What are the materials of flame retardant wires and cables?
Flame-retardant wire refers to wires that are fireproof and flame-retardant. Generally, under test conditions, after the wire is burned, if the power is cut off, the fire will be controlled within a certain range and will not spread. It has the performance of flame retardancy and suppression of toxic smoke. As an important part of electrical safety, the selection of materials for flame-retardant wires is crucial. At present, the commonly used flame-retardant wire materials on the market include PVC, XLPE, silicone rubber, and mineral insulation materials.
Material selection of flame-retardant wires and cables
The higher the oxygen index of the material used for flame-retardant cables, the better the flame-retardant performance, but as the oxygen index increases, some other properties will be lost. If the physical properties and process properties of the material are reduced, the operation is difficult, and the material cost is increased, so the oxygen index should be reasonably and appropriately selected. Generally, if the oxygen index of the insulating material reaches 30, the product can pass the test requirements of Class C in the standard. If the sheath material and the filling material are both flame-retardant materials, the product can meet the requirements of Class B and Class A. Materials for flame-retardant wires and cables are mainly divided into halogen-containing flame-retardant materials and halogen-free flame-retardant materials;
1. Halogen-containing flame-retardant materials decompose and release hydrogen halides when heated during combustion. Hydrogen halides can capture active free radicals HO roots, thereby delaying or extinguishing the combustion of the material and achieving the purpose of flame retardancy. Commonly used materials include polyvinyl chloride, chloroprene rubber, chlorosulfonated polyethylene, ethylene propylene rubber, etc.
1) Flame-retardant polyvinyl chloride (PVC): Due to its low price, good insulation, and flame retardancy, polyvinyl chloride is widely used in ordinary flame-retardant wires and cables. To improve the flame retardancy of PVC, halogen flame retardants (decabromodiphenyl ether), chlorinated paraffin, and synergistic flame retardants are often added to the formula to improve the flame retardancy of polyvinyl chloride; Ethylene propylene rubber (EPDM): It is a non-polar hydrocarbon with excellent electrical properties, high insulation resistance and low dielectric loss, but EPDM is a flammable material. It is necessary to reduce the degree of cross-linking of EPDM and reduce the low molecular weight substances produced by molecular chain disconnection to improve the flame retardancy of the material;
2) Low smoke and low halogen flame retardant materials are mainly for polyvinyl chloride and chlorosulfonated polyethylene. Add CaCO3 and A(lOH)3 to the formula of polyvinyl chloride. Zinc borate and MoO3 can reduce the HCL release and smoke of flame-retardant polyvinyl chloride, thereby improving the flame retardancy of the material and reducing the emission of halogen, acid mist and smoke, but may slightly reduce the oxygen index.
2. Halogen-free flame retardant materials
Polyolefin is a halogen-free material composed of hydrocarbons. It decomposes carbon dioxide and water when burned, and does not produce obvious smoke and harmful gases. Polyolefins mainly include polyethylene (PE) and ethylene-vinyl acetate (E-VA). These materials themselves are not flame retardants, and inorganic flame retardants and phosphorus series flame retardants need to be added to be processed into practical halogen-free flame retardant materials; however, due to the lack of polar groups on the molecular chain of non-polar substances, they are hydrophobic and have poor affinity with inorganic flame retardants, making it difficult to combine firmly. To improve the surface activity of polyolefins, surfactants can be added to the formula; or polymers containing polar groups can be mixed into polyolefins for blending, thereby increasing the amount of flame retardant fillers, improving the mechanical properties and processing properties of the material, and obtaining better flame retardancy. It can be seen that flame-retardant wires and cables are still very advantageous and are very environmentally friendly to use.
The difference between PE, PVC, XLPE, and EPR materials
1.1 The selection of cable insulation type shall comply with the following provisions:
1 Under the operating voltage, working current and its characteristics and environmental conditions, the cable insulation characteristics shall not be less than the normal expected service life.
2 It shall be selected based on factors such as operational reliability, ease of construction and maintenance, and the comprehensive economy of the maximum allowable operating temperature and cost.
3 It shall meet the requirements of fire-proof places and shall be conducive to safety.
4 When it is clear that it needs to be coordinated with environmental protection, environmentally friendly cable insulation types shall be selected.
1.2 The selection of insulation types for commonly used cables shall comply with the following provisions:
1 The selection of insulation types for medium and low voltage cables shall comply with the provisions of Articles 1.3 to 1.7 of this Code. Low voltage cables shall use polyvinyl chloride or cross-linked polyethylene extruded insulation types, and medium voltage cables shall use cross-linked polyethylene insulation types. When it is clear that it needs to be coordinated with environmental protection, polyvinyl chloride insulated cables shall not be used.
2 Cable lines in high-voltage AC systems shall use cross-linked polyethylene insulation types. In areas with more operating experience, self-contained oil-filled cables can be used.
3 For high-voltage direct current transmission cables, non-drip-impregnated paper insulation and self-contained oil-filled types can be selected. When it is necessary to increase the transmission capacity, it is advisable to select a type constructed with semi-synthetic paper materials. Ordinary cross-linked polyethylene cables should not be used for direct current transmission systems.
1.3 For mobile electrical equipment and other circuits that are often bent or have high flexibility requirements, rubber insulation and other cables should be used.
1.4 In places where radiation is applied, cables with radiation irradiation strength such as cross-linked polyethylene or EPDM insulation should be selected according to the requirements of the insulation type.
1.5 In places with high temperatures above 60°C, heat-resistant cables such as heat-resistant polyvinyl chloride, cross-linked polyethylene or EPDM insulation should be selected according to the requirements of the high temperature, its duration and the insulation type; in high-temperature environments above 100°C, mineral insulated cables should be selected. Ordinary polyvinyl chloride insulated cables should not be used in high-temperature places.
1.6 In low-temperature environments below -15°C, cross-linked polyethylene, polyethylene insulation, and cold-resistant rubber insulation cables should be selected according to the low-temperature conditions and insulation type requirements. Polyvinyl chloride insulated cables should not be used in low-temperature environments.
1.7 In crowded public facilities and places with low-toxic flame retardancy and fire protection requirements, cross-linked polyethylene or ethylene-propylene rubber and other halogen-free insulated cables can be used. When low toxicity is required for fire protection, polyvinyl chloride cables should not be used.
1.8 Except for the cases required by Articles 1.5 to 1.7 of this Code, polyvinyl chloride insulated cables can be used for circuits below 6kV.
1.9 For 6kV important circuits or cross-linked polyethylene cables above 6kV, the type with the characteristics of inner and outer semi-conductive and insulating layers co-extrusion process should be selected.
The difference between polyethylene, polyvinyl chloride, cross-linked polyethylene, and ethylene-propylene rubber materials：
The difference between the four materials
1. Polyethylene. English abbreviation PE, it is a polymer of ethylene, non-toxic. Easy to color, good chemical stability, cold resistance, radiation resistance, and good electrical insulation.
2. Polyvinyl chloride. English abbreviation PVC, it is a polymer of vinyl chloride. It has good chemical stability and is resistant to acids, alkalis, and some chemicals. It is resistant to moisture, aging, and flame retardant. The temperature when it is used cannot exceed 60°C (polyvinyl chloride will release toxic HCl smoke when burning), and it will harden at low temperatures. Polyvinyl chloride is divided into soft plastics and hard plastics.
3. Cross-linked polyethylene. XLPE in English is an important technology to improve the performance of PE. PE modified by cross-linking can greatly improve its performance, not only significantly improving the mechanical properties, environmental stress cracking resistance, chemical corrosion resistance, creep resistance, and electrical properties of PE, but also significantly improving the temperature resistance level, which can increase the heat resistance temperature of PE from 70°C to above 90°C, thereby greatly broadening the application range of PE. At present, cross-linked polyethylene (XLPE) has been widely used in pipes, films, wire and cable materials, and foam products.
4. Ethylene propylene rubber (EPR). The full name is cross-linked ethylene-propylene rubber, which has oxygen resistance, ozone resistance and partial discharge stability; the dielectric loss factor is large, so it is only used in power cable lines with voltage levels below 138kV. Due to the good water resistance of EPDM, EPDM cables are suitable for submarine cables, and because EPDM has good softness, it is more suitable for laying in mines and ships.
What is shielded cable? What is the cable shield?
Shielded cable has the word "shielded" in it. As the name implies, it is a cable with the ability to resist external electromagnetic interference formed by adding a shielding layer to the transmission cable. The so-called "shielding" in the cable structure is also a measure to improve the distribution of the electric field. The cable conductor is made of multiple strands of wires twisted together. It is easy to form an air gap between it and the insulation layer. The surface of the conductor is not smooth, which will cause electric field concentration.
1. Cable shielding layer
1). Add a shielding layer of semi-conductive material on the surface of the conductor. It has the same potential as the shielded conductor and has good contact with the insulation layer, thereby avoiding local discharge between the conductor and the insulation layer. This layer of shielding is also called the inner shielding layer. There may also be gaps at the contact between the insulation surface and the sheath. When the cable is bent, the insulation surface of the oil-paper cable is prone to cracks. These are factors that cause local discharge.
2). Add a shielding layer of semi-conductive material on the surface of the insulation layer. It has good contact with the shielded insulation layer and has the same potential as the metal sheath, thereby avoiding local discharge between the insulation layer and the sheath. To make the conductive core and the insulating electric field uniform, medium and high voltage power cables of 6kV and above generally have conductor shielding layers and insulating shielding layers, and some low voltage cables do not have shielding layers. There are two types of shielding layers: semi-conductive shielding and metal shielding.
2. Shielded cable The shielding layer of this type of cable is mostly made of metal wires woven into a mesh or metal film, and there are many different ways of single shielding and multi-shielding. Single shielding refers to a single shielding net or shielding film, which can wrap one or more wires. Multi-shielding means multiple shielding nets and shielding films are in one cable. Some are used to isolate electromagnetic interference between wires, and some are double-layer shielding to enhance the shielding effect. The mechanism of shielding is to ground the shielding layer to isolate the induced interference voltage of the external connection to the wire.
1). Semi-conductive shielding The semi-conductive shielding layer is usually set on the outer surface of the conductive core and the outer surface of the insulating layer, respectively called the inner semi-conductive shielding layer and the outer semi-conductive shielding layer. The semi-conductive shielding layer is composed of a semi-conductive material with very low resistivity and thin thickness. The inner semi-conductive shielding layer is to even out the electric field on the outer surface of the core, and avoid partial discharge between the conductor and the insulation due to the uneven surface of the conductor and the air gap caused by the twisting of the core. The outer semi-conductive shielding layer is in good contact with the outer surface of the insulation layer, and is at the same potential as the metal sheath, avoiding partial discharge with the metal sheath due to defects such as cracks on the cable insulation surface.
2). Metal shielding For medium and low voltage power cables without metal sheaths, in addition to the semi-conductive shielding layer, a metal shielding layer must be added. The metal shielding layer is usually wrapped with copper tape or copper wire and mainly plays the role of shielding the electric field. Because the current passing through the power cable is relatively large, a magnetic field will be generated around the current. In order not to affect other components, the shielding layer can be added to shield this electromagnetic field in the cable. Moreover, the cable shielding layer can play a certain role in grounding protection. If the cable core is damaged, the leaked current can flow along the shielding layer like the grounding grid, playing a role in safety protection. It can be seen that the role of the cable shielding layer is still very large.
What principles should be followed in selecting power cables?（1）
The selection of power cables should follow the following principles:
1. Rated voltage:
Select appropriate wires and cables according to the voltage level of the place of use, and ensure that the rated voltage of the cable is not lower than the actual use voltage.
2. Current capacity:
Select appropriate wire and cable cross-section according to the load current to ensure that the cable will not overheat under the maximum load, and the voltage drop is within an acceptable range.
3. Safety requirements:
According to safety requirements, non-flammable cables, flame-retardant cables, halogen-free flame-retardant cables, fire-resistant cables, etc. can be selected.
4. Mechanical strength:
When it is necessary to withstand mechanical tension, pressure and large-span creep resistance, reinforced cables such as copper wire or steel belt armored structural cables can be selected.
5. Economy:
Under high load conditions, select according to economic current density, considering that power loss and capital investment should be within the most reasonable range.
6. Laying conditions:
Select the model and specification of the cable according to the cable laying environment and laying method to ensure that the cable can adapt to specific laying conditions.
7. Environmental factors:
Calculate the resistance and voltage drop of the cable considering the cable laying length and laying method, and select the flame retardant grade of the cable according to the safety requirements of the power system.
8. Comprehensive considerations:
When selecting power cables, it is also necessary to comprehensively consider various factors such as purpose, voltage, environment, etc., and more accurately select the appropriate cable for a specific application through example calculations.
Through the above principles, it can be ensured that the selection of power cables not only meets the actual use needs, but also has safety and economy.
What factors affect the insulation resistance of wires and cables?
In the production of wires and cables, the phenomenon of low insulation resistance is often encountered. There are many factors that affect the insulation resistance value of cables. In fact, there are four main factors that have a great influence on the insulation resistance coefficient.
1. The influence of temperature
As the temperature increases, the insulation resistance coefficient decreases. This is due to the increase in thermal motion, the increase in ion generation and migration. Under the action of voltage, the conduction current formed by ion movement increases, and the insulation resistance decreases.
Theory and practice show that the insulation resistance coefficient decreases exponentially with the increase in temperature, and the conductivity increases exponentially with the increase in temperature.
2. The influence of electric field strength
When the electric field strength is in a relatively low range, the mobility of ions increases in a proportional relationship with the increase in electric field strength. Ionic current and electric field strength follow Ohm's law. When the electric field strength is relatively high, as the electric field strength increases, the mobility of ions gradually changes from a linear relationship to an exponential relationship. When the electric field strength is close to breakdown, a large amount of electron migration occurs, thereby greatly reducing the insulation resistance coefficient.
The withstand voltage test voltage of various wire and cable products specified in the standard is in the stage where the ion mobility increases proportionally with the electric field strength, so the influence of the electric field strength on the insulation resistance coefficient cannot be reflected. When the sample is subjected to a breakdown test, the influence of the electric field on the insulation resistance coefficient is clearly reflected.
3. The influence of humidity
Due to the high conductivity of water, the size of water molecules is much smaller than that of polymer molecules. Under the action of heat, the polymer macromolecules and the constituent chain segments move relatively, so that water molecules can easily penetrate into the polymer, increase the conductive ions in the polymer, and reduce the insulation resistance.
The standard specifies immersion tests for various wires and cables. For example, before measuring the insulation resistance, the rubber specimen is immersed in water for 24 hours. The purpose is to meet the influence of moisture and water on electrical properties during use.
Insulation resistance is one of the main electrical properties of insulating materials and an important indicator of wire and cable products or materials. Generally, the insulation resistance is required to be not less than a certain value. If the insulation resistance value is too low, the leakage current along the wire and cable line will inevitably increase, resulting in a waste of electrical energy. At the same time, the electrical energy will be converted into thermal energy, preparing for thermal breakdown and increasing the possibility of thermal breakdown.
4. Influence of material purity
Impurities are mixed into the material, increasing the conductive particles in the material and reducing the insulation resistance. Therefore, the insulation resistance of a certain rubber and plastic material will reflect the purity of the material and verify whether it meets the standard.
During the production of wires and cables, the process does not strictly follow the operating procedures, mixed impurities and materials bubble due to moisture, insulation core deviation or outer diameter size is smaller than the standard, insulation delamination or cracks, insulation scratches, etc. , will reduce the insulation resistance of the product.
Therefore, in order to check the insulation resistance, it is necessary to check whether there are any problems in the process operation. During the use of wires and cables, measuring the changes in insulation resistance can also check the insulation damage and prevent accidents.
Tips on storing wires and cables
There are many types of wire and cable products, and their application range is very wide. If they are not stored properly, it will affect the life and safety of the cables, and even cause unnecessary disasters. Therefore, how to store them is an issue that needs attention.
1. When storing wires and cables, avoid water sources, and do not contact acids, alkalis and mineral oils. The outer skin of the wires is mostly plastic. Contact with corrosive liquids will cause the outer skin of the wires to swell, accelerate the damage of the outer skin and cause leakage, which is very dangerous.
2. Wires and cables cannot be exposed to the sun or in an ultra-high temperature environment for a long time, otherwise it will cause cracks or peeling on the outer sheath of the cable.
3. In the environment where wires and cables are stored, it is strictly forbidden to have gases that are harmful to cables, such as corrosive gases and flammable and explosive gases.
4. Wires and cables should be stored regularly, according to specifications and production time. The storage period is limited to the product's factory date, and generally should not exceed one and a half years.
5. Long-term storage of wires and cables will be affected by extrusion pressure, which may cause deformation of the sheath and cable. The cables should be rolled regularly. After rolling, the cables should be checked to see if they are intact to avoid damage that affects subsequent safe use. (Cable reels are not allowed to be laid flat)
6. The transportation of wires and cables is also the key to the storage and protection of wires. It is strictly forbidden to throw cable reels from high places during transportation, which may cause cracks in insulation and sheath, and damage the conductivity and mechanical properties of the cables.
Why do we need to analyze the impurity elements of aluminum alloys for wires and cables?
In the wire and cable manufacturing industry, aluminum rods, aluminum alloy wires, aluminum alloy strips, profiles, etc. for electrical use are also important materials. One of the important testing items for conductive aluminum alloys is chemical composition analysis. In addition to determining the grade of aluminum alloys, another important purpose of composition analysis is to determine the content of impurity elements.
The reason why we need to analyze the impurity elements of conductive aluminum alloys is that the manufacturing process of aluminum alloys is to add a certain proportion of alloying elements to pure aluminum. These added alloying elements are usually trace elements, especially the percentage of trace elements added to conductive aluminum alloys. The mass fraction is generally not more than 1.0%. The trace alloying elements we commonly add are Cu, Mg, Fe, B, Zr and other elements, but Zr, Cr, V, Mn, Li and Ti have a serious impact on the resistivity of aluminum alloy conductor materials. Therefore, we must strictly control the content of Zr, Cr, V, Mn, Li 7 and Ti in aluminum alloy conductor materials. Reduce the harmful effects of impurity elements on the conductivity of aluminum alloys.
Which cable products will have high market demand in 2024?(2)
New energy vehicles
New energy vehicle cables can be divided into in-car cables, charging pile cables and on-board charging cables according to different application scenarios. The rapid development of new energy electric vehicles has provided good market opportunities for its supporting cable industry. As vehicle manufacturers increase their investment in the field of new energy vehicles, vehicle electrification has become a general trend, and new energy vehicle cables will also usher in new growth points. It is expected that the size of my country's automotive cable market will reach 18.06 billion yuan in 2025. Whether from the perspective of industrial transformation or energy strategy, the prospects of new energy automobile cables are very broad. In the next five years, the field of new energy automobile cables will usher in huge development space.
Marine construction
China's submarine cable industry has shown a fluctuating upward trend in recent years. In 2020, driven by the "rush to install" offshore wind power, the size of the submarine cable market increased significantly by 12.64% year-on-year, reaching approximately 13.4 billion yuan, reaching its peak in recent years. Based on the future demand for offshore wind power, international communication network upgrades, and offshore oil platform development in multiple application fields, China's submarine cable market is expected to reach 20 billion yuan in 2027, with a compound annual growth rate of approximately 6%.
Special equipment
At present, industries such as shipbuilding, rail transportation, clean energy, aerospace, petrochemicals, and new energy vehicles all require the use of a large number of special cables. With the advancement of science and technology, the transformation and upgrading of traditional industries, and the vigorous development of strategic emerging industries and high-end manufacturing, my country's economy and society are further developing towards safety, environmental protection, low-carbon energy conservation, informatization, and intelligence. The construction and modernization of national smart grids Urban construction, large-scale transformation of urban and rural power grids, and new energy power station construction have put forward higher requirements for the application of wires and cables, which also provide new development opportunities for the development of special wires and cables.
Which cable products will have high market demand in 2024?(1)
The wire and cable market is a key infrastructure market. With economic development and technological advancement, the demand for wire and cable continues to increase. In the next few years, including 2024, some cable markets will develop significantly, and some cable products will usher in broad market demand. Some people believe that markets are currently relatively stable and will continue to improve in the future, such as the following markets:
Power grid construction
my country's power grid construction is still in the development stage. The higher the voltage level, the more conducive to long-distance power transmission. In the future, large-scale cross-regional power grid construction in China will require long-distance power transmission. Currently, judging from the construction planning of high-voltage and ultra-high-voltage lines, supporting cables The demand is on the rise. According to the State Grid's plan, investment will increase to 520 billion yuan in 2023, a year-on-year increase of 4%. Power grid investment and new infrastructure are the driving force for the development of the cable market.
Photovoltaic/energy storage/hydrogen energy market
The energy sector is an important area of the wire and cable market. With the continuous development of my country's photovoltaic industry, my country's photovoltaic cable industry will still be in a stage of rapid development. It is expected that the size of my country's photovoltaic cable market will reach 18.56 billion yuan in 2023. In recent years, in order to implement the country's strategic deployment of "dual carbon" goals and promote the green and low-carbon transformation of energy, the Chinese government has introduced a series of policies and measures. In the next few years, new energy industries such as photovoltaics, wind power, and energy storage will maintain rapid growth, and the rapid development of their industries will promote the development of photovoltaic cable companies.
Thirty cable common problem knowledge popularization（5）
23. Where are the inner shielding layer and outer shielding layer of power cables located? What materials are used? What does it do?
Answer: In order to have better contact between the insulation layer and the cable conductor and eliminate the increase in electric field intensity on the conductor surface caused by the roughness of the conductor surface, the conductor surface is generally covered with an inner shielding layer of metallized paper or semiconductor paper tape. In order to ensure better contact between the insulation layer and the metal sheath, an outer shielding layer is generally wrapped around the insulation layer. The outer screen layer is made of the same material as the inner screen layer, and sometimes it is also bound with copper tape or braided copper wire tape.
24. What should we pay attention to during the transportation, loading and unloading of cables?
Answer: (1) During transportation, loading and unloading, cables and cable drums should not be damaged. It is strictly forbidden to push cable drums directly off the vehicle. Cables should generally not be transported or stored flat.
(2) Before transporting or rolling the cable drum, it must be ensured that the cable drum is firm and the cable is wound tightly. The oil pipe between the oil-filled cable and the pressure oil tank should be fixed and not damaged. The pressure oil tank should be secure and the pressure indication should meet the requirements.
25. What aspects should be considered when selecting the cross-section of power cables?
Answer: The following aspects should be considered:
(1) The long-term operating current allowed by the cable;
(2) Thermal stability in the event of short circuit;
(3) The voltage drop on the line cannot exceed the allowable working range.
26. What are the advantages of power cables compared with overhead lines?
Answer: (1) Reliable operation. Because it is installed in hidden places such as underground, it is less damaged by external forces and has fewer chances of failure. The power supply is safe and will not cause harm to people;
(2) The maintenance workload is small and frequent inspections are not required;
(3) No need to erect poles and towers;
(4) Helps improve power factor.
27. What measures are taken to prevent cable fire?
Answer: (1) Use flame-retardant cables;
(2) Use fireproof cable brackets;
(3) Use fire retardant coatings;
(4) Fire partition walls and fire baffles should be installed at cable tunnels, mezzanine exits, etc.;
(5) Overhead cables should avoid oil pipelines and explosion-proof doors. Otherwise, local pipe penetration or heat insulation and fire prevention measures should be taken.
28. What is a cable failure? How many common types are there?
Answer: Cable failure refers to the failure of insulation breakdown of the cable during preventive testing or the failure of the cable line to cause a power outage due to insulation breakdown, wire burnout, etc. during operation. Common faults include ground faults, short circuit faults, disconnection faults, flashover faults and mixed faults.
29. According to the "Regulations on Safety in Electrical Industry", what are the conditions that electrical workers must meet?
Answer: The following conditions must be met:
(1) Healthy as determined by a doctor, with no illness that would hinder work;
(2) Have necessary electrical knowledge, master relevant procedures, professional techniques and safe operation techniques according to their duties and nature of work, and pass the examination;
(3) Be proficient in first aid methods for electric shock.
30. Where are the inner shielding layer and outer shielding layer of power cables located? What materials are used? What does it do?
Answer: In order to have better contact between the insulation layer and the cable conductor and eliminate the increase in electric field intensity on the conductor surface caused by the roughness of the conductor surface, the conductor surface is generally covered with an inner shielding layer of metallized paper or semiconductor paper tape. In order to ensure better contact between the insulation layer and the metal sheath, an outer shielding layer is generally wrapped around the insulation layer. The outer screen layer is made of the same material as the inner screen layer, and sometimes it is also bound with copper tape or braided copper wire tape.
Thirty cable common problem knowledge popularization（4）
18. What are the requirements for the mechanical strength of cable conductor connection points?
Answer: The mechanical strength of the connection point is generally lower than the tensile strength of the cable conductor itself. For fixedly laid power cables, the tensile strength of the connection point is required to be no less than 60% of the tensile strength of the conductor itself.
19. What are the main properties of the insulation layer material of power cables?
Answer: It should have the following main properties:
(1) High breakdown strength;
(2) Low dielectric loss;
(3) Quite high insulation resistance;
(4) Excellent discharge resistance;
(5) Has certain softness and mechanical strength;
(6) The insulation performance is long-term and stable.
20. The applications of wires and cables are mainly divided into three categories:
(1), power system
The wire and cable products used in the power system mainly include overhead bare wires, busbars (busbars), power cables (plastic cables, oil-paper power cables (basically replaced by plastic power cables), rubber sheathed cables, overhead insulated cables), branch cables (replacing some busbars), electromagnetic wires, and electrical equipment wires and cables for power equipment, etc.
(2), Information transmission system
The wires and cables used in information transmission systems mainly include local telephone cables, television cables, electronic cables, radio frequency cables, optical fiber cables, data cables, electromagnetic wires, power communication or other composite cables, etc.
(3), mechanical equipment, instrumentation systems
In addition to overhead bare wires, almost all other products in this section are applied, but mainly power cables, electromagnetic wires, data cables, instrumentation cables, etc.
21. Wire and cable products are mainly divided into five categories:
(1), Bare wires and bare conductor products
The main characteristics of this type of product are: pure conductor metal, without insulation and sheath layers, such as steel core aluminum stranded wire, copper aluminum busbar, electric locomotive wire, etc.; the processing technology is mainly pressure processing, such as smelting, rolling, drawing system, stranding/compression stranding, etc.; the products are mainly used in suburban areas, rural areas, user main lines, switch cabinets, etc.
(2), power cable
The main features of this type of product are: extruding (winding) the insulation layer on the conductor, such as overhead insulated cables, or twisting several cores (corresponding to the phase line, neutral line and ground wire of the power system), such as overhead insulated cables with more than two cores , or add a sheath layer, such as plastic/rubber sheathed wire and cable. The main process technologies include drawing, stranding, insulation extrusion (wrapping), cabling, armoring, sheath extrusion, etc. There are certain differences in the different process combinations of various products.
The products are mainly used in the transmission of strong electric energy in generation, distribution, transmission, transformation and power supply lines, with large currents (tens of tens of amps to thousands of amps) and high voltages (220V to 500kV and above).
(3) Wires and cables for electrical equipment
The main features of this type of products are: a wide range of varieties and specifications, a wide range of applications, most of the operating voltages are 1kV and below, and new products are constantly derived for special occasions, such as fire-resistant cables, flame-retardant cables, low-smoke halogen-free/low-smoke Smoke-resistant low-halogen cables, termite-proof, mouse-proof cables, oil-resistant/cold-resistant/temperature-resistant/wear-resistant cables, medical/agricultural/mining cables, thin-walled wires, etc.
(4), communication cables and optical fibers (brief introduction)
With the rapid development of the communications industry in the past two decades, products have also developed at an alarming rate. From the simple telephone and telegraph cables in the past, it has developed into thousands of pairs of voice cables, coaxial cables, optical cables, data cables, and even combined communication cables.
The structural dimensions of such products are usually small and uniform, and require high manufacturing precision.
(5), electromagnetic wire (winding wire)
Mainly used in various motors, instruments, etc.
Derivatives/new products of wires and cables are mainly due to different application situations, application requirements, convenience of equipment, and reduction of equipment costs. They use new materials, special materials, or change the product structure, or improve process requirements, or will be different. A variety of products are produced by combining them.
Use different materials such as flame-retardant cables, low-smoke halogen-free/low-smoke low-halogen cables, termite-proof, mouse-proof cables, oil-resistant/cold-resistant/temperature-resistant cables, etc.; change the product structure such as: fire-resistant cables, etc.; improve technology Requirements such as: medical cables, etc.; combined products such as: OPGW, etc.; convenient installation and reduced equipment costs, such as: prefabricated branch cables, etc.
22. What requirements should be met when laying cables?
Answer: The following requirements should be met:
(1) In terms of safe operation, try to avoid all kinds of external damage and improve the power supply reliability of cable lines;
(2) Economically, consider the aspect of saving the most investment;
(3) In terms of construction, the path of the cable line must be convenient for work and maintenance after operation.
Thirty cable common problem knowledge popularization（3）
11. What should be stated on the cable sign? What are the requirements for writing?
Answer: The cable line design number, cable model, specification and starting point should be indicated on the signboard. Cables used in parallel should have sequence numbers. The handwriting is required to be clear and not easy to fall off.
12. How should the yellow wax silk ribbon, black glass paint ribbon, alkali-free glass ribbon, etc. used for making cable joints be dehumidified before construction?
Answer: ① Constant temperature drying method: roll the insulating tape into a small roll with a diameter of 25~30mm, put it into a constant temperature drying oven at 110~120℃ for 4~5 hours, cool and dry, take it out, and put it into a dry sealed cylinder.
②Oil immersion moisture drainage method: Put the small roll of insulation tape into the cable oil with a constant temperature of 120~130℃, keep a distance of 30mm from the bottom of the pot. After a certain period of time, the oil surface will no longer produce foam, take it out, and put it into the stored cable. In oil barrels, the oil level should exceed all contained objects and be sealed.
13. What is the function of the cable outer sheath?
Answer: Protect the inner protective layer from mechanical damage and chemical corrosion and enhance mechanical strength.
14. What requirements should outdoor cable trenches meet?
Answer: The upper part of the cable trench should be slightly higher than the ground and covered with a concrete cover. The cables should be laid flat on the bracket and have good drainage pipes.
15. What is the function of the inner sheath of the cable?
Answer: Keep the insulation layer from coming into contact with water, air or other objects, prevent the insulation from getting damp and prevent the insulation layer from mechanical damage.
16. What should you pay attention to when using wire cutters?
Answer: Before use, be sure to check whether the insulation of the insulated handle is intact. Do not use wire cutters to cut metal wires exceeding the specifications allowed. It is also prohibited to use wire cutters instead of hammers to hit the tool to avoid damage.
17. What is insulation strength?
Answer: When an insulating material is in an electric field, it will be broken down when the electric field intensity increases to a certain limit. This electric field intensity that leads to insulation breakdown is called insulation strength.
Thirty cable common problem knowledge popularization（1）
1. What are the types of commonly used wires and cables according to their uses?
Answer: According to the purpose, it can be divided into bare wires, insulated wires, heat-resistant wires, shielded wires, power cables, control cables, communication cables, radio frequency cables, etc.
2. What kinds of insulated wires are there?
Answer: Common insulated wires are as follows: PVC insulated wire, PVC insulated flexible wire, nitrile polyvinyl chloride mixture insulated flexible wire, rubber insulated wire, agricultural underground direct buried aluminum core plastic insulated wire, rubber insulated cotton yarn Textile flexible wires, PVC insulated nylon sheathed wires, PVC insulated flexible wires for electricity and lighting, etc.
3. What are the cable accessories?
Answer: Commonly used electrical accessories include cable terminal junction boxes, cable intermediate junction boxes, connecting pipes and terminals, steel plate junction slots, cable trays, etc.
4. What is the cable intermediate joint?
Answer: The device that connects the conductor, insulation shielding layer and protective layer of the cable to the cable to connect the cable line is called the cable intermediate joint.
5. What aspects should be considered when selecting the cross section of the power cable?
Answer: The following aspects should be considered:
(1) The working current that the cable is allowed to pass through for a long time;
(2) thermal stability in case of short circuit;
(3) The voltage drop on the line cannot exceed the allowable working range.
IEA: Global solar power overtakes coal power within four years
The International Energy Agency recently stated that by 2027, solar power generation is expected to surpass coal-fired power generation and become the main way of generating electricity. So, why is solar power likely to become the main force of new energy in the future?
More than a decade ago, solar energy was insignificant in the global energy race, accounting for the smallest share of all major sources of electricity, less than 1%. But things have changed now, with the International Energy Agency (IEA) saying that within three years, solar will generate more electricity than natural gas. Within four years, by 2027, it could overtake coal as the dominant form of electricity generation.
Solar electricity installation costs have dropped dramatically in recent years
An important reason is that the installation cost of solar power has dropped significantly. Data show that for utility-scale solar energy, the average cost of construction and operation has continued to decline since 2009, and will only be about $36 per megawatt-hour by 2021, a drop of about 90% compared to 2009. The cost of coal has changed little, at about $108 per megawatt-hour in 2021. Bahar, an analyst for the International Energy Agency's renewable energy market, said that solar power is expected to account for almost 60% of new power installations in the next five years.
Governments are increasingly paying attention to the development of renewable energy
In addition, in recent years, governments of various countries have paid more and more attention to energy security, and have also introduced corresponding policies to support it. According to the EU plan, by 2025, its installed capacity of solar photovoltaic power generation will more than double that of 2020, reaching 320 GW, and by 2030 it will reach 600 GW. The U.S. Inflation Reduction Act is expected to allow solar developers to enjoy certain tax credits within 10 years to carry out long-term and large-scale construction.
Home solar power market has broad prospects
Another point that cannot be ignored is that the construction scale of solar energy can be large or small. In addition to huge arrays, it can also be a single battery panel on the roof. Therefore, household solar power generation is also an important market. The CEO of a solar energy company in the United States mentioned in an interview with CNBC that the surge in demand for electric vehicles today may also drive the demand for household solar power generation in the future because it is convenient, cheap and reliable.
High performance cable should provide the best in durability, flexibility and shielding!
Cable manufacturers are constantly challenged with wider temperature ranges, more shielding functions and higher mechanical durability, as well as characteristics such as bending resistance and chemical resistance required for extremely harsh environments and increasingly complex applications. However, cable failures and system downtime still occur from time to time, why?
Cable Faults Many problems caused by cable faults, especially those operating in extreme and harsh environments, can be avoided if the cables are selected correctly from the outset. People might say that choosing a cable is easy, but is that really the case? Indeed, matching the correct temperature range and relying on a PVC jacket for protection is simple. However, there are far more issues to consider.
Engineers have many details to consider before finalizing a perfectly matched cable. Flex and flex cables require specific flex shields. When the shield is torn and continuity is lost, the choice of standard foil shielding can lead to system failure. The distinction between flexibility and bendability should be kept in mind. It is important that the cables be able to be bent and fitted, the flexible cables are easier to install and also simplifies fault detection in cabinets and cable trays.
When the cable is used to connect to the cabinet, the round cable provides a better seal than the typical spiral cable. Therefore, it is necessary to correctly select the degree of bending after considering the line. In some manufacturing applications, cables will be constantly being bent. Ability to withstand millions of bends is more complicated than flexibility. So, how to choose a curved cable? The first thing to consider is the type of bending, is it uniaxial, twisted, or multi-axial? Each type requires different characteristics of the cable.
How to select cable outer sheath?
The choice of cable sheath should be made in accordance with the requirements of relevant standards in combination with different situations.
1 The selection of cable sheath should meet the following requirements:
1.1 For single-core power cables in AC systems, when it is necessary to enhance the cable’s resistance to external forces, non-magnetic metal armor layers should be used, and steel armor without effective non-magnetic treatment should not be used.
1.2 For cables in humid, chemically corrosive environments or susceptible to water immersion, the metal layer, reinforcement layer, and armor should have polyethylene outer sheaths, and the thick steel wire armor of cables in water should have extruded outer sheaths.
2. The selection of the outer sheath of the cable during direct burial laying shall meet the following requirements:
2.1 When the cable is subjected to high pressure or has the risk of mechanical damage, it should have a reinforcement layer or steel tape armor.
2.2 In the soil where displacement may occur, such as quicksand layer and backfill land zone, the cable should be armored with steel wire.
2.3 For extruded cables used in areas seriously endangered by termites, outer sheaths with higher hardness should be selected, or thin outer sheaths with higher hardness can be extruded on ordinary outer sheaths. The material can be nylon or special polyolefin copolymerized Objects, etc., can also be armored with metal sleeves or steel tapes.
3. The selection of cable sheath for fixed laying in the air shall meet the following requirements:
3.1 When the small cross-section extruded plastic insulated cables are directly laid on the arm support, they should be armored with steel tape.
3.2 In places with high safety requirements and serious rodent infestation, such as underground passenger transportation and commercial facilities, plastic insulated cables should be armored with metal tape or steel tape.
3.3 When the cables are under high-drop force conditions, the multi-core cables shall be armored with steel wires, and the AC single-core cables shall comply with the provisions of Item 1
4 The selection of cable sheath for underwater laying shall meet the following requirements:
4.1 Steel tape armoring can be used for cables that do not require armored layers to bear tension in ditches, unnavigable creeks, etc.
4.2 For cables in rivers, lakes and seas, the type of steel wire armor selected should meet the stress conditions. When the laying conditions have protection requirements such as mechanical damage, the outer sheath that meets the protection and corrosion resistance enhancement requirements can be selected.
What are the purposes and selection principles of rubber sheathed cables?（2）
Characteristics of rubber sheathed cables:
1. incomparable softness of other wires and cables;
2. Good electrical insulation performance and chemical stability;
3. Good physical and mechanical properties and wear resistance;
4. Requirements for oil resistance, flame retardancy, cold resistance, and heat resistance.
Choosing a cable that suits you has become a key issue.
1： Have a detailed understanding of the performance indicators of cables in various aspects, such as the wear resistance, compression resistance, and service life of rubber sheathed cables. Conduct a detailed inquiry and understanding, and then determine whether it meets your own usage conditions
2： The influence of the surrounding environment on the usage of cables. During the use of cables, in addition to being limited by their own usage conditions, there are also some external factors that play a decisive role. For example, if there is interference from magnetic fields, the cables need to be shielded; If it is a welding robot, due to the long working time and high temperature, it poses a great challenge to the outer sheath of the cable. Therefore, the selection should be based on the actual situation.
3： Clarify the use function of cables, whether it is control cables or rubber sheathed cables, no matter how excellent their performance is. What we need to do is to install the cables in positions suitable for their use. Only in this way can we achieve the original performance and service life of the cables.
What are the purposes and selection principles of rubber sheathed cables?（1）
Among our commonly used power cables, rubber sheathed cables are also one of them. Rubber sheathed cable is a kind of soft and movable cable with multi-strand thin copper wire as conductor, rubber insulation and rubber sheath. Generally speaking, it includes general-purpose rubber-sheathed flexible cables, electric welding machine cables, submersible motor cables, radio device cables, and photographic light source cables. So what are the uses of rubber sheathed cables and what are the selection principles? Here is a brief introduction.
Application of Rubber-sheathed Cables Rubber-sheathed cables are widely used in various electrical equipment, such as household appliances, electric machinery, electrical equipment and portable power cords for appliances, and can be used indoors or outdoors. According to the external mechanical force of the cable, the product structure is divided into three types: light, medium and heavy, and there are appropriate connections in the section. Generally, light-duty rubber-sheathed cables are used in household appliances and small electric equipment, requiring softness, lightness, and good bending performance; medium-duty rubber-sheathed cables are widely used in agricultural electrification except for industrial use, and heavy-duty cables are used in such as port machinery, searchlights, Large-scale hydraulic irrigation and drainage stations for family business and other occasions. This type of product has good versatility, complete series of specifications, good and stable performance.
How to identify the advantages and disadvantages when purchasing wires?
First of all, look at the color. The copper core is yellowish and reddish, indicating that the quality of the copper used is better, while the yellowish white is the reaction of low-quality copper. For aluminum core wires, regular ones must be shiny, shining silver-white light under the light, while those that are dark and look dark are of poor quality.
Secondly, bend the wire by hand to test its toughness. A good wire has good toughness and can be bent very well. Some unqualified wires are bent a few times and their insulation layer is broken, and some can even be peeled off by hand. Insulation.
Then, it must be checked whether the length and the thickness of the wire core have been tampered with. According to the relevant standards, the error of the length of the wire cannot exceed 5%, and the diameter of the cross-section cannot exceed 0.02%. Short of two catties, the phenomenon of falsification on the cross-section.
Also intercept a section of insulation to see if its core is in the middle of the insulation. What is not centered is the phenomenon of core eccentricity caused by low craftsmanship. When using it, if the power is low, it will be safe. Once the amount is large, the thinner side is likely to be broken down.
Finally, we can also check whether the identification is complete. There should be the name of the cable factory, wire model, specification, cross-sectional area, length, rated voltage, date of manufacture, and the implemented certification number or certification mark. If these signs are incomplete or absent, consumers should be cautious when purchasing.
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Some regulations for electrical cable exposion to moisture
UNE 20460-3:1996 standard regulations about the cable usage under dverse environmental conditions, especially to what extent an electrical cable can be exposed to moisture.
AD1 grade: The cable can be used in which the walls do not generally show traces of water, but can appear in small periods, for example, in the form of steam and which dries quickly thanks to good ventilation.
AD2 grade: cables can be used under situlations in which the water vapour occasionally condenses in the form of water drops or when vapour may occasionally be present.
AD3 grade: Water droplets fall at an angle of more than 60º to the vertical, location in which water vapour appears as a continuous film on the walls and/or floors.
AD4 grade: Water jets in all directions, locating where the cable may be subject to water projections, for example, application to certain luminaires or cabinets installed outdoors.
AD5 grade: Water jets in any direction AD5, locating at where hoses are regularly used in the presence of water (patios, car washes).
AD6 grade: used in locations at the edge of the sea, such as beaches, docks, etc. There are possibility of water waves.
AD7 grade: Used in locations susceptible to flooding and/or where the water can reach a maximum of 150 mm above the highest point of the equipment, the lowest part of the equipment can be more than one metre below the surface of the water. Shortly, there is possibility of intermittent, partial or total flooding.
AD8 grade: Used in locations such as swimming pools, where the electrical equipment is completely covered with water and permanently subjected to a pressure of more than 1 bar. Surrounding environment has the possibility of permanent and total water flooding.
Types and properties of common flame-retardant wires and cables
1. Ordinary flame-retardant wires and cables
The insulating and sheathing materials of ordinary flame-retardant wires and cables are generally polymer materials containing halogen (or modified by adding halogen containing flame retardant). Polyvinyl chloride (PVC) is commonly used. Ordinary PVC resin has the characteristics of high electrical insulation, chemical resistance, abrasion resistance, aging resistance and low price. However, when PVC burns, it will release hydrogen chloride, carbon monoxide, carbon dioxide, various aromatic hydrocarbons, chlorinated compounds and other toxic and harmful gases.
2. Low smoke halogen-free flame retardant wire and cable
The insulation and sheath materials of low smoke and halogen-free flame-retardant wires and cables are mostly thermoplastic elastomer materials, which do not contain halogens such as fluorine, chlorine, bromine and iodine. Mercury, chromium, cadmium, lead and other heavy metal elements that pollute the environment are excluded from the production process. Polyamide is often used as the material. The flame-retardant mechanism of this cable is that of interrupt switching. Interrupted exchange flame retardant refers to taking away part of the heat generated during the combustion of flame retardant materials, so that the materials can not maintain the thermal decomposition temperature, and therefore can not continue to produce combustible gas, so the combustion is self extinguished.
Zhenglan Cable Technology Co., Ltd manufacture flame retardant wire, low smoke halogen-free flame retardanet wire, fire resistant wire, flame retardant and fire resistant wire. Welcome your inquiry.
Why Single core Armored Cable Should Use Non magnetic Materials？
When a single core cable is started or stopped by alternating current or direct current, a corresponding alternating magnetic field will be generated around the cable, and an induced current will be generated in the metal material. This current flows inside the metal material, much like a vortex of water, so it is called eddy current, or eddy current for short. The thermal effect of eddy current can heat the metal materials in a short time. If the heat cannot be emitted in time, it will cause the cable insulation layer to melt or accelerate the aging, and the insulation performance will be weakened, thus causing cable breakdown.
The armored steel strip has good magnetic conductivity, which can be magnetized under a small magnetic field and generate eddy current. Non magnetic materials such as stainless steel tape, copper tape, aluminum tape or non-magnetic metal wire shall be used for armouring of single core cables.
In addition, it is better to lay single core cables in finished form during construction. Single core cables should avoid magnetic materials as far as possible, such as iron pipes, iron clamps, etc., which can form closed loop magnetic materials.
In addition, for a three core cable, the alternating magnetic fields generated by the three core phase relationship cancel each other, so that the sum of the induced current vectors is 0, and no magnetic force lines pass through the armor. Therefore, steel tape armouring can be used.
Why solar cable adopts tinned copper conductor?
Tinned copper wire has a silver appearance because tin is a silver metal. The process of tinned copper wire is a little more complicated than that of bare copper wire. At room temperature, tin is very stable in the air, because a dense oxide film will be formed on the surface of tin to prevent the continued oxidation of tin. Therefore, the copper surface is tinned, the first does not affect the resistance, and the second can improve the oxidation resistance of copper to a certain extent.
The purpose of tinning, silver plating (or even gold plating) for wire and cable conductors is to prevent copper wires from being oxidized and blackened at high temperature and humidity, and to improve conductor solderability and reliability. The operating environment of photovoltaic power plants is generally harsh, and they are often installed in deserts, barren mountains, water surfaces, roofs and other environments. It is required that the resistivity of photovoltaic cables must be good, not easy to oxidize, and can be used for a long time. Therefore, tinned copper wire is selected as the conductor will best fits the use environment and has the most stable electrical performance.
Zhenglan Cable supply power cable, solar cable, feel free to send us your quote.
Importance of power cable sheath
Power cables are widely used to transmit and distribute electric energy. They are often used in urban underground power grids, outgoing lines of power stations, internal power supply of industrial and mining enterprises, and underwater transmission lines across rivers and seas.
The main lines in the power system are generally power cables used to transmit and distribute high-power electric energy, including 1-500kv and above voltage levels. Therefore, the quality of cable products is very important, and the quality and thickness of cable sheath are equally important.
What effect does the thickness of cable sheath have on the cable?
1. Affect the service life of power cables
The first is the environment. After the construction of power cables, they are basically buried in the ground, immersed in water, in the open air or in an environment prone to corrosion, plus the corrosion of external media for a long time, the insulation level and mechanical level of the thinnest point of the cable sheath will decline. In case of line grounding fault, the thinnest point of cable sheath may be broken down, increasing the hidden danger of safety accidents.
The other is the internal consumption of heat energy generated by cables. The cable will produce a lot of heat energy in the process of transmitting electric energy, which is a consumption of the sheath. If the thickness of the cable sheath is not enough, the copper core of the conductor will directly melt the sheath material after heating, which will cause circuit failures and other related safety problems.
2. Impact on Construction
According to the current requirements, more and more environmental requirements require that the outer diameter of high-voltage cable products must be small, and it is necessary to consider leaving gaps in the laying process, so as to dissipate the heat generated by the cable after it is powered on. The thickness of the sheath is too thick, which will increase the difficulty of laying, so the thickness of the cable sheath must strictly comply with the relevant national standards, otherwise it cannot protect the cable conductor.
China's first solar and tidal energy complementary smart photovoltaic power station realizes full-capacity grid-connected power generation
On May 30, the country's first tidal-light complementary smart photovoltaic power station - National Energy Group Longyuan Zhejiang Wenling Chao-light complementary smart photovoltaic power station achieved full-capacity grid-connected power generation, creating a new energy comprehensive application of photovoltaic and tidal power generation in perfect harmony. This indicates that my country has made new achievements in the comprehensive utilization of marine energy and the three-dimensional development and construction of new energy.
The power station is the first and currently the only Chaoguang complementary smart photovoltaic power station in China. It is located in Wugen Town, Wenling City, Zhejiang Province. Silicon bifacial modules. The power station complements China's largest tidal power station, comprehensively utilizes solar energy and tidal energy, forming a scene of "the sun and the moon work together, and the water and the water generate power together".
It is understood that the level of intelligence and automation of the power station has reached the domestic first-class level, realizing few people and no one on duty. The power station uses UAV inspection technology and AI intelligent diagnosis system, relying on the big data analysis of the digital platform, to carry out remote diagnosis of photovoltaic power generation equipment health monitoring, to detect potential equipment problems in advance, and the early warning accuracy rate is over 85%, reaching the industry's leading position, achieving from The transformation from "people looking for information" to "information looking for people", equipment operation and maintenance has changed from passive to active, which effectively guarantees the economic benefits of the power station.
Power transmission steps
Transmission process
The transmission of electric energy, together with power transformation, distribution and consumption, constitutes the overall function of the power system. Through power transmission, the power plants far away (up to thousands of meters) are connected with load centers, so that the development and utilization of electric energy go beyond the regional limits.
Transmission lines can be divided into overhead transmission lines and underground transmission lines according to their structural forms. The former consists of line towers, conductors and insulators, which are erected on the ground; The latter is mainly laid underground (or underwater) with cables. Transmission can be divided into DC transmission and AC transmission according to the nature of the transmitted current.
This process uses different types or overhead bare conductors such as AAC, AAAC, ACSR, etc.
Transformation process
In the power system, the power plant converts the natural primary energy into electric energy and sends power to the remote power users. In order to reduce the power loss on the transmission line and the line impedance voltage drop, it is necessary to increase the voltage; In order to meet the security needs of power users, the voltage should be reduced and distributed to each user, which requires a substation that can increase and decrease the voltage and distribute power. Therefore, the substation is an electrical device in the power system that converts voltage, receives and distributes electric energy through it. It is an intermediate link between the power plant and power users. At the same time, the power grid of various voltage levels is connected through the substation. The function of the substation is to transform voltage, transmit and distribute electric energy. The substation is composed of power transformer, power distribution device, secondary system and necessary auxiliary equipment.
The transformer is the central equipment of the substation, which uses the principle of electromagnetic induction.
This process uses different types of cables such as high voltage, medinum voltage and low voltage power cable, aerial bundled cable, electrical wires.
Introduction to the use of cables and materials commonly used in solar photovoltaic power stations
During the construction of a solar photovoltaic power station, in addition to the main equipment, such as photovoltaic modules, inverters, and step-up transformers, the photovoltaic cable materials connected to the photovoltaic power station have the same effect on the overall profitability, operation safety, and high efficiency of the photovoltaic power station. plays a vital role..
According to the system of solar photovoltaic power station, cables can be divided into DC cables and AC cables. According to the different uses and use environments, they are classified as follows:
1. DC cable
(1) Serial cables between components.
(2) Parallel cables between the strings and between the strings and the DC distribution box (combiner box).
(3) The cable between the DC distribution box and the inverter.
The above cables are all DC cables, and there are many outdoor layings. They need to be moisture-proof, sun-proof, cold-resistant, heat-resistant, and UV-resistant. In some special environments, they also need to be protected from chemicals such as acid and alkali.
2. AC cable
(1) The connecting cable from the inverter to the step-up transformer.
(2) The connecting cable from the step-up transformer to the power distribution device.
(3) The connecting cable from the power distribution device to the power grid or the user.
This part of the cable is an AC load cable, which is laid in the indoor environment and can be selected according to the general power cable selection requirements.
3. Photovoltaic special cable
A large number of DC cables in photovoltaic power plants need to be laid outdoors, and the environmental conditions are harsh. The cable materials should be determined according to the resistance to ultraviolet rays, ozone, severe temperature changes and chemical erosion. The long-term use of ordinary material cables in this environment will cause the cable sheath to be fragile, and even decompose the cable insulation. These conditions will directly damage the cable system, but also increase the risk of short-circuiting the cable. In the medium and long term, the possibility of fire or personal injury is also higher, which greatly affects the service life of the system.
4. Cable conductor material
Most of the DC cables used in photovoltaic power plants work outdoors for a long time. Due to the limitation of construction conditions, connectors are mostly used for cable connection. Cable conductor materials can be divided into copper core and aluminum core.
5. Cable insulation sheath material
During the installation, operation and maintenance of photovoltaic power plants, cables may be routed in the soil below the ground, in overgrown rocks, on the sharp edges of roof structures, or exposed to the air, and the cables may be impacted by various external forces. If the cable jacket is not strong enough, the cable insulation will be damaged, affecting the service life of the entire cable, or causing problems such as short circuits, fire and personal injury hazards.
The Hazards of Moisture to Power Cable
The rapid development of electric power industry has promoted the development of the electrical industry supporting the electric power industry, especially the wire and cable industry. The variety development of wire and cable shows a diversified trend. Wires and cables have developed from simple power transmission to multi-function, that is, some new characteristics have been added according to different uses, such as the water resistance requirements of power cables. With the deepening of the research and understanding of insulation water absorption and water tree, people are more and more aware of the importance of waterproof performance for medium and high voltage power cables. In areas with high groundwater level or perennial rainfall. More and more users require waterproof performance for cables.
After water is immersed in the cable, the main influence is on the conductor and insulation of the cable. As far as the conductor is concerned, the cable is in a thermal stable state during normal operation, and the conductor temperature is generally above 60. If there is water immersion, it will lead to conductor oxidation and increase the energy loss resistance between conductor single wires, which increases the conductor resistance and the energy loss of transmission line,
In terms of insulation, although polyethylene is a non-polar hydrophobic material that is very difficult to dissolve in water, polyethylene is a semi crystalline polymer composed of crystalline phase and amorphous phase. The phase structure of polyethylene is compact, but there are defects at the grain boundary; The molecular arrangement in the amorphous phase is loose. There is a large gap between molecules. Water molecules are polar. Under the combined action of diffusion force and electric field force under alternating electric field, water molecules can easily penetrate into the capacity gap of amorphous phase and grain boundary defects of crystalline phase of polyethylene. The above problems also exist in the molecular structure of cross-linked polyethylene. At the same time, there are many cross-linked by-products in cross-linked polyethylene as impurities, so cross-linked polyethylene also has large water absorption under alternating electric field. Cross linked polyethylene and polyethylene insulation will produce water tree after absorbing water, which will cause breakdown and damage to the running cable.
Zhenglan Cable Technology Co., can do radinal water prevention structure by adding water prevention tape into different layer of the MV cable. If you are looking for such performance for MV cable, please come to us.
The function of Control cable's shield
Shielded control cable is generally used as the connecting line of electrical instruments, which is suitable for the connecting line of electrical instruments with AC rated voltage of 450 / 750V and below and the transmission line of automatic control system. It has excellent properties such as oil resistance, waterproof, wear resistance, acid and alkali resistance, various corrosive gases, aging resistance and non combustion.
Shielded control cable is a cable with a layer of mesh copper wire or metal wire braided around one or more wires. This layer of mesh wire can prevent lightning stroke, and external signals can not interfere with its. The shielding layer can also play a certain role in leakage protection.
If the cable is damaged and electric leakage occurs during use, the shielding layer can lead the leaked current to the grounding wire, which plays a certain role in safety protection. At the same time, it can also protect the cable conductor.
The function of shielding layer and grounding wire of shielding control cable is: the shielding layer is divided into internal shielding and external shielding. They are all designed to make good contact between the cable conductor and the insulating layer, and between the cable insulating layer and the inner protective layer, so as to eliminate the increase of surface electric field intensity caused by the unsmooth surface of the conductor and the inner protective layer
Service characteristics of shielded control cable:
(1) Allowable bending radius of cable: the minimum bending radius of non armored cable is 6 times of the outer diameter of the cable. Fluoroplastic insulated and sheathed cables shall be at least 8 times of the outer diameter of the cable. Copper tape shielded or steel tape armored cable shall be at least 12 times of the outer diameter of the cable.
(2) Maximum working temperature: the insulation of polyperfluoroethylene propylene (F46) shall not exceed 200 ℃. Soluble polytetrafluoroethylene (PFA) insulation shall not exceed 260 ℃.
(3) Minimum ambient temperature: PVC sheath: fixed laying - 40 ℃, non fixed laying - 15 ℃. Fluoroplastic and silicone rubber sheath: fixed laying - 60 ℃, non fixed laying - 20 ℃. The cable installation and laying temperature shall not be lower than 0 ℃ (fluoroplastic, silicone rubber and nitrile sheathed cable shall not be lower than - 25 ℃).
What are the advantages of copper core cable over aluminum core cable?
1. Low resistivity: the resistivity of aluminum core cable is about 1.68 times higher than that of copper core cable.
2. Good ductility: the ductility of copper alloy is 20 ~ 40%, that of electrical copper is more than 30%, and that of aluminum alloy is only 18%.
3. High strength: the allowable stress of copper is 7 ~ 28% higher than that of aluminum at room temperature. Especially the stress at high temperature, the difference between the two is very far.
4. Fatigue resistance: aluminum is easy to break after repeated bending, while copper is not. In terms of elasticity index, copper is also about 1.7 ~ 1.8 times higher than aluminum. (low voltage power cable, medinum voltage power cable)
5. Good stability and corrosion resistance: copper core is resistant to oxidation and corrosion, while aluminum core is vulnerable to oxidation and corrosion.
6. Large current carrying capacity: due to low resistivity, the allowable current carrying capacity (maximum current that can be passed) of copper core cable with the same section is about 30% higher than that of aluminum core cable
7. Low voltage loss: due to the low resistivity of copper core cable, when the same current flows through the same section. The voltage drop of copper core cable is small. The same transmission distance can ensure high voltage quality; Under the condition of allowable voltage drop, the transmission of copper core cable can reach a long distance, that is, the power supply coverage area is large, which is conducive to network planning and reduce the number of power supply points.
8. Low heating temperature: under the same current, the heating capacity of copper core cable with the same section is much smaller than that of aluminum core cable, making the operation safer. (Aluminum conductor steel reinforced, ACSR)
9. Low energy consumption: due to the low resistivity of copper, compared with aluminum cable, the power loss of copper cable is low, which is obvious. This is conducive to improving the utilization rate of power generation and protecting the environment.
10. Oxidation resistance and corrosion resistance: the connector of copper core cable has stable performance and will not cause accidents due to oxidation. The joint of aluminum core cable is unstable, and accidents often occur due to the increase of contact resistance and heating due to oxidation. Therefore, the accident rate is much higher than that of copper core cable.
11. Convenient construction:
The copper core has good flexibility and small allowable bending radius, so it is convenient to turn and pass through the pipe;
The copper core is anti fatigue and not easy to break after repeated bending, so the wiring is convenient;
The copper core has high mechanical strength and can bear large mechanical tension, which not only brings great convenience to the construction and laying, but also creates conditions for mechanized construction. (overhead insulated cable, electrical control cable)
How to reasonably choose the conductors of overhead lines?
1. The principle of wire selection
The conductor and ground wires of power transmission lines operate in the wilderness, mountainous areas or the edge of lakes and seas for a long time, and need to withstand the effects of external loads such as wind and ice, drastic changes in temperature and attack by chemical gases, etc., and are also subject to national resources and line costs And other factors. Therefore, in the design, especially for large spans, the material and structure of the wires must be carefully selected.
Generally, the following principles should be considered when selecting the material and structure of the wire:
⑴ The conductor material should have high conductivity. However, considering national resources, copper wires should not be used in general.
⑵The conductor and ground wire should have high mechanical strength and vibration resistance.
⑶ The conductor and ground wire should have certain chemical resistance and oxidation resistance.
⑷ When choosing the wire material and structure, in addition to meeting the transmission capacity, the cost of the line should be economical and technically reasonable.
2. Selection of wire cross section
The cross section of the overhead transmission line conductor is generally selected according to the economic current density, and should be checked according to the heating conditions, voltage loss, mechanical strength and corona in the event of an accident. When necessary, it is determined through technical and economic comparison; but for lines of 110KV and below, corona is often not the decisive factor in selecting the conductor cross section.
1) Choose the wire section according to the economic current density
According to the economic current density to select the transmission capacity used for the conductor cross-section, the development plan of the power system should be considered for 5-10 years after the line is put into operation. In the calculation, the maximum load that frequently recurs under the normal operation mode must be adopted. But when the system is not clear, care should be taken not to make the wire cross section too small.
2) Check the cross-section of the wire according to the corona condition
With the continuous increase of operating voltage in my country, the probability of corona and discharge of wires, insulators and fittings has increased. For the cross-section of wires of 220KV and above voltage lines, corona conditions often play a major role.
The corona generated by the wire will bring about two undesirable consequences: ① It increases the power loss of the power transmission line; ② It interferes with radio communication and carrier communication.
Regarding the corona loss, if the corona loss of the transmission line is directly calculated, the advantage is that the concept of quantity is very clear, but the disadvantage is that the calculation is cumbersome. This method is rarely used at present. It tends to be measured by the ratio of the maximum working electric field strength Em (unit: KV/cm) of the wire to the critical electric field strength E0 of the overall corona. The ratio of Em/E0 should not be greater than 80%-85%.
How to choose cable's nominal cross sectional area?
1. Select the cable cross-sectional area according to the long-term allowable current-carrying capacity
1.1 In order to ensure safety and the service life of the cable, the temperature of the cable after power-on should not exceed the specified long-term allowable working temperature. The temperature is 70 degrees for polyvinyl chloride insulated cables and 90 degrees for XLPE insulated cables. According to this principle , It's very simple to look up the table and choose the cable.
1.2 Examples:
A certain factory has a transformer capacity of 2500KVa and uses 10KV power supply. If XLPE insulated cables are used to lay in the bridge, what is the cross-sectional area of the cable?
Step 1: Calculate the rated current 2500/10.5/1.732=137A
Step 2: Check the cable selection manual to know
YJV-8.7/10KV-3X25 current carrying capacity is 120A
YJV-8.7/10KV-3X35 current carrying capacity is 140A
Step 3: Choose YJV-8.7/10KV-3X35 with a cable carrying capacity greater than 137A, which can theoretically meet the requirements. Note: This method does not consider the requirements of dynamic stability and thermal stability.
2. Choose the cable cross-sectional area according to the economic current density
Simply understand the economic current density. The cross-sectional area of the cable affects the line investment and power loss. In order to save investment, it is hoped that the cable cross-sectional area should be smaller; in order to reduce the power loss, it is hoped that the cable cross-sectional area should be larger; based on the above considerations, determine a reasonable one The cross-sectional area of the cable is called the economic cross-sectional area, and the corresponding current density is called the economic current density.
3. Select the cable cross-sectional area according to the voltage drop of the power grid
When we use the first and second methods to select the cross-sectional area of the cable, if the cable is very long, a certain voltage drop will occur during operation and startup, and the voltage on the device side will be below a certain range, which will cause the device to heat up.
4. Select the cross-sectional area of the cable according to the thermal stability coefficient (that is, select the cross-sectional area of the cable according to the short-circuit current)
4.1 When the 0.4KV cable is protected by an air switch, the general cable can meet the thermal stability requirements, so there is no need to verify it according to this method.
4.2 For cables above 6KV, after selecting the cross-sectional area of the cable using the above method, you must verify whether it meets the thermal stability requirements according to the following formula. If it does not meet the requirements, choose a larger cross-sectional area.
Formula: Smin=Id×√Ti/C
Among them, Ti is the breaking time of the circuit breaker, which is 0.25S, C is the thermal stability coefficient of the cable, which is 80, and Id is the three-phase short-circuit current value of the system.
For example: when the system short-circuit current is 18KA, how to choose the cable cross-sectional area.
Smin=18000×√0.25/80=112.5
Conclusion: If the system short-circuit current reaches 18KA, even if the rated current of the equipment is smaller, the cable cross-sectional area should not be less than 120mm2.
How to prevent electric shock in rainy days?
1. There are wires in the street lamp pole. For safety, stay away from them on rainy days.
2. Construction section of the road. The road condition around the construction section is poor and complex, and the safety cannot be guaranteed. Once there are loopholes in the construction, it is easy to cause the "big scene" of "sky thunder and earth fire"
3. Power equipment. Generally, transformers and electric boxes are treated safely and are safe without active touch and climbing. However, the situation of rainstorm weather is complex, and various unexpected situations may occur. For safety consideration, please stay away from them.
What should I do after an electric shock?
1. If someone is found to be electrocuted and fall to the ground in the water, do not rush to help with your hands, and make the electrocuted person quickly get out of the power supply. When there is a power switch or socket around, pull down the switch or unplug the power plug immediately; If the power supply cannot be disconnected, use a dry wooden stick to pick up the wire on the person who gets an electric shock.
2. After an electric shock, the human body often appears "fake death". To carry out first aid for the injured by electric shock, make them lie flat on their back on the spot and ensure that the airway is unblocked. Judge whether the injured has breathing by observing whether the injured has breathing movement in the abdomen and chest corridor, or by touching whether the neck artery beats. If no breathing is found, resuscitate immediately and contact the emergency center.
Features Of Aerial Bundled Cable
Overhead insulated cable has the main characteristics of high power supply reliability, good power supply safety, convenient erection and maintenance and reasonable economy
1. High power supply reliability. The use of overhead cable can greatly reduce all kinds of short-circuit faults (especially the common flashover faults of overhead bare conductor), and the fault rate is 4-6 times lower than that of overhead bare conductor.
2. Good power supply security. When the overhead cable is energized, when the human body or other animals accidentally touch the cable insulation surface, as long as the cable is not broken down, it will not cause harm to people and animals.
3. Convenient erection and maintenance. Overhead cables can be erected on any kind of pole and tower or along the wall. In special cases, they can also pass through the trees and be directly fixed on the tree pole with hardware. There is no need for special patrol inspection, and there will be no short-circuit tripping accident due to branch flashover, littering by residents, or false collision of crane boom, which greatly reduces the maintenance and overhaul of the line.
4. Reasonable economy. Although the overhead cable is more expensive than the overhead bare conductor, it is cheaper than the ordinary underground installation cable. Therefore, although the one-time investment of overhead cable is slightly higher, combined with other factors, its operation cost will be significantly lower than that of overhead bare conductor.
Zhenglan Cable Technology Co., Ltd can produce different types of aerial insulated cable as per different standards inculding IEC, NFC-33109, AS NZS3560, etc.. Welcome your inquiry.
What is a waterproof cable?
Cables that can be normally used in water are collectively referred to as water blocking (waterproof) power cables. When the cable is laid underwater, it is often immersed in water or wet places, the cable is required to have the function of water prevention (resistance), that is, it is required to have the function of full water resistance, so as to prevent water from immersing into the cable and causing damage to the cable and ensure the long-term stable operation of the cable under water. The difference between waterproof cable and ordinary cable is that ordinary cable cannot be used in water.
Waterproof cables mainly fall into the following three categories:
An oil paper insulated cable is the most typical water-resistant cable. Its insulation and conductor are filled with cable oil, and there is a metal sheath (lead sheath or aluminum sheath) outside the insulation. It is the cable with the best water resistance. In the past, oil paper insulated cables were mostly used for submarine (or underwater) cables, but oil paper insulated cables are limited by the drop, which has the trouble of oil leakage and inconvenient maintenance. Now they are used less and less.
Second, the ethylene propylene rubber insulated cable widely used in medium and low voltage underwater transmission lines is due to its superior insulation performance without the worry of "water tree". Waterproof rubber sheathed cable (JHS type) can operate safely in shallow water for a long time.
Three crosslinked polyethylene (XLPE) insulated power cable has become the most widely used insulating material because of its excellent electrical, mechanical and physical properties, simple production process, light structure, large transmission capacity, convenient installation, laying and maintenance, and not limited by drop. However, it is particularly sensitive to moisture. If the insulation is soaked with water during manufacturing and operation, It is prone to "water tree" breakdown, which greatly shortens the service life of the cable. Therefore, XLPE insulated cables, especially medium and high voltage cables under AC voltage, must have "water blocking structure" when used in water environment or humid environment. The so-called "water blocking structure" includes radial water blocking structure and longitudinal water blocking structure.
Characteristics and application occasions of fire-resistant and flame-retardant cables
1. fire-resistant XLPE insulated, PVC sheathed power cable
It can be laid indoors, in tunnels and pipelines, and can withstand certain laying traction, but the cable cannot bear external force, and single-core cable is not allowed to be laid in magnetic material pipelines. If you need to bear the external force of machinery and wrap the steel tape armour.
Suitable for special requirements, such as large-capacity power plants, nuclear power plants, underground railways, high-rise buildings, etc.
2. XLPE insulated, PVC sheathed power cable
It can be laid indoors, in tunnels and in pipelines, and can withstand certain laying and traction, but the cable cannot bear external force, and single-core cable is not allowed to be laid in magnetic material pipelines. If you need to bear the external force of machinery and wrap the steel tape armour.
3. Flame retardant PVC insulated, PVC sheathed power cable
It can be laid indoors, tunnels, cable trenches, pipelines, flammable and severely corroded places, but cannot bear external mechanical forces. If you need to bear the external force of machinery and wrap the steel tape armour.
Features: In the case of open flame burning, remove the fire source, ≤ 12S automatic extinguishing.
4. Flame retardant cross-linked polyethylene insulated, polyvinyl chloride fuel sheathed power cable
It can be laid indoors, in tunnels and pipelines, and can withstand certain laying traction, but the cable cannot bear external force, and single-core cable is not allowed to be laid in magnetic material pipelines. If you need to bear the external force of machinery and wrap the steel tape armour.
Features: In the case of open flame burning, remove the fire source, ≤ 12S automatic extinguishing.
5. Fire-resistant PVC insulated, PVC sheathed power cable
It can be laid indoors, tunnels, cable trenches, pipelines, flammable and severely corroded places, but cannot bear external mechanical forces. If you need to bear the external force of machinery and wrap the steel tape armour. Suitable for special requirements, such as large-capacity power plants, nuclear power plants, underground railways, high-rise buildings, etc.
What kind of cables are used in photovoltaic power station?
In the process of photovoltaic power station construction, in addition to the main equipment, such as photovoltaic modules, inverters, step-up transformers, the supporting connected photovoltaic cable materials also play a vital role in the overall profitability, operation safety, and efficiency of the photovoltaic power station. The following is a detailed introduction to the use and use environment of the common cables and materials in the photovoltaic power station.
According to the system of photovoltaic power station, cables can be divided into DC cables and AC cables, which are classified as follows according to different uses and environments:
1. DC cable
(1) Series cables between components.
(2) Parallel cables between strings and between strings and DC distribution box (junction box).
(3) Cable between DC distribution box and inverter.
The above cables are DC cables, which are laid outdoors. They need to be moisture-proof, sun proof, cold resistant, heat-resistant and UV resistant. In some special environments, they also need to be resistant to acid-base and other chemicals.
2. AC cable
(1) Connecting cable from inverter to step-up transformer.
(2) Connecting cable from step-up transformer to power distribution device.
(3) The connecting cable from the power distribution device to the power grid or users.
This part of the cable is AC load cable, laying more indoor environment, can be selected according to the general power cable selection requirements.
Zhenglan Cable Technology Co., Ltd can supply you both AC&DC use cables. Welcome your inquiry.
Function and difference of metallic shield for medium voltage cable
As an important structure of medium voltage power cable, metal shielding layer will pass capacitive current under normal operation of the cable, and act as the path of short-circuit current in case of short circuit; At the same time, the electromagnetic field generated when the cable is electrified is shielded in the insulated core to reduce the electromagnetic interference to the outside world.
The copper strip shielding is composed of a layer of overlapped soft copper strip, and the double-layer copper strip can also be used for gap wrapping. The nominal thickness of copper strip for single core cable shielding is not less than 0.12mm. The copper wire shield is composed of loosely wound soft copper wire, and its surface is tightly tied with reverse wound copper wire or copper tape. The average gap between adjacent copper wires shall be no more than 4mm.
The shielding method of copper wire and copper strip winding can improve the disadvantages of shielding method of copper strip winding from the structure. It has neither oxide layer produced by copper strip overlapping, nor strong bending and hot and cold deformation, and the copper strip winding is not easy to arch and embed into the insulation shielding layer.
The cross-section of the metal shield directly affects the ability of the cable to withstand the short-circuit current in case of fault. If the cross-section is too small, the short-circuit current will overheat or burn out and damage the insulation. Therefore, it is necessary to determine the cross section of metal shield according to the fault current capacity.
In 10kV and below cable, when conductor section is more than 500, try to use copper wire shielding! If you insist on using copper tape shielding, you need to thicken the thickness of copper tape! According to the conditions of cable laying, if it needs to carry a large short-circuit current, it is recommended to use copper wire shielding. Therefore, the difference between copper tape shielding and copper wire shielding is the ability to carry short-circuit current. Copper wire is slightly larger (also depends on the effect of copper wire). Copper tape is homogenizing magnetic field and shielding.
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