Finding method for broken core of flame retardant cable

Power cables are known as the nerves of modern industry. Modern human life and production cannot do without the help of wires and cables. Since the founding of the People’s Republic of China, China has realized the important role of wires and cables in the future economic development, so it has spent a lot of manpower, material resources and financial resources. With investment in construction and research, China has become the world’s largest cable manufacturer.

In the past few decades, the productivity formed by my country’s cable manufacturing industry has made the world look at it with admiration. With the continuous expansion of my country’s power industry, rail transit industry, data communications industry, automobile industry, and mines, the demand for the cable market is also increasing. This is one reason why China’s wire and cable industry has developed so fast.
With the continuous improvement of people’s awareness of fire protection, in project construction, people increasingly prefer to use flame-retardant cables with fire-retardant properties. The market demand for flame-retardant cables is also increasing, but the cables may be used when they are in use. There will be some faults, such as cable breakdown, cable conductor damage, broken cores and other faults. The conductor of the flame-retardant cable has a small cross-sectional area and may be broken during the production of the cable or during the extrusion process. So how to check the disconnection of flame-retardant cables?

In the cable industry, there are usually three ways to check the broken core of flame-retardant cables. The first is the energized capacitance method, which uses continuous electricity to accurately determine the disconnection point of the cable. This method is extremely inefficient, and one is often checked. It takes several hours to break the line, so this inefficient method has been abandoned by many people.
There is also a method of combining capacitance method and induction method, which is to use the capacitance to find the approximate location of the disconnection, and then use the induced voltage to find the accurate disconnection point. This double combination method can locate faster than the pure capacitance method. The disconnection point has also become a more commonly used method in the industry.
Another method is the combination of constant current source and bridge method. This method is also often used. The principle is to burn and puncture the insulation at the broken core of the flame-retardant cable with a constant current source. Using the bridge method fault locator to locate, its efficiency is very high and accurate.

Analysis of Operation Failure of Armored Cable

At present, there are various on-site treatment methods for the armor layer of low-voltage direct-buried cables, including single-ended grounding and two-end grounding. There are also those that are not grounded at both ends. According to the different treatment methods of the steel tape armor at both ends of the field cable, after the cable fails, the appearance of the fault point will be different.
The steel strips at both ends of the cable are all suspended and not grounded. After a short-circuit fault occurs in the cable, the breakdown point may only be a burn-through hole in a local location of the cable line, which will not cause long-distance and large-area burning and carbonization. Because when the cable is partially damaged by accidental mechanical damage and the sheath insulation is damaged, the system may not immediately trip and power off. The damaged point will cause intermittent flashover discharge on the earth due to the action of moisture and moisture in the soil, which will eventually develop into Permanent grounding and short-circuit between phases cause a trip and power failure. Since the discharge current of the live wire to the ground is limited to the location of the damaged point of the cable, the discharge current does not form a branch circuit to the ground through the steel belt, so there is generally only one point in the entire cable after the cable fails. malfunction. However, the surface of the armor layer will be electrified at this time. In consideration of safe use of electricity, the armor layer exposed at both ends of the cable must be insulated and sealed.

The steel belt of the cable line adopts single-ended grounding or double-ended grounding. After a short-circuit fault occurs in the cable, the fault may be a section of the cable, and the local area of ​​the cable may have long-distance surface burnt and carbonized adhesion. Because after the steel belt adopts this connection method, when a single-phase ground fault occurs in the cable, a relatively large ground short-circuit current will flow in the steel belt of the cable; at the same time, the three-phase load current of the cable will also appear unbalanced. Eddy current may also occur in the belt. After the two currents flow through the steel belt, the steel belt will be like a high-power electric furnace, heating the cable sheath and insulation, and the customer’s switch selection is not appropriate, and the soil is localized. Poor heat dissipation, excessive thermal resistance, partial accumulation of cable coils, poor heat dissipation and other unfavorable reasons may cause long-distance and large-area burning and carbonization of the cable insulation and sheath. The burned area is relatively random. It may be near the fault point, or in another section. It is often the section with the most difficult heat dissipation and the section with the largest thermal resistance that burns the most. The system may not trip until the single-phase grounding develops into a two-phase short circuit and cannot be reclosed to transmit power.

For low-voltage cable armored cables, it is necessary to strengthen the real-time online detection and monitoring of the three-phase current of the cable. At the same time, after the armor layer is grounded, an armor layer current transformer should be installed to monitor the current of the steel strip from time to time. The single-phase grounding short-circuit fault of the cable should be detected and dealt with in advance to avoid the long-distance burning of the cable and cause unnecessary power economic loss, and to ensure the economy, reliability, stability and safety of the grid operation.
According to normal analysis, after a short-circuit fault occurs in a directly buried low-voltage cable, there should generally be only one fault point. However, during the actual field excavation and processing of cable fault points, it is found that low-voltage cable faults may have two or more fault points, and may also be accompanied by long-distance insulation sheath heating and burning and carbonization adhesion. The author believes that the difference in the failure of low-voltage armored cables may be related to the grounding or non-grounding of the cable armor, and the opinions and opinions may not be correct. It is hoped that professionals who have sincere insights into such phenomena can provide more scientific and authoritative analysis and opinions. To uncover the underlying cause of this phenomenon.

How does the submarine cable work?

Many people are full of curiosity about submarine cables. Submarine cables are actually a kind of long-distance optical fiber. Generally, long-distance optical cables in the world use submarine cables. So how do submarine cables be laid?
Compared with submarine cables, the laying of terrestrial cables is much simpler. You only need to dig the cable trench and bury the cables in it. Submarine cables are not that simple. To lay the submarine cables, you must first have a ship. The submarine optical cable laying ship puts the submarine cable on the ship, and then the ship slowly sinks the cable into the seabed according to the prescribed route. It sounds not difficult, but the actual operation is actually very difficult. At present, the international long-distance submarine cable laying is almost unfavorable. Developed countries such as Japan and Europe have a monopoly. However, the domestic cable industry has developed rapidly in recent years. Leading companies such as Huawei have the technology and ability to lay long-distance submarine cables.

The laying of submarine optical cables is usually done by a cable laying machine that digs the seabed. The working principle is a bit like the plow used in plowing the field. During operation, the rows of water jet holes at the bottom of the cable burial machine simultaneously spray high-pressure water jets to the seabed to flush out the seabed sediment to form an optical cable trench. At the same time, the fairlead on the upper part of the equipment can guide the optical cable to the bottom of the optical cable trench. The cable laying machine is towed forward by the submarine optical cable laying vessel, and transmits various instructions through the working optical cable through the laying vessel.
In order to avoid damage to the optical cable due to too small bending radius or excessive tension, the laying of the optical cable-laying ship must use underwater monitors and underwater remote control vehicles to continuously monitor and adjust to control the sailing speed of the laying ship and the release speed of the optical cable. Control the angle of entry of the optical cable into the water and the laying tension and avoid uneven places and reefs. Of course, after the fiber optic cable is laid, there will be landfill work. In the past, sea currents were used to allow sand to naturally cover the trenches to save time for burying cables, but it was also vulnerable to sea currents and other unstable factors (such as sharks). Therefore, it is now common to use an underwater robot equipped with a high-pressure water pump to flush a ditch and then put it in and bury the soil.

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.

Rubber insulation of cables

1. Preparation of raw materials
The preparation of raw materials requires warm glue and glue cutting. The weighing of raw materials is a crucial process of preparation.
2. Plasticizing
Rubber has high elasticity at room temperature and is not easy to process. Therefore, it is necessary to change its high elasticity to make it have a certain degree of plasticity. The process of converting rubber from a highly elastic state to a plastic state is called plasticizing.
Factors affecting mastication; roll distance, temperature, mastication time, speed ratio and number of revolutions
Natural rubber must be masticated, while synthetic rubber may not be masticated.
Three, mixing
Mixing is to scoop all kinds of compounding agents into the rubber to make 2 rubber materials with a certain degree of plasticity. One strand is divided into open mixer mixing, internal mixer mixing, and continuous mixing.

Fourth, filter rubber
The requirements for the mixed rubber materials used for insulation and thin sheath products are relatively high. In the actual production process, various rubber materials inevitably contain impurities, and impurities will also be mixed in the transportation and mixing processes. The purpose is to eliminate the above-mentioned various impurities.
There are two methods for filtering rubber: raw rubber after plastic refining and rubber filtering during mixing. Under normal circumstances, raw rubber does not need to be filtered.
l Extrusion process and equipment
Extrusion is a process that uses a rubber extrusion machine to squeeze the insulation layer on the conductor or squeeze the rubber jacket layer on the cable core.
Extrusion process: warm glue, selection and adjustment of molds, control of extruding temperature, cold feed extrusion process
The equipment used to squeeze insulating rubber or sheath rubber has become the main extruder and is divided into eight types: 30.45, 60.90, 120, 150, 200, and 250.
The squeezing machine is composed of a main engine, a traction device, a take-up device, a meter counter, a cooling device and a transmission system, etc.
Main technical parameters: screw, outer diameter, screw length-to-diameter ratio, screw speed range, glue output per hour, main motor model power, equipment center height and overall dimensions

l Vulcanization process
Under heating conditions, the raw rubber in the rubber compound chemically reacts with the vulcanizing agent, so that the rubber is cross-linked from linear structure macromolecules into three-dimensional network structure macromolecules, resulting in a significant improvement in the physical and mechanical properties and other properties of the rubber compound. This process is called vulcanization.
The entire vulcanization process is divided into four stages: vulcanization induction stage (scorch), pre-vulcanization stage (low sulfur), normal vulcanization stage (normal sulfur), and over-bowling stage (over)
The scorch time refers to the time when the rubber begins to harden and the Men’s viscosity increases, and the thermoplastic flow cannot be carried out from then on. The stage between the scorch time and the positive vulcanization is called under-sulfur, which seriously affects the aging performance. Rubber should strictly control the lack of sulfur phenomenon: normal sulfur means that the degree of vulcanization cross-linking meets the process requirements, and the physical and mechanical properties meet the vulcanization time required by the use. The positive vulcanization time is called the vulcanization flat zone, and the vulcanization flatness refers to the wide area in the positive vulcanization zone. Flat vulcanization curve: Excessive sulfur indicates that the vulcanization crosslinking temperature is too high, at this time the tensile strength and fixed extension are reduced.
Vulcanization process: fixed vulcanization of vulcanized tube, continuous vulcanization
Vulcanization conditions include vulcanization temperature, vulcanization time, and vulcanization pressure. Correctly setting vulcanization conditions is a decisive factor to ensure quality.
The most basic principle of continuous vulcanization: use the method of increasing the temperature to speed up the vulcanization rate. According to the relationship between the vulcanization speed and the vulcanization temperature, it can be seen that for every 10 degrees increase in the vulcanization temperature, the vulcanization speed can be doubled on average, that is, the vulcanization time can be reduced by half.
According to the position of the vulcanizing tube, it can be divided into four types: horizontal, inclined, catenary and vertical. In addition to saturated steam, there are superheated steam, low melting point metal salts and infrared rays.
Continuous vulcanization has many advantages compared with tank line vulcanization: high production efficiency, good product quality, product length is not limited by equipment, easy to operate, continuous vulcanization has become the most important vulcanization method in the wire and cable industry, vulcanization tube vulcanization Be in a secondary position.

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.