Matters needing attention in power cable installation

1. Keep a distance of 2m when the mine AAAC cable is installed in parallel with the thermal pipeline, and keep 0.5m when crossing.
2. When the cable is installed in parallel or across other pipes, a distance of 0.5m must be maintained.
3. When the cable is directly buried, the depth of the 1-35kV cable shall not be less than 0.7m.
4. When the cables of 10kV and below are installed in parallel, the mutual clear distance shall not be less than 0.1m, 10-35kV shall not be less than 0.25m, and the cross distance shall not be less than 0.5m.
5. The minimum bending radius of the cable must not be less than 15D for multi-core cables and 20D for single-core cables (D is the outer diameter of the cable).

6. Cable joints of 6kv and above.
A. When installing the cable terminal head, the semi-conductive shielding layer must be stripped off, and the insulation must not be damaged during operation. Knife marks and unevenness should be avoided, and sandpaper should be used if necessary. The shielding end should be flat and graphite The layer (carbon particles) is removed.
B. The copper shield and steel armor of the plastic insulated cable end must be well grounded. This principle should also be followed for short circuits to avoid induced electromotive force at the steel armor end during unbalanced operation of three-phase, or even “fire” and burn the sheath. Wait for the accident. The grounding lead wire should be tinned braided copper wire, and soldering iron should be used when connecting with the copper tape of the cable. It is not suitable to use a blowtorch to seal and solder, so as not to burn the insulation.
C. The three-phase copper shield should be connected to the ground wire separately. Note that the shield ground wire and the steel armor ground wire should be led out separately and insulated from each other. The position of the welding ground wire should be as low as possible.

7. The basic requirements for cable ends and intermediate joints: a. Good conductor connection; b. Reliable insulation, it is recommended to use radiation cross-linked heat-shrinkable silicone rubber insulating materials; c. Good sealing; d. Sufficient mechanical strength, Can adapt to various operating conditions.
8. The cable end must be waterproof and corroded by other corrosive materials to prevent breakdown due to aging of the insulation layer caused by water trees.
9. Cable loading and unloading must use cranes or forklifts. Horizontal transportation or laying flat is prohibited. When installing large cables, cable cars must be used to prevent cables from being damaged by external forces or scratching the insulation layer due to manual dragging.
10. If the cable cannot be laid in time for some reason, it should be stored in a dry place to prevent sun exposure and water ingress into the cable end.

What are the requirements for environmental protection cables

As the second largest manufacturing industry in China after automobile manufacturing, the wire and cable industry should also play a leading role in environmental protection. In recent years, environmentally friendly cables have become more and more popular in the market. In developed countries such as the European Union, non-environmental protection has been banned. Cables, China also attaches great importance to this aspect. China’s relevant laws and regulations explicitly require important buildings to prohibit the use of polyvinyl chloride wires and cables. Halogen-free and low-smoke cross-linked PVC wires and cables must be used to avoid a large amount of smoke and chlorine in the event of a fire. Casualties.
Environmental protection cables are the main direction of the future development of the cable industry, which can effectively enhance the competitiveness of cable companies. Because of the many excellent characteristics of environmental protection cables, they are also favored by more and more customers in the market.

Compared with ordinary cables, environmental protection cables have many excellent characteristics, such as no heavy metals, no halogens, no corrosive gas, no soil pollution, etc. If summed up, the requirements of environmental protection cables can be roughly divided into three aspects.
The first is that it does not contain heavy metals. Common PVC cables often contain heavy metals such as lead, cadmium and barium, which are harmful to the human body. Later, some countries stipulated that the content of eight types of heavy metals should not be higher than the specified value, and one of the main advantages of environmentally friendly cables It does not contain heavy metals, which is also its popular selling point in the market.
The second requirement of environmentally friendly cables is low-smoke and halogen-free. When ordinary cables are burnt, they will release a large amount of smoke and toxic gases, which will seriously pollute the air environment and cause harm to the human body. The low-smoke and halogen-free characteristics of environmentally friendly cables can not only protect the environment, but also It can help people evacuate and carry out fire rescue work when a fire occurs.

Secondly, it must be non-toxic. All component materials used in PVC formulations should be non-toxic. Cable material contains a lot of plasticizers, but non-toxic plasticizers must be used to make non-toxic materials. Therefore, this PVC material has higher requirements than lead-free and heavy metal-free materials, and the price is naturally more expensive.
Many countries have different requirements for environmental protection cables. For example, the European Union will restrict environmental protection cables containing asbestos. my country has not been as perfect as the EU in terms of related policy formulation and mandatory application. In this regard, China still has a long way to go. The way to go.

Factors restricting the development of the cable industry

The cable industry has developed to now, and the overall size is very large, with a large number of companies. China has surpassed the United States to become the world’s largest cable manufacturer. However, in this rapid development process, many problems have gradually been exposed.
The first problem is that there are few large domestic cable companies, and they lack competitiveness with foreign cable companies in high-end products. Even in 2018 or so, the annual output value of the top ten companies in  ACSR cable production scale is not as good as the total output value of the industry. 20% of the total, which is in sharp contrast with developed countries. However, it is roughly the same as my country’s current economic structure, and it is basically the same as that of other industries.

The second problem is that the homogeneity of products is serious and the market competition is fierce. There are a large number of cable companies in China, most of which are small and medium-sized enterprises. The operation mode, management and technical level of these companies present serious homogeneity problems. The problem of homogenization has aggravated overcapacity. In a homogeneous product market, users are mainly concerned with price, and competition is almost entirely concentrated on price. The greater the surplus of homogenized production capacity, the fiercer the price competition, the thinner the profit, and the more difficult it is for a company to survive.

The third problem is that the pressure of funds is huge. The xlpe cable industry is a typical heavy-material and light-industry industry and a capital-intensive industry. Therefore, the cable industry is always facing the pressure of the capital chain. The most significant phenomenon is the application of many companies. The total amount of money collected accounts for a high percentage of annual revenue, many of which are 30%. This also leads to financial difficulties for companies, and China’s cable industry is mostly small and medium-sized enterprises, so these companies are generally facing financial pressures. The problems of difficult financing, expensive financing, and high financing costs have sharply increased the risks in the capital chain of enterprises. In the past two years, due to the tightening of the entire financial system, many companies have found it difficult to cope and shut down and revert.

Talking about the definition and function of weak current wires

1. Definition of weak current wires
Weak current cables refer to cables used for security communications, electrical equipment and related weak current transmission. There is no strict boundary between “wire” and “cable”. Generally, products with a small number of cores, small product diameters, and simple structures are called wires, those without insulation are called bare wires, and the others are called cables; those with a larger conductor cross-sectional area (greater than 6 square millimeters) are called large wires. Small (less than or equal to 6 square millimeters) are called small wires, andXLPE insulated cables are also called cloth wires.
RVS fire wire
2. The role of weak current wires
The main processing object of weak wires is information, that is, the transmission and control of information, which is characterized by low voltage, low current, low power, and high frequency. The main consideration is the effect of information transmission, such as the fidelity, speed, breadth and reliability of information transmission, that is, the line that realizes the transmission of weak electrical signals.

RVVP shielded wire
3. Types of weak current wires
1. Telephone line, large logarithmic HYA: wire specifications are 2*1, 2*0.5, 4*1, 4*0.5, large logarithmic HYA has 10 pairs, 20 pairs, 30 pairs, 50 pairs, 100 pairs And so on, are all in pairs.
2. Video cable SYV series and SYWV series: SYV is a video cable for monitoring, such as video cable SYV75-5; SYWV is a cable TV cable, which belongs to physical foaming; there is also an elevator frequency cable SYXV.
3. Power cord RVV series: mainly used for weak current power supply, sometimes also used for control, such as RVV2*1.0.
4. RVS, RVB, RVVB series, including common type, fire-resistant type, and flame-retardant type. RVS is generally used in fire fighting systems.
5. Network cable: UTP is unshielded, FTP is shielded, such as: Category 5 unshielded network cable UTPCAT.5e, Category 6 shielded network cable is FTPCAT.6e.
6. Shielded wire RVVP series: The appearance is similar to the RVV power cord, except that there is an extra layer of shielding net in the structure, and a letter P is added to the model. Generally, wires with P have a shielding layer.

Why should the length of power cable be reserved?

It is very difficult to repair and replace600V 90°C XLPE ACWU90 AC90 Cable, especially when the middle section is in trouble, because the cable is laid in the open, the bridge, the buried, the cable trench and the pipe. So in the cable laying is required to reserve. Not only in the cable trench in the feeder, but also to reserve the end; if it is tube or cable trench laying, in the middle of the maintenance wells to reserve a certain length.

Advantages: When the power cable is connected to the feeder circuit or equipment, the copper nose needs to be pressed and the outer protective layer of the cable needs to be removed And the distribution cabinet, control cabinet itself is also relatively easy to affect the cable, so the cable in both ends need to reserve a certain length to deal with the subsequent maintenance.

Otherwise, it will be difficult to deal with the problem in the figure below. The advantage of the reserved maintenance well: When the power cable is laid secretly, a maintenance well must be set up at a certain distance, which is mainly used to deal with the inspection and repair of the fault in the middle part ofPVC XLPE Insulated Power Cable 25mm² ~ 400mm². If a section is damaged by external forces or problems, the amount reserved in the manhole can be used nearby, making maintenance convenient and time-saving. Otherwise, it is very difficult to deal with the following problem.

Other benefits: due to the general cable laying path is generally more complex, often need to turn bend, calculation of cable length can not be accurate, appropriate length can also be reserved for laying a variety of special circumstances.

Cable maintenance tips

Everyone knows that everything will deteriorate after being used for a long time, and the same goes for wires. WhenAerial Bundled Cable (ABC) HD 626 S1 Standard is aging for household or commercial use, it is easy to cause danger if it continues to be used, and timely inspection can eliminate potential safety hazards. But how to detect wire aging in time requires some tricks.
The wire is mainly insulated by the outer layer of sheath. After a long time, it will be corroded by corrosive gas, and the insulation performance will gradually decrease. It will gradually age and become hard, become brittle or fall off, and then it will not be insulated. In fact, the direct cause of the aging failure of the wire and cable is the breakdown of the insulation due to the degradation.
1. “Check the appearance along the wire, darkening and hard cracks are seen. Bending the wire with both hands for insulation, stiff and cracked skin.” It means to observe the insulation layer along the wire. If the color of the insulation layer is found to be tarnished, darkened, or changed Hard, cracked, and partially peeled off.

When the insulated conductor is bent with both hands, the wire is stiff, even the insulation layer is cracked, the insulation layer falls off, etc., which shows that the wire has experienced different degrees of aging and severe aging.
2. “Accurate method to measure insulation, megohm is not low. The humidity value in rainy days can be small, and the value can be less than half.” It means that the insulation resistance meter can be used to measure the insulation of electrical circuits to determine the insulation status of the circuit more accurately.

3. If the wires cannot be replaced in time, you can also choose to use good internal materials to reduce hidden dangers. Once the insulation of the sheath of the wire casing is damaged, the possibility of fire will increase. The length of time for causing a disaster has a lot to do with the quality of the oxygen barrier. The newly produced diamond mud ceramic silica gel with silicone rubber as the base material by Shanghai Tengruina Chemical Technology Co., Ltd. has good high temperature resistance, fire resistance and fire resistance. The effective prevention and control of fire sources is to prevent fires to a certain extent. avoid lost. If there is a fire around the line, the shell of diamond mud ceramic silicon rubber can also ensure that it will not melt or drip in the flame, which effectively protects the normal use of the line and avoids explosions.
Finally, the editor still has a small reminder: the wire is aging, and the wire needs to be replaced in time. Don’t have a fluke mentality. The diamond mud oxygen barrier can only reduce the possibility of fire. Once a fire occurs, it will affect manpower, material resources and financial resources. The losses should not be underestimated!

What effect does the cable sheath have on the PVC Sheath Flexible Cable ?

The sheath is the “skin” of the wire and cable and the appearance that people look directly at. It must be smooth and round, uniform in color, not eccentric, not damaged, free of impurities, free of bubbles, and not flattened, twisted, etc., except In addition to being unsightly, the thickness of the sheath also has a certain impact on the quality of H05VV-F H03VV-F PVC Insulated cable.

  1. Reduce service life
    After the cable is laid, it will be energized for a long time, which will generate heat. The allowable working temperature of the conductor is 70℃. The long-term use temperature of polyvinyl chloride should not exceed 65℃. If it is summer, the working temperature will rise, and these temperatures will pass outside. When the sheath is emitted, the thickness of the sheath increases, and the heat energy is difficult to dissipate, which will affect the service life of the cable. Due to the heat of PVC, the insulation layer will undergo a series of physical and chemical changes and lose its original excellent performance. , Resulting in a significant decrease in insulation performance, and even a short circuit, affecting the normal operation of the unit.
  2. Material performance defects
    The performance of the material is not reflected by the thickness. According to the requirements of the GB8815-2002 standard, if one of its indicators does not meet the standard, the flame-retardant PVC material, its oxygen index is lower than 30.
  1. There are problems with the cable structure
    Conductor, insulation layer, and braid density are strictly controlled in accordance with the requirements of the standard. If the outer diameter of the cable is normal but the sheath is too thick, it is very likely that other structures are cutting corners.
  2. Increase the difficulty of cable laying
    At present, cable laying is mainly based on bridges or pipes. Many companies are implementing tight cable requirements and small outer diameters. There can be gaps during the laying process to dissipate heat and ensure that the outer sheath of PVC cable is not damaged. Otherwise, the construction unit and Cable laying brings difficulties.
    To sum up, the thickness of the sheath should be strictly controlled in accordance with the standard, which not only saves resources, reduces material consumption, and increases profits for the enterprise, but also ensures the quality of the cable and creates high-quality and low-cost products.

the advantages of overhead insulated cables

The Aerial Bundled Cable series products are composed of pressed copper, aluminum (aluminum alloy) conductors, inner shielding layer, weather-resistant insulating material and outer shielding layer. They have both the power transmission characteristics of power cables and the strong mechanical properties of overhead cables. Compared with bare wires, this product has the advantages of small laying spacing, high safety and reliability, and excellent resistance to atmospheric aging
  1. Uses of overhead insulated cables Overhead insulated cable products are a new series of products for power transmission through overhead transmission lines, and are preferred for power grid construction and transformation of 10kV transmission lines. It is the most suitable series of products for line maintenance and safety. Soft copper core products are suitable for the lower leads of transformers.
  2. Overhead cable implementation standards
  3. 1KV overhead insulated cable: GB12527-90 is equivalent to the International Electrotechnical Commission IEC60502, IEC227;
  4. 10KV overhead insulated cable: GB14049-93 is equivalent to the International Electrotechnical Commission IEC60502. Overhead insulated cable Third, the characteristics of (ABC) HD 626 S1 Standard
  5. Rated voltage: 0.6/1KV, 10KV;
  6. The long-term allowable working temperature of the cable: 70°C for PVC insulation and 90°C for XLPE insulation.
  1. When short-circuited (the longest time is no more than 5 seconds), the maximum temperature of the cable: 160°C for PVC insulation, 150°C for high-density polyethylene insulation, and 250°C for cross-linked polyethylene insulation;
  2. The ambient temperature during cable laying is not lower than -20℃;
  3. Allowable bending radius of cable: (1) Cables with rated voltage below 1KV: cable outer diameter (D) less than 25mm should not be less than 4D, cable outer diameter (D) of 25mm and above, should not be less than 6D;
  1. (2) The rated voltage of 10KV cable should not be less than 20 (D+d). Where: D—the actual outer diameter of the cable, d—the actual outer diameter of the cable conductor. Overhead fixed laying of soft copper core products is used for transformer down-conductor; when laying cables, a certain distance between cables and trees should be considered, and frequent contact between cables and trees is allowed during cable operation. For overhead fixed laying and cable erection, a certain distance between the cable and the tree should be considered, and frequent contact between the cable and the tree is allowed when the cable is running. Overhead fixed laying; When installing cables, consider keeping a certain distance between cables and trees. When cables are running, only short-term contact between cables and trees is allowed.

Analysis of commonly used PVC materials for wire and cable sheath

Commonly used plastics for wires and cables include polyethylene, cross-linked polyethylene, polyvinyl chloride, polypropylene, polyolefin, fluoroplastics, nylon, etc.
Polyethylene is currently the most widely used plastic with the largest consumption. From the data in the table, it can be seen that polyethylene has low meson loss, high resistivity, high breakdown field strength, good weather resistance and manufacturability. It is currently the best electrical Insulation Materials. However, due to its low operating temperature, it is mainly used as insulation for communication cables. Medium-density and high-density polyethylene have high strength and hardness, and their water permeability is low, and they are mostly used as cable sheaths. However, polyethylene has the biggest disadvantage, that is, it is easy to burn and has strong black smoke, so its application brings many hidden dangers to the environment.
Cross-linked polyethylene is an excellent thermosetting insulating material formed by adding a cross-linking agent to low-density polyethylene. On the basis of inheriting many excellent properties of polyethylene, it has improved mechanical properties, weather resistance and allowable working temperature, thus becoming the best insulation material for power cables.
Due to the different crosslinking agents added, different crosslinking processes are formed. At present, there are three kinds of chemical crosslinking, warm water crosslinking, and radiation crosslinking that are most used. Chemical crosslinking is mainly used for medium and high voltage cables (such as 10KV and above); warm water crosslinking and radiation crosslinking are mainly used for low voltage cables (1kV and below).
The insulation conductor performance of cross-linked polyethylene is closely related to its purity. The insulation of high-voltage and ultra-high voltage cables above 35KV must be made of ultra-clean cross-linked polyethylene, which not only requires high purity of raw materials, but also requires high cleanliness of cross-linking process equipment and environment, and the process is stable and reliable.
It should be particularly pointed out that the insulation properties of polyethylene and cross-linked polyethylene have a “quirk”, that is, they are suitable for AC insulation, not DC insulation, especially DC high voltage will reduce their insulation life. Therefore, the insulation of DC cables is mostly rubber insulation or oil-paper insulation. Furthermore, polyethylene and cross-linked polyethylene insulation have “waterphobia”, and their breakdown is often related to the presence of water, that is, “water branches” are formed under high voltage, leading to insulation damage. Therefore, when polyethylene and cross-linked polyethylene are used for the insulation of high-voltage and ultra-high-voltage cables, they are particularly “water-proof” during their processing, storage and transportation, and insulation extrusion, and there should be a water-blocking structure outside the cable insulation shield, such as metal jacket.
Compared with polyethylene, polyvinyl chloride and paper insulation, one of the biggest advantages of cross-linked polyethylene insulation is that the working temperature is increased by 20°C, which improves the safety of the cable and reduces the input cost of the cable. For example, when the line flow is the same (such as 300A), the cross-sectional area of ​​the copper conductor of the polyethylene or PVC insulated cable (such as the YV type or VV type) needs 120mm2, while the cross-linked polyethylene insulation tape male basketball copper conductor cross-sectional area only needs 70mm2 is sufficient. It can be seen how remarkable the advantages of cross-linked polyethylene insulated cables are.
Polyvinyl chloride has good physical and mechanical properties and excellent process performance. It is the most used plastic in the 20th century. It is also the main insulation material and sheath material for low-voltage wires and cables. But entering the 21st century, PVC will gradually shrink or even fade out in the cable market. There are two reasons for this. On the one hand, people’s safety awareness has increased and they hope to adopt halogen-free materials, so many halogen-free materials have emerged. There is no doubt that it will become the new favorite of the 21st century cable industry and squeeze the market. On the other hand, PVC has five weaknesses: one is its high density, which is about 1.5 times that of cross-linked polyethylene, and its insulation cost is high; the other is its low working temperature; and the third is its higher dielectric loss than cross-linked polyethylene. One hundred times higher; fourth, poor cold resistance (brittle at -15 degrees); fifth, toxic gas (HCL) is released during combustion. In recent years, the mechanical properties, electrical heating properties, and insulation resistance of cross-linked polyvinyl chloride developed in recent years have been greatly improved. Some small cross-section cables have been introduced into the market by irradiation technology, and they have been used in equipment and installation wires, high-voltage lead wires, automotive wires and building wiring. Application, but its shortcoming of halogen cannot be changed.
Fluoroplastics are widely used in wires and cables due to their high working temperature, small medium, insulation, weather resistance, acid and alkali resistance, oil resistance, and good flame retardancy. Among them, polyperfluoroethylene propylene is particularly popular due to its good manufacturability. But it is expensive, and users have to think twice.
Low-smoke halogen-free polyolefin is a new type of cable sheathing material that has not been developed in the 20th century. Its greatest advantage is its flame retardancy, low smoke and non-toxic gas during combustion, and it is increasingly widely used in important public buildings.

Different influencing factors, the degree of cross-linking of cross-linked cables is also different

Cross-linked cable is the abbreviation of cross-linked polyethylene insulated cable. It is composed of conductor, insulating material, internal and external semi-conductive material, sheath material, shielded copper tape, armored steel tape/steel wire, inner lining, isolation sleeve, filling material, etc. Part of the cable. Different components have their own usage requirements and characteristics. For example, XLPE insulated cables are the insulating medium material of XLPE, and the temperature resistance can reach 90°C. Therefore, the XLPE insulated cables cannot Compared with the advantages, it has simple structure, light weight, good heat resistance, strong load capacity, non-melting, chemical resistance, and high mechanical strength. It is mostly used in power transmission and distribution lines with power frequency AC voltage of 500KV and below.
In order to improve the temperature resistance of polyethylene, chemical or physical methods are usually used to make it into a body-shaped molecular structure. This is called cross-linking, which is the basic principle of cross-linking. So, do you know what is the degree of cross-linking of cross-linked cables? The following is an introduction to the factors that affect the degree of cross-linking of cross-linked cables for your reference.
1. Temperature
The temperature here not only refers to the working temperature of the cross-linked cable during cross-linking, but also includes the extrusion temperature. Specifically, it is:
(1) The cross-linking process is completed in the heating section of the vulcanized tube. Therefore, when other factors remain unchanged, the higher the temperature of the vulcanized tube, the higher the degree of cross-linking of the cross-linked cable. This is a certain point. Generally speaking, considering various factors, the temperature of the vulcanized tube for dry cross-linking should be around 290~310℃, otherwise the cross-linking degree of the cross-linked cable during cross-linking will be affected and will be greatly changed. Small, it is not a good thing for the use of cross-linked cables.
(2) Extrusion temperature. Because the cross-linked cable is processed, an extruder is required. If the cross-linking degree of the cross-linked cable is suitable, it is necessary to use a suitable extrusion temperature during the processing of the extruder, and the extrusion temperature may be related to the formula of the raw material, so this requires The material is fully plasticized without pre-crosslinking.
2. Linear speed during crosslinking
Obviously, the higher the line speed, the higher the production efficiency, but the degree of crosslinking will be lower. Therefore, when crosslinking, the line speed should be suitable. The line speed will be affected by factors such as rated voltage, cable specifications, cooling water temperature and water level, vulcanizing tube, etc. The larger the cable cross section, the greater the amount of glue required from the extruder, so the line speed cannot be too fast; The higher the temperature and the longer the pipeline, the faster the line speed; the higher the voltage, the thicker the insulation and the slower the crosslinking speed…
Well, the above is an introduction to the factors that affect the degree of cross-linking of cross-linked cables. I hope everyone can understand, and then cross-link correctly according to actual conditions and requirements.