Smart grid boosts urban green development

In the future, smart cities will not only focus on high-efficiency and intelligent goals, but also include green, environmental protection and low-carbon development goals. The construction of smart grids will promote the green development of cities. With uneven energy distribution, a strong smart grid can greatly improve the grid’s ability to accept clean energy and optimize the allocation of energy resources on a large scale. More and more smart cities in our country are incorporating clean energy into the overall planning of smart cities. Especially abc cables played a huge role in this plan,realize the transformation of the economic development direction and the optimization and upgrading of the industrial structure. The goal is to build a modern and fully internationalized world ecological garden city, and the goal is to build a smart, green, and low-carbon livable city.

In the process of realizing the smart grid to promote urban green development, power cables play a prominent role in the construction of smart grids,the State Grid took the lead in practicing and established the National Wind and Solar Storage and Transmission Demonstration Project. The project is currently the world’s leading new energy comprehensive utilization platform integrating wind power, photovoltaic power generation, energy storage, and smart power transmission. Wind power will reach 1 million kilowatts, the total scale of photovoltaic installations will reach The scale reaches 110,000 kilowatts.

There are many participants in the construction of smart grids. With the construction of smart grids, its R&D and manufacturing levels will continue to improve, and the overall strength of the aaac industry will continue to improve. City-related industries will also develop rapidly and share market shares, creating conditions for smart grid-related industries to enter the international market. In addition, the improvement of the safe and stable operation of the power grid, the improvement of power supply reliability, and the high-quality power supply have also laid the foundation for the rapid growth of traditional industries and the rise of high-tech industries.

The important influence of aluminum alloy cables on wind power generation

The proposal of “carbon peak” and “carbon neutral” goals has accelerated the development of new wind and solar energy. In 2021, onshore wind power subsidies will be refunded, which will also intensify the demand for cost reduction of wind power, resulting in a rapid increase in the application of aluminum alloy cables. In addition, the introduction of new foreign technologies has promoted the rapid advancement of domestic wind power cost reduction programs.

The application of aluminum alloy cables in wind power has mature domestic cases, mainly in the fixed laying section of the tower. The introduction of new foreign technologies has further expanded the application of aluminum cables. The use of 8030 aluminum alloy conductors and the design of category 5 conductors make it possible to apply aluminum alloy cables in the torsion section.
By benchmarking the performance of foreign aaac conductors, the aluminum conductor adopts the same stranding process as the copper cable. Because the aluminum wire is lighter, the advantage of the aluminum cable is more obvious from the point of view of flexibility.

Reducing this cost saving is the eternal theme of the sustainable development of enterprises. The weight of the aluminum alloy conductor is reduced, and the load-bearing requirements of the sheath are simultaneously reduced, and the thickness of the sheath is also reduced in response, so the loss is smaller. Using aluminum alloy torsion cable design, the cable can be designed as a whole laying plan, which reduces the design of intermediate joints and can further reduce risks and costs.

Wind power has always been the main force in the development of new energy. How to ensure the long-term fast and efficient operation of wind turbines is the direction that wind power mainframe companies have been pursuing. Development of aluminum alloy cables has reduced the cost of wind turbine cables, reduced the risk of cable decline due to its own weight, and promoted the rational application of my country’s aluminum resources.

How does the submarine cable work?

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

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

What should I pay attention to when buying Aerial Bundled Cable?

As the main carrier of power transmission,Aerial Bundled Cable  HD 626 S1 Standard is widely used in electrical equipment, lighting circuits, household appliances, etc. Its quality directly affects the quality of the project and the safety of consumers’ lives and properties. There are many types of wires in the market, and you must use the appropriate wires according to your own electricity load.
Some of the wires sold in the market are cheaper and some are more expensive, and some people tend to be cheaper first. However, cheap wires often have a lot of performance that does not meet the performance described by him, and they may bring themselves Many security risks. The production technology of the wire is not too high, and the raw materials are not too different. If it is too cheap, either it is cutting corners or the quantity is not enough. How to identify it. Let me tell you several methods that are easier to identify:

  • Take a look at the packaging. National standard wires are often made better, neat, and have a sense of quality when held in hand.
  • Open the package and take a look at the wires inside. The wire thickness (insulation thickness) of the national standard wire of 1.5-6 square meters is 0.7mm. If it is too thick, it is non-standard, and its inner core is definitely not enough. , You can pull the thread hard, the ones that are not easy to tear are generally the national standard.
  • Burn it with fire, the ones that are extinguished within 5s after leaving, and those with certain flame-retardant function are (ABC) ASTM B230 Standard .Look at the inner core, the higher the brightness of the inner core material (copper), the better the copper, and the brightness is uniform, shiny, and without layering. The national standard requires oxygen-free copper to be used in the core. Non-standard, such as black rod copper, may have potential accidents.
  • The thickness of the acsr core has certain national requirements, but it is not very strict. But you can’t go wrong a lot, it’s just a small error, which is generally invisible to the eye.
    The length, the country does not mandate that the rice must be beaten, but many manufacturers have also beaten the rice, and the rice that is beaten is not necessarily the national standard, but the general national standard generally does not. Non-standard rice harvesting is just a means.
  • The country stipulates that there must be a certain mark on the wire, and the maximum size will not exceed 500mm, and the next same mark will be printed. Generally, there are product trademarks, manufacturer names, and implementation standards.

Carbon fiber composite coreconductor

Carbon fiber composite wire is a high-strength carbon fiber composite power transmission wire. It has a core and a ring-shaped conductive layer wrapped around the core. The core is a conductive core composed of carbon fiber, and there is a composite conductive core composed of carbon fiber. It is composed of carbon fiber and aluminum or copper wire twisted.
This kind of carbon fiber composite core wire has many advantages and is the strength of contemporary scientific and technological development. It uses the high strength and corrosion resistance of carbon fiber to produce a new type of wire. Compared with the conventional steel core aluminum stranded wire, the carbon fiber The fiber composite core conductor has obvious advantages. It has many characteristics such as light weight, high tensile strength, high temperature resistance, radiation resistance, and large current carrying capacity. It can be said that all aspects of performance are upgraded.

The carbon fiber composite core wire has a very strong transmission capacity. It can effectively reduce power loss during the process of transporting electrical energy. It has high heat resistance and can continue to work under a high temperature environment of 160 degrees, even in a peak environment. Can fully meet the demand.

The tensile strength of general steel wire is 1240MPa, while the strength of carbon fiber composite core can reach more than 2400MPa, and the strength safety factor of carbon fiber composite core wire is increased by nearly 2 times. Not only the strength is enhanced, the expansion coefficient of the carbon fiber composite core wire is also very small, which avoids the thermal expansion sag of the traditional steel core cable. The height of the poles and towers can be reduced, and the distance between the poles can be increased, thereby reducing the transmission line corridors and saving land resources. This makes it not only have a strong comprehensive benefit advantage in the transformation of the old line; even in the construction of the new line, it also has a competitive advantage.

Industry Standard for high-strength aluminum alloy conductor overhead insulated cables

Aluminum power cable is a new type of power cable, which is made of AA8030 series aluminum alloy material and adopts the advanced technology such as special roll-forming wire stranding and annealing treatment. The alloy power cable makes up the deficiency of the traditional pure aluminum cable. Although the electric conductivity of the cable has not been improved, the bending, creep and corrosion resistance of the cable have been greatly improved, the AA-8030 series aluminum alloy conductor can improve the electric conductivity and high temperature resistance of the aluminum alloy cable, at the same time, the problems of pure aluminum conductor and creep are solved.

The electrical conductivity of aluminum alloy is 61.8% of copper IACS, and the current carrying capacity is 79% of copper, which is superior to pure aluminum standard. But at the same volume, aluminum alloys actually weigh about a third as much as copper. Therefore, at the same ampacity, the weight of the aluminum alloy cable is about half that of the copper cable. Using aluminum alloy cable instead of copper cable can reduce cable weight, reduce installation cost, reduce equipment and cable wear, make installation work easier. The new standard specifies the terms and definitions, specifications, technical requirements, test methods, inspection rules, marking, packaging, transportation and storage of medium strength aluminum alloy core insulated overhead cables. The Standard Product is suitable for the aluminum alloy conductor overhead insulated cables with rated AC voltage of 20kV or less for fixed overhead laying in cities, forests, scenic spots and other power distribution fields. The main technical contents include medium strength aluminum alloy conductor structure, conductor DC resistance, insulation thickness, AC voltage level and test items and methods. The medium strength aluminum alloy conductor overhead insulated cable has the characteristics of light weight, large breaking force and low resistance. It is a kind of overhead insulated cable with excellent comprehensive performance and better economical operation in the whole life cycle. The establishment of the industry standard further promotes the progress of this technology, and unifies the structural design and manufacturing process of Medium Strength Aluminum Alloy conductors, which is of great significance to the development and application of medium strength aluminum alloy core overhead insulated cables, on the basis of this, international standards can be formed to promote China technological progress, promote industrial transformation, and substantially participate in international standard activities.

What’s The Difference Between ACSR and AAAC cable ?

Following are some Q&A people interested about wire and cables :

1. What types of commonly used wires and cables are classified by purpose?
Answer: According to the purpose, it can be divided into bare conductors , insulated wires, heat-resistant wires, shielded wires, power cables, control cables, communication cables, radio frequency cables, etc.

2.What is the difference between ACSR cable and AAAC cable ?
AAAC:This bare concentric-lay-stranded conductor, made from round aluminum alloy 6201 -T81 wires, is constructed with a central core surrounded by one or more layers of helically laid wires.
it provide better corrosion resistance than the one produced by the aluminum conductor steel reinforced(ACSR).
ACSR: This bare concentric-lay-stranded conductor is made from round aluminum 1350-H19 (extra hard) wires and round zinc-coated or aluminum-coated steel core wire(s) to be used as overhead electrical provides better strength than AAAC cable.

3. What kinds of insulated wires are there?
Answer: There are the following types of insulated wires: PVC insulated wires, PVC insulated cords, nitrile and polyvinyl chloride compound insulated cords, rubber insulated wires, direct buried aluminum core plastic insulated wires for agricultural use, and rubber insulated cotton yarn Textile cords, PVC insulated nylon sheathed wires, PVC insulated cords for power and lighting, etc.

4. What kind of occasion is the cable tray suitable for?
Answer: The cable tray is suitable for the overhead laying of power cables and control cables indoors and outdoors in general industrial and mining enterprises, and can also be used for indoor and outdoor installations in telecommunications, radio and television departments.

5. What are the cable accessories?
Answer: Commonly used electrical accessories include cable terminal junction box, cable intermediate junction box, connecting pipe and terminal block, steel plate junction box, cable tray, etc.

6. What is the cable middle connector?
Answer: The device that connects the cable and the cable’s conductor, insulation shielding layer and protective layer to connect the cable line is called the cable intermediate joint.

7. What is electrical main wiring?
Answer: The electrical main wiring is the connection method of the main electrical equipment and the bus in power plants and substations, including the connection of the main bus and the auxiliary power system according to certain functional requirements.

8.When choosing the cross section of the power cable, which regulations should be followed?
Answer: The selection of power cables should follow the following principles:
(1) The rated voltage of the cable should be greater than or equal to the rated voltage of the power supply system at the installation point;
(2) The continuous allowable current of the cable should be equal to or greater than the maximum continuous current of the power supply load;
(3) The cross-section of the core must meet the requirements of stability of the power supply system when it is short-circuited;
(4) Check whether the voltage drop meets the requirements according to the cable length;
(5) The minimum short-circuit current at the end of the line should enable the protection device to operate reliably.

9. What are the advantages of XLPE cables and oil-paper cables?
Answer: (1) Easy to install, because it allows a small minimum bending radius and light weight;
(2) Not restricted by line drop;
(3) Good thermal performance, high allowable working temperature and large transmission capacity;
(4) The cable accessories are simple and all are dry structure;
(5) Simple operation and maintenance, no oil leakage problem;
(6) The price is lower;
(7) High reliability and low failure rate;
(8) There are few manufacturing procedures, simple process and remarkable economic benefits.


Stranded and twisted prefabricated branch cable

With the acceptance of prefabricated branch cables by the majority of users, a variety of prefabricated branch cables have entered the market under the situation of rapid increase in usage. This situation has brought a certain degree of selection to building electrical designers. difficult. The choice of stranded type, also called twisted type, branch cable is introduced below.

1. Defects of twisted type
The so-called twisted type and twisted type are multiple single-core power cables twisted together. For the core wires of power cables, the purpose of twisting multiple copper cable or aluminum wires is to increase the cross-section of the wires. Because they are all in the same phase and the same electromagnetic angle, there will be no problems with the distribution and change of capacitance and inductance due to any difference in electromagnetic phase angle. However, the influence of heat dissipation and the decrease of current-carrying value have also appeared. Therefore, the larger the cross-section, the lower the unit current intercept value. And it is still on the special equipment, according to the specified pitch and twisting force, the whole strip is finished at one time. This kind of twisting is consistent in terms of torque, pitch and uniformity, and there will be no change in pitch or uneven elasticity. The following only takes the round conductive core as an example, and the stranding rules are as follows:
(1). The center is generally a single wire, and the second layer has six single wires. In the future, each layer will increase by six more than the original number of the inner layer. The single wire adopts the same wire diameter;
(2). The stranding direction of each layer of single wires should be opposite to the previous layer, and generally the outermost layer is twisted to the left.
Stranded and twisted prefabricated branch cables, that is, multiple single-core power cables are twisted and used as three-phase three-wire, three-phase four-wire or three-phase five-wire power supply circuits. First of all, let’s start with “stranding”. This kind of “stranding”, whether in the production plant of prefabricated branch cables or the completion of the “stranding” process at the construction and installation site, is a special “stranding” equipment that has neither specialized , There is no corresponding pitch, strength, tightness, and uniformity regulations or requirements to follow. What is even more difficult to deal with is the branch cables and branch connectors of various sizes and locations with no rules, which are enough to determine the “multi-core cable” after the “stranding”, whether it is in terms of torque, pitch, density, The tightness, uniformity, and external dimensions will all be unknown. Therefore, it is determined that this “stranded” “multi-core cable” has become the most basic parameters and indicators in terms of the distribution of inductance and capacitance, and the electromagnetic theory of electromagnetic vibration, attraction and repulsion. The chaotic “Brownian motion”.

In the actual operation after construction and installation, first, the distribution, pitch, and tightness of inductance  and capacitance are chaotic, which will inevitably lead to chaos in the entire power supply circuit and some local heat dissipation and temperature rise. Even for several power cables without branches and without branch connectors, the power cables that are twisted under the conditions of strict control of their twisting strength, tightness, and pitch, are affected by heat dissipation and temperature rise. The actual allowable current carrying capacity cannot be compared with single-core power cables laid horizontally or vertically in accordance with the specifications.

Secondly, under the operating state of balanced or unbalanced current, when the load current, temperature, environment change or influence, the resistance between each cable and each cable itself in terms of absorption, repulsion, extension, contraction, up and down, etc. Irregularities in force and movement. This phenomenon is extremely detrimental to the stability and reliability of the entire power supply loop, and it may even cause damage to the sheath and insulation at the location where the cable is installed and tightened, which may cause an accident.

Thirdly, this kind of “twisted” power cables in a chaotic manner is really unsightly when placed in cable wells or cable channels. At the same time, it will also bring a defect in the design and construction of electrical system drawings, electrical system construction and engineering quality that fail to comply with the “horizontal, horizontal and vertical” regulations.

2. Relevant regulations in the electrical design code for civil buildings

2.1 Regulations for parallel laying of cables
When cables with the same voltage in the “Code for Electrical Design of Civil Buildings” promulgated and implemented by the Ministry of Construction in 1993, the net distance of the cable should not be less than 35 mm and should not be less than the outer diameter of the cable. It is stipulated in the article that when cables are laid side by side, a certain distance should be kept between cables to ensure the safe operation of the cables and the needs of maintenance and overhaul, so as to avoid the burning of adjacent cables when the cables fail. Reduce current carrying capacity, affect maintenance and cause mechanical damage. In addition, the distribution and influence of inductance and capacitance are also important reasons for increasing operating temperature and decreasing current carrying capacity. Obviously, “twisted type” and “twisted type” cannot meet the requirements of this article.

2.2 Regulations for cable selection
The electrical design code of civil buildings stipulates: “The power cable used in the three-phase four-wire system should be a four-core cable.” In the article description, it is stipulated in the three-phase four-wire system that an additional three-core cable is used. Conductor or single-core cable is used as the neutral line. When the three-phase system is unbalanced, it is equivalent to the operating state of single-core cable, which is easy to cause power frequency interference. For bare armored cables, it will also accelerate the corrosion of the metal sheath and armor layer, so four-core cables are required. “This article explains that although the distribution and change of inductance and capacitance are not clearly raised, it also indirectly pointed out their influence. It is not possible for a three-core power cable to be used as a neutral line, let alone four or five single cables. “Twisted” and “twisted” of core power cables? Obviously, “twisted” and “twisted” types cannot meet the requirements of this article.

2.3 Regulations for laying of power cables
The laying of power cables, whether indoor or outdoor, whether it is in the “Code for Electrical Design of Buildings”, “Code for Construction of Electrical Construction”, the “Codes” for the design and construction of various power systems, and whether it is the “Codes” of China or IEC standards, NEC “regulations”, Japanese standards, and standards of other countries all have a clear stipulation: whether it is installed vertically or horizontally, it must meet the requirements of “horizontal, horizontal and vertical” in order to ensure the acceptance of the project quality. Obviously, “twisted type” and “twisted type” can not meet the requirements of this regulation.

Throughout the development history of power cables, from the advent of single-core power cables to the present, we have fully realized in theoretical research and use practice: “twisting” and “twisting” four or five single-core power cables together , As a three-phase four-wire, three-phase five-wire system power supply circuit inside the building facilities, it is not advisable, nor feasible. my country has always followed the practice and regulations of parallel laying, which is based on its theory and practice. If in order to reduce or compress its laying and use space, just “twisting” or “twisting” can meet all requirements from theory to practice, then there is no need for multi-core power cables to come out. Throughout the domestic and international “standards”, “standards”, “regulations” and examples of outstanding well-known buildings, there are no regulations or allow four or five single-core power cables to be “twisted” or “twisted” as Precedents for the use of three-phase three-wire, three-phase four-wire, and three-phase five-wire power supply circuits. In irregular, small and sporadic construction facilities, use “twisted” or “twisted” multiple single-core power cables as three-phase three-wire, three-phase four-wire, three-phase five-wire power supply circuits exception.

In foreign power supply circuits embedded in the soil, it is allowed to use three single-core power cables twisted and embedded. Its purpose is: the twisted cable has a certain degree of flexibility, and it can play a certain buffering role when the cable is damaged or impacted by the local changes and land subsidence. But it must be twisted in strict accordance with the specified pitch and strength inside the factory, and no branches are allowed.

Single-core Parallel Type and Multi-core Twisted Type Cable

The advent of power cables has greatly improved the safety of power generation, transmission, transformation, supply, distribution, and use of electricity. Single-core power cables appeared first. As there are more and more occasions for three-phase four-wire power supply, three-phase five-wire power supply and multi-loop power supply in actual use, the requirements for occupied space and laying occasions are also getting higher and higher. When multiple and multi-layer laying are required, and the space occupied and laying conditions are limited, single-core power cables cannot be used conveniently. Therefore, multi-core power cables have been developed and quickly entered the field of power applications, and are accepted and used by the majority of users.

With the rapid growth of power cable usage, even if single-core power cables are used in actual use, the joints and branches shall be stripped and insulated on site, and the branches or joints shall be crimped before using epoxy resin insulation The method of material encapsulation treatment still has disadvantages such as large site occupation, long construction time, high cost, multiple equipment, high technical requirements, and high difficulty, especially the joints or branches after the completion of the on-site construction, and their insulation Strength, reliability, and consistency are difficult to guarantee. Therefore, the busway was developed, and after the development was put into the market, it was quickly accepted and used by a large number of users.
With the increase in user usage, it is found that the bus duct also has some defects, such as too many parts connected by * screws, complicated installation and construction, and large maintenance and high maintenance costs. In the process of operation, it often encounters the influence of electromagnetic vibration, thermal expansion and contraction, expansion coefficient, external force and other factors, which will cause the loosening of the screw. If a screw is loose, there will be heat and high temperature at the fault point, which will affect the stability of the entire bus duct. In particular, the improper use of the five-wire bus duct will also cause the contact resistance of the PE wire to increase. It violates the basic requirements for the continuity of the PE wire that is clearly stipulated in the building electrical design code and construction code. However, bus ducts still have their own advantages in the case of large capacity. Because when the current reaches thousands of amperes, if a cable is used, even a single-core cable must be laid in multiple, otherwise the corresponding large current capacity will not be reached, and the busway will show its own advantages at this time.

2. Prefabricated branch cable
With the development of technology and the increasing market demand, prefabricated branch cables have been developed and developed from single-core prefabricated branch cables to multi-core prefabricated branch cables, which also include flame-retardant, fire-resistant, and armored prefabricated branch cables. That is, in the factory, in accordance with the cable specifications, models, cross-sections and specific locations of the branches specified in the architectural design drawings, special production equipment and molds are used on the professional production line, which can be completed in one time. Its advantage lies in the high insulation strength, the encapsulated injection-molded branch joint connector and the outer insulating sheath of the cable are tightly bonded together, and it has excellent water tightness and air tightness. Because it is made of factory-specific equipment and molds, It has excellent reliability and consistency, and it is extremely convenient for users to install and use. When installing vertically, only the main cable can be evenly fastened to the corresponding bracket. In horizontal, pre-buried, overhead, tunnel, airport runway, port Construction and installation under environmental conditions such as docks, mines, and modern industrial plants are simpler and more convenient. The requirements for site, equipment, technical level of construction personnel, and costs during the installation and construction process are much lower than those for handling cable branches or cables at the construction site. Busway: It saves a lot of maintenance costs during operation and reduces the power outage time. In some cases, it can achieve the effect of maintenance-free. In the case of small cable shafts and cable channels, it can show its unique advantages. Therefore, branch cables are ideal products to replace bus ducts in medium and small capacity power supply occasions.

3. Stranded and twisted prefabricated branch cables
With the acceptance of prefabricated branch cables by the majority of users, a variety of prefabricated branch cables have entered the market under the situation of rapid increase in usage. This situation has brought a certain degree of selection to building electrical designers. difficult. The choice of stranded type, also called twisted type, branch cable is introduced below.

4. Multi-core prefabricated branch cable
The multi-core power cable is the core wire conductors are individually insulated, and are collectively and parallelly enclosed in the same outer sheath. Inside the outer sheath of the entire power cable, whether it is armored or unarmored, all power cable core wires that have been independently insulated and encapsulated are parallel and tightly encapsulated in the outer insulation. Set of interior. During the entire encapsulation process of the outer insulating sheath, no part or any power cable is allowed to “cross”, “displace”, or “twist” inside the sheath. Of course, “twisting” is not allowed. If any of the above phenomena occurs, the entire power cable will be judged as “unqualified” and not allowed to leave the factory. Therefore, the multi-core power cable itself is a qualified product that uses special production equipment in a professional production plant and strictly follows the relevant standards. Regardless of the distribution of inductance and capacitance and the basic requirement that the vector sum of any part is equal to zero, good consistency can be guaranteed. This cannot be achieved by any “stranded conductor type” or “twisted type”, and is a basic requirement that must be guaranteed on the power distribution circuit. Therefore, prefabricated multi-core branch cables made of qualified multi-core power cables can ensure that various technical parameters and basic requirements will not be destroyed, and can ensure the stability and reliability of operation. Of course, compared with single-core prefabricated branch cables, multi-core prefabricated branch cables are much more complicated and difficult regardless of the required technical level, the complexity of the manufacturing process, and the production equipment and investment.

In summary, the use of “twisted” or “twisted” prefabricated branch cables in the three-phase three-wire, three-phase four-wire, and three-phase five-wire power supply loops is used as the power supply loop to ensure the safety of its operation. And stability are extremely disadvantageous. The author also consulted related materials, regulations, specifications, standards such as IEC, NEC, etc., which clearly stipulated the distance between cables and cables when laying in parallel, and the correction coefficient of the current carrying capacity of cables at various distances. The author believes: This is also enough to explain the use of power cables. The series of processes from design to laying must fully consider the distribution of capacitance and inductance during operation, electromagnetic attraction, repulsion, vibration, etc.; the temperature rise during operation (capacitance And the distribution of inductance, electromagnetic attraction, repulsion, vibration, etc. are all part of the’temperature rise’) and heat dissipation environment and conditions. Therefore, only stipulating the different correction factors for the ampacity at different distances is sufficient to explain the nature and essence of the problem. What’s more, these are facts proved by theory and practice

Power Cable Fire Protection Technology

According to incomplete statistics, there have been more than 100 major accidents caused by cable fires spreading across the country in the past ten years, and more than 320,000 meters of cables have been burned. The restoration and reconstruction work is expensive and time-consuming, and the loss of power supply alone amounts to more than 100. 100 million yuan. The cable fire accident has its special hazards, that is, the failure of the control circuit causes the accident to expand and even damage the main equipment, and it is difficult to repair, and production cannot be resumed for a long time.

Power cables are an important part of the normal operation of power plants and substations. The widespread distribution of cables in power plants and substations, the flammability of cables, the serial ductility of cable fires, and the seriousness of the consequences of cable fires make the fire protection of cables highly valued by power departments, firefighting agencies and scientific research institutions. In view of the frequent occurrence of cable fire accidents, it is necessary to discuss the fire safety measures for cables.

1. Create a good operating environment to avoid accelerated aging and damage of cable insulation
Cable trenches and cable tunnels must have good drainage facilities, such as shallow drainage ditches and water collection wells, and can effectively hold water. If necessary, install automatic start and stop pumping devices to prevent water accumulation and keep the interior dry. The longitudinal drainage slope of cable trenches and tunnels should not be less than 1% to 2%, and should be at least greater than 0.5% to prevent water, corrosive gas or liquid, and flammable liquid or gas from entering. Cable trench, cable tunnel. The cable tunnel should be naturally ventilated, but when the normal load of the cable causes the air temperature in the tunnel to be higher than 40℃~50℃, a combination of natural exhaust and mechanical exhaust can be used for ventilation. The fan of the ventilation system should be interlocked with the fire detector to ensure that the air supply can be automatically stopped in the event of a fire in the tunnel. The cable tunnel shall not be used as the air inlet of the ventilation system.


Avoid placing the cable fire door in a normally closed state, using a fire barrier to completely seal the cable, and filling and sealing all gaps in the cable trench cover, which affect the ventilation and heat dissipation of the cable. Moreover, completely enclosing the cable also makes normal inspection of the cable impossible, and the cable failure cannot be found in time.

In addition, there must be complete facilities for preventing the intrusion of rats and snakes to prevent small animals from destroying the insulation cable and causing accidents.

2. Strengthen the preventive test of cables
The preventive test of cables should not only look at the qualified and unqualified test data, but also compare and analyze the data. It can be compared with the test data of the same cable or with the historical test data of this cable to explore the law of the test data. For example, when the DC withstand voltage test is performed, if the measured leakage current value rises faster with the increase of the test voltage value or the increase of the pressure time, or the value increases more than the same cable, or if the The measured data shows an obvious upward trend, or the leakage current imbalance coefficient between the three is relatively large, etc., which should be carefully analyzed. If it is not caused by improper test method, the test voltage can be appropriately increased or the test time can be extended to determine whether the cable meets the conditions for continued operation.

3. It is necessary to strengthen the management and operation monitoring of the production quality of cable heads
According to statistics, cable fire and explosion accidents caused by cable head failure account for about 70% of the total cable accidents. Therefore, it is necessary to strictly control the quality of the materials and workmanship of the cable head. It is required that the service life of the made cable head should not be less than the service life of the cable. The rated voltage level and insulation level of the connector shall not be lower than the rated voltage level and insulation level of the connected cable. The withstand voltage between the insulation pads on both sides of the insulation head shall not be less than 2 times the insulation level of the cable sheath. The form of the connector should be compatible with the environmental conditions set, and should not affect the flow capacity of the cable. Within the range of 2 to 3 meters on both sides of the cable head, fire-resistant tapes shall be used for fire-resisting and flame-retardant cable treatment.

Generally speaking, the cable head is the weak link of the cable insulation, so strengthening the monitoring and management of the cable head is an important part of cable fire protection. The terminal cable head must not be placed in the cable trench, cable tunnel, cable trough box, or cable interlayer. The intermediate cable heads placed in the cable trenches, cable tunnels, cable trough boxes, and cable interlayers must be registered and monitored using a variety of monitoring equipment. When the cable head is found to have abnormal temperature rise or smell or smoke, exit the operation as soon as possible to avoid the cable head from catching fire during operation.

There should be sufficient safety length between the middle cable heads. Two or more cable heads should not be placed in the same position. Tight sealing measures should be taken between the cable heads and other cables.

4. Prevent other equipment from catching fire and igniting the cable
Oil-filled electrical equipment, coal conveying, pulverizing systems, and steam engine oil systems can be ignited by cables. Corresponding measures must be taken for them; the cable trench cover near the oil-filled electrical equipment should be sealed to prevent the oil from flowing into the cable trench to ignite the cable when the equipment fails and catches fire. The dust accumulation on the electric blanket near the coal conveying and pulverizing system should be cleaned regularly to prevent the spontaneous combustion of the pulverized coal from igniting the cable. The cables facing the explosion-proof door of the pulverizing system must be packed in a fire-proof box to prevent the fire-proof door from igniting the cable. The cables under the head of the turbine should be packed in a fire-proof trough box.

5. Use measures such as sealing, blocking, coating, isolation, and wrapping to prevent the cable from spreading

Fire-retardant paint has the characteristics of thin coating, does not affect normal heat dissipation, and can play a good heat insulation and flame retardant effect, but it also has many defects.
Therefore, it is not advisable to apply a large number of fire-retardant coatings to the cable to be flame-retardant. Instead, a large number of methods of sealing, blocking and isolation should be used. When using sealing, blocking, and isolation methods, the following issues should be noted:

(1). Use the methods of sealing, blocking and separating to ensure that the fire of a single cable does not extend to multiple cables. Cables enter cable trenches, cable tunnels, and cable trough boxes; the nozzles of the cable interlayer should be tightly fireproofed to prevent a single cable or a small number of cables from igniting a large number of cables. A fire wall and fire door shall be installed every 60 to 100 meters in cable trenches and cable tunnels. Fire barriers shall be arranged in layers in the shafts. Fire barriers shall be arranged between power cables and control cables. The control cables shall be fully fireproofed. Flame-retardant cables are used to ensure that the main equipment can safely stop running in any emergency. Important cable channels should be equipped with automatic alarm and automatic fire extinguishing devices, such as water spray and water mist fire extinguishing devices, to achieve early detection and early fire fighting.

(2). The tightness and thickness of the fire-proof sealing must be guaranteed. If the fire-proof sealing is not tight, the sealing effect will be lost, especially where the cables are concentrated, it is best to use soft blocking materials to ensure tight sealing. During maintenance and inspection, the damaged blockage should be restored in time. The thickness of the blocking material is not enough, and the fire will pass through the blocking material and burn after the cable catches fire. The thickness of the plugging material should be proportional to the number of cables on the plugging surface, the more the number of cables, the thicker the plugging. The fire door should have a device that automatically closes after a fire occurs.

(3). The fire blocking layer must have sufficient mechanical strength. Because the cable catches fire, especially the electrical short circuit, it will cause the rapid expansion of the air to produce a certain impulse, destroy the fireproof sealing layer with low mechanical strength, and make the fireproof sealing useless.