Causes of power cable failure

1.The insulation has deteriorated due to aging. The insulation of power cables is subject to thermal, chemical and mechanical actions that are accompanied by electrical action, so that physical and chemical changes occur in the insulating medium, and the insulation level of the medium is reduced. The insulation is damp. Intermediate joints or terminal heads are damp due to the top and bottom sealing of the structure or poor installation quality; defects such as blisters or cracks are left when the abc cable is covered with lead, which will also make the cable damp.

2.The cable is overheated. There are many reasons for the overheating of the cable. The internal cause is that the internal air gap of the cable insulation causes local heating, which causes the insulation to be carbonized. The external cause is the cables installed in densely-cable areas, cable tunnels, etc. The aac cables passing through the drying pipes and the cables close to the pipes will cause accelerated insulation damage due to cable overload or poor heat dissipation.
3.mechanical injury. Mainly refers to cable damage caused by external force. This is mainly due to mechanical action such as vehicle vibration, which deforms the cable. Deformation of the cable leads to excessive bending, damaging the internal insulation or causing an air gap inside the insulation.

4.Corrosion of the protective layer. The lead bag of the cable corrodes due to electrolysis or chemical action. Due to the different nature and degree of corrosion, the lead bag has red, yellow, orange and light yellow compounds or fine pores like sponge.
5.Overvoltage causes breakdown. Atmospheric overvoltage and internal overvoltage cause the stress on the cable insulation to exceed the allowable value and cause breakdown.
6.Moreover, analysis of actual failures shows that many outdoor terminal head failures are caused by atmospheric overvoltages.
7.Problems in the design and manufacturing process of the intermediate joint and terminal head. When the semiconductor is peeled off, the internal insulation is damaged or there are particles, dust and other impurities on the insulation surface; poor sealing of the cable head causes moisture inside the insulation, resulting in damp insulation; non-standard cable joint technology and non-standard sealing, resulting in grounding; high humidity in the production environment , Causing the insulation integrity of the production part (cable head) to be damp; the cable grounding error occurs, causing the grounding wire to form a circulating current or break.

The problem of using multiple single-core power cables in parallel

In the actual parallel use of cables, there are many single-core cables in parallel. During the actual parallel use of single-core PE Cables, due to the influence of the laying method, the actual current carrying capacity may not meet the actual load needs, and it may appear in actual use. Overload phenomenon. In fact, when 6 cables are laid in the air and laid side by side with no gap, the actual reflow can only reach about 60% of the theoretical carrying capacity. If the load of the cable is added to the theoretical selection, it is not laid according to the actual installation. Correct the situation. It is very likely that the cable will be in a full-load operation state during the actual power-on process, causing the cable to generate heat during power-on operation. Therefore, in the process of parallel laying of cables, the actual current carrying capacity is not simply a relationship of “1+1=2”. It is very likely that “1+1=1.5” or even “1+1=1” will appear, causing the cable Severe heating occurred during actual operation. Now we give a simple example, such as a three-phase asynchronous motor load with a capacity of 570KW and a rated current of about 1140A. Two YJV-0.6/1KV-1*300 cables are used for power supply in parallel, and the given value is calculated according to the theoretical design. , YJV-0.6/1KV-1*300 single cable is laid in the air, the theoretical calculation current carrying capacity is about 750A, and the theoretical parallel current carrying capacity of two cables can reach about 1500A, which can fully meet the actual use needs of the equipment. We now assume that there are 32 cables that are all concentrated on a bridge, stacked side by side and laid out randomly, and the above two YJV-0.6/1KV-1*300 power supply in parallel are also located in it. After consulting related materials, it is found that when 6 cables are stacked in the air without gaps, the actual current carrying capacity of the cables will drop to 60% of the theoretically calculated value. Then the actual current carrying capacity of the original cable is 1500×60%=900A, and the actual carrying capacity allocated to each cable is about 450A, which is nearly 300A different from the theoretically calculated carrying capacity of 750A, so that the cable will have serious overload and heat during actual use. phenomenon.

And the number of Copper cables actually laid is far more than 6, so the actual cable reflow may be smaller than 900A. How to solve this problem, some people have proposed to connect another YJV-0.6/1KV-1*120 cable in parallel to reduce the current distributed by the other two cables. Now we theoretically assume and calculate that after the three cables are connected in parallel, the load current In the actual distribution situation, assuming that the length of 3 cables used in parallel is 1 km, the laying temperature is all calculated at 20°C. Moreover, it is assumed that the conductor resistances of two YJV-0.6/1KV-1*300 cables connected in parallel for 1 km are exactly the same. In fact, due to manufacturing process problems, it is impossible to achieve complete consistency, and there is still a slight difference in conductor resistance. In the actual calculation process, we ignore the above influence. The maximum DC resistance of copper conductor at 20℃ is 0.0601Ω/km for 300mm2 copper core, 0.153Ω/km for 120 mm2, and the actual distribution calculation of 1140A current
The distribution current of the 120 mm2 cross-section is (0.0601*0.0601/0.153*0.0601+0.153*0.0601+0.0601*0.0601)=187A, and the current distributed on the remaining 300 mm2 cross-section is 953A, and each 300 mm2 cable actually flows The load current is about 477A. ​​In this case, the actual power on of the cable still has an overload phenomenon. The actual disaster flow of the cable 120 in this case is 435*60%=261A, which still has a large margin, but the current distribution law does not distribute the current to the 120 cross-section cable. In fact, The original problem remains unresolved. And our assumption is that there are only 6 cables, which does not meet our established requirements. Imagine adding another cable with a cross-section of 300 mm2. The actual current-carrying capacity distribution law is 1140*1/3=380A. Therefore, in the actual parallel cable process, the cross-section of the cable must be calculated strictly before proceeding. Use in parallel, otherwise the problem may not be solved by adding cables in time. The best case is to use cables with the same specifications and ensure the same length, so as to ensure that the current distribution is basically even. In fact, it is very difficult to re-install and rework the on-site cable after all on-site installation is completed. Therefore, the formal design, laying and installation of the cable in the early stage is very important, and the method adopted in the later stage is often only a remedial measure, and it is difficult to solve the problem fundamentally.

In addition, there are some problems in the parallel use of multi-core cables. For armored cables, the main core A, B, and C of each cable should be staggered in parallel for parallel use of armored cables. All wires of armored multi-core cables cannot be used in parallel. The new parallel connection is used as a single-core cable on one phase. If this is done, an eddy current effect will be generated in the armored steel strip of the cable, which will cause the cable to heat up and cause thermal breakdown. Although this is a very simple principle of electricity, in the process of the author’s many visits to users, sometimes users have asked similar questions and practices. In the three-phase four-wire unbalanced lighting load, the wiring and distribution method of our load should ensure that the load is distributed as evenly as possible, and the three-phase current is balanced as much as possible, otherwise it may be caused by the serious imbalance of the three-phase current. Alternating induced current is generated in the shaped steel strip, which causes heating of the cable.
The parallel use of cables should also pay attention to the tightness of the lugs at the end of each line, because the load capacity of parallel cables is generally relatively large, and the conductor resistance per kilometer is below 0. If it is once at any end of the line Loose wire noses and poor contact will double the conductor resistance of the line, causing uneven current distribution and even bypassing. This will cause individual cables connected in parallel to generate heat and cause malfunctions.
At the same time, the conductor resistances of the actual lines of the cables may not be completely consistent. Therefore, the current distribution of the cables of the same model and specifications cannot be absolutely evenly distributed, and there may be some differences in the actual current distribution process.
Therefore, during the actual parallel use of multiple single-core cables, corrections should be made according to their actual laying conditions, otherwise it may cause heat generation during the parallel use of the cables, which will affect the normal use of the cables.

Difficulties in locating cable faults

Due to changes in the environment in which Power Cables are laid and the application of new materials for cables and their accessories in the cables, it is increasingly difficult to locate faults on the power cable site.
The difficulty of field cable fault location is mainly reflected in the fault location of directly buried power cable lines. At present, despite the relevant classic technical literature and advanced fault detectors, it is still available for high resistance faults in power cable lines. However, when using a professional cable fault locator to locate on site, sometimes you will encounter some special and difficult faults that cannot be located. For example, using a professional cable fault locator, part of the creepage flashover fault on the insulation surface of the medium voltage cross-linked power cable terminals and intermediate joints, and accurately determining the metal short-circuit fault, often appears powerless or powerless.

For common cable faults, you can use a cable fault locator purchased on the market to determine the location of the fault point within minutes or hours. However, when you encounter special difficult faults and the detection is not stable, you may need to call multiple cable fault detectors with different functions to repeat the test, and take turns to detect, locate, compare and confirm. The types of these fault devices mainly include various cable fault detectors designed, manufactured and developed based on the principles of bridging method and wave method. In this way, it may take several days or even longer to locate the fault. In this way, if you are lucky, you can determine the location of the fault point. If you are unlucky, the location of the fault point is still uncertain.
In northern China, the ground freezes in winter, and the directly buried cables fail at this time. The actual fault detection and handling process is actually a difficult task. First of all, the cable fault locator used must have high accuracy, and secondly, the corresponding personnel must have a clear understanding of the actual cable laying route. Although some cable fault detection instruments are now equipped with cable path testers, they must also be equipped with cable path testers. Only on-site personnel who understand the approximate laying path of the cable can cooperate to improve the positioning accuracy. The actual handling of cable faults sometimes depends on man-made three points and machine-made seven points.

At present, there are many manufacturers selling cable fault detection instruments on the market, and there are many types of detection instruments, but in fact, it is impossible to locate all cable faults. In actual use, the instrument usually can only effectively locate one or several types of faults, but still cannot do anything about some faults. The current electric power department hopes to spend a lot of money to purchase a universal cable fault tester with complete functions and high positioning accuracy (including rough and precise measurement points) to quickly and effectively solve all actual cable faults. But it’s actually hard to buy. There are various updated cable fault detectors on the market. However, the actual on-site inspection will still encounter some technical problems that cannot be located using the cable fault table. I think the reasons are mainly from two aspects: First, the various insulation, filling and wrapping materials used in the cable and its accessories are constantly being developed and updated, which leads to continuous changes in the types of cable failures. The other is that the market demand for cable fault detectors is limited, and related R&D personnel are scarce, resulting in a delay in the start of portable, high-precision, intelligent and multi-functional cable fault detectors. It is believed that with the advent of the smart grid era and the rapid development of Aerial Bundled Cable ASTM B231 Standard fault detection technology, the location of cable faults will become very simple and easy.

A big explanation of high-voltage cables

Power cables have become a necessity in human life and production, and play an important role in many fields and industries, including home appliances, automobiles, houses, engineering, transportation, and so on. The demand for high-voltage power cables has been increasing in recent years, and cable companies have also entered the market.

The main technology for the production of high-voltage cables is CV continuous vulcanization production. This production line converts polymers into high-performance insulating materials and wraps metal conductors to form cables. As far as China’s high-voltage cable market is currently in a state of overcapacity, Chinese cable companies have invested in building a large amount of production capacity, but demand cannot keep up with the substantial expansion of production capacity.

Statistics show that China’s high-voltage power cable production accounted for 40% of the world’s total in 2014. At present, there are more than 185 continuous vulcanization production lines in China that can theoretically produce conductors for high-voltage power cables, accounting for 50% of the global production of high-voltage cable CV continuous vulcanization production lines. Although many of these CV lines are not in production, or have not even obtained relevant approvals, China’s high-voltage cable production capacity still exceeds its demand by three times. Today, the output of high-voltage cables will continue to increase until 2021.
As the traditional high-voltage cable market is saturated with overcapacity and its competition is becoming increasingly fierce, some powerful cable companies have turned to high-voltage submarine cables. This field has higher requirements for technical thresholds. Only a few companies in China have Strong production, and with the construction of wind farm projects in many countries around the world, the demand for high-voltage submarine cables will increase in the future.

Carbon fiber heating cable has excellent performance

Fiber heating cables have been used more and more frequently in recent years, and the occasions for use are also expanding. For example, underfloor heating was only popularized in the north in the past, but with the change of concept, more and more southerners are also laying underfloor heating in general. In addition, with the continuous improvement of carbon fiber heating technology, carbon fiber heating cables have become more and more adaptable to ultra-low temperature environments, and have greater application space.

Long ago, electric heating technology using metal materials as heating elements has been widely used in various fields. However, the surface of the metal wire is easily oxidized at high temperature. Due to the continuous thickening of the oxide layer, the area for effective current passing is reduced and the current load is increased, so it is easy to burn. Under the same allowable current load area, the strength of the metal wire is 6-10 times lower than that of the carbon fiber, and it is easy to break during use.   Carbon fiber is composed of a kind of graphite hexagonal lattice layer structure, which is a kind of “all black body material”, so it has high electrothermal conversion efficiency in electrothermal applications. Under certain conditions, high temperature does not oxidize, and the current load intensity and mechanical strength per unit area do not change. At present, carbon fiber heating cables are widely used in low-temperature radiation heating cables, floor heating systems, constant temperature brood boxes, flower houses, nurseries, vegetable greenhouses, etc., heat preservation and heating, road snow removal, airport runway snow removal, pipelines, tank insulation and antifreeze, football field lawns And the public green space soil insulation, etc.

In terms of snow melting on roads and airport runways, carbon fiber cables can be used for floor heating in concrete structures, as well as snow melting devices to prevent frost on roof rainwater and drainage pipes, and can also be used for soil heating. In terms of heat preservation and anti-freezing of pipelines and tanks, electric heating products have been vigorously promoted and applied in China. Its application fields are mainly concentrated in petroleum, chemical industry, electric power, railway and civil or commercial buildings. With the development of China’s electric power industry, the market prospect of electric heating products using clean, non-secondary pollution electric energy as the main energy source is very broad. At the same time, higher requirements are put forward for the performance of electric heating products. In the field of soil insulation for football field lawns and public green spaces, solar water heaters are mainly used to supplement heat energy when the water temperature of solar water heaters cannot meet the needs of life and engineering due to long-term rainy days or cold winter seasons due to insufficient light. of. It has strong heat resistance, severe cold and high temperature and humidity environment performance, and has the function of preventing dry burning. Even if the water tank is short of water and energized by mistake, the electric heater and water tank will not be burned out, so safe use can be ensured.
In addition, carbon fiber heating cables can adapt to harsh environments such as high and low temperatures. Carbon fiber is as thin as spider silk, and the specific strength of type 3 carbon fiber is more than 62 times that of steel. It has good forming process and is a new generation of engineering materials. Its elastic modulus is high, its resistance to degeneration is more than twice that of steel, its tensile strength is 30-40t/cm2pa, and its specific gravity is less than one-fourth of steel, one-half of aluminum alloy, and high elastic modulus. It is 16 times larger than steel and 12 times larger than aluminum alloy. Carbon fiber is softer than steel, so it can be used to strengthen the core of cables that require load-bearing and not easy to damage internal components, such as submarine optical cables.
Carbon fiber can withstand low temperatures of -180°C. Under this condition, many materials become very brittle, even the strong steel becomes more easily broken than glass, and carbon fiber is still very soft under this condition. Therefore, the carbon fiber composite core can be used for the design and manufacture of power transmission carriers under extremely cold conditions (such as Antarctic research, etc.). In addition, carbon fiber can withstand a high temperature of 3000°C to 3500°C. At this high temperature, the best heat-resistant steel also becomes molten steel, but in the absence of oxygen, the carbon fiber does not change. The carbon fiber will not burst even if it is quickly cooled from a high temperature of 3000°C to room temperature, so it can work in a rapidly cold and hot environment. This provides the possibility for the design of cables for high temperature and high temperature occasions in the steel, metallurgy, boiler and other industries.
Carbon fiber rope and carbon fiber cloth can be used in the design and selection of fire-fighting cable products. Carbon fiber has superior corrosion resistance. The strongest corrosion resistance among metals is gold and platinum. Gold and platinum will be corroded in a solution called “Aqua regia” made of one part of nitric acid (70% concentration) and three parts of sulfuric acid (concentration 39%). Sores are full of holes, but the carbon fiber in “Aqua regia” is safe and sound. It provides a new idea for the design of light-duty chemical-resistant cables in various chemical environments.
In summary, the application prospects of carbon fiber heating cables are constantly expanding, and the future application prospects of carbon fiber heating cables are very impressive.

The Bare conductor has no sheath, is it safe?

In daily life, many people will see high-voltage power cables in the suburbs. They are often erected in mid-air, but many people may not observe carefully. Many of the high-voltage wires that are erected in the air are bare wires. The so-called bare wires are not insulated. The cable of the skin.

Usually the wires and cables we buy have a layer of insulation. The function of the insulation is to protect the inside of the cable from damage, and to prevent us from getting an electric shock. However, the high-voltage line has no insulation, and the second is a bare wire. Why? What?
The voltage of domestic high-voltage transmission lines is often above 10,000 volts, while China’s unique ultra-high voltage technology has a higher voltage, and the cables used in high-voltage lines are basically bare wires. Generally, lines above 10 kV will be used. .

The reason whyBare conductors are used in high-voltage lines is very simple. If the high-voltage lines are to be insulated for cables, the thickness of the ordinary insulation layer is far from enough. If the insulation layer is to be used, its thickness needs to be increased. , This will make the weight of the cable become very large, will increase the maintenance cost of the later line. Moreover, such a thick insulating layer will also affect the heat dissipation of the cable. The final result of poor heat dissipation is to increase the consumption of electric energy. Therefore, comprehensively considered, the benefits of adding an insulating layer cannot offset the negative effects brought about, so simply don’t need an insulating layer. Attach bare wires directly.
From the design point of view, bare wires are obviously better than cables with insulation, but if you consider their safety issues, will the use of bare wires cause harm to people? In fact, you don’t need to worry. High-voltage lines sound terrible, but the high-voltage lines are difficult for ordinary people to reach. They are all in remote suburbs and are elevated in the air, so ordinary people can hardly touch them.
The operation of the staff also has strict operating specifications in the industry. There are air gaps between the wires and the ground, between the wires and the wires, between the wires and the ground, and between the wires and the tower. Perform accurate calculations and leave a sufficient safety distance.
So generally speaking, it is not very dangerous, but if there are high-voltage lines in the area where you are moving, you should still keep a safe distance.

What is power cables overload?

During the operation of the wire and cable, heat will be generated due to the existence of resistance. The resistance of the wire is generally very small, and its heating power can be expressed by the formula q=I^2R. q=I^2R indicates: for a piece of Power Cable in actual use (R is basically constant), the larger the current through the wire, the greater the heating power; if the amount of current is constant, the heating power of the wire is also constant . The heat released during operation will be absorbed by the wire itself and cause the temperature of the wire to rise. Although the wire is constantly absorbing the heat released by current work, its temperature will not rise indefinitely. Because the wire is absorbing heat, it is also constantly releasing heat to the outside world. The facts show that the temperature of the wire gradually rises after the wire is energized, and finally the temperature is constant at a certain point. At this constant point, the wire has the same heat absorption and heat dissipation power, and the wire is in a thermal equilibrium state. The ability of the wire to withstand higher temperature operation is limited, and operation exceeding a certain maximum temperature will be dangerous. This maximum temperature naturally corresponds to a certain maximum current, and running a wire that exceeds this maximum current is an overload. The overload of the wire directly causes the temperature of the wire itself and nearby objects to rise. The increase in temperature is the most direct cause of this type of fire.

Overload damages the insulation layer between the twin Overhead Cable and causes a short circuit, which burns down the equipment and causes a fire. The double-stranded wires are separated by the insulating layer between them, and overload causes the insulating layer to be softened and destroyed, which leads to direct contact between the two wires to cause a short circuit and burn the equipment. At the same time, the high temperature generated by the large current at the moment of short-circuit causes the line to catch fire and fuse, and the resulting molten beads fall to combustibles and cause fire. Overload temperature rise can also directly ignite nearby combustibles. The heat transfer of the overload wire increases the temperature of nearby combustibles. For nearby combustibles with low ignition point, it is possible to ignite them and cause a fire. This danger is particularly prominent in warehouses that store flammable materials and buildings that are easy to use and combustible decorations.

The output of high-performance fireproof cables reaches 40,000 kilometers

ThePower Cable industry is an industrial basic industry, and its products are widely used in energy, transportation, communications, automobiles, petrochemicals and other fields, occupying an extremely important position in my country’s national economy, and the market demand is huge.
Since the 21st century, China’s economy has continued to grow at a high speed. In particular, large-scale projects such as power grid transformation and UHV have been successively invested in upgrading and construction, providing a huge market space for the development of the wire and cable industry. Among them, the market demand for special cables such as high-temperature superconducting cables, aerospace cables, and high-performance fire-resistant cables is increasing.
Despite the huge market space in the entire industry, high-performance special cables with increasing demand have always been the shortcomings of my country’s wire and cable industry, occupying a relatively low proportion in the entire industry, showing that foreign-funded enterprises are leading the way and domestic enterprises are closely following the situation. In terms of market segments, the high-end market for special cables has the characteristics of high technical content, high entry barriers, strict protection of intellectual property rights, and high added value of products. Therefore, how to upgrade the technical level of domestic cable manufacturers, pry open the high-end market, continuous research and development, strengthen innovation, and build brands is the key.

At present, economic construction is shifting from traditional infrastructure such as “Tie Gongji” to “new infrastructure”, which brings new opportunities and new challenges to the wire and cable industry. The cable industry has entered a reshuffle period, and the industry concentration will further increase; “One Belt One Road” The implementation of the strategy has led to a significant increase in the role of overseas markets in the market structure; industry consensus and restrictions on safety, environmental protection, and energy conservation force cable companies to accelerate their entry into the high-end specialOverhead Cable market.

During the “14th Five-Year Plan”, China’s wire and cable industry will usher in new developments, and the market for high-performance special cables will exceed 100,000 kilometers. Wire and cable companies must firmly seize major development strategic opportunities such as power investment, rail transit construction, high-voltage and ultra-high-voltage transmission and distribution network construction, aerospace industry, and deep-sea mining, relying on technological innovation and focusing on digital and intelligent manufacturing. , Focusing on the fields of ultra-high voltage and ultra-high voltage power cables, high-performance fireproof cables, high-temperature superconducting cables, aerospace cables, special cables for urban rail, special cables for nuclear power, etc., strengthen the research and development of key materials and equipment, and strengthen process research , Accelerate the research and development of various new products, strive to make new breakthroughs in basic technologies and common technologies, strengthen the foundation of industrial technology upgrading, seize the commanding heights of international industrial competition, and seek the initiative for future development to promote the optimization and upgrading of the entire industrial chain of the industry, and accelerate Build an industrial basic capability system for the cable industry in the new era, create a modern industrial chain with stronger innovation, higher added value, safer and more reliable, and better support the construction of a modern industrial system.

Recommendations for BTLY cable cross-section selection

1. Select the cross section according to the temperature rise of the core
When the load current is passed, the core temperature does not exceed the long-term working temperature allowed by the cable insulation. That is to say, select according to the allowable current-carrying capacity.
Suggestion: The cable passes through different heat dissipation conditions. The corresponding core operating temperature will be different, and the section should be selected according to the area with severe heat dissipation conditions (usually no more than 1 meter).

2. Select the cross section according to the allowable range of voltage loss
When the terminal voltage of the electrical equipment actually deviates from the rated value, its performance will be affected, and the extent of the impact will be determined by the magnitude and duration of the voltage deviation.
Suggestion: The voltage loss increases due to the sharp rise of the core temperature during fire. The voltage loss should be calculated according to the fire conditions to ensure the continuous operation of important equipment. Due to the excellent heat insulation and heat dissipation characteristics of BTLY products, it is only necessary to enlarge the cable selected according to the normal situation by one to two. Usually, it can meet the condition that the voltage deviation under fire conditions is not more than -10%.
Three, select the cross section according to the economic current
The total cost during the economic life is small. That is, the initial investment and the cost of line loss during the economic life are small.
The so-called economic current is the working cable (range) corresponding to the applicable cross-section (range) during the life of the cable, the sum of investment and conductor loss costs. For details, please refer to “Low Voltage Cable Economic Current Density Range Table”.

Suggestion: BTLY products should have good heat dissipation characteristics. If the cross section is selected according to the temperature rise of the core, the selection can be reduced by one level. But taking into account the economic current factor. Therefore, it is not recommended. If selected in accordance with the routine, the line loss will be reduced by 4-7%, which is of great economic significance.
Fourth, the selection of the cross section of the neutral power cable and the ground wire
(1) In a single-phase two-wire circuit, regardless of the size of the phase wire cross section, the neutral wire and ground wire should be the same cross section as the phase wire.
(2) In the three-phase five-wire power distribution system, the allowable current carrying capacity of the neutral wire and ground wire should not be less than the sum of the large unbalanced load current and harmonic current in the line. When the phase wire core is not larger than 16mm2, the neutral wire and ground wire should have the same cross-section as the phase wire. When the phase wire core is larger than 16mm2, if the neutral wire current is small, the cross section of the phase wire can be selected, but it should not be less than 50% of the phase wire cross section and not less than 16mm2.
Suggestion: Use the aluminum metal sheath in the BTLY cable as the grounding core. The aluminum pipe grounding wire is connected by a dedicated connector, and the connection is firm and reliable. The equivalent resistance of the aluminum tube section of the BTLY cable meets the grounding needs of the corresponding copper core

Fire-retardant design of power cables in subway construction

With the acceleration of modernization, my country’s wire and cable industry is also rising. However, in the current vigorous development of the industry, my country’s per capita consumption of wires and cables is low, and counterfeit and inferior products on the market are prevalent. All have restricted the healthy development of the wire and cable industry. Therefore, we must pay close attention to the key aspects of quality inspection. Improving the quality of wires and cables is a problem that the industry should pay attention to.
Current status of wire and cable quality
In the production process of the wire and cable industry, the use of raw materials is more important than the processing technology. The cost of raw materials determines the cost of the product. In recent years, the development of the power cable industry has caused the price of raw materials to continue to rise. Large enterprises control costs by optimizing structures and improving production processes. Small and medium-sized enterprises can only survive by “cutting corners”. Some companies turn a blind eye to the latest product technical standards, and use ordinary raw materials to replace the required fire-resistant and flame-retardant materials; or use some hands and feet on the wire and cable cross-sections. This way, although the cost is controlled, the quality of the product is also greatly reduced.
After long-term development, most enterprises have been on the right track, and the production technology has become more advanced and the quality of products has gradually improved. However, quality problems still occur from time to time. The reason is that on the one hand, the enterprise squanders product technical standards in order to seek benefits; on the other hand, it is also because of the negligence of quality inspectors. Therefore, the quality inspection work of ASTM 477 MCM ACSR Cable products also requires multiple efforts to jointly recommend the healthy development of the industry.

The body is more harmful. Therefore, the application of flame-retardant cable materials can prevent corrosive gases from appearing in the cable during combustion, and only produce a small amount of dense smoke, which also reduces the damage to the equipment and the human body, which is beneficial to the follow-up rescue work after the fire. The cost of insulating layer and protective material of low-smoke flame-retardant cable is based on polyvinyl chloride resin, and then plasticizers and absorbents, high-efficiency flame retardants and marital inhibitors are added to it, and then passed It is produced by a special process. This material can greatly reduce the release of dense smoke and toxic gases produced by the burning of the material, thereby ensuring the safety of the victims and equipment under the subway. So as to reduce economic losses.