Burning test for ACSR Conductor production

There are two key links in the wire and cable manufacturing industry, namely theAluminum conductors steel-reinforced production link and the wire and cable testing link, especially the wire and cable testing link. This is the last stop for quality control and a comprehensive assessment of the performance of wires and cables.
The burning test of the cable is an extremely important one of its many tests. The national cable performance classification has special grade requirements for it, such as the number GB/T31248-2014. This standard divides the burning of the cable into 4 grades, A Class (non-flammable cable or optical cable, equivalent to metal sheathed cable or optical cable), Class B1 (flame-retardant B1 cable or optical cable, equivalent to halogen-free low-smoke flame-retardant cable or optical cable), Class B2 (flame-retardant B2 cable or Optical cable, equivalent to low-halogen, low-smoke flame-retardant cable or optical cable) and Class B3 (ordinary cable or optical cable).


Especially for fire-resistant and flame-retardant special cables, the burning test is a very important test for their professional performance. These fire-resistant and flame-retardant cables are required to have certain flame-retardant properties, and they must also have a certain flame-retardant performance. The characteristics of normal operation for a certain period of time, so the burning test is also a test of the performance of this type of cable.
In addition, there are a number of data for various combustion conditions. The values ​​need to be tested. For example, the heat release rate of the cable is the heat energy released by the combustion of the cable within a certain period of time under the specified conditions. This value is the normal combustion of the cable. Detect the data, and the value of the data will be affected by many factors, such as the combustion state, and the amount of non-metallic materials.


There is also an average heat release rate, which refers to the average heat release rate within 30 seconds. The average heat release rate during the combustion process is also a value that changes with the continuation of the combustion time. The peak heat release rate is the maximum value of the average heat release rate during the entire combustion period. The standard stipulates that the combustion time is 1200 seconds, which is the maximum value among the 40 average heat release rates. This value is related to the combustion state of Aerial Bundled Cable during combustion. If the flame is particularly large in a certain period of time within 1200 seconds, the peak heat release rate may not meet the requirements. The total amount of heat release refers to the integral value of the heat release rate within a specified time.
The various test data of the cable in the flame combustion can reflect the performance and influence of the cable in the flame, and can fully reflect whether the cable is qualified and up to the standard, and whether the fire performance of the fire-resistant cable meets the requirements, these are extremely important Therefore, the burning test is also one of the routine tests of wire and cable manufacturers.

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.

The basic structure of the wire

1. Single round wire The main varieties are copper single wire, aluminum single wire and copper-aluminum alloy wire. The diameter of the wire is used as the structural parameter, ranging from 0.01mm to 3.00mm. Except for some of the round single wires used directly as products, most of them are semi-finished products used by twisting single wires into multiple twisted wires.
In addition to the round single wire of a single material, there are also compound round single wires. Commonly used are bimetal round single wires, such as aluminum clad steel wire (high conductivity of aluminum, strong tensile strength of steel wire), copper clad aluminum wire (high conductivity of copper, light aluminum) and coated single wire, such as tinned copper wire, Nickel-plated copper wire.
2. The round stranded wire and cable are products of large length, which have to withstand many times of winding and unwinding during production, installation and use. If the wires with larger cross-sections are not used to twist small-diameter single wires into a certain cross-section Twisted wire, the product cannot be manufactured and used. Different use conditions and conditions require wires and cables to have different flexibility-that is, bendable or twistable. Therefore, the stranded wires used in various products have different requirements in terms of flexibility, etc. Therefore, 7 kinds of wire structures are specified in the wire standard. Table 1 is the wire structure specified by the standard.


Wires with the same material and the same cross-section can be composed of several structures, that is, the number and diameter of single wires are different. The more single wires in the same cross-section (the thinner the single wire diameter), the higher the flexibility of the wire.
The structural parameters of  round stranded wire are the cross-sectional area of ​​the wire (in mm2), the number of single wires and the diameter (mm), the stranded pitch diameter ratio, etc.
3. Derivative structure of round stranded wire
(1) Compact round stranded wire In the wire stranding process, the stranded wire is pressed tightly by means of a pressing wheel, etc., so that the conductor occupancy rate in the cross-section reaches about 90%. One is to flatten the protruding shape of the wire surface, which is beneficial to squeeze the thin (0.5-1mm), inner semiconductor layer (for uniform electric field) of the medium and high voltage XLPE cable, which is not easy to puncture. The second is to reduce the gap between the single lines.


(2) The diameter of the inner groove of the round stranded wire with inner hollow groove is generally 14-18mm. There are two kinds of product requirements, namely, oil-filled cables are used as oil grooves for oil flow, and high-current cables are used as channels for internal cooling through gas or liquid. (Can increase the energizing capacity). The conductor of the oil-filled cable is generally formed by twisting a Z-line or arc-shaped single wire to form a ring-shaped cross-section, and it can also be formed by twisting a round single wire into a spiral tube. As the internal cooling type forced cooling, the internal hole groove adopts a sealed metal tube.
(3) The sector conductor is the conductor structure used in the medium and low voltage 3-4 core oil-paper insulated power cable (1-10kv). It is used to make the insulated cores of the paper wrap insulation into three 120 shapes, which are twisted into a circle when the cable is formed. Shape (four-core cable is three 100, and the neutral wire 60 is sector-shaped), in order to save a lot of outer material. The line is rarely used.

International Advanced Level of Environmental Protection Wire and Cable Indicators

Environmental protection wire refers to the material is environmental protection wire.

The material includes insulating material, conductor material and shielding material. Insulation such as PVC, irradiated cross-linked PVC (XL-PVC), irradiated cross-linked polyethylene (XL-PE), low smoke free (Halogen-free), silicone rubber, Teflon Telflon and so on. The environmental protection of insulation materials is mainly the EU’s RoHS environmental protection directive and the EU’s environmental regulations on children’s toys do not contain 6P (Non-6P), that is, does not contain phthalates. Now the most environmentally friendly is low smoke halogen-free, does not contain halogen elements.

The most common conductor material is copper. Copper has bare copper (brass, red copper), tinned copper, silver-plated copper wire, etc., which are essentially copper, but the surface is plated with other substances. Now there are copper – coated aluminum and copper – coated steel conductors on the market. If the electrical performance requirements are high, copper is the best. The environmental protection of conductors is mainly required to be free of heavy metals (RoHS).

Environmental protection cable means that it does not contain lead, cadmium, hexavalent chromium, mercury and other heavy metals, and does not contain brominated flame retardants. The environmental protection performance of the cable is tested by SGS recognized testing institutions, and it is in line with the European Union Environmental Protection Directive (ROSH) and higher than its index requirements. No harmful halogen gas, no corrosive gas, less fever when burning, no pollution of soil wires and cables.

Main technical indicators:

  1. Rated voltage: 450/750V and below
  2. The maximum permissible operating temperature of the conductor shall not exceed 70 ℃, 90 ℃ and 125℃ respectively.
  3. Cable combustion smoke density in line with GB/T 17651-1998 (equivalent to IEC1043) standard requirements, light transmittance ≥60%.
  4. Cable halogen acid content test conforms to GB/T 17650-1998 (equivalent to IEC 754-2) standard requirements.

(1) PH ≥4.3

(2) Conductivity ≤10μs/mm

  1. The flame retardant performance of the cable conforms to the requirements of GB/T 12666-1990.

6.Toxicity index of cable ≤3.

The discrimination of flame-retardant cables

Nowadays, electricity is used more and more frequently, and life is inseparable from electricity. Today, the editor brings you a mine-used flame-retardant cable worthy of trust in mines.
Advantages and disadvantages of mine flame retardant cables
The characteristic of flame-retardant cable is to delay the spread of flame along the cable so that the fire will not expand. Because of its low cost, it is a large number of cable varieties used in fire-resistant cables. Regardless of whether it is a single cable or a bundle laying, the cable knows that the flame spread can be controlled within a certain range when burning, so it can avoid major disasters caused by fire and prolonged combustion, thereby improving the fire protection level of the cable line.
The difference between mine flame-retardant cable and fire-resistant cable


1 The difference in principle
The principle of fire-resistant cables is different from that of flame-retardant cables. The flame-retardant principle of halogen-containing cables is based on the flame-retardant effect of halogen, and the flame-retardant principle of halogen-free cables is to extinguish the fire by reducing the temperature of the precipitated water. Fire-resistant cables rely on the fire-resistant and heat-resistant characteristics of the mica material in the refractory layer to ensure the cable It also works fine during a fire.
2 The difference between structure and material


The structure and materials of fire-resistant cables are different from those of flame-retardant cables.

Safe Use of Cable: How to Prevent Wires and Cables from Catching Fire Due to Overload of Wres

Wire and cable in the process of operation, due to the existence of resistance will be heated.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 that: for a section of wire in use (R has been basically constant), the greater the current through the wire, the greater the heating power;If the current constant, then the wire heating power is constant.The heat released during operation will be absorbed by the wire itself, thus causing the temperature of the wire to rise.

Although the wire is constantly absorbing the heat released by the current in the process of operation, its temperature will not rise unlimitlessly.Because while the wire is absorbing heat, it’s also releasing heat into the outside world, and it turns out that the temperature of the wire increases gradually when it’s energised until it stays at a certain point.At this constant point, the heat absorption and release power of the wire are the same, and the wire is in thermal equilibrium.There is a limit to the ability of wires to withstand higher temperatures, and operating above a certain maximum temperature may be hazardous.This maximum temperature also corresponds to a certain maximum current, above which the wire is overloaded.Overloading of the wire directly causes the temperature of the wire itself and the objects nearby to rise.Rising temperatures are the most direct cause of such fires.

Overload causes the insulation layer between the two wires to be damaged, causing a short circuit, burning down the equipment and causing a fire.The double wire is separated by the insulation layer between them. Overload makes the insulation layer soften and destroy, which leads to the direct contact between the two wires, causing short circuit and burning 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 molten beads generated fall to the combustible material to cause the fire.Overload temperature rise can also directly ignite nearby combustibles.The heat transfer of overload wire raises the temperature of combustibles nearby, and it is possible for combustibles nearby with low ignition point to ignite and cause fire.In the storage of flammable goods in the warehouse and the use of easy, combustible decoration of the building, this risk is particularly prominent.

 

The overload also puts the connections in the line under conditions of overheating, which speeds up the oxidation process.Oxidation makes the connection point produce a thin layer of oxide film, which is not easy to conduct electricity. The oxide film increases the resistance between the contact points, resulting in ignition and other phenomena, causing fire.So, how to prevent the overload of wires and cables caused by fire?

In the process of line design, we should accurately check and ratify the capacity of the site, fully consider the possibility of new capacity in the future, and choose the right type of wire.Large capacity, should choose a thicker wire.Circuit design and reasonable selection are the key steps to prevent overload.If the design selection is not correct, it will leave a congenital hidden danger that is difficult to rectify.Some small projects, places not serious design and selection.Arbitrary selection and laying of lines, this is very dangerous.New electrical appliances, electrical equipment should be fully considered the bearing capacity of the original line.If the original line does not meet the requirements, it should be re-designed and transformed.

The line should be laid by qualified electricians according to the relevant specifications.The laying conditions of the circuit directly affect the heat dissipation of the conductor.Generally speaking, the line laying should not pass through easy and combustible materials and stacking, which will lead to poor heat dissipation of the wire and heat accumulation, resulting in the possibility of igniting combustible items around, and increasing the risk of fire caused by overload;The lines laid in the ceiling of the decoration of public entertainment places should be protected by steel pipes to separate the ceiling from the line. In the case of overload and short circuit, even if there are molten beads, they will not fall off to avoid fire.

Strengthen electricity management, avoid disorderly wiring, random wiring, careful use of mobile socket.Disorderly wiring, random wiring, the use of mobile socket is actually in a certain line to add electrical equipment, increase the current and may cause overload.The jack of the mobile socket is obviously more than the fixed socket on the wall. If too much electrical equipment is used on the mobile socket, the original line must be difficult to bear.Separate lines should be set for high-power equipment and electrical appliances, and mobile sockets should not be used as wiring sources.

Accelerate the renewal and transformation of old lines to eliminate fire hazards.Old enterprises, old residential areas and other units, due to the use of a long time, many lines have been aging, more than the service life.Even if the carrying capacity of some lines is not large, the aging lines are difficult to bear such carrying capacity, and also have the risk of overload.Especially in the old residential areas, the lines have long been aging, but with the improvement of people’s living standards and the increase of household appliances, the electricity consumption is still rising year by year, which is really worse.For old lines, we should timely supervise and coordinate, and promote their rectification as soon as possible, so as to eliminate fire hazards and ensure safety.