What are the common installation methods of cable tray?

Bridge, also known as cable bridge, is composed of support, tray, cover plate and installation accessories. In a computer room project, compared with expensive and high-tech hardware and software, the bridge is very insignificant and rarely paid attention to, but it is also an indispensable part of the whole wiring project. Today, let’s talk about the process and common installation methods of bridge during construction.

1、 Common installation methods of bridge:
1. Horizontal hoisting (lifting frame)
It is applicable to the hoisting of trough and tray bridges with width < = 100mm
2. Horizontal hoisting (cross arm)
It is applicable to the hoisting of trough and tray bridges with width > 100mm
When the width is less than 600mm, the through wire suspender shall be used
Width > = 600mm, use angle steel suspender
3. Horizontal wall (supporting arm)
It is applicable to the horizontal installation of bridge against the wall
4. Vertical wall (horse stool / word stand)
It is ACSR Cables to the vertical installation of bridge along the wall
2、 Installation and construction process of cable tray:
Installation process flow of cable tray
1. Positioning and setting out → embedded iron parts or expansion bolts → support, hanger and bracket installation → bridge installation → protective grounding installation
2. Determine the position from the beginning to the end according to the construction drawing, mark the direction along the drawing, find the horizontal, vertical and curved connection, snap lines or draw lines along the bridge direction on the walls, ceilings, floors, beams, plates, columns, etc., and draw the positions of supports, hoists and brackets with uniform span.


3. Embedded iron parts or expansion bolts
(1) The self-made processing of embedded iron parts shall not be less than 120mm × 80mm × 6mm, and the diameter of anchor round steel shall not be less than 10mm.
(2) Closely cooperate with the construction of civil structure, keep the plane of embedded iron parts close to the formwork, and fix the anchor round steel on the reinforcement in the structure by binding or welding; After the concrete formwork is removed, the plane of embedded iron parts is exposed, and the support, hanger or bracket shall be welded on it for fixation.
(3) Select the corresponding expansion bolt and drill bit according to the load borne by the support; After the bolts are embedded, the supports or hangers can be directly fixed on the metal expansion bolts with nuts and corresponding washers.
Bridge installation
1. When the length of steel cable tray in straight section exceeds 30m, and the length of aluminum alloy or FRP cable tray exceeds 15m, expansion joints shall be set, compensation devices shall be set at the crossing of expansion joints, and bridges with expansion joints can be used.
2. The bolts between the bridge and the support and the bolts of the bridge connecting plate are fastened without omission, and the nuts are located outside the bridge. When the aluminum alloy bridge and the steel support are fixed, there are mutual insulation and anti electrochemical corrosion measures, and asbestos pad can be used generally.
3. The cable tray laid in the shaft and crossing different fire zones shall be provided with fire isolation measures according to the design requirements. The ABC Cable tray laid in the electrical shaft can be fixed with angle steel
When the cable tray passes through the firewall and fire floor, fire isolation measures shall be taken to prevent the fire from spreading along the line; For the fire separation wall and plate, the opening shall be reserved in cooperation with the civil construction, and the edge protection angle steel shall be embedded at the opening. During construction, L50 shall be used according to the number of layers and cables laid × fifty × 5. The angle steel shall be used as the fixed frame, and the fixed cabinet shall be welded on the edge protection angle steel at the same time; The frame can also be installed in the wall and slab during masonry or concrete pouring in civil construction.


Grounding of bridge
When the design allows the use of bridge system to form grounding trunk circuit, the following requirements shall be met:
1. The metal cable conduit led in or out of the metal cable tray and its support must be reliably grounded (PE) or connected to neutral (pen), and must comply with the following specifications:
(1) The total length of metal cable tray and its support shall be connected with grounding (PE) or neutral (pen) trunk line at least 2 places, so that the whole tray is an electrical path.
(2) The two ends connected between non galvanized AAAC Cable trays shall be connected with copper core grounding wire, and the minimum allowable cross-sectional area of grounding wire shall not be less than 4mm2.
(3) The two ends of the connecting plate between galvanized cable trays may not cross the grounding wire, but the two ends of the connecting plate shall not be less than 2 connecting and fixing bolts with anti loose nuts or anti loose washers.
2. The connection resistance between the end of tray and ladder shall not be greater than 0.00033 Ω, and shall be tested with equipotential bonding tester (continuity meter) or micro Ω meter. The test shall be carried out on both sides of the connection point. The connection resistance at both ends of the whole bridge length shall not be greater than 0.5 Ω or determined by the design, otherwise the grounding point shall be added to meet the requirements. The coating shall be removed from the grounding hole, and the flat pad on one side of the bolt in contact with the coating shall use a special grounding washer with claw.
3. The expansion joint or soft connection shall be connected with braided copper wire. When another grounding main line is laid along the whole length of the bridge, the tray and ladder of each section (including non-linear section) shall be reliably connected with the grounding main line at least at a small point; Spring washers shall be installed at the connection of grounding parts to avoid loosening.

How to choose wires for home decoration

Recently, the home decoration needs to buy Wires for construction. At this time, I don’t know which kind to buy, and I don’t know how to choose wires? So, today in this article, we will use three easy to understand steps to explain the relevant knowledge of wires in decoration, and let them know which is good, including how to choose.

Step 1: first understand what types of wires are used in home decoration
There are many kinds of wires, and the AAAC Cables that can be used for home decoration are fixed. The specific classification is as follows:
Bv wire (hard wire)
BVR wire (Multi Strand flexible wire)
RVs thread (plush thread)
BLVVB wire (aluminum sheathed wire)
BVVB wire (copper sheathed wire)
BLV wire (single strand aluminum core wire)
RVV line (copper core cable) household weak current line: closed circuit line, network line, telephone line, audio line, etc.
In other words, among the wires available for home decoration, with the continuous improvement of wire use requirements and user requirements, BV wires (hard wires) are currently used for strong wires, and BVVB wires (copper sheathed wires) will still be used in some areas. For weak wires, RVV wire (copper core cable) is used.

Step 2: understand why bv wire is suitable for home decoration ACSR Cables
1. What is bv line
Bv wire refers to copper core PVC insulated wire, where B represents category and V represents insulated PVC, with bv1.5m ²、 BV2.5m ²、 BV4.0m ²、 BV6m ² Wait, wire diameter classification. Bv line can be divided into BV and ZR-BV, among which ZR-BV is flame retardant bv line. In home decoration, most of them can meet the use requirements by using bv line. Only a few owners and decoration companies will use ZR-BV line to use home decoration wires. No matter which one of BV and ZR-BV is used, it can be applied to power devices and daily appliances with AC voltage of 450 / 750V and below, that is, it can ensure the daily power demand and safe use at home.
2. Why bv line is suitable for home decoration
Bv line can stand out among many household wires. Of course, it must have sufficient advantages and persuasion. Otherwise, it will not become the dominant type of wires for home decoration. Specific advantages are as follows:
Convenient construction: bv wire is a single strand wire, which is very convenient whether threading or wiring during construction. This provides convenience in construction. At the same time, because the BV line is a single strand line and a single cycle line, it is also very convenient to take it. It can save the time of construction workers during construction. Therefore, the master is willing to recommend users to buy this kind of wire. Under the same labor cost, using the bv line can save at least one man hour. From the side, it is to make the construction earn more money.
High safety: for BV wire, because it is a copper core PVC insulated wire, its internal is a single strand copper core, and the external is insulated with PVC, which is the best in use safety. Meanwhile, BV wire is made of 99% pure oxygen free copper, because the oxygen free copper core has low resistivity, excellent conductivity, large current carrying capacity, good ductility, oxidation resistance, corrosion resistance, strong stability and high safety.
Affordable price: the price of wires is the main factor affecting consumers’ purchase. Under the condition of ensuring safety, the price of BV line is only a little higher than that of traditional line, and the cost of single lap is not very high, which is within the range acceptable to consumers. Therefore, as consumers, with high safety and affordable price, they will naturally choose to use bv line.
Strong tensile resistance: bv wire needs to be threaded for construction when power is used for home decoration. At this time, the construction of threading and pulling wire will occur. Whether through the steel ratio or the wire itself, it will produce a certain tensile force on the wire. At this time, BV wire will not have any impact on the constructors when they pull wire normally, and will not damage the internal single strand copper core, If PVC insulation material is used externally, consumers will naturally feel relieved to use it, which also shows its high safety from the side.
Long service life: for BV wire, the inner part of the base is a single strand copper core and the outer part is PVC insulating material. Through such protection, the inner single strand copper core can have stronger corrosion resistance and oxidation resistance, so as to prolong the service life of the ABC Cable, which also meets the service life requirements of home decoration wires. Generally speaking, it is no problem to use it for 10 years.
Through the above basic explanation and advantages of BV line, we can clearly know why bv line is suitable for home decoration, and it is also the best strong current line for home decoration at present.

Step 3: how to select wires?
Now that we know that the wires used for home decoration are bv wires, the next step is to know how to choose. I believe this is also a matter of great concern to most consumers. The specific selection steps are as follows:
The first step in selecting high-quality wires is to look at the wire diameter: bv wires can be divided into bv1.5m due to different wire diameters ²、 BV2.5m ²、 BV4.0m ²、 BV6m ² And so on. For home decoration, it is often bv2.5m ²、 BV4.0m ² Mainly used in lighting and socket circuits. For the earliest bv1.5m ² Generally speaking, bv2.5m is rarely used in lighting, and bv2.5m is directly used ² To be used as a lighting circuit. BV6m ² Wires are often used for independent circuits, as well as high-power electrical appliances for home decoration, such as central air conditioning and fast heating hot water products.
The second step of selecting high-quality wires is to look at the color: I believe that after you understand the wire diameter of BV wire, you will find that there are many colors when you see bv wire in the market, and the merchant will tell you which color to buy for use. And this is also the BV, which needs to pay attention to details, because different colors represent different meanings. Red is used as the fire line L; Blue, yellow and green are used as zero line n; The yellow green two-color wire is used for the ground wire PE. Different colors should be used in different positions, and the construction should be carried out according to the standard color wire. In this way, whenever the home wire needs to be maintained and reinstalled with new electrical appliances, it is very convenient to recognize the fire, zero and ground wire of the wire, so naturally there will be no wiring errors and major potential safety hazards.
The third step of selecting high-quality wires is to look at the brand: the brand is also reflected in the wire industry. As a large domestic brand, the quality of wires produced can be guaranteed. But sometimes, because of the reasons why sales are not suck, the local production lines can be recognized by consumers in many city. Therefore, when purchasing wires, we must decide the local conditions according to the local conditions. If the local people recognize their local brands, then they can choose their local brands, so we need not worry about the quality at this time. Because the local brand wire is recognized by consumers.
The fourth step of selecting high-quality wires is to look at the trademark: the trademark mentioned here does not mean the trademark of the wire brand, but the specific information on the wire packaging and 3C certification, because the formal wire brand must have specific information about the goods on its outer packaging during production. In addition, there must be strong safety standards implemented by the industry. With this information, Wires can be used safely.
The fifth step of selecting high-quality wire is to look at the copper core: for BV wire, its interior is a single strand copper core, and the copper core is made of 99% pure oxygen free copper, so pay attention to the brightness of the copper core when purchasing. Generally speaking, the higher the copper quality, the better, and the brightness is uniform and shiny. When buying, you can simply do an experiment. If you bend the wire for many times, it means that the bending resistance is good, which means that the copper quality is good. If you break after bending a few times, it means that you can’t buy if the copper quality is not up to the standard.
The sixth step of selecting high-quality wires is to look at the appearance: for BV wires, the external PVC insulation material is also very key, which is an important factor to ensure the safety of wires. Therefore, pay attention to the appearance and check the color and texture of PVC insulation materials. Generally speaking, whether the high-quality PVC insulation material has bright color and fine texture; The inferior PVC insulation material uses recycled plastic, so the appearance color is dim and the texture is loose, so such wires can not be selected.
The seventh step of selecting high-quality wire is to look at the meter number: for BV wire, it is usually written on the commodity packaging that it is 100 meters, but in fact it is only about 95 meters. Such a meter number shows that it is full meters, which is also the rule of the industry. For some wires, the number of meters is only about 90 meters, less than 95 meters, so we need to pay attention. Such wires belong to non-national standards, and their quality can not be used safely.

summary
Recently, for home decoration, buying bv hard wire is the best choice for wire use. It is a wire that can ensure quality and safety. At the same time, as long as we follow the above seven steps of selecting wires, we can select high-quality wires and be assured and worry-free.

Why do low-voltage power cables use four cores?

The low-voltage power grid in urban residential areas generally adopts the three-phase four wire system. The four core cable used in the low-voltage power grid, except for the three-phase conductor, is called the neutral wire. It can pass through the unbalanced current of three-phase AC and has the function of protective grounding. Three core cable and one conductor cannot be used as neutral wire to connect to three-phase four wire low-voltage power grid, because in this case, part of the three-phase unbalanced current will pass through the armor of three-core ABC Cable, which will heat the armor layer and reduce the current carrying capacity of the cable.


The measured load data of low-voltage power grid in some sections show that the difference of three-phase load may be several times. Due to the unbalanced power load of household appliances and the different timing of household appliance load, the three-phase load is unbalanced, which is difficult for the power department to grasp and manage. At the beginning of the 20th century, in some low-voltage power grids in urban residential areas, accidents of ACSR Cable damage caused by neutral line overload occurred from time to time, especially the low-voltage cable insulated with polyvinyl chloride (PVC), sometimes even burning out the PVC insulation of the whole cable due to overheating. After analysis, the cause of the accident is that when the unbalanced current of the power grid is too large, the neutral line of the low-voltage cable is seriously overloaded due to too small section. Therefore, the power department requires cross-linked polyethylene as the insulation of low-voltage cables, and appropriately increase the cross-section of low-voltage cables. At the same time, the cable factory is required to produce four core low-voltage cables with equal cross-section. Under the condition of extremely unbalanced three-phase load, the cable neutral line can have sufficient ability to pass through unbalanced current.


3.5 number of power cable cores
3.5.1 when the neutral point of 1kV and below power supply is directly grounded, the number of cable cores of three-phase circuit shall comply with the following provisions:
1. When the protective conductor is connected with the exposed conductive part of the power receiving equipment for grounding, the following provisions shall be met:
1) For TN-C system, when the protective conductor and neutral conductor share the same conductor, 4-core cable shall be selected;
2) For TN-S system, when the protective conductor and neutral conductor are independent, 5-core cable should be selected; When the provisions of article 5.1.16 of this standard are met, it can also be composed of 4-core cable and another protective conductor laid close to the phase conductor;
3) When TN-S system is not equipped with neutral conductor or the circuit does not need neutral conductor to be led to the power receiving equipment, 4-core cable should be selected; When the provisions of article 5.1.16 of this standard are met, the 3-core cable can also be composed of another protective conductor laid close to the phase conductor.
2 for TT system, when the protective grounding of the exposed conductive part of the power receiving equipment is independent of the neutral point grounding of the power supply system, 4-core cable shall be selected; When the neutral conductor is not provided or the circuit does not need the neutral conductor to be led to the power receiving equipment, 3-core cable should be selected.
3 for TN system, when the exposed conductive parts of power receiving equipment are reliably connected to the public grounding grid distributed in the whole plant and station, 3-core cables should be selected for motors and other electrical equipment that are fixedly installed and do not need neutral conductors.
4 when the section of phase conductor is greater than 240mm2, single core cable can be selected, and the section of neutral conductor and protective conductor of its circuit shall comply with the provisions of articles 3.6.9 and 3.6.10 of this standard.
3.5.2 when the neutral point of 1kV and below power supply is directly grounded, the number of ACAR Cable cores of single-phase circuit shall comply with the following provisions:
1. When the protective conductor is connected with the exposed conductive part of the power receiving equipment for grounding, the following provisions shall be met:
1) For TN-C system, when the protective conductor and neutral conductor share the same conductor, 2-core cable shall be selected;


2) For TN-S system, when the protective conductor and neutral conductor are independent, 3-core cable should be selected; When the provisions of article 5.1.16 of this standard are met, it can also be composed of 2-core cable and another protective conductor laid close to the phase conductor.
2. For TT system, when the protective grounding of exposed conductive parts of power receiving equipment is independent of the neutral point grounding of power supply system, 2-core cable shall be selected.
3 for TN system, when the exposed conductive parts of power receiving equipment are reliably connected to the public grounding grid distributed in the whole plant and station, the fixed electrical equipment should use 2-core cable.
3.6 conductor section of power cable
3.6.9 when the neutral point of 1kV and below power supply is directly grounded, the section of cable neutral conductor or protective grounding neutral conductor of three-phase four wire system shall not be less than the minimum section required for continuous operation according to the maximum unbalanced current of the line; The circuit affected by harmonic current shall comply with the following provisions:
1. For the circuit with gas discharge lamp as the main load, the neutral conductor section shall not be less than the phase conductor section.
2 when there is high-order harmonic current, the current of neutral conductor shall be calculated and the effect of harmonic current shall be included. When the neutral conductor current is greater than the phase conductor current, the cable phase conductor section shall be selected according to the neutral conductor current. When there is harmonic current in the three-phase balance system, and the materials of neutral conductor and phase conductor in 4-core or 5-core cable are the same and the section is the same, the reduction coefficient of cable ampacity shall be determined according to the provisions of table 3.6.9.

Causes of appearance defects of five kinds of rubber sheathed cables

In the production process of rubber sheathed AAC Cable, there are often appearance defects, such as unsmooth surface; Clinker particles (early vulcanized rubber particles) or impurities on the surface; Scratch and scratch on the surface of wires and cables; Surface collapse; There are hemp patterns on the surface.

The following are five common causes of appearance defects of rubber sheathed ACSR Cables:
1. The die sleeve bearing line is too long or too short, the die opening is not smooth and the hole diameter is too large; Low head, die or body temperature; Low plasticity of rubber may lead to unsmooth surface of rubber sheathed cable.
2. The supplied rubber is not clean and contains impurities; The scorch time of rubber is too short; The temperature of rubber extrusion body, head or die is too high; The rubber flow in the head is not smooth, and there is a dead corner of rubber retention; Unsmooth screw and viscose may lead to clinker particles (early vulcanized rubber particles) or impurities on the surface of rubber sheathed cable.
3. The die sleeve is not smooth and has no chamfer; Impurities or clinker particles block the die mouth; Abrasion of dragging pipe in vulcanization pipe; The small aperture of the sealing rubber gasket at the outlet of the vulcanization pipe may cause scratches and scratches on the surface of the rubber sheathed cable.
4. The hole diameter of die sleeve is too large; The gap between the outer strands and monofilaments of the conductive core is too large, and the outer diameter of the cable core is uneven; The rubber has small plasticity and poor viscosity; Impurities in rubber; Small mold distance and pressure may cause the surface collapse of rubber sheathed cable.
5. The hole diameter of die sleeve is too small; Insufficient rubber extrusion and insufficient filling of wire core gap; Conductive core or cable core jumper; Short distance between molds may lead to twist on the surface of rubber sheathed cable.

Rubber sheathed cable is a kind of soft and movable cable with multi strand fine copper wire as conductor and wrapped with rubber insulation and rubber sheath. Generally speaking, it includes general rubber sheathed flexible cable, electric welding machine cable, submersible motor cable, radio device cable and photographic light source cable.
Rubber sheathed cables are widely used in various electrical equipment, such as mobile power lines for daily appliances, electric machinery, electrical devices and appliances. At the same time, it can be used under indoor or outdoor environmental conditions. According to the external mechanical force on the cable, the product structure is divided into light, medium and heavy. There is also appropriate connection on the section.
General light rubber sheathed cables are used in daily electrical appliances and small electric equipment, which are required to be soft, lightweight and good bending performance;
Medium sized rubber sheathed cables are widely used in agricultural electrification except for industrial use;
Heavy duty cables are used in such occasions as port machinery, searchlights, large hydraulic drainage and irrigation stations in domestic industry, etc. This kind of products have good universality, complete series specifications, good and stable performance.
Waterproof rubber sheathed cable and submersible pump cable: mainly used for supporting submersible motor, with models of JHS and JHSB.
Cables for radio devices: now we mainly produce two kinds of rubber sheathed ABC Cables (one shielded and one unshielded), which can basically meet the requirements. The models are wyhd and wyhdp.
Photographic cable products: with the development of new light sources, they have small structure and good performance, meet the needs of indoor and field work, and gradually replace some old products with heavy weight and poor heat resistance.
Operation method:
1. Set the temperature and time according to the vulcanization system of the compound
2. Wipe and wash the repair place with rubber and ink diluent, especially the joint shall be fully treated.
3. Cut the repair rubber properly according to the size of the gap, and pay attention not to be too much or too little,
4. Plug the cut rubber in the gap, and pay attention that the rubber shall not be higher than the circumference of the wire.
5. Wrap it with high temperature resistant PP tape. And put it into the tubular die cavity slightly smaller than the wire diameter, lock the upper and lower dies, and make the supplemented position have a certain pressure. Note that the die cavity diameter is slightly smaller than the wire diameter by 0.1 ~ 0.2mm.
6. When the vulcanization time is up, take out the product. If a small amount of rubber overflows, repair it with a sharp blade and wipe it with diluent.

Realize the “perspective” management of underground cables

Based on the underground cable informatization model developed by China Electric Power Research Institute, the “perspective” management of underground cables can significantly improve the design, construction, operation and maintenance and management level of underground ACAR Cable lines.


Firstly, this technology can make the route planning and design of underground cable engineering more reasonable. Using three-dimensional technology, technicians can check the underground ABC Cable project and the laying of surrounding pipelines at any time, carry out the calculation and analysis of electromagnetic environment, structural load and safe distance, so as to realize the safe, effective and rational utilization of underground space.
Secondly, the technology can guide accurate construction. Due to its concealment, the maintenance difficulty, cost and time of underground cable are greater than those of overhead transmission line, but the biggest difficulty is the accurate location of fault point. With the help of three-dimensional digitization and sensor technology, the operation of underground cable lines can be monitored in the remote control center, the fault can be monitored and warned in real time, the construction team can be guided to locate the fault quickly and accurately, avoid repeated ground excavation, save construction time, and ensure the safe use of electricity and normal life of residents.


Thirdly, the technology can realize cross departmental and cross professional data sharing and collaborative office. To ensure the construction and safe operation of a power cable project line, it requires the cooperation of multiple departments such as planning, design, construction, supervision, operation and maintenance and management, and the joint efforts of multiple professionals such as system, electrical, structure and survey. For departments and disciplines with upstream and downstream relations, the three-dimensional digital model can directly realize data sharing; For the work that needs to be completed through multi-party intelligent negotiation, three-dimensional visual discussion can be carried out based on the same underground cable information model to realize collaborative office, which is conducive to the improvement of project construction quality and efficiency.


At this stage, 3D digital technology has been applied in various fields of underground cable construction to varying degrees. However, to expand to the whole process of underground AAAC Cable line construction, go deep into the business needs of all parties and cross domain data sharing, we still need to continue to carry out in-depth research on digital application; Based on the established digital design system of power cable engineering, cetca will continue to explore the application research of the whole life cycle of underground cable engineering construction, so as to provide technical support for the construction of big data center of power transmission and transformation engineering.

Underground cable is the trend of urban development

Install “perspective eyes” for underground cables
In many cities in China, especially in some metropolises or new urban areas, power towers and wires are basically invisible, but thousands of households can use electricity normally. Where does people use electricity come from? In fact, this mainly depends on underground cables to transmit electric energy.
Underground cable is an important way of power transmission. The continuous power supply is realized by establishing underground channels and laying cables. In recent years, scientific and technological personnel have become more and more capable of controlling underground cables, and new technologies have been introduced, popularized and applied, which has laid a solid foundation for the all-round development of underground AAC Cables.


◆◆
Underground cable is the trend of urban development
◆◆
With the acceleration of China’s economic development and urbanization, the contradiction between power facilities and urban development is becoming increasingly prominent. In order to ensure the power safety of urban residents and keep the city clean and beautiful, it is necessary to reduce the starry overhead transmission lines over the city, set them underground and develop underground ACSR Cables.
According to statistics, the proportion of underground power transmission in some modern cities in the world, such as Berlin, Tokyo, Osaka and Copenhagen, has exceeded 70%. At present, China is also accelerating the construction of overhead wire into the ground, underground cable project and underground comprehensive pipe gallery. By 2017, the total length of Beijing underground cable tunnel is about 800 km. It is expected that by the end of the 13th five year plan, the underground cable utilization rate in Beijing’s core area will increase to 94% and the power supply reliability rate will increase to 99.999%.
In 2014, the State Council issued the guidance of the general office of the State Council on strengthening the construction and management of urban underground pipelines. In 2016, the Ministry of housing and urban rural development issued the 13th five year plan for the development and utilization of urban underground space. These documents require deployment to strengthen the construction and management of urban underground pipelines and ensure the safe operation of the city. As a national new area planning, xiong’an new area will adopt the underground pipe gallery mode for the construction of underground pipe network, and deploy water, electricity and urban transportation to the underground space.
In response to the call of the state, State Grid Corporation of China issued document No. 1459 notice on the planning and use management specification of urban power cable channel and the guidance on the planning and construction of power cabin of urban comprehensive pipe gallery in 2014. In the face of the increasing number of underground transmission lines, State Grid Corporation of China further standardized and strengthened the management of underground cables.


With the rapid development of underground cables, the number of underground pipelines will become larger and larger, and the space will become more and more crowded. Construction, operation and maintenance, management and other parties will face great difficulties and pressure. Therefore, there is an urgent need for an effective method to solve this problem. With the rapid development of information technology, three-dimensional digital technology stands out. Using this technology can realize the “perspective” and intelligent management of underground cables.
◆◆
What is 3D digital technology?
◆◆
The so-called “three-dimensional digitization” is to use three-dimensional tools (software or instruments) to realize a series of digital operations such as virtual creation, modification, improvement and analysis of the model. Generally speaking, it is to use computer technology to virtually appear any scene and object in real life in the computer, so as to realize the undifferentiated mapping from the real world to the computer virtual world.
The traditional three-dimensional digital technology mainly focuses on the modeling of the physical appearance. Based on the modeling software, the solid appearance is simulated in the computer by using the solid construction and rendering technology, which mainly meets the needs of display. At this stage, the three-dimensional digital technology has been upgraded on the original basis. In addition to truly simulating the appearance of the real object, it also includes a series of relevant information such as accurate size, volume, weight, material and management. The three-dimensional digital model constructed in this way belongs to the information model, which can not only meet the visualization requirements, but also carry out a series of calculation, analysis and management.


In August this year, China Electric Power Research Institute Co., Ltd., a scientific research institution directly under the State Grid Corporation of China, used three-dimensional digital technology to build a digital design system for power cable engineering. The system supports the construction of underground cable information model with voltage level of 35 kV to 500 kV, including different types of underground cable lines such as pipe arrangement, tunnel, comprehensive pipe gallery (power cabin), cable trench, bridge and direct burial. It not only realizes the three-dimensional digitization of the underground cable engineering body, but also supports the above ground buildings in the power corridor 3D visualization of the surrounding environment of other types of underground pipelines. Based on the completed three-dimensional digital model, the safe distance between the underground cable engineering body and the surrounding environment can be calculated, and a series of work such as cable engineering body planning, design, construction and management can be carried out. In addition, in order to save the construction time of underground cable informatization model and improve the model accuracy, the system has built three-dimensional general model libraries such as pipe arrangement, tunnel, cable trench, bridge and working well according to the general design library of State Grid, and provided parametric modeling tools such as pipe arrangement, tunnel, comprehensive pipe gallery (power cabin), AAAC Cable trench, bridge and direct burial, Have the ability to automatically build a 3D model by inputting parameters.

Introduction to the characteristics of btly flexible mineral insulated cable!

Btly is also called gn-al, ng-a and ng-a (btly)
Btly is a flexible mineral insulated cable with copper tube sheath replaced by aluminum tube sheath.
This product is the first in China and there is no prototype in the world. Compared with bttz series metal sheathed AAC Cable, the product can achieve continuous large length and multi-core cable within 240mm, which overcomes the disadvantage of too many joints. However, the product has complex structure, large outer diameter and weight, and its electrical performance is weaker than that of bttz, yttw and bbtrz cables. The fire resistance of aluminum protective sleeve is relatively weak, and it is prone to electrical corrosion. It is difficult to deal with the aluminum copper transition of the joint, and the requirements for the installation process capacity are still very high.


Basic product parameters
Conductor: round copper stranded wire (softer than solid copper rod of BTT).
Insulation: pure phlogopite tape (no longer composed of extruded insulating material, so as to eliminate the generation of carbon particles and improve the electrical stability).
Filling layer: dense filling with mineral compounds.
Sheath: aluminum soft sheath is adopted.
Refractory layer: it is covered with non fusible, non combustible and expandable flame retardant inorganic matter Mg (OH) or Al (OH)).
Outer sheath: low smoke halogen-free or better plastic material.
Metal sleeve: continuously extruded aluminum metal pipe (greatly simplifying bttz copper pipe drawing process)
Mineral insulated cable
Product executive standard
1. BS 6387:1994 performance requirements for ACSR Cables to maintain circuit integrity under flame conditions;
2. GB / t12706.1 extruded insulated power cables and accessories with rated voltage from 1KV (UM = 1.2KV) to 35kV (UM = 40.5kV);
3. Follow the corresponding enterprise standards.
Product use characteristics
Voltage level: 0.6/1kv, working voltage: light load 500V, heavy load 1000V.
Working environment: the long-term working temperature is 90 ℃.
Bending radius: minimum allowable bending radius ≥ 12D.

Btly flexible mineral insulated cable
Product features
1. The fire resistance standard can pass three tests of bs6387: no breakdown under 950 ℃ flame for 3h, water spray for 15min after 30min at 650 ℃ (direct immersion is also acceptable), knocking vibration for 15min under 950 ℃ flame without damage, so as to fully meet the BTT assessment standard in fire resistance performance.
2. The product can produce 1 ~ 37 cores in 1.5 ~ 6 square meters, 1 ~ 5 cores in 10 ~ 240 square meters and single cores in 300 ~ 630 square meters. The length can be delivered in a whole plate without joints according to the needs of users.
3. There is no need to wear another pipe during laying, and it has the same waterproof and anti impact functions as BTT.
4. It has good mouse, ant and radiation protection functions, which can ensure the stability, long service life and durability of the cable.


5. Low working temperature, small line loss, strong overload resistance, long service life and high safety. It is especially suitable for application in projects with environmental protection requirements
6. Explosion proof (the highly compacted insulating material in the AAAC Cable and the cable terminal installed with special sealing sleeve can prevent steam, gas and flame from entering the electrical equipment connected with the cable, so it is used in places with explosion risk and the connection of various explosion-proof equipment and equipment).
7. Corrosion resistance (the metal sheath of BTT (L) series mineral insulated cables has high corrosion resistance. For most devices, it does not need to take additional protective measures; Even where the metal sheath of the cable is vulnerable to chemical corrosion or serious industrial pollution, because the outermost layer of the cable is protected by the plastic outer sheath, it is still safe).

How to train cable line operators?

The operation of cable line is a highly professional work. The technical training of AAAC Cable operators should focus on cultivating various basic skills. The learning contents mainly include:
1) basic knowledge of electrical theory;
2) structure and characteristics of power cable;
3) cable laying and manufacturing methods of joints and terminals;
4) understand the cable line design, power system operation diagram and assembly drawing of joint process;
5) performance, processing and storage methods of various common insulating materials;
6) high altitude operation skills on poles and towers;
7) cable test technology;
8) be familiar with safety and quality management procedures and systems (including urban construction, public utilities, transportation and other relevant regulations);
9) computer and other related skills.
in addition to the necessary classroom explanation and on-site practice, these basic skills should be carried out in combination with the on-site conditions. Cable line operators must be trained in the above basic skills, have certain on-site work experience, and then learn the professional knowledge of ACSR Cable operation in order to be competent for the operation of cable line.

The above text is excerpted from the technical Q &amp; A on power cable installation and operation)
reference:
[1] Shi Chuanqing, editor in chief. Q &amp; A on power cable installation and operation technology. Beijing: China Electric Power Press, 2007
Requirements for technical training in DL / T 1253-2013 operation specification for power cable lines
7.8 technical training
7.8.1 cable operators shall receive special technical training and pass the examination before they can carry out various operation work, and post assessment shall be carried out at least once a year.
7.8.2 operators shall have the following basic knowledge and skills:
a) Relevant laws and regulations, systems, plans, standards, etc;
b) Basic theoretical knowledge of power cable line;
c) Drawing of cable route map;
d) Finding method of cable fault;
e) Cable test and live detection technology;
f) Various laying methods of ABC Cable lines;
g) Key points of process construction methods of various cable accessories;
h) Work at height on Tower:
i) State evaluation and state management requirements.


Relevant training discussion in the three-year action plan for improving the professional level of high voltage cable 2019-2021:
3. The contradiction between the high requirements for the whole process control of cables and the low level of personnel and equipment is becoming increasingly prominent
With the rapid growth of equipment scale and assets, the business volume of operation and maintenance, maintenance and engineering cooperation of cables and channels is growing rapidly. In order to ensure high reliability power supply of urban power grid, the requirements for the whole process control of high-voltage cables are becoming higher and higher. However, some cable professionals have insufficient skills in inspection, test, maintenance and project acceptance, lack of civil engineering and other professionals, insufficient equipment allocation for test and detection, and there is still a gap with the actual work requirements. At the same time, the training of professionals is still lack of the support of practical training system, and the talent training mode needs to be improved.

What is the difference between yttwy and ng-a btly mineral insulated cables?

Ng-a (btly) series isolated fire-resistant ACSR Cables are flame-retardant and fire-resistant cables. The insulating layer is phlogopite tape (fire resistance temperature 750 ℃ ~ 800 ℃), the sheath is aluminum tube (fire resistance temperature 660 ℃), and the outer sheath is plastic. It is not in the same category as yttw and bttz mineral insulated cables. We can make a comparison from the following technical data.
The structure diagram of yttwy copper core copper sheathed mineral insulated cable and ng-a btly isolated (flexible) mineral insulated cable is as follows:
(1) Yttw series metal sheathed inorganic mineral insulated cables are fireproof cables composed of copper core, copper sheath and inorganic mineral insulating materials. They are produced in strict accordance with the national industrial standard JG / t313-2014.
1) Yttw series metal sheathed inorganic mineral insulated cables are wrapped with natural inorganic mineral insulating tape (high temperature resistance above 1370 ℃). The sheath adopts copper sheath (high temperature resistance of 1083 ℃), which is continuously rolled, has fast heat dissipation and can be bent.
2) Metal sheathed inorganic mineral insulated cable can be made into pre branch cable to realize trunk power distribution system.

(2) Ng-a (btly) series isolated fire-resistant ABC Cables are organic and inorganic mixed fire-resistant cables, which will produce low smoke and low toxicity during combustion, which can not be compared with the smokeless and non-toxic of inorganic mineral insulated cables.
1) The refractory layer is made of glass fiber cloth, which is softened and damaged at about 840 ℃;
2) The filling layer adopts hydrated metal oxide, which is a gypsum like semi fluid containing organic components. During combustion, water vapor escapes and colloidal becomes solid (aluminum oxide). It is unclear whether it is toxic or not;
3) The isolation sleeve is generally cross-linked polyethylene (XLPE), with low smoke and low toxicity during combustion;
4) The metal sheath and aluminum material have poor mechanical and electrical properties. The flame temperature melts at 660 ℃, so it is not suitable for the metal sheath of fireproof cable;
5) The mineral insulation layer adopts phlogopite tape. The fire resistance characteristic of phlogopite is only class B (750 ℃ ~ 800 ℃), which can only be used as class B fire-resistant cable. It cannot be used in class A (950 ℃ ~ 1000 ℃) fire-resistant cables.
To sum up, yttw series metal sheathed inorganic mineral insulated cable has the following essential advantages compared with ng-a btly
a. The cable structure shall be free of any combustible organic material;
b. The high temperature resistance of the cable is greatly improved, and the calorific value is zero;
c. The cable is non combustible as a whole;
d. Non toxic and smokeless during cable combustion;
e. The thermal overload and long-lasting withstand voltage performance of the cable are greatly improved;
f. The durability of the cable has doubled.


Moreover, there is no unified standard for ng-a (btly) series isolated fire-resistant cables in China, and only individual manufacturers produce them according to enterprise standards.

How to skillfully use aluminum alloy cable in photovoltaic system?

The cost of control system is very important in the era of photovoltaic affordable Internet access. Over the past decade, the price of modules and inverters has decreased by 90%, which has made a great contribution to the overall cost reduction of photovoltaic system, but the cost of cables has not decreased. In large projects, the proportion of cables in the system reaches 10%, which is higher than that of inverters. In fact, as long as the design and installation are proper, on the premise of ensuring the normal operation and safety of the system, some AC cables adopt aluminum alloy cables, which can reduce some costs.
The cables of photovoltaic power station are divided into DC cables and AC cables. The DC cables between components and between components and inverter are generally required to use photovoltaic special DC cables, while the cables from inverter to AC distribution cabinet and from distribution cabinet to transformer are not required to use any ACSR Cables.


What is aluminum alloy cable: aluminum alloy cable is a new material power cable with aa8030 series aluminum alloy material as conductor. The resistivity of aluminum alloy is between aluminum and copper, higher than copper and slightly lower than aluminum. Under the premise of the same current carrying capacity, the weight of aluminum alloy conductor with the same length is only half of that of copper.
When the cross-sectional area of aluminum alloy conductor is 1.5 times that of copper, aluminum alloy ACSR Cable and copper cable achieve the same current carrying capacity, resistance and line loss.
Service life: different metal oxides are formed after the metal surface reacts with oxygen. Aluminum oxide can form a dense surface protective film with a certain hardness. Copper oxide, commonly known as copper green, is a toxic substance between the above two.
Economically, this is the most important aspect. The cost of aluminum alloy cable is about 25% ~ 50% of that of copper core cable. The cost advantage of aluminum alloy cable is relatively large. We can make a comparison. In a 400KW village level poverty alleviation power station, the distance from the AC distribution cabinet to the step-up transformer is 1500 meters, and the maximum output current of the 400KW power station is 580A. If copper cables are used, two 150 square meters are required for each phase and six for three phases, with a total length of 9000 meters and a price of 864000; If you use two 240 square meters of aluminum alloy, the total length is 9000 meters, and the price is 450000 yuan, 414000 yuan can be saved, and the loss of 240 square meters of aluminum wire is lower than that of 150 square meters of copper wire.


There is also a rare earth aluminum alloy cable, which is made of high elongation aluminum alloy material. By adding rare earth trace element materials such as boron to pure aluminum and treated by rolling technology and special annealing process, the cable has good flexibility. When its surface is in contact with air, it can form a thin and firm oxide layer, which can withstand all kinds of corrosion. Even when overloaded or overheated for a long time, it can ensure the stability of the connection, and the cost is about 10% higher than that of ordinary aluminum alloy cable.
Application scope of aluminum cable: aluminum cable can be considered for long-distance overhead line, underground cable trench with large space and places with reliable fixed bridge.
Precautions for use of aluminum cable:
The melting point of copper is 1080 ℃, while that of aluminum and aluminum alloy is 660 ℃, so copper conductor is a better choice for fire-resistant cable. At present, some aluminum alloy AAC Cable manufacturers claim that they can produce fire-resistant aluminum alloy cables and have passed the relevant national standard tests, but there is no difference between aluminum alloy cables and aluminum cables. If they are in the fire center, that is, when the temperature is higher than the melting point of aluminum alloy and aluminum cables, no matter what heat insulation measures are taken, the cables will melt in a very short time and lose their conductive function, Therefore, aluminum alloy should not be used as fire-resistant cable conductor, nor in densely populated urban distribution network, buildings, factories and mines.


Compared with aluminum core cable, the copper core is flexible, the allowable bending radius is small, and it is not easy to break after repeated bending. Therefore, aluminum cable should not be used when there are many bends, many pipes or complex lines.
As the terminals of electrical switchgear are made of copper, copper and aluminum are directly connected, and the chemical reaction of primary battery will occur after power on: aluminum with higher activity will accelerate oxidation, resulting in higher resistance and lower current carrying capacity at the joint. Therefore, some measures need to be taken when copper and aluminum are connected, such as using copper aluminum transition terminal or copper aluminum transition terminal block, Eliminate electrochemical reaction.