Fire resistant cable

Current situation of power cable and accessories

by

Power cables and accessories are the key products used for transmission and distribution of electric energy in the main line and distribution network line of power system, mainly including AC power cables and accessories with rated voltage U0 / u 0.6/1kv ~ 290 / kV. Among them, the rated voltage of 1.8/3kv and below is low-voltage power cable, 3.6/6kv ~ 26 / 35kV is medium voltage power cable, 66kV ~ 110kV is high-voltage power cable, and 220kV and above is ultra-high voltage AAC Cable. In recent years, China has promoted the development and application of flexible DC cables, including DC power cables and accessories of various voltage levels within the rated voltage uo10kv ~ 525kv.


Power cables are basically distinguished according to the types of insulating materials. Extruded solid insulated power cables represented by XLPE insulation materials have been widely used. At the same time, there are a small number of oil immersed paper insulated (hereinafter referred to as “Mi cable”) power cables and oil filled (hereinafter referred to as “of cable”) insulated power cables“ During the 13th Five Year Plan period, superconducting power cables and Gil gas insulated lines have also been continuously developed and applied in engineering. PP (polypropylene) thermoplastic insulation material with environmental protection characteristics is known as a new type of ACAR  Cable, which is being developed and applied in engineering demonstration in China.
Power cables are divided into land cables and submarine cables according to use scenarios. In recent years, submarine cables have been rapidly developed and widely used, especially the development of offshore renewable energy (wind power generation), which promotes a large demand for submarine cables.
6kV and above power cables need to be equipped with cable accessories of corresponding voltage level. Cable accessories include terminals and intermediate joints, including wrapping, molding, cold shrinkage, heat shrinkage, prefabrication, combination and other forms.


Power cables, whether land cables or submarine cables, whether AC cables or DC cables, are characterized by a wide range of voltage levels, from 1kV to 500kV. At present, the voltage level tends to be higher; Wide specification range, from 1.5 mm ² To 3500 mm ²， At present, the conductor section tends to be larger. Power cable is not only widely used in distribution network, but also an important foundation and indispensable product of power transmission in backbone network (Note: concentrated in urban power supply system). With increasing transmission capacity, operation safety and reliability are becoming more and more important. People not only pay attention to the quality improvement and technical improvement of power cables and accessories, but also study the operation reliability of AAAC Cable system, including electrical factors, mechanical factors, temperature and environmental factors, as well as mutual integration and coordination; It also pays more attention to the economy and long-term operation of power cable system, including transmission capacity, loss, maintenance cost and rapid recovery ability in emergency. Therefore, the power cable system is facing the challenges of quality improvement, operation economy, reliability and durability, involving material innovation, structure innovation and manufacturing process innovation. Facing the new requirements of social progress, urban development and environmental coordination, the challenge of long-distance transmission underground cable with large capacity, low loss, convenient laying, operation and maintenance and intelligent control, as well as the development and application of marine resources and new energy, and the challenge of safe power transmission reliability in complex environments such as seabed.


In recent years, China’s cable industry has made great progress in the above fields, but there is also a lot of room for improvement, improvement and promotion. In the manufacturing field, the integration of fine management, informatization, equipment automation and digitization of power cable manufacturing to realize high-quality intelligent manufacturing and development is still on the road. In the application field, there is still a big gap between the construction of high-voltage, large capacity and long-distance underground and submarine transmission networks and the development and application of corresponding materials and high-end equipment and the technical level of advanced countries.

Simple repair method after cable line failure?

by

After the cable line breaks down (including the breakdown during preventive test), it must be repaired immediately to avoid a large amount of water invading and expanding the scope of damage.
The elimination of faults must be thorough and clean. Otherwise, although it can be used after repair, it will still cause faults in the future, resulting in repeated repair and greater losses.
to repair the fault, the damp part of the ACSR Cable must be removed, and the insulating agent or insulating layer must be checked for carbonization. This paper introduces several simple fault repair methods.

(1) single phase grounding of cable line (without tripping): the conductor damage caused by this kind of fault cable may be local. If it is a mechanical damage, only the AAC Cable insulation is damaged, the conductor is slightly singed, and the land near the fault point is relatively dry, it can generally be repaired locally. The cable core can not be sawed off, only the damaged part of the conductor can be treated smoothly, and the insulation can be wrapped and sealed.
(2) breakdown of cable joint in preventive test: because the voltage of preventive test is high and the insulation strength of the joint decreases gradually during operation, such faults often do not make the ACAR Cable subject to water intrusion. In this case, the connector can be disassembled to check whether the cable conductor is intact and whether the insulation is damp. Check 1 ~ 2 layers of insulating paper on the peelable surface of the oil paper cable, wash with hot oil, and completely remove the moisture if any.


(3) if the indoor cable terminal is broken down in the pre-test, it can also be disassembled and partially repaired. The process is similar to reinstallation, but requires moisture removal. Generally, there is some residual wire left at the terminal part, so the sheath can be appropriately cut for another section, and the operation is more convenient than dismantling the joint.

Does the fireproof cable really not burn?

by

Fireproof cable has become an indispensable item in our daily life and production, followed by accidents caused by wires and cables, especially when wires and cables explode after combustion, it is easy to cause casualties. Every year, all kinds of wires and cables cause accidents. The fire accident continues. Most of the shells of ordinary wires and cables are plastic and rubber products. These materials will release a lot of smoke and toxic gases after the fire. Once the ABC Cable burns and explodes, it will also cause serious damage to the surrounding residents and environment.


Why do some cables catch fire or even explode? There are many reasons for AAAC Cable fires. Xiaobian summarized five common situations: short circuit, overload, breakdown, burning of cable head and external fire source. Generally, the insulation layer of the cable is damaged, resulting in cable short circuit. The outer sheath material will burn and severe heating will occur if the cable is overloaded for a long time. If the old cable is running at this time, it is easy to break the line and cause a fire.
Another very common reason is that the cable head is burned. If the surface of the cable head is wet or dirty, the ceramic sleeve of the cable head will break and the conductor is too small, which will cause arcing and fire, thus insulating the surface of the cable head and causing the conductor. Of course, another reason for the burning of the insulation layer is that the external fire source burns the cable, causing the cable to burn or even explode.
Therefore, in order to reduce the loss caused by cable burning, a fireproof cable is designed. Fireproof cable is a general term for the characteristics of flame retardant cable and fireproof cable. They all have certain flame retardancy, but many people can’t distinguish flame retardancy. The concept of cable and fireproof cable. In terms of its characteristics, fireproof cable can replace flame-retardant cable, but flame-retardant cable cannot replace fire-retardant cable. This is because they work differently.


The working principle of flame retardant cable is realized through the flame retardant effect of halogen, as well as halogen-free flame retardant cable. It uses precipitated water to reduce the temperature, but the working principle of fireproof cable is different from that of flame retardant cable. The material of fireproof cable contains a kind of mica material, which has high fire resistance and can be used normally in fire.
After understanding the working principles of the two, it can be seen that the flame-retardant cable is also afraid of fire, but due to the use of flame-retardant materials, it can stifle the fire in the communication base, and the flame-retardant cable is different. It has a fireproof layer structure. Normal operation can be maintained even in a fire, so in many cases, fireproof cables can be used instead of flame retardant cables.


Will flame retardant cables and fireproof cables not burn? Flame retardant ACAR Cables are highly nonflammable, with small combustion distance, and can be extinguished automatically after the fire source disappears, but the flame retardant cables themselves will still burn and cannot burn completely. Burning. Similarly, fireproof cables are the same and will burn. Flame retardant cables reduce the temperature through the flame retardant effect of special materials, and flame retardant cables rely on their unique flame retardant layer to ensure that they can work normally in fire. Therefore, flame retardant cables are better than flame. In some cases, flame retardant cables are used.

Methods to prevent cable corrosion

by

(1) The cable manufacturer is required to use the protective layer outside the metal sheath of the AAC Cable when manufacturing the cable, and the aluminum sheathed cable must have polyethylene or PVC outer sheath.
2) When selecting the cable route, it is necessary to make full investigation, collect the soil data near the area where the line passes, and carry out chemical analysis, so as to judge the degree of soil and groundwater erosion. If necessary, measures should be taken, such as changing the route of the line, partially replacing the bad soil, or adding special protective measures, such as putting the cable through the corrosion-resistant pipe.


Prevent external damage and theft of facilities
Design and infrastructure stage
The setting of cable route, auxiliary equipment and facilities (ground grounding box, entrance and exit, ventilation Pavilion, etc.) shall be approved by the planning department. It should be avoided that the cable passage is adjacent to the thermal pipeline, flammable and explosive pipeline (oil and gas) and corrosive medium pipeline.
Note: it is a new clause. It is proposed that the route, auxiliary equipment and facilities should be approved by the planning department, and the requirements of avoiding the cable passage adjacent to thermal pipelines, flammable and explosive pipelines (oil and gas) and pipelines with corrosive media should be avoided.
It is difficult to understand the corrosion degree of the cable on the running cable line. In the area where the corrosion of the cable has been found or the leakage of some chemicals piled on the ACSR Cable line, the soil should be dug to check the cable, and the nearby soil should be chemically analyzed to determine the damage degree
2. Methods to prevent electrolytic corrosion
(1) strengthen the insulation between the metal sheath of the cable and the huge metal objects nearby.
(2) installation of drainage or forced drainage, polarity drainage equipment, cathode station, etc.
(3) for areas with serious electrolytic corrosion, shielding pipes should be installed.
stray current is related to the distribution of electrical track, the maintenance of joints and the layout of other underground metal pipelines. In order to protect the underground pipelines and communication cables, the departments of underground oil and gas pipelines and local communication cables sometimes adopt cathodic protection. Therefore, the cable operation Department must systematically measure the potential difference between the lead sheath and the earth and other pipelines, the stray current density of the lead sheath and the current density flowing into the earth, so as to accumulate data. When we know which area is in danger of corrosion, we should take preventive measures in time, and work together with relevant units to try to eliminate the source of stray current and do a good job of corrosion prevention.


the operation experience shows that when the current density from the cable metal sheath reaches the average value of one day and night, the metal sheath will be corroded. This paper introduces a method of measuring stray current density auxiliary electrode method,
the auxiliary electrode is made of a section of cable similar to the tested cable, and its length should be such that the contact surface between the electrode and the earth is not less than 500. Peel off the outer protective layer of the electrode surface, wipe off the armored surface, weld the connecting wire, and pour asphalt or other insulating materials on the solder joint insulation and both ends of the electrode.
In addition to cable corrosion, there are also corrosion phenomena such as metal bracket, metal hoop and grounding wire in cable channel.

Requirements for fire protection certification of cables

by

In order to solve the long-standing problem of the lack of flame retardant classification standards in the AAC Cable industry and the imperfection of the evaluation index dimension in the original flame retardant standard system, the former Sichuan Fire Protection Research Institute of the Ministry of public security organized relevant units to take the lead in formulating the national mandatory standard GB 31247-2014 “classification of burning performance of cables and optical cables”, which was issued on December 5, 2014 and officially implemented from September 1, 2015. On the basis of full investigation and verification test, combined with the relevant requirements of EN 13501-6:2014 and the actual grading assessment needs of domestic cables and optical cables, GB 31247-2014 finally forms four grades A, B1, B2 and B3. The assessment dimensions include the main grading indexes such as combustion calorific value, flame spread, heat release, smoke production characteristics and smoke density, and the main grading indexes such as combustion droplet / particle, smoke emission and so on The toxicity and corrosivity of flue gas are three additional classification indexes. Generally speaking, these assessment indexes can more truly reflect the combustion characteristics of cables under actual fire conditions, and the evaluation of cable combustion performance grade will be more scientific, reasonable and practical.


In order to promote the flame retardant cable classification standard and link up the related testing and certification work, China Quality Certification Center and National Center for quality supervision and inspection of fire resistant building materials (nftc) have cooperated closely since the standard drafting stage to develop cqc17-463416-2015 “implementation rules for classification certification of burning performance of cables for construction Engineering”, Since 2015, we have held publicity and implementation meetings on standards and certification in Nanjing, Yixing, Guangzhou, Jinan, Chengdu and other places, actively promoting the application and acceptance of standards to relevant architectural design units and architectural design specifications, and achieved good promotion results. This work also lays a foundation for the domestic flame retardant cable export to meet the relevant technical requirements of the European Union CPR building product regulations.
Considering the identification and type selection requirements of cables with different flame retardant grades, the new version of the implementation rules (cqc17-463416-2020) in 2020 adds the model naming provisions of cables with flame retardant grades, and adds some products with flame retardant grades B1 and B2, such as wdzb1-yjy, zb2-bv, etc., and provides the new products to Jiangsu Shangshang, Wuxi Jiangnan, Wuxi Jiangnan, etc Some excellent cable enterprises such as Jiangsu Zhongmei and Sichuan Xinshiji have issued the first batch of new CQC fire prevention certificates.


The new version of CQC fire prevention Certification Implementation Rules includes power cable, wiring, control cable, computer cable, flexible cable, communication cable, optical cable and other construction cable products. The CQC fire prevention certification mark shown in Figure 1 can be applied to the certified products to prove that the products meet the relevant requirements of each flame retardant grade. After the implementation and promotion of flame retardant classification standards and certification, many laboratories including the National Center for quality supervision and inspection of fire resistant building materials, the National Center for quality supervision and inspection of wire and cable products (Yixing) and Shanghai ABC Cable wisdom Testing Technology Co., Ltd. (istcw) have obtained the relevant recognition of the flame retardant classification certification.
3、 Some misunderstandings and development prospects of flame retardant graded cables
In recent years, with the popularization and application of GB / T 19666 “general rules for flame retardant and fire resistant wires, cables or optical cables” and the flame retardant categories of ZA, ZB, ZC and ZD, due to the common sense tendency to code a-b-c-d level arrangement and the non-metallic content from high to low in the test, there are a large number of manufacturers, users and technical institutions in the industry that bundle flame retardant ZA, ZB, ZC and ZD are flame retardant levels, It is also understood that flame retardant class A is superior to (covering) class B, class C, and then to class D.
However, the standard analysis shows that the main difference of bunched flame retardant (ZA, ZB, ZC, ZD) categories lies in the different application and evaluation occasions, and the grade relationship or classification concept is not mentioned in the relevant standards. In particular, in the article “understanding and suggestions on the requirements of Flame Retardancy for wiring bundles” recently received in the Journal of quality and certification, verification tests were carried out on five groups of samples of typical wiring products from different manufacturers: za-bv 450 / 750V 2.5 and wdza-byj 450 / 750V 2.5, and the above ten groups of samples were tested in accordance with GB / T 18380 series standards Class C and class D combustion tests. By analyzing the carbonization height of the samples before and behind the steel ladder after the combustion test, the results show that the carbonization height of most of the bundles of this kind of wire products is higher than that of class A, and even some of the samples have passed the flame retardant class a test, and the flame retardant class D is unqualified. The bundle combustion verification test of this cloth and wire product also proves that the traditional bundle flame retardant ZA, ZB, ZC and ZD do not belong to the classification of flame retardant performance, and there is no relationship between high and low levels.


In contrast, GB 31247-2014 “classification of burning performance of cables and optical cables” scientifically and systematically classifies the burning performance of cables used in construction projects through multi-dimensional index assessment and evaluation, which is close to the requirements of actual building fire safety scenarios, and gives a clear description of the performance grade in the standard, for example, the burning performance B1 is flame retardant 1 cable (optical cable), The combustion performance of grade B2 is flame retardant grade 2 cable (optical cable), etc（ This also lays a solid foundation for the reference and acceptance of GB 31247-2014 flame retardant classification in GB 51348 standard for electrical design of civil buildings.
It is believed that with the promulgation and heavy implementation of GB 51348 “standard for electrical design of civil buildings” and subsequent relevant design specifications, a more unified and clear understanding and application of the classification of combustion performance of cables and optical cables will be formed from user units, design units, supervision units, testing and certification Institutions to manufacturers and other relevant policies, The flame retardant cables and optical cables used in domestic construction projects will also usher in a brighter development prospect.

For more information about wires and cables, please click Joy ’cable Blog

Finding method for broken core of flame retardant cable

by

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.

Fire-retardant design of power cables in subway construction

by

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.

Structure composition of cable products

by

b230 standardThe structural elements of wire and cable products can generally be divided into four main structural components: wire, insulation layer, shielding and protective layer, as well as filling elements and tensile elements. According to the requirements and applications of the product, some products have a very simple structure, with only one structure of wires, such as overhead bare wires, catenary wires, copper and aluminum busbars (bus bars), etc.; the external electrical insulation of these products depends on installation and laying Use insulators and space distance (that is, use air insulation) to ensure.The vast majority of wire and cable products are products with the same cross-section (cross-section) shape (ignoring the errors caused by manufacturing) and elongated products. This is because they are used as features to form circuits or coils in systems or equipment. Decided. Therefore, to study and analyze the structural composition of cable products, only need to observe and analyze from its cross section.

image

1. Lead wire Lead wire is the most basic and essential main component for the product to carry out electric current or electromagnetic wave information transmission function. Wire is the abbreviation of conductive core, made of copper, aluminum and other non-ferrous metals with excellent conductivity. The optical fiber aerial bundled cables ASTM b230 standard  used in the optical communication network, which have developed rapidly in the past 30 years, use optical fibers as wires.

2. Insulation layer is a component that is wrapped around the periphery of the wire and plays an electrical insulation role. That is to say, it can ensure that the transmitted current, electromagnetic waves, and light waves only travel along the wires and do not flow to the outside. The potential on the conductors (that is, the potential difference formed to the surrounding objects, that is, the voltage) can be isolated, that is, the normal transmission of the wires must be ensured Function, but also to ensure the safety of external objects and people. Wire and insulation are the two basic components that must be equipped to form cable products (except bare wires).

3. Protective layer When wire and cable products are installed and operated in various environments, they must have a component that protects the product as a whole, especially the insulating layer, which is the protective layer.

Because insulating materials are required to have excellent various electrical insulating properties, they must have extremely high purity and minimal impurity content; often they cannot take into account their ability to protect the outside world. Therefore, for the outside world (that is, installation, use occasions and in-use ) The endurance or resistance of various mechanical forces, the resistance to atmospheric environment, the resistance to chemicals or oils, the prevention of biological damage, and the reduction of fire hazards must be borne by various protective layer structures.

Many aerial bundled cable NFC 33-209  products dedicated to a good external environment (such as a clean, dry, and non-mechanical external room), or products with a certain mechanical strength and weather resistance of the insulation material itself, can be without the protective layer. .

Take you to understand the A, B, C grades of flame-retardant cables

by

1. Classification and difference of flame-retardant cables
The ABC category of flame-retardant cables is classified according to the GB/T18380-2008 standard and is used to evaluate the ability of vertically installed bundles of wires and cables or optical cables to inhibit the vertical spread of flame under specified conditions.
1. Flame-retardant Class A means:Fire Retardant Cable is installed on the test steel ladder so that the non-metallic materials contained in the test in the total volume is 7L/m, and the fire supply time is 40 minutes. After the cable burning stops, dry the sample and measure The maximum carbonization range of the sample shall not be higher than 2.5m from the bottom of the torch
2. Flame-retardant Class B refers to: the cable is installed on the test steel ladder so that the non-metallic materials contained in the test in the total volume is 3.5L/m, and the fire time is 40 minutes. After the cable burning stops, dry the sample. The measured maximum carbonization range of the sample shall not be higher than 2.5m from the bottom of the torch


3. Flame-retardant category C refers to: the cable is installed on the test steel ladder so that the non-metallic materials contained in the test in the total volume is 1.5L/m, and the fire time is 20 minutes. After the cable burning stops, dry the sample. The measured maximum carbonization range of the sample shall not be higher than 2.5m from the bottom of the torch.
2. Which grade of flame-retardant cable is the highest?
It can be seen from the difference between the above three types of flame retardant ABC that the conditions of type A flame retardant are the most stringent, so the flame retardant rank order is A>B>C. A has the highest flame retardant level.
Three, flame-retardant cable application
Flame-retardant cables can be used in oil tank farms, important wooden structure public buildings, high-temperature places and other situations where fire resistance requirements are high and the installation and economic performance are acceptable. If self-contained oil-filled cables are laid in public corridors, passenger tunnels, bridges, etc. where fire protection is required, they can be laid in sand. Close to high voltage current,
For cable trenches of oil-containing equipment such as voltage transformers, the section trench cover should be sealed. When laying power cables in pipe bridges or exposed pipes, you need to choose fire-resistant ones. When laying through pipes in concrete, choose fire-retardant ones. Flame-retardant ones cannot replace fire-resistant ones, but fire-resistant ones can replace flame-retardant ones. When it comes to cost, it is better to choose cables with corresponding functions.

How to Improve Pass Rate of Fire-resistant Cable Fire Test

by

As fire-resistant cables are now more and more widely used, many manufacturers are producing them, but often the quality cannot be guaranteed. Therefore, under normal circumstances, when companies develop fire-retardant cable products, they first try to manufacture a section of the product, send it to the relevant national inspection agency, and then start mass production after obtaining the test report. A few cable manufacturers have established their own fire-resistant test inspections. As everyone knows, the fire resistance test is an inspection of the process results of the cables produced. The same process plan and the performance of the cables produced in different periods have certain differences. For companies that produce fire-resistant cables, it is like the fire-resistant test of the fire-resistant cable. With a pass rate of 99%, the fire-resistant cable has a 1% safety hazard, which is 100% dangerous for users. So how to improve the pass rate of fire-resistant cable fire-resistant experiments, from the raw materials, conductor selection, production process control and other aspects to explain1. There are three types of mica, synthetic mica, phlogopite, and muscovite. The quality performance of each is the best synthetic mica and the worst muscovite. For small-sized power cables, synthetic mica tape must be selected for wrapping, and mica tape cannot be layered. Use, long-term storage of mica tape is easy to absorb moisture, so the temperature and humidity of the surrounding environment must be considered when storing mica tape.

2. When selecting mica tape wrapping equipment, it should be used with good stability. The wrapping angle is best to wrap around 300-400. The mica tape is wrapped evenly and tightly. All guide wheels and rods that touch the equipment must be smooth. The wiring is neat, the tension is not too large, and the side plate and cylinder of the take-up tooling wheel are flat and smooth.

3. For the circular core with axial symmetry, the mica tape is wrapped tightly in all directions, so the conductor structure of the fire-resistant cable should adopt a circular compact conductor. The reasons are as follows:

①Some users propose that the conductor is a stranded flexible cable, which requires the company to communicate with users from the reliability of the cable to a round compact conductor. The soft structure of the bundle and the twisting can easily cause damage to the mica tape as a fire-resistant Cable conductors are not desirable, but some manufacturers think that users need what kind of fire-resistant cables, and manufacturers should meet user needs. I think users do not fully understand the details of cables after all. Cables are closely related to human life. Yes, cable manufacturers must clarify related technical issues to users.

②Sector-shaped conductors are not suitable, because the pressure of the mica tape of the fan-shaped conductor is unevenly distributed. As shown in the figure, it can be seen that the pressure at the three fan-shaped corners of the fan-shaped core around the mica tape is the largest Yes, because mica is a sheet-like silicate polymer, the molecular attraction between the layers is much weaker than the s1-0 covalent bond in the crystal. The layers are easy to slide and adhere to silicon, but the bonding strength is also Low, it is easy to fall off and split when external force is scraped and squeezed, especially when the fan-shaped structure is adopted, the wrapped wire core passes through the guide wheel, the wire splitting rod and the wire to the edge of the side plate of the tooling wheel, and the rear track When the process extrudes the insulation into the core, it is easy to be scratched and bumped, which leads to a decrease in electrical performance. In addition, from the perspective of cost, the section perimeter of the sector-shaped conductor structure is larger than the section perimeter of the circular conductor, which increases the precious material mica Belt, although the outer diameter of the circular structure cable has increased. The amount of polyvinyl chloride sheathing material has increased, but the product material is compared with the total cost, and the overall cost of the circular structure cable is still saved. Based on the above description, from the technical and economic analysis, it is best to use a circular structure for the conductor of the fire-resistant power cable.