cable insulation pipe, cable terminal and refrigeration system, loss of liquid nitrogen overcoming cycle resistance, etc. Considering the efficiency of refrigeration system, the operating loss of HTS cable is about 50% ~ 60% of that of conventional cable when transmitting electric energy of the same capacity.
The interconnection of large power grids is the trend of power development. With the interconnection of major power grids and the increase of power demand, the short-circuit current level of the system will further rise after short-circuit fault. How to solve the problem of fault current has attracted more and more attention of the power department. The transmission conductor of superconducting cable is superconducting material. Under normal working conditions, the transmission density of superconducting cable is large and the impedance is very low; In the case of power grid short-circuit fault and transmission current greater than the critical current of superconducting material, superconducting material will lose its superconducting ability, and the impedance of superconducting cable will be much greater than that of conventional copper conductor; When the fault is eliminated, the superconducting cable will restore its superconducting ability under normal working state. If the high temperature superconducting cable with certain structure and technology is used to replace the traditional cable, the power grid fault current level can be effectively reduced. The ability of superconducting cable to limit fault current is directly proportional to the cable length. Therefore, the large-scale superconducting transmission network composed of superconducting cables can not only improve the transmission capacity of the power grid and reduce the transmission loss of the power grid, but also improve its internal fault current limiting capacity and improve the safety and reliability of the whole power grid.


Internationally, the research and development process of HTS cable can be divided into the following three stages. The first stage is the preliminary exploration of HTS cable technology. With the development of bismuth (BI) high temperature superconducting tape technology, the research on high temperature superconducting cable has attracted extensive attention. The main contents of the research include: the research on the structure of superconducting AAAC Cable, including room temperature insulated (WD) high temperature superconducting cable, cold insulated (CD) high temperature superconducting cable, three-phase coaxial structure, three core in one structure, etc; Carry out research on electrical performance and transmission characteristics of superconducting cable. The second stage is the research and development of CD insulated HTS cable that can truly realize commercial application in the future. At the end of 1999, the 30m, three-phase, 12.5kv/1.25ka cold insulated HTS cable developed by southwire was connected to the grid, which has taken a solid step towards the practicability of HTS technology. The third stage is the demonstration project research of CD insulated HTS cable. In the past 10 years, the United States, Japan, South Korea, China, Germany and other countries have successively carried out a number of demonstration projects on CD insulated HTS cables.


When the traditional cable is running, the heat generated by the transmission loss is directly distributed to the surrounding environment, and its current carrying capacity is very sensitive to the external heat source. Generally, the current carrying capacity will decrease by 8% ~ 10% when the ambient temperature increases by 10 ℃. Therefore, intensive laying will lead to mutual heating of cables and sharp decline of current carrying capacity. According to the calculation, 2 × 4 rows of pipes, 3 × 3 rows of pipes and 4 × The current carrying capacity of traditional cables with dense 4-row pipes will be reduced by about 20%, 30% and 40% respectively. At the same time, because the traditional cable uses combustible organic materials as the main insulation, it is very easy to cause fire in case of failure. The outermost layer of CD insulated HTS cable is a composite vacuum insulation layer, which has good thermal insulation performance. The heat generated by the cable is taken away by circulating liquid nitrogen. Therefore, the thermal field of superconducting cable is relatively independent and the cable has stable current carrying capacity. At the same time, due to the good electromagnetic shielding function of CD insulated superconducting cable, it can completely shield the electromagnetic field generated by the cable conductor in theory, so it will not cause electromagnetic pollution to the environment. Due to these advantages, superconducting cables can be laid in dense ways such as underground pipes, which will not affect the operation of surrounding power equipment, and because it uses non combustible liquid nitrogen as refrigerant, it also eliminates the risk of fire.

Current situation of power cable and accessories

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Insulating materials and shielding materials for power cables, especially materials for high-voltage and ultra-high-voltage XLPE insulated AAAC Cables, are prominent “soft ribs” or “short boards” of China’s cable industry in this field (all sheath materials have been localized).

1. Medium and low voltage power cable materials
Medium and low voltage power cables are mostly insulated with cross-linked polyethylene (XLPE). XLPE takes low-density polyethylene resin (LDPE below) as the main raw material, adds antioxidant and peroxide cross-linking agent, and is made into cable material through mixing, plasticization and granulation. It has many categories, including chemical cross-linking, hospital cross-linking, irradiation cross-linking, ultraviolet cross-linking, etc. XLPE insulating materials of 35kV and below have all been localized.
Among them, chemical crosslinking and silane crosslinking technologies and applications are very mature, irradiation crosslinking and UV crosslinking materials have also been widely used, and water tree resistant materials for medium voltage cables have been more and more applied.
The performance of XLPE insulating materials of 35kV and below fully meets the use requirements, but there are still gaps in process performance stability and long-term service life reliability compared with foreign advanced products: first, the performance stability of synthetic resin in chemical industry; Second, the fierce market competition forces the cable material production enterprises to consider the cost too much and seek to use low-cost raw materials.
Domestic manufacturers with batch supply capacity of 35kV XLPE cable materials mainly include Zhejiang Wanma polymer, Qingdao hancable, Shanghai chemical plant, Henan Wanbo Plastic Co., Ltd.

2. 110kV High Voltage Cable Materials
High voltage and ultra-high voltage ACSR Cables require that the insulating materials must be ultra purified. The main foreign suppliers are petrochemical enterprises, which complete the manufacturing from the fully enclosed ultra purification production process of petroleum cracking ethylene polymerization ultra clean material synthesis, such as Nordic chemical, Dow Chemical of the United States, NUC of Japan, Hanhua of Korea, etc.
At the initial stage of domestic high-voltage cable manufacturing (including the early 35kV cross-linked polyethylene cable material), all imported materials are used, especially Nordic chemical and American Dow Chemical (formerly United Carbon Corporation) account for a relatively high proportion in the domestic market.
During the 12th Five Year Plan period, China’s 110kV high-voltage cable insulation material made a technological breakthrough and realized domestic small batch production. Since 2012, 110kV ultra clean insulation material has been gradually used in cable manufacturing and power engineering.
During the 13th Five Year Plan period, great progress was made through independent research and development, introduction of key process equipment and cooperation with upstream petrochemical enterprises. Among them, major high-voltage cable manufacturing enterprises or cable material manufacturing enterprises jointly with petrochemical enterprises to form a preliminary manufacturing chain from basic resin synthesis to cable material manufacturing and then to high-voltage cable manufacturing and application. For example, the cooperation between Qingdao hancable Co., Ltd. and Yanshan Petrochemical Company, the cooperation between Zhejiang Wanma Gaoli Materials Co., Ltd. and Yangzi Petrochemical Company, the cooperation between Jiangsu Dewei new materials Co., Ltd. and Yangzi BASF company, and the introduction of a full set of equipment and technology by Yanshan Petrochemical Company have formed mass production capacity.
At present, the process technology and production capacity of producing high-voltage cross-linked polyethylene insulating material and shielding material with different equipment and process methods have been formed, with a total production capacity of about 80000 tons / year (including the material capacity for ultra-high voltage cable).

3. EHV cable materials
Insulation and shielding materials for 220kV EHV AAC Cables have higher requirements for purification, such as impurity content, quantity and size. The main bottleneck of ultra clean insulating material is the localized supply of ultra clean special raw material LDPE. In addition to the basic resin, the selection of compounding agent system, formulation technology, storage and transportation environment of insulating materials, factory production environment, etc. will eventually affect the insulation performance of cables.
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The main problems of LDPE raw materials are processing rheological properties, melt index, molecular weight distribution uniformity, impurity content and other technical requirements. First, there are strict requirements on the fluctuation range of LDPE melt index, which determines the softening temperature range of LDPE and ensures the uniform plasticization of cable insulation layer, process dimensional stability and surface smoothness under certain process conditions. Second, the requirements for impurity content are very strict. The production workshop is required to reach level 1000, and the special process is even level 100. Materials do not contact with the outside world from production, packaging (tank car or pipeline) to use. Pay attention to the control of impurities and water content from the beginning of resin synthesis.
At present, Qingdao hancable Co., Ltd., Zhejiang Wanma polymer Co., Ltd. and Jiangsu Dewei new materials Co., Ltd. have the batch production capacity of super clean XLPE insulation and shielding materials for 220kV EHV cables, but the actual use is almost imported, with an annual consumption of more than 20000 tons, and the consumption of domestic materials is very small.
Semi conductive shielding materials for high-voltage and ultra-high-voltage cables are mainly used for the internal and external shielding layers of high-voltage XLPE cables. They are also required to be super clean and super smooth. The impurity content in the shielding material, the smoothness of the shielding layer and the adhesion between the shielding layer and the insulating layer will greatly affect the performance of XLPE cable. At present, several domestic semi-conductive shielding materials for 35kV and below cables have been produced and can meet the cable performance requirements, but the semi-conductive shielding materials for 110kV and above have more stringent requirements on basic resin, additives, carbon black types, extrusion equipment, manufacturing process and production environment. China is still in the stage of R & D and trial in this field, The shielding materials used are mainly imported by Nordic chemical and Dow chemical companies, and a small amount are provided by domestic enterprises.
According to statistics, the total domestic annual demand for insulation and shielding materials (including submarine cables and DC cables) for 110kV and above high-voltage and ultra-high-voltage cross-linked cables in 2019 is about 70000 tons, of which the actual use of domestic materials is about 10000 tons (mainly 110kV land AC cables), and another about 2000 tons are exported to the international market.
At present, compared with international advanced technologies, processes and products, the domestic production of 110kV and above XLPE ultra clean cable materials mainly has the following gaps:
1) There is a lack of systematic research on the basic resin of ultra-high pressure and ultra clean polyolefin material, and the development, polymerization, ultra clean synthesis process and material performance evaluation technology of basic resin need to be solved urgently;
2) As the domestic production process from the preparation of ultra clean polyethylene resin to the synthesis of ultra clean materials has not been formed, it brings new difficulties to the storage and transportation guarantee. There are also many new technical problems in the ultra clean technology and process of ultra clean material preparation (including impurity filtration technology, performance evaluation and quality control system) to ensure the stability and continuity of polyolefin cable material preparation;
3) The production time of localization is not long, and more process test and application data still need to be accumulated. In particular, the evaluation and evaluation of the long-term service reliability of the made cable is also an important work to obtain the full confidence of power users in the materials and recognize the application.
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4. Materials for high voltage and ultra-high voltage submarine cables
High voltage and ultra-high voltage submarine cables require higher production technology and more complex service environment, so they have higher requirements for cable materials.
At present, the most important raw materials for the production of high-voltage submarine cables – insulating materials and shielding materials have not been localized. Whether it is AC high-voltage submarine cables or DC high-voltage submarine cables, only Nordic chemical and American Dow Chemical Company can provide them in the international market.
The insulation and shielding materials of high-voltage and ultra-high-voltage submarine cables used by China’s submarine cable manufacturing enterprises all rely on imports, including DC cable materials. Due to the imbalance between supply and demand, there is an obvious seller’s market. The R & D and production of high-voltage submarine cable insulation and shielding materials is also an urgent task for China’s cable industry. It is necessary to continue to deepen research and production on the basis of localization of high-voltage and ultra-high-voltage cable materials.

Underground cable is the trend of urban development

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Install “perspective eyes” for underground cables
In many cities in China, especially in some metropolises or new urban areas, power towers and wires are basically invisible, but thousands of households can use electricity normally. Where does people use electricity come from? In fact, this mainly depends on underground cables to transmit electric energy.
Underground cable is an important way of power transmission. The continuous power supply is realized by establishing underground channels and laying cables. In recent years, scientific and technological personnel have become more and more capable of controlling underground cables, and new technologies have been introduced, popularized and applied, which has laid a solid foundation for the all-round development of underground AAC Cables.


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Underground cable is the trend of urban development
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With the acceleration of China’s economic development and urbanization, the contradiction between power facilities and urban development is becoming increasingly prominent. In order to ensure the power safety of urban residents and keep the city clean and beautiful, it is necessary to reduce the starry overhead transmission lines over the city, set them underground and develop underground ACSR Cables.
According to statistics, the proportion of underground power transmission in some modern cities in the world, such as Berlin, Tokyo, Osaka and Copenhagen, has exceeded 70%. At present, China is also accelerating the construction of overhead wire into the ground, underground cable project and underground comprehensive pipe gallery. By 2017, the total length of Beijing underground cable tunnel is about 800 km. It is expected that by the end of the 13th five year plan, the underground cable utilization rate in Beijing’s core area will increase to 94% and the power supply reliability rate will increase to 99.999%.
In 2014, the State Council issued the guidance of the general office of the State Council on strengthening the construction and management of urban underground pipelines. In 2016, the Ministry of housing and urban rural development issued the 13th five year plan for the development and utilization of urban underground space. These documents require deployment to strengthen the construction and management of urban underground pipelines and ensure the safe operation of the city. As a national new area planning, xiong’an new area will adopt the underground pipe gallery mode for the construction of underground pipe network, and deploy water, electricity and urban transportation to the underground space.
In response to the call of the state, State Grid Corporation of China issued document No. 1459 notice on the planning and use management specification of urban power cable channel and the guidance on the planning and construction of power cabin of urban comprehensive pipe gallery in 2014. In the face of the increasing number of underground transmission lines, State Grid Corporation of China further standardized and strengthened the management of underground cables.


With the rapid development of underground cables, the number of underground pipelines will become larger and larger, and the space will become more and more crowded. Construction, operation and maintenance, management and other parties will face great difficulties and pressure. Therefore, there is an urgent need for an effective method to solve this problem. With the rapid development of information technology, three-dimensional digital technology stands out. Using this technology can realize the “perspective” and intelligent management of underground cables.
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What is 3D digital technology?
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The so-called “three-dimensional digitization” is to use three-dimensional tools (software or instruments) to realize a series of digital operations such as virtual creation, modification, improvement and analysis of the model. Generally speaking, it is to use computer technology to virtually appear any scene and object in real life in the computer, so as to realize the undifferentiated mapping from the real world to the computer virtual world.
The traditional three-dimensional digital technology mainly focuses on the modeling of the physical appearance. Based on the modeling software, the solid appearance is simulated in the computer by using the solid construction and rendering technology, which mainly meets the needs of display. At this stage, the three-dimensional digital technology has been upgraded on the original basis. In addition to truly simulating the appearance of the real object, it also includes a series of relevant information such as accurate size, volume, weight, material and management. The three-dimensional digital model constructed in this way belongs to the information model, which can not only meet the visualization requirements, but also carry out a series of calculation, analysis and management.


In August this year, China Electric Power Research Institute Co., Ltd., a scientific research institution directly under the State Grid Corporation of China, used three-dimensional digital technology to build a digital design system for power cable engineering. The system supports the construction of underground cable information model with voltage level of 35 kV to 500 kV, including different types of underground cable lines such as pipe arrangement, tunnel, comprehensive pipe gallery (power cabin), cable trench, bridge and direct burial. It not only realizes the three-dimensional digitization of the underground cable engineering body, but also supports the above ground buildings in the power corridor 3D visualization of the surrounding environment of other types of underground pipelines. Based on the completed three-dimensional digital model, the safe distance between the underground cable engineering body and the surrounding environment can be calculated, and a series of work such as cable engineering body planning, design, construction and management can be carried out. In addition, in order to save the construction time of underground cable informatization model and improve the model accuracy, the system has built three-dimensional general model libraries such as pipe arrangement, tunnel, cable trench, bridge and working well according to the general design library of State Grid, and provided parametric modeling tools such as pipe arrangement, tunnel, comprehensive pipe gallery (power cabin), AAAC Cable trench, bridge and direct burial, Have the ability to automatically build a 3D model by inputting parameters.

How to solve these problems in PVC

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1、 Troubleshooting of common faults in injection molding of ACSR Cables
Under note
Fault analysis and Troubleshooting:
(1) The temperature of the melt is too low. The forming temperature should be increased properly.
(2) Forming cycle is too short. It should be extended appropriately.
(3) Insufficient injection pressure. It should be improved appropriately.
(4) The injection rate is too slow. It should be accelerated appropriately.
(5) Insufficient supply. The supply shall be increased.
(6) The temperature of the die is too low, so it should be properly raised. In particular, the cooling circuit of the mold should be set reasonably to keep the temperature of the mold uniform.


(7) The shape and structure of plastic parts are not designed reasonably or the wall is too thin. Adjustments should be made in the event of possible changes.
(8) The structure size of the pouring system is small. Gate and runner sections shall be enlarged appropriately.
(9) The exhaust of the mold is poor. The exhaust hole should be added to improve the exhaust performance of the AAAC Cables.
(10) The strength of the die is not enough. The rigidity should be improved as much as possible.
· shrinkage marks
Fault analysis and Troubleshooting:
(1) The barrel temperature is too high. The barrel temperature shall be properly reduced.
(2) Insufficient injection pressure. It should be improved appropriately.
(3) The holding time is too short. It should be extended appropriately.
(4) The cooling time is too short. The cooling efficiency shall be improved or the cooling time shall be prolonged.
(5) Insufficient supply. The supply shall be increased.
(6) The temperature of the die is not uniform. The cooling system of the mould should be adjusted and the cooling circuit should be set reasonably.
(7) The shape structure design of plastic parts is unreasonable or the wall of plastic parts is too thick. Adjustments should be made where possible.
(8) Gate cross section is too small. It should be increased appropriately.
· weld marks
Fault analysis and Troubleshooting:
(1) The temperature of the melt is too low. The forming temperature should be increased properly.
(2) Insufficient injection pressure. It should be improved appropriately.
(3) The injection rate is too slow. It should be accelerated appropriately.
(4) The temperature of the die is too low, so it should be properly raised.
(5) The gate section is too small. It should be increased appropriately.
(6) Poor exhaust of mould. The exhaust hole should be added to improve the exhaust performance of the die.
(7) The structure size of cold material hole is too small or the position is not correct. It should be adjusted reasonably.
(8) Impurities are mixed in the raw materials. Foreign matters and impurities shall be removed thoroughly or new materials shall be used.
(9) The dosage of release agent is too much. The amount of the product should be minimized.
(10) The insert is not set up reasonably. It should be adjusted appropriately.
(11) The raw material is not uniformly colored. The colorant with good dispersibility and the mixing time should be prolonged to make the raw material coloring even.
Flow marks
Fault analysis and Troubleshooting:
(1) The temperature of the melt is too low. The forming temperature should be increased properly.
(2) Insufficient injection pressure. It should be improved appropriately.
(3) The holding time is too short. It should be extended appropriately.
(4) The temperature of the die is too low, so it should be properly raised.
(5) The temperature of the die is not uniform. The cooling system of the mould should be adjusted and the cooling circuit should be set reasonably.
(6) Gate cross section is too small. It should be increased appropriately.
(7) The structure size of cold material hole is too small or the position is not correct. It should be adjusted reasonably.
(8) The raw material is not uniformly colored. The color additive with good dispersibility should be selected, and the mixing time should be prolonged.


Poor gloss
Fault analysis and Troubleshooting:
(1) The temperature of the melt is too low. The forming temperature should be increased properly.
(2) The molding cycle is too long. It should be shortened appropriately.
(3) Screw back pressure is too low. It should be improved appropriately.
(4) The temperature of the die is too low, so it should be properly raised.
(5) The structure size of the pouring system is small. Gate and runner sections shall be enlarged appropriately.
(6) Poor exhaust of mould. The exhaust hole should be added to improve the exhaust performance of the die.
(7) Impurities are mixed in the raw materials. Foreign matters and impurities shall be removed thoroughly or new materials shall be used.
(8) The dosage of release agent is too much. The amount of the product should be minimized.
(9) Raw materials are not fully dried. The drying temperature and time should be increased appropriately.
· bubbles
Fault analysis and Troubleshooting:
(1) The barrel temperature is too high. The barrel temperature shall be properly reduced.
(2) The molding cycle is too long. It should be shortened appropriately.
(3) Insufficient injection pressure. It should be improved appropriately.
(4) The injection speed is too fast. It should be slowed down appropriately.
(5) The holding time is too short. It should be extended appropriately.
(6) The temperature of the die is not uniform. The cooling system of the mould should be adjusted and the cooling circuit should be set reasonably.
(7) The shape structure design of plastic parts is unreasonable or the wall of plastic parts is too thick. Adjustments should be made where possible.
(8) Gate cross section is too small. It should be increased appropriately.
(9) The exhaust of the mold is poor. The exhaust hole should be added to improve the exhaust performance of the die.
(10) Raw materials are not fully dried. The drying temperature and time should be increased appropriately.
? uneven color
Fault analysis and Troubleshooting:
(1) The barrel temperature is too high. The barrel temperature shall be properly reduced.
(2) The molding cycle is too long. It should be shortened appropriately.
(3) The raw material is not uniformly colored. The color additive with good dispersibility should be selected, and the mixing time should be prolonged.
Burnt and black
Fault analysis and Troubleshooting:
(1) The barrel temperature is too high. The barrel temperature shall be properly reduced.
(2) The molding cycle is too long. It should be shortened appropriately.
(3) The injection pressure is too high. It should be reduced appropriately.
(4) The injection rate is too fast. It should be slowed down appropriately.
(5) Screw back pressure is too high. It should be reduced appropriately.
(6) Gate cross section is too small. It should be increased appropriately.
(7) The exhaust of the mold is poor. The exhaust hole should be added to improve the exhaust performance of the die.
(8) The dosage of release agent is too much. The amount of the product should be minimized.
(9) Raw materials are not fully dried. The drying temperature and time should be increased appropriately.
· overfill edge


Fault analysis and Troubleshooting:
(1) The temperature of the melt is too high. The temperature of the barrel and the nozzle shall be properly reduced.
(2) The injection pressure is too high. It should be reduced appropriately.
(3) The injection rate is too fast. It should be slowed down appropriately.
(4) The holding time is too long. It should be shortened appropriately.
(5) There is too much supply. It should be reduced appropriately.
(6) The closing force is insufficient. It should be improved appropriately.
(7) The mold temperature is too high. It should be reduced appropriately.
(8) The shape structure design of plastic parts is unreasonable, and should be adjusted appropriately in case of possible changes.
(9) The strength of the die is not enough. We should try to increase its rigidity.
(10) The insert is not set up reasonably. According to the shape of plastic parts and the structure of the mold, proper adjustment shall be made.
Warping and deformation
Fault analysis and Troubleshooting:
(1) The barrel temperature is too low. It should be improved appropriately.
(2) Forming cycle is too short. It should be extended appropriately.
(3) The injection pressure is too high. It should be reduced appropriately.
(4) The injection speed is too fast. It should be slowed down appropriately.
(5) The holding time is too long. It should be shortened appropriately.
(6) The mold temperature is too high. It should be reduced appropriately.
(7) The cooling system of the mould is not reasonable, and the cooling circuit should be set reasonably according to the cooling requirements of the plastic structure.
(8) Gate cross section is too small. It should be increased appropriately.
(9) The setting of ejector is unreasonable. The area of jacking out and the point of jacking shall be increased as much as possible.
(10) The strength of the die is not enough. We should try to increase its rigidity.
· delamination
Fault analysis and Troubleshooting:
(1) If the melt temperature is too low, the temperature of the barrel and nozzle should be increased properly.
(2) The injection rate is too fast. It should be slowed down appropriately.
(3) The mold temperature is too low. It should be improved appropriately.
(4) Impurities are mixed in the raw materials. Foreign matters and impurities shall be removed thoroughly or new materials shall be used.
? discoloration of the surface
Fault analysis and Troubleshooting:
(1) The barrel temperature is too high. It should be reduced appropriately.
(2) The molding cycle is too long. It should be shortened appropriately.
(3) The injection rate is too fast. It should be slowed down appropriately.
(4) Screw back pressure is too high. It should be reduced appropriately.
(5) The gate section is too small. It should be increased appropriately.
(6) Poor exhaust of mould. The exhaust hole should be added to improve the exhaust performance of the die.
(7) Impurities are mixed in the raw materials. Foreign matters and impurities shall be removed thoroughly or new materials shall be used.
2、 Troubleshooting of common faults in injection molding of soft PVC
Poor gloss on the surface of the product
Fault analysis and Troubleshooting:
(1) The processing temperature is too low, and the material is not plasticized. The processing temperature should be improved properly to improve the plasticizing effect.
(2) The mold temperature is too low. The mold temperature should be increased appropriately.
(3) The material fluidity is too bad, the raw material should be replaced or the raw material formula should be adjusted.
(4) The surface finish of mold cavity is too poor. The surface finish of mold cavity should be improved properly.
(5) During the forming process, the auxiliary agent precipitates, and forms scaling on the surface of the mold. The mold surface scale should be removed in time. If it is serious, the formula should be adjusted.
(6) Too much recycled material. The amount of recycled material shall be reduced appropriately.
(7) The material temperature is too high, and the resin is decomposed. The injection temperature should be reduced and the thermal stability system should be improved.
? shrinkage deformation
Fault analysis and Troubleshooting:
(1) The holding time is too short. The time of pressure preservation should be prolonged, especially when shrinkage occurs near the gate, the method of prolonging the pressure holding time can be used to solve.
(2) The pressure holding pressure is too low. The pressure holding time should be improved properly.
(3) Injection pressure is too low. Injection time should be improved appropriately.
(4) The molding temperature is too high. The forming temperature shall be reduced appropriately.
(5) The amount of feed is insufficient. The amount of feed shall be increased appropriately.
(6) The mold temperature is too high or the heating is uneven. The cooling efficiency of the mould should be improved.
(7) The mold is opened too early and the product cooling is insufficient. The cooling time of the product in the mold shall be extended.
(8) The thickness difference of the products is too big, and the parts of the thickness of the products in process are prone to sag shrinkage due to the insufficient pressure. The design of the product shall be modified.
(9) Gate cross section is too small. It should be increased appropriately.
Under injection, lack of material
Fault analysis and Troubleshooting:
(1) Injection pressure or pressure retaining pressure is too low. Injection pressure or pressure retaining pressure should be increased appropriately.
(2) The holding time is too short. The holding time shall be extended appropriately.
(3) The processing temperature is too low. The processing temperature should be raised appropriately.
(4) The injection rate is too slow. The injection speed should be increased appropriately.
(5) The temperature of the mold or nozzle is too low. The temperature of the mold or nozzle shall be increased appropriately.
(6) Impurities or decomposition are blocked at the nozzle. The injection molding machine nozzles shall be cleaned.
(7) The gate section is too small. It should be increased appropriately.
(8) The exhaust hole of the mold is blocked. The plug in the die vent should be removed.
(9) Injection rate of injection molding machine is too small. The injection volume should be increased appropriately.
Coking decomposition
Fault analysis and Troubleshooting:
(1) The injection temperature is too high, the material is coking and decomposed, and the focus of the product is formed with the injection mold of the molten material. The injection temperature should be properly reduced to remove foreign matters from the dead angle of the barrel and the runner.
(2) Injection speed is too high. The injection rate should be reduced properly.
(3) Impurities or decomposition are blocked at the nozzle. The injection nozzle shall be cleaned.
(4) The thermal stability of raw materials is too poor. The material should be replaced or the formula adjusted to improve the thermal stability system.
(5) The lubricant is not used enough. The lubricant dosage should be increased appropriately.
(6) Poor exhaust of mould. The die exhaust system should be improved.
(7) The gate section of the mold is too small. The gate section of the mold shall be expanded appropriately.

What is the difference in the temperature resistance of cables?

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UL standard

In UL standard, the common temperature resistance grades are 60 ℃, 70 ℃, 80 ℃, 90 ℃, 105 ℃, 125 ℃ and 150 ℃. How do these temperature ratings come? Is it the long-term operating temperature of the conductor? In fact, these so-called temperature ratings are called rating temperature in UL standards. It is not the long-term operating temperature of the conductor.
▍ rated operating temperature
If the reverse push method is adopted in UL standard system, it can be concluded that: a material aged for 300 days at a temperature a ℃ and its elongation rate is no more than 50%. Then the temperature a is subtracted by 5.463, and then divided by 1.02 to obtain the temperature B ℃, and the rated temperature of temperature B ℃ can be determined. This rated temperature is by no means the maximum long-term working temperature of the conductor allowed by the insulating layer. Because the “long term” in the long-term maximum working temperature should be the service life of the cable at this working temperature, which should be calculated at least in years. For example, in the photovoltaic AAC Cable standard en50618, the service life of the cable is designed to be 25 years, and the rated temperature in UL standard is generally higher than the long-term maximum working temperature of the conductor.


▍ short term aging temperature
The short-term aging temperature of materials, that is, the most common 7 days and 10 days in the standard, such as 105 ℃ materials, aging conditions are 136 ℃ × Seven days. So what is the relationship between this and the rated temperature? In UL standard, the temperature of short-term aging is obtained by the long-term experience of materials, but some methods are also summarized to confirm. The short-term aging temperature of a material is determined as described in ul2556-2007, chapter 4.3.5.6 and appendix D. First, select a rated temperature, aging temperature and aging time according to Table 1-1. If the elongation change rate of the material tested according to the above conditions is greater than 50%, it is recognized that the aging temperature can be determined according to this condition. If the elongation change rate is more than 50%, the rated temperature and short-term aging temperature of the material shall be reduced by one grade.

En/iec standards

In en/iec standards, rated temperature is rarely seen as UL standard, instead of conductor long-term operating temperature or temperature index. So what is the difference between the two temperatures?
In fact, in the en/iec standard system, the evaluation of the temperature resistance of AAAC Cables is mainly conducted according to en 60216 or IEC 60216. This standard is mainly used to evaluate the thermal life of insulating materials. The evaluation method is to test the aging of the material at different temperatures, and take the change rate of elongation at break as the end point of aging, and get the aging days of the materials at different temperatures. Then, the aging days and aging temperature are treated by linear regression, and a linear relationship curve is obtained. Then, the maximum operating temperature is determined according to the life of the cable, or the service life of the cable is determined according to the long-term working temperature. The temperature index refers to the temperature corresponding to the change rate of elongation at break when the change rate of insulation material is 50% after the heat aging of 20000h. Taking the PV cable standard EN 50618:2014 as an example, the design life of the cable is 25 years, the long-term working temperature is 90 ℃, and the temperature index is 120 ℃. The short-term aging temperature of insulating materials is also derived from the linear relationship. Therefore, the aging temperature of insulation materials in en 50618:2014 is 150 ℃. This aging temperature is very close to the aging temperature of materials rated 125 ℃ in UL standard series at 158 ℃.


It is not difficult to see that the long-term working temperature of the same conductor is different due to the different design life of the cable, and the aging temperature may be different. Under the same long-term working temperature, the shorter the design life of cable, the lower the short-term aging temperature of insulation materials can be required. For example, the long-term maximum working temperature of XLPE insulation required in IEC 60502-1:2004 is 90 ℃, while the aging temperature of this material is 135 ℃. The 135 ℃ here is very close to the aging temperature of 136 ℃ rated at 105 ℃ in UL standard, but it is much different from the aging temperature of insulation in en 50618:2014, which is also the longest-term maximum working temperature of 90 ℃. Although the design life of the cable was not found in 60502-1:2004, the design life of the two cables must be different.

National and industrial standards

In the process of compiling national and industrial standards, many contents refer to UL standard or en/iec standard. But because it is a multi-party reference, some of the statements I think are inaccurate. For example, in gb/t 32129-2015, jb/t 10436-2004 and jb/t 10491.1-2004, the temperature resistance grades of both materials and wires are 90 ℃, 105 ℃, 125 ℃ and 150 ℃, which is obviously used for reference to UL standard system. However, the expression of heat resistance is the maximum allowable conductor operating temperature for a long time. The expression of heat resistance is also clearly referred to the IEC standard system. In IEC standard system, the long-term maximum working temperature of conductor should be related to the design life of cable. However, there is no expression of cable life in these national standards and line standards. Therefore, the expression of “the maximum allowable operating temperature of the applicable cable conductor in a long term is 90 ℃, 105 ℃, 125 ℃ and 150 ℃” remains to be discussed.
Can XLPE of silane crosslink reach the temperature resistance level of 125 ℃? The more rigorous answer should be that the silane crosslinked XLPE can reach the rated temperature of 125 ℃ specified in UL standard, because in the general provisions of insulation and sheath materials in ul1581 chapter 40, it is clearly proposed that no provisions on the chemical composition of the materials are made. Whether the XLPE conductor can work at 125 ℃ for a long time is related to the design life and the use situation of the cable. At present, no relevant data system has been found to evaluate the life of the material. It is estimated that if the design life of cable is 25 years, the maximum temperature of conductor allowed in long term can be more than 90 ℃. In IEC standard, the maximum working temperature of traditional power cable, building line and solar cable design conductor will not exceed 90 ℃, but it does not mean that the maximum allowable temperature of long-term maximum working temperature of materials used for such cables cannot be greater than 90 ℃. It is also impossible to say that the irradiation crosslinking material can reach the temperature resistance level of 125 ℃, while the silane crosslinking material can not reach the temperature resistance level of 125 ℃, which is unreasonable.
In short, whether a material can reach a certain temperature level cannot be simply answered, or not, but should be considered in combination with the evaluation method of material temperature resistance grade or the design life of cable, and it is not allowed to mix several standard systems with random use.

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What is the difference between copper conductor and copper alloy cable?

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Copper bar is the main raw material of AAC Cable industry. There are two main production methods: continuous casting, continuous rolling and continuous casting. Due to different processes, the oxygen content and appearance of copper rods are also different. When the oxygen content is lower than 10ppm, it is called oxygen free copper rod; When the oxygen content is less than 10ppm, it is called oxygen free copper rod.


Low oxygen copper rod
Disadvantages of process D:
The electrolytic copper melts when it is added. There is no complete reduction condition for copper water. The whole smelting process and copper water process are inseparable from oxygen, so the oxygen content is very high. The fuel for molten copper is usually gas. In the process of gas combustion, it will directly affect the chemical composition of liquid copper. Sulfur and hydrogen are the most important factors.
Process advantages:
(1) High yield. Generally, the output of small units can reach 10-14 tons per hour.
(2) The layout of copper bar adopts plum blossom type, which is convenient for wire drawing machine.
(3) Bearing capacity, generally not more than 4 tons per plate.
Grade and characteristics of low oxygen copper rod: low oxygen copper rod
It is divided into three levels: T1, T2 and T3. The low oxygen copper bar is hot rolled, so it is a soft bar, code R.
(1) T1: production of low oxygen copper rod with high purity electrolytic copper as raw material (copper content greater than 99.9975%).
(2)T2：1 × The low oxygen copper rod (copper content above 99.95%) is made of electrolytic copper.
(3)T3：2 × The low oxygen copper rod (copper content above 99.90%) is made of electrolytic copper. Due to high purity electrolytic copper and 2 × Electrolytic copper is very few, generally 1 × Electrolytic copper is used as raw material, so the grade of low oxygen copper rod is T2R.


Oxygen free copper rod
Oxygen free copper rod is pure copper without oxygen or any deoxidizer residue. But in fact, it still contains a very small amount of oxygen and some impurities. According to the standard, the oxygen content is not more than 0.02%, the total impurity content is not more than 0.05%, and the copper purity is more than 99.95%.
It is generally produced by electrolytic copper, and its resistivity is lower than that of low oxygen copper rod. Therefore, oxygen free copper rod is more economical in the production of products with strict resistance requirements; High quality raw materials are needed to make oxygen free copper rods;
According to the oxygen content and impurity content, the oxygen free copper rod can be divided into TU1 and TU2 copper rods. The purity of TU1 oxygen free copper rod is 99.99%, and the oxygen content is not more than 0.001%; The purity of TU2 oxygen free copper is 99.95%, and the oxygen content is not more than 0.002%.


The difference between the two
Due to different manufacturing methods, low oxygen copper rod and oxygen free copper rod have their own characteristics.
1、 On the removal of oxygen and its existing state
Oxygen content of low oxygen copper rod is generally 200 (175) – 400 (450) ppm, so oxygen is inhaled into liquid copper. On the contrary, the oxygen in the oxygen free copper rod is reduced and removed after a certain period of time. Generally, the oxygen content of bar is below 10-50ppm, and the lowest is 1-2ppm. Oxygen content in oxygen free copper is very low, so the structure of copper is uniform and single-phase, which is conducive to toughness.
2. Difference between impurity content and existing hot rolling defects
The tensile properties of oxygen free copper bar are better than that of oxygen free copper bar in all wire diameters. In addition to the above microstructure reasons, the oxygen content of oxygen free copper bar is less and stable, there is no possible defect in hot rolling, the oxygen monitoring is not strict, and the oxygen content is unstable, which will directly affect the performance of copper bar. If the oxide on the surface of the bar can be made up in the continuous cleaning of the subsequent process, the problem is that there are quite a lot of oxide under the skin, which has a more direct impact on the broken wire.
3. The toughness of low oxygen copper rod is different from that of oxygen free copper rod
Both can be pulled to 0.015 mm, but the distance between low temperature grade oxygen free copper wires is only 0.001 mm.
4. Low oxygen copper rod
The wire making process of copper rod is different from that of oxygen free copper rod. The wire making process of low oxygen copper bar should be the same as that of oxygen free copper bar, at least the annealing process of the two should be different. Because the softness of wire rod is greatly affected by material composition, bar manufacturing, wire manufacturing and annealing process, it can not be simply said that low oxygen copper or oxygen free copper is soft or hard.

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Discussion of the cable production process: conductor stranding

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Discussion on the cable production process: conductor twisting and twisting
: the process of twisting many small diameter monofilaments into a large cross-section conductive core according to certain rules.
1. There are two types of twisted wires: normal twisted wires and irregular twisted AAC Cables.
Ordinary strands can be divided into ordinary concentric single stranded strands and ordinary concentric single stranded strands
(1) Ordinary stranded wire: single wires of the same diameter are twisted layer by layer according to concentric circles, and the direction of each layer is opposite.
(2) Combined stranded wire: made of a single wire of the same diameter, different materials or different diameters and different materials (representative products (such as overhead conductors))
Ordinary concentric stranded wire: a multi-stranded ordinary stranded wire or bundle Stranded wire concentrically stranded.
Irregular stranding (strand): strands formed by multiple single strands in the same direction, which does not comply with the law of twisting. The positions of the single strands are not fixed to each other, and the shape of the strands is difficult to maintain Round.

2. The biggest difference between the bundle wire and the ordinary stranded wire is that each single wire of the ordinary stranded wire has a fixed position and is regularly twisted layer by layer. There is no fixed position between the single wires of the bundle According to the law of twisting, the position will not be twisted together.
3. The characteristics of irregular twisting (bundling) : Since each single wire in the bundle is twisted in one direction, there is a residual amount of sliding between each single wire during bending. The amount is large and the bending resistance is small, so the bending performance of the bundle is particularly good. For wire and cable products that need to be flexible and frequently moved, the wire bundle is used as the conductor core.
4. The characteristics of the stranded core:
(1) Flexibility Good; by using a core composed of several single wires with smaller diameters, the bending resistance of the cable can be improved, and the processing, manufacturing, installation and laying of the wires and cables are convenient.
(2) Good stability; the core is It is composed of multiple single wires twisted according to a certain direction and twisting rules, because each single stranded wire is located in the stretched area above the twisted wire in the twisted wire, and is located in the lower compressed area When the stranded wire is bent in sequence, the stranded wire will not be deformed.
(3) Good reliability; due to material inhomogeneity or defects in twisting, using a single wire as the cable and the conductor of the cable easily affects the reliability of the conductor core. The defects of the conductor core formed by multiple single wires are scattered and will not be concentrated on a certain point of the conductor, so the reliability of the conductor core is much stronger.
(4) High strength; the strength of the single-stranded core is higher than that of the single-stranded core.

5. Explanation of terms:
(1) Pitch: the distance that a single filament advances one circle along the axis.
(2) Pitch diameter ratio: the ratio of the pitch length to the strand diameter.
(3) The relationship between the pitch and the flexibility of the strands: the smaller the pitch, the better the flexibility of the strands; on the contrary, the larger the spacing, the worse the flexibility of the strands.
(4) Stranding factor: the ratio of the actual length of a single wire to the pitch length in the pitch of the twisted wire.
(5) Twisting direction of the stranded wire: right direction (z direction) left direction (s direction)
(6) Compact conductor: common compact conductors are compact round, sector and compact tile-shaped (five-core cables) Semi-circular (two-core cable)
6. Compression purpose:
(1) Compact sector conductor: reduce the outer diameter of the cable, save product costs, and reduce the weight of the cable.
(2) Compact circular conductor: Improve the surface quality of the stranded conductor, reduce the diameter of the conductor, and increase the filling factor of the conductor. The compacted conductor surface is smooth without burrs, and the electric field on the conductor surface is uniform. Save materials and reduce costs (to learn more about cable technology, please click here. A lot of dry goods are waiting for your visit.)
7. Conductor classification:
According to GB/t3956 “Cable Conductor”, there are four types of conductors, namely the first One, the second, the fifth and the sixth. The first is a solid conductor, and the second is a stranded conductor, both of which are suitable for fixed laying of cables. The fifth and sixth types are stranded conductors, which are used for flexible cables and cords. The sixth is softer than the fifth.
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Tips for ACSR cable fault location

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The occurrence of ACSR Cable 336.4 MCM  faults is accompanied by the laying and use of cables. The location of cable faults varies with cable laying methods, and the difficulty in locating is gradually increasing. Among them, the positioning and searching of bridges, tunnels, and trenches are relatively simple, while the direct-buried method is the most difficult to locate. When the nature of the fault is simple, a dedicated cable fault location device can be used to locate the fault within tens of minutes. When the fault is special, it often takes 4-5 days or even longer to locate the fault.
When using the echo method to locate cable faults, sometimes through the transfer of faulty phases and wiring methods, complex faults are often transformed into simple faults, and the fault location can be quickly determined to gain time for on-site line repairs. This is important for power supply departments. Significant.


Low-voltage power cables are generally multi-core cables. After a fault occurs in continuous use after laying, they generally show two-core and multi-core phase-to-phase or relative-to-ground short-circuit faults. Sometimes when it is detected that the fault waveform collected by a certain core is not ideal, consider switching the wiring to other faulty cores for fault waveform detection. Unexpected effects will often occur, and the collected and detected waveforms will become More typical and regular, so you can quickly determine the specific location of the cable fault point.
In the long-term on-site measurement process of cable customers, it is found that after the failure of small cross-section copper core direct-buried power cables (35mm2 and below) and aluminum core cables, there may be short-circuit and disconnection faults at the same time. During on-site detection, according to the nature of the failure of each faulty core The difference between the short-circuit fault and the disconnection fault measurement will often get twice the result with half the effort.


For low-voltage cable and  direct-buried power cables with extruded armored inner lining, most of the faults are caused by external mechanical damage. When the insulated core fails, the inner lining may have been damaged. When encountering a special cable insulation fault, it is difficult to use a professional cable fault meter to collect waveforms. Consider using the acoustic measurement method to directly apply high-voltage pulses between the steel strip and the copper shielding layer of the cable, which will often quickly fix the point.
During the on-site measurement process, we also found that when the low-voltage cable fault point is determined by the acoustic measurement method, when the high-voltage wire and the ground wire are connected between the bad phase and the metal shield or armor, the insulation resistance of the two shows a low-resistance metallic connection. State, the sound is very small, the probe cannot be used to listen to the fixed point, and the effect is not ideal. Through the actual listening side many times, it was found that the distance between the discharge ball gaps was appropriately increased, and the high voltage and grounding wires were reconnected between the two phases where the fault occurred. Often the discharge sound will become louder, and the fault point will be quickly determined. .

Overhead lines need “nine checks”

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The inspection of overheadcable is one of the basic contents of the operation and maintenance of overhead lines. Defects can be found in time through inspections so that preventive measures can be taken to ensure the safe operation of the line. Usually, line inspectors should do “nine inspections” when inspecting overhead lines.
Check the pole tower. Check whether the tower is collapsed, tilted, deformed, decayed, damaged, whether the foundation is cracked, and whether the iron components are bent, loose, skewed or rusted. Check whether the wire length of the iron bolts or iron screw caps of the tower is insufficient, the screws are loose, the binding wires are broken and loose. Check whether there are bird nests and other objects on the tower.
Second, check the crossarm and fittings. Check whether the cross arm and fittings are displaced, whether they are firmly fixed, whether the weld seam is cracked, whether the nut is missing, etc.
Three check the situation along the line. Check whether flammable, explosive or strongly corrosive substances are piled on the ground along the line, whether there are illegal structures near the line, whether there are buildings and other facilities that may harm the line during thunderstorms or strong winds; check the poles and towers Whether to erect other power lines, communication lines, broadcast lines, and install broadcast speakers, etc.; check whether the lines are connected to electrical equipment without authorization.

Four check the route. Check the wires and lightning protection wires for broken strands, back flowers, corrosion, damage from external forces, etc.; check whether the distance between the wires, the ground and adjacent buildings or adjacent trees, sag, etc. meet the requirements, and whether the sag of the three-phase wire is unbalanced Phenomenon: Check whether the wire connector is in good condition, whether there are signs of overheating, severe oxidation, and corrosion.
Five check insulators. Check the insulator for cracks, dirt, burns and flashover marks; check the deflection of the insulator string and the damage to the iron parts of the insulator.
Six check lightning protection devices. Check whether the size of the protection gap is qualified and whether the auxiliary gap is intact. Check whether the external gap of the tubular arrester changes and whether the grounding wire is intact. Check whether the porcelain sleeve of the valve-type arrester is cracked, dirty, burned, or flashover marks, and the sealing is good. Check whether the down conductor of the arrester is intact, whether the grounding body is exposed by water washing, and whether the connection between the grounding down conductor and the grounding body is firm.

Seven check pull lines. Check the power cable for rust, slack, broken strands and uneven force on each strand. Whether there is any decay or damage to the cable pile and protection pile Whether the cable anchors are loose, lack of soil and sinking of soil irrigation. Whether the wire rod, wedge-shaped wire clamp, UT-shaped wire clamp, and wire-holding hoop are corroded, whether the nut of the UT-shaped wire clamp is missing, and whether the stop device of the turnbuckle is in good condition. Whether the pull cord is pulled into the wood pole at the binding place.
Switch equipment on eight check poles. Check whether the switchgear is installed firmly, whether there is any deformation, damage or discharge traces, whether the operating mechanism is intact, and whether the distance between the leads and the ground meets the regulations.
Nine check crossing points. Check whether there are new crossing points, whether the crossing distance meets safety requirements, and whether the original crossing points endanger the safe operation of the line. Whether the protective measures are perfect.