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.

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.

Structure composition of cable products

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.


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

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

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.

Fire Resistant Cables Introduction

At present, the electrical system industry is accustomed to collectively refer to fire-retardant (Fire retardant), halogen-free and low-smoke (LS0H) or low-halogen and low-smoke (Lowsmokefume, LSF), fire resistant (Fire resistant) and other electrical appliances with certain fire resistance properties as fire-resistant cables.

1. Flame retardant cable
The characteristic of flame-retardant cables is to delay the spread of flame along the electricity so that the fire will not expand. Because of its low cost, it is a large number of cable varieties used in fire-proof electricity. Regardless of whether it is a single wire or a bunch of laying conditions, when the cable is burned, the flame can be controlled within a certain range, so it can avoid major disasters caused by the cable fire and prolonged combustion, thereby improving the fire protection of the electric line Level.

2.Halogen-free low-smoke flame-retardant cable (LSOH)
The characteristics of halogen-free low-smoke cables are that they not only have excellent flame retardant properties, but also that the materials that constitute low-smoke and halogen-free do not contain halogens. They have low corrosiveness and toxicity during combustion, and produce a very small amount of smoke, thereby reducing the impact on humans and instruments. In addition, the damage caused by the design is conducive to timely rescue in the event of a fire. Although the non-branch low-smoke flame-retardant cable has excellent flame-retardant, corrosion resistance and low smoke concentration, its mechanical and electrical properties are slightly worse than ordinary cables.

3. Low halogen and low smoke flame retardant cable (LSF)
Low-halogen, low-smoke and flame-retardant cables have a hydrogen chloride release and smoke density index between flame-retardant cables and halogen-free low-smoke flame-retardant cables. Low halogen (Lowhalogen) cable material will also contain halogen, but the content is lower.
The characteristic of this kind of cable is that it not only possesses flame retardant properties, but also emits less smoke and hydrogen chloride during combustion. This kind of low-halogen, low-smoke flame-retardant cable is generally made of polyvinyl chloride (PVC) as the base material, and then processed with high-efficiency flame retardants, HCL absorbents and smoke suppressants. Therefore, this flame-retardant material significantly improves the combustion performance of ordinary flame-retardant polyvinyl chloride materials.

4. Fire resistant cable (Fireresistant)
Fire-resistant and fire retardant cables can maintain normal operation for a certain period of time under the condition of flame burning, and can maintain the integrity of the circuit (Circuitintergrity). Fire-resistant and flame-retardant cables produce less acid gas and smoke when they burn, and their fire-resistant and flame-retardant properties are greatly improved. Especially when they are burned, accompanied by water spray and mechanical shock, the cable can still keep the line intact.