Insulating materials and shielding materials for power cables, especially materials for high-voltage and ultra-high-voltage XLPE insulated AAAC Cables, are prominent “soft ribs” or “short boards” of China’s cable industry in this field (all sheath materials have been localized).
1. Medium and low voltage power cable materials
Medium and low voltage power cables are mostly insulated with cross-linked polyethylene (XLPE). XLPE takes low-density polyethylene resin (LDPE below) as the main raw material, adds antioxidant and peroxide cross-linking agent, and is made into cable material through mixing, plasticization and granulation. It has many categories, including chemical cross-linking, hospital cross-linking, irradiation cross-linking, ultraviolet cross-linking, etc. XLPE insulating materials of 35kV and below have all been localized.
Among them, chemical crosslinking and silane crosslinking technologies and applications are very mature, irradiation crosslinking and UV crosslinking materials have also been widely used, and water tree resistant materials for medium voltage cables have been more and more applied.
The performance of XLPE insulating materials of 35kV and below fully meets the use requirements, but there are still gaps in process performance stability and long-term service life reliability compared with foreign advanced products: first, the performance stability of synthetic resin in chemical industry; Second, the fierce market competition forces the cable material production enterprises to consider the cost too much and seek to use low-cost raw materials.
Domestic manufacturers with batch supply capacity of 35kV XLPE cable materials mainly include Zhejiang Wanma polymer, Qingdao hancable, Shanghai chemical plant, Henan Wanbo Plastic Co., Ltd.
2. 110kV High Voltage Cable Materials
High voltage and ultra-high voltage ACSR Cables require that the insulating materials must be ultra purified. The main foreign suppliers are petrochemical enterprises, which complete the manufacturing from the fully enclosed ultra purification production process of petroleum cracking ethylene polymerization ultra clean material synthesis, such as Nordic chemical, Dow Chemical of the United States, NUC of Japan, Hanhua of Korea, etc.
At the initial stage of domestic high-voltage cable manufacturing (including the early 35kV cross-linked polyethylene cable material), all imported materials are used, especially Nordic chemical and American Dow Chemical (formerly United Carbon Corporation) account for a relatively high proportion in the domestic market.
During the 12th Five Year Plan period, China’s 110kV high-voltage cable insulation material made a technological breakthrough and realized domestic small batch production. Since 2012, 110kV ultra clean insulation material has been gradually used in cable manufacturing and power engineering.
During the 13th Five Year Plan period, great progress was made through independent research and development, introduction of key process equipment and cooperation with upstream petrochemical enterprises. Among them, major high-voltage cable manufacturing enterprises or cable material manufacturing enterprises jointly with petrochemical enterprises to form a preliminary manufacturing chain from basic resin synthesis to cable material manufacturing and then to high-voltage cable manufacturing and application. For example, the cooperation between Qingdao hancable Co., Ltd. and Yanshan Petrochemical Company, the cooperation between Zhejiang Wanma Gaoli Materials Co., Ltd. and Yangzi Petrochemical Company, the cooperation between Jiangsu Dewei new materials Co., Ltd. and Yangzi BASF company, and the introduction of a full set of equipment and technology by Yanshan Petrochemical Company have formed mass production capacity.
At present, the process technology and production capacity of producing high-voltage cross-linked polyethylene insulating material and shielding material with different equipment and process methods have been formed, with a total production capacity of about 80000 tons / year (including the material capacity for ultra-high voltage cable).
3. EHV cable materials
Insulation and shielding materials for 220kV EHV AAC Cables have higher requirements for purification, such as impurity content, quantity and size. The main bottleneck of ultra clean insulating material is the localized supply of ultra clean special raw material LDPE. In addition to the basic resin, the selection of compounding agent system, formulation technology, storage and transportation environment of insulating materials, factory production environment, etc. will eventually affect the insulation performance of cables.
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The main problems of LDPE raw materials are processing rheological properties, melt index, molecular weight distribution uniformity, impurity content and other technical requirements. First, there are strict requirements on the fluctuation range of LDPE melt index, which determines the softening temperature range of LDPE and ensures the uniform plasticization of cable insulation layer, process dimensional stability and surface smoothness under certain process conditions. Second, the requirements for impurity content are very strict. The production workshop is required to reach level 1000, and the special process is even level 100. Materials do not contact with the outside world from production, packaging (tank car or pipeline) to use. Pay attention to the control of impurities and water content from the beginning of resin synthesis.
At present, Qingdao hancable Co., Ltd., Zhejiang Wanma polymer Co., Ltd. and Jiangsu Dewei new materials Co., Ltd. have the batch production capacity of super clean XLPE insulation and shielding materials for 220kV EHV cables, but the actual use is almost imported, with an annual consumption of more than 20000 tons, and the consumption of domestic materials is very small.
Semi conductive shielding materials for high-voltage and ultra-high-voltage cables are mainly used for the internal and external shielding layers of high-voltage XLPE cables. They are also required to be super clean and super smooth. The impurity content in the shielding material, the smoothness of the shielding layer and the adhesion between the shielding layer and the insulating layer will greatly affect the performance of XLPE cable. At present, several domestic semi-conductive shielding materials for 35kV and below cables have been produced and can meet the cable performance requirements, but the semi-conductive shielding materials for 110kV and above have more stringent requirements on basic resin, additives, carbon black types, extrusion equipment, manufacturing process and production environment. China is still in the stage of R & D and trial in this field, The shielding materials used are mainly imported by Nordic chemical and Dow chemical companies, and a small amount are provided by domestic enterprises.
According to statistics, the total domestic annual demand for insulation and shielding materials (including submarine cables and DC cables) for 110kV and above high-voltage and ultra-high-voltage cross-linked cables in 2019 is about 70000 tons, of which the actual use of domestic materials is about 10000 tons (mainly 110kV land AC cables), and another about 2000 tons are exported to the international market.
At present, compared with international advanced technologies, processes and products, the domestic production of 110kV and above XLPE ultra clean cable materials mainly has the following gaps:
1) There is a lack of systematic research on the basic resin of ultra-high pressure and ultra clean polyolefin material, and the development, polymerization, ultra clean synthesis process and material performance evaluation technology of basic resin need to be solved urgently;
2) As the domestic production process from the preparation of ultra clean polyethylene resin to the synthesis of ultra clean materials has not been formed, it brings new difficulties to the storage and transportation guarantee. There are also many new technical problems in the ultra clean technology and process of ultra clean material preparation (including impurity filtration technology, performance evaluation and quality control system) to ensure the stability and continuity of polyolefin cable material preparation;
3) The production time of localization is not long, and more process test and application data still need to be accumulated. In particular, the evaluation and evaluation of the long-term service reliability of the made cable is also an important work to obtain the full confidence of power users in the materials and recognize the application.
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4. Materials for high voltage and ultra-high voltage submarine cables
High voltage and ultra-high voltage submarine cables require higher production technology and more complex service environment, so they have higher requirements for cable materials.
At present, the most important raw materials for the production of high-voltage submarine cables – insulating materials and shielding materials have not been localized. Whether it is AC high-voltage submarine cables or DC high-voltage submarine cables, only Nordic chemical and American Dow Chemical Company can provide them in the international market.
The insulation and shielding materials of high-voltage and ultra-high-voltage submarine cables used by China’s submarine cable manufacturing enterprises all rely on imports, including DC cable materials. Due to the imbalance between supply and demand, there is an obvious seller’s market. The R & D and production of high-voltage submarine cable insulation and shielding materials is also an urgent task for China’s cable industry. It is necessary to continue to deepen research and production on the basis of localization of high-voltage and ultra-high-voltage cable materials.
concentric cable
The causes and solutions of overheating of wires and cables
When the power cable passes through a certain load current, it will be heated. With the increase of load current, the higher the cable surface temperature is. If it is not managed in time, the consequences can be imagined. For example, PVC cable is considered with core temperature of 70 ℃ as the upper limit, and the surface temperature will be 5-10 degrees lower. Therefore, the ACSR Cable surface temperature is basically safe below 60 degrees. Considering the power supply maintenance, the lower the temperature is, the better.
The causes of heating during operation of cables are as follows:
1. The resistance of ABC Cable conductor does not meet the requirements, which causes the cable to generate heat during operation.
2. Improper cable selection causes the conductor cross-section of the cable used is too small, and overload occurs during operation. After a long time of use, the heating and heat dissipation imbalance of the cable cause heating phenomenon.
3. The cable is arranged too densely, the ventilation and heat dissipation effect is not good, or the cable is too close to other heat sources, which affects the normal heat dissipation of the cable, and may also cause the heating phenomenon of the cable in operation.
4. The joint manufacturing technology is not good, and the crimping is not tight, which causes the contact resistance at the joint is too large, and the cable will generate heat.
5. The insulation performance of the cable is not good, which causes the insulation resistance is small, and the heating phenomenon will also occur in the operation.
6. The partial sheath of armored cable is damaged, which causes slow damage to the insulation performance after water inflow, which results in the gradual decrease of insulation resistance and also the heating phenomenon in the operation of the cable.
After the cable has a heating phenomenon, if the cause is not found, the cable will continue to be powered on continuously and will cause insulation thermal breakdown. The short circuit between phases of the cable trip phenomenon, serious fire may be caused.
After the cable has a heating phenomenon, if the cause is not found, the cable will continue to be powered on continuously and will cause insulation thermal breakdown. The short circuit between phases of the cable trip phenomenon, serious fire may be caused.
The reason and solution of plug power cord heating are everywhere in family life. The electric appliances can not be separated from the power cord. This small power cord may despise him.
The heat of the power cord of water heater is usually caused by the poor coordination with the socket. Meanwhile, the normal heating phenomenon should be considered. If the surface temperature of the plug is less than the ambient temperature plus 50 ℃, it is normal. If abnormal heat is abnormal, it is necessary to consider replacing the socket or checking the cooperation between the plug and the socket.
1. the connection between plug and socket is poor, and the load power is high, which causes the plug to heat up. Such as electric kettle, electric iron, etc.
2. the thread head in the new plug is loose, which is caused by rough production process and other reasons.
3. the old plug is used for a long time, and the insulation performance is reduced (or the plug is loose).
How to use plug wire safely
The main reason for the heating of plug wire is that the load of the wire is increased due to the long-term power consumption of electrical equipment. Special multi-function socket, if connected with several high-power electrical equipment at the same time, the power line of the socket must be overloaded, and in that case, it is very easy to cause the wire to burn.
Therefore, we should pay attention to the reasonable distribution of electricity in our life, and regularly check the plug wires and sockets to see if the wires are old and whether the contact between the plug and socket is bad. Sometimes because the production department process is not fine, the plug wire head will not be firm, so the plug in the plug power supply will cause poor contact and lead to plug heating. At the same time, every household should pay attention to that the plug will be old for a long time, and the insulation property will be reduced. It should be replaced in time. For plug wires of high-power appliances, we suggest that the wire core is used to increase the type, and it is better to use the pin with grounding. If it is found that the power socket or wire plug is hot, which causes the electric appliances to burn, do not act recklessly, and take care of the management.
For more information on cables, click Joy ’cable Blog
What is the difference between copper conductor and copper alloy cable?
Copper bar is the main raw material of AAC Cable industry. There are two main production methods: continuous casting, continuous rolling and continuous casting. Due to different processes, the oxygen content and appearance of copper rods are also different. When the oxygen content is lower than 10ppm, it is called oxygen free copper rod; When the oxygen content is less than 10ppm, it is called oxygen free copper rod.
Low oxygen copper rod
Disadvantages of process D:
The electrolytic copper melts when it is added. There is no complete reduction condition for copper water. The whole smelting process and copper water process are inseparable from oxygen, so the oxygen content is very high. The fuel for molten copper is usually gas. In the process of gas combustion, it will directly affect the chemical composition of liquid copper. Sulfur and hydrogen are the most important factors.
Process advantages:
(1) High yield. Generally, the output of small units can reach 10-14 tons per hour.
(2) The layout of copper bar adopts plum blossom type, which is convenient for wire drawing machine.
(3) Bearing capacity, generally not more than 4 tons per plate.
Grade and characteristics of low oxygen copper rod: low oxygen copper rod
It is divided into three levels: T1, T2 and T3. The low oxygen copper bar is hot rolled, so it is a soft bar, code R.
(1) T1: production of low oxygen copper rod with high purity electrolytic copper as raw material (copper content greater than 99.9975%).
(2)T2：1 × The low oxygen copper rod (copper content above 99.95%) is made of electrolytic copper.
(3)T3：2 × The low oxygen copper rod (copper content above 99.90%) is made of electrolytic copper. Due to high purity electrolytic copper and 2 × Electrolytic copper is very few, generally 1 × Electrolytic copper is used as raw material, so the grade of low oxygen copper rod is T2R.
Oxygen free copper rod
Oxygen free copper rod is pure copper without oxygen or any deoxidizer residue. But in fact, it still contains a very small amount of oxygen and some impurities. According to the standard, the oxygen content is not more than 0.02%, the total impurity content is not more than 0.05%, and the copper purity is more than 99.95%.
It is generally produced by electrolytic copper, and its resistivity is lower than that of low oxygen copper rod. Therefore, oxygen free copper rod is more economical in the production of products with strict resistance requirements; High quality raw materials are needed to make oxygen free copper rods;
According to the oxygen content and impurity content, the oxygen free copper rod can be divided into TU1 and TU2 copper rods. The purity of TU1 oxygen free copper rod is 99.99%, and the oxygen content is not more than 0.001%; The purity of TU2 oxygen free copper is 99.95%, and the oxygen content is not more than 0.002%.
The difference between the two
Due to different manufacturing methods, low oxygen copper rod and oxygen free copper rod have their own characteristics.
1、 On the removal of oxygen and its existing state
Oxygen content of low oxygen copper rod is generally 200 (175) – 400 (450) ppm, so oxygen is inhaled into liquid copper. On the contrary, the oxygen in the oxygen free copper rod is reduced and removed after a certain period of time. Generally, the oxygen content of bar is below 10-50ppm, and the lowest is 1-2ppm. Oxygen content in oxygen free copper is very low, so the structure of copper is uniform and single-phase, which is conducive to toughness.
2. Difference between impurity content and existing hot rolling defects
The tensile properties of oxygen free copper bar are better than that of oxygen free copper bar in all wire diameters. In addition to the above microstructure reasons, the oxygen content of oxygen free copper bar is less and stable, there is no possible defect in hot rolling, the oxygen monitoring is not strict, and the oxygen content is unstable, which will directly affect the performance of copper bar. If the oxide on the surface of the bar can be made up in the continuous cleaning of the subsequent process, the problem is that there are quite a lot of oxide under the skin, which has a more direct impact on the broken wire.
3. The toughness of low oxygen copper rod is different from that of oxygen free copper rod
Both can be pulled to 0.015 mm, but the distance between low temperature grade oxygen free copper wires is only 0.001 mm.
4. Low oxygen copper rod
The wire making process of copper rod is different from that of oxygen free copper rod. The wire making process of low oxygen copper bar should be the same as that of oxygen free copper bar, at least the annealing process of the two should be different. Because the softness of wire rod is greatly affected by material composition, bar manufacturing, wire manufacturing and annealing process, it can not be simply said that low oxygen copper or oxygen free copper is soft or hard.
For more information on cables, click Joy ’cable Blog
Composition of flexible mineral insulated cable (bbtrz)
Flexible mineral insulated acsr cable is composed of copper strand, mineral compound insulation and mineral compound sheath. It adopts flexible structure, and the main materials are inorganic materials, which make up for the defects of hard structure, easy to burn and toxic. It also has some advantages that other cables can not have, such as: fire resistance, high load flow, impact voltage resistance, mechanical damage resistance, halogen-free, non-toxic, explosion-proof, waterproof, corrosion-resistant, long life, safety, overload resistance, high temperature resistance and low cost.
The flexible mineral insulated cable (bbtrz) has the characteristics of general products. Because the insulation is made of organic polymer, it is easy to carbonize and lose its insulation function under the condition of flame. Because the main materials of flexible mineral insulated fire-proof cable (bbtrz) are composed of mineral compounds, it will not cause fire itself, and it is impossible to burn or support combustion. These materials generally have a high melting point of more than 1500 ℃, so fire-proof cable can play a normal transmission function even when used in flame condition, which is a kind of fire-proof cable in the real sense.
The process structure of the flexible mineral insulated fire-proof cable (bbtrz) is identical with the traditional cable. It successfully solves many shortcomings of the products determined by the production process of the bttz.
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Advantages summary:
1. It is really flexible, and the structure is as soft as the ordinary aaac cable.
2. The process structure is the same as that of ordinary cable, and the theoretical production is infinite, and one cable can be produced with fixed length
3. The installation is without joint, the construction is simple, the reliability is improved and the cost of investment is reduced.
4. The multi-core can produce 300mm2, overcome the shortage of single core with rigid bttz of 25mm2 or more. 5. The cable can be reused if the line is reconstructed and adjusted.
Characteristics of flexible mineral insulated cables
1. improve the insulation stability: not only the fire resistance of rigid mineral insulated cable is retained, but also the characteristics of not suitable for moisture absorption, so the insulation is more stable.
2. the voltage resistance level is improved: the voltage withstand level can reach 1000V, which reduces the impact voltage caused by the frequent start of inductor and frequency converter, and correspondingly improves the service life of the line system.
3. full series: it can be processed into single core or multi-core structure according to the actual needs of users, and can achieve 96 cores at most, covering almost all kinds of building cable requirements of power cable and control cable.
4. no intermediate joint: mature strand and cable forming technology are adopted, which can be produced according to the user requirements, not only reducing the cost of joint, but also improving and realizing the whole line consistency.
5. flexible and easy to install: because of the traditional cable structure such as strand and cable forming, the cable is softer, and it is more convenient to install and lay because of the need for special terminal joint.
6. space saving: because of the multi-core cable with large section and large length, unnecessary waste of laying space caused by multiple arrangement and intermediate joints is avoided.
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7. public welfare: due to the improvement of structure, a large number of minerals and mineral compounds are used, which not only saves copper, magnesium and other resources, but also saves a lot of energy consumption correspondingly. The public welfare value is also very significant.
Installation and laying of flexible mineral cable
When cables are laid in open, cable supports, hooks or metal ropes shall be used along the whole length. The maximum span shall meet the following requirements:
1. meet the bearing capacity of support parts, the outer layer of the non-destructive cable and its cable core;
2. make sure the cables can be arranged neatly with each other;
3. adapt to the layout requirements under working conditions
Flexible mineral insulated fire-proof cable can ensure emergency use after installation. It can also be used as halogen-free flame retardant cable and fire-resistant cable with temperature resistance of 125 ℃ at ordinary times. Because of its wide coverage, it overcomes the defects of rigid Mi cable, plays the advantages of flexible Mi cable, and provides practical products for key projects, especially in the application of super high-rise buildings, It makes people’s life and property security guaranteed reliably, and promotes the broad development of their industry.
What specifications should be used for household wires?
Home wiring is an indispensable part of our life, and the quality of pvc wire selection will be directly related to home safety. Home safety is your own safety, so you must compare more when you buy, choose the wire with guaranteed quality. So what specifications should the general home wiring choose? What about the BVR copper wire for home decoration? Now I will make a simple analysis for you.
General home decoration line specifications
The power cord for home decoration generally adopts BV2 × 2.5 and bvv2 × 1.5 model of BVV line, BVV line is the national standard code, copper sheath line bvv2 × 2.5 and bvv2 × 1.5 represents 2-core 2.5 square mm and 2-core 1.5 square mm respectively. In general, bvv2 × 2.5 main line, bvv2 × 1.5 make single electrical branch line, switch line, share bvv2 for air conditioning special line × 4 model, with special ground wire.
We all know that BVV wires are commonly used in household wires, and there is another kind of BVR wires. How much do you know about BVR wires?
BVR copper core flexible wire for home decoration
BVR wire is a kind of special soft wire for distribution cabinet, also called secondary wire. The full name is PVC insulated non sheathed wire and cable, the model specification and rated voltage are BVR 450 / 750V 2.5-95, and the production execution standard is JB / T 8734.2-2012.
The copper core PVC insulated flexible wire is used in the occasions where the fixed wiring requires softness, and the conductor temperature is 70 ℃ in normal use.
The number of bvr6 square wires, wire diameter of 19 / 0.64mm and outer diameter of 5.2mm. The conductor material of the product is made of 99.99% oxygen free copper. The copper wire has bright appearance and low resistivity, which improves its conductivity.
The only difference between BVR wire and bv wire is that the conductor diameter of R wire is soft copper wire. That is: increase the number of conductors, reduce the diameter of a single conductor, the diameter of a single conductor is less than 1 mm. In this way, the BVR wire is very soft, the laying angle requirements are greatly reduced compared with BV wire, and it is more convenient and fast when threading the conduit and trunking, which reduces the work intensity and greatly improves the work efficiency. Very popular with the majority of electrical and architectural decoration personnel welcome!
BVR wire can be divided into flame retardant wire, fire-resistant wire and low smoke halogen-free wire according to different materials, which can be flexibly controlled by users. Low smoke and halogen-free produce a very small amount of smoke in the case of flame combustion, the released gas does not contain low halogen elements, non-toxic. In case of fire, it can greatly reduce the harm to instruments, equipment and human body.
It is not difficult to see that BVR wire has many advantages, but it does not absolutely match the needs of any place. Or have to combine their own needs to buy, of course, good brand is also the key! So I hope the above can bring some help to the friends who are facing the problem of choosing household wires.
How to use insulation megger to measure insulation resistance of power cable
1. The performance of power cable insulation material decreases irreversibly with service time and environment, which is called insulation aging. The manifestations of insulation aging are as follows: breakdown strength decreases, dielectric loss tangent increases, local leakage and discharge increase, mechanical strength and other properties decrease.
2. In the aging process, the time required for the insulation performance to fall below the specified allowable range is usually called insulation life. Under normal service conditions, the service life of XLPE cable and oil immersed armored cable is 30 years and 40 years respectively. Under the action of power frequency AC voltage, partial discharge in insulation material is the main reason for insulation aging of power cable. In the oil immersed cable, the partial discharge leads to the decomposition of impregnant and paper fiber and the formation of waxy crystalline state. In XLPE cables, the insulation material is gradually damaged by partial discharge, forming micropores, cracks and dendritic buds, which gradually develop in depth in the insulation material until insulation breakdown.
3. The insulation aging degree of power cable can be measured by insulation resistance test and dielectric loss tangent tan δ Test, withstand voltage test and other electrical tests. Insulation resistance test shall be conducted for power cables below 6kV. 500 ~ 1000V grounding resistance tester (megohmmeter or megger) is used for cables with voltage below 1KV; 1000 ~ 2500V grounding resistance tester is used for 1kV and above cable.
The following items should be noted during the test.
① The method of measuring the insulation resistance is suitable for the cable which is not too long. Measure the insulation resistance and calculate the absorption ratio. Under the same test conditions, the better the insulation value is, the greater the absorption ratio is.
② Generally, the insulation resistance value of power cable is not specified, and the test value should be compared with the original record. Generally, the insulation resistance of 1 ~ 3KV cable should not be less than 200m Ω； 6 ~ 10kV cable should not be less than 400m Ω； 35kV Cable should not be less than 600m Ω； The unbalance coefficient of three-phase insulation shall not be greater than 2.5. During the test, the temperature, air humidity and other weather conditions shall be recorded for reference.
③ Before measurement, the cable shall be fully discharged, that is, the cable core and the metal sheath of the cable shall be grounded.
④ The surface of cable terminal bushing shall be wiped clean before testing. Use the other insulating core of the cable as the shielding circuit, connect the conductors at both ends of the insulated core to the bushing or insulation of the insulated core to be tested with flexible metal wires, wind them for several turns, and then connect them to the shielding terminal g of the grounding resistance tester.
⑤ After each test, the cable shall be grounded and discharged. The longer the cable line is, the better the insulation condition is, and the longer the grounding discharge time is, generally not less than 1min.
Discussion about Low Voltage Concentric Power Cable
In the China wire and cable products, there is no very small structure with a concentric cable. Some developed countries abroad are committed to research in this area and put it into practice. In the British Standard, BS4553-92 copper core PE insulated cable for power supply, the same core layer can be used as The sexual conductor and the grounding conductor are made of unplated annealed copper wire in accordance with BS4109.If the number, diameter and resistivity of the copper wires in each specification cable are the same as the core layer, the right winding should be adopted.
So what does concentric neutral mean?
The Concentric Neutral is the current flowing from one end to the other, then into the ground and back into the wire at the starting position.
The wrapping pitch and the number of threads should make the minimum coverage rate reach 90%, and the wrapping tape that does not absorb moisture should be overlapped immediately outside the same core layer. The NYCY type in the German standard DIN57271-83 adopts the same core layer conductor and can be used as a neutral wire, a ground wire or a neutral wire, and it can be used as a shield wire at the same time. The number, diameter and resistivity of unplated annealed copper wires are also specified. Compared with the same type of cable, it has a compact structure and a round shape, which can save about 10% of the sheath cable material. Therefore, according to the above structure.
The characteristics, cross-sectional area requirements, equipment and production technology used to formulate the structural design principles of low power cable concentric conductors.
- In order to facilitate production and management, the wire diameter of the same core conductor should be unified as much as possible.
- According to the production equipment, the minimum wire diameter shall be specified under the condition that it is evenly distributed on the stranded insulating core around the cladding and the spacing is not greater than 4mm. The number of concentric conductors is as small as possible.
- In order to ensure the uniformity of the same-core conductors without relative sliding, and to ensure that the
The cable appearance is round. Using layered non-woven fabric or PVC wrapping method, that is, insulating core into cable wrapping tape + concentric conductor twisted spiral copper tape wrapping + non-woven fabric tape overlapping wrapping.
- There are three types of structures. The structure of three-phase four-wire cable is a structure, and the structure of three-phase five-wire cable is b and c.
In the structure, the concentric conductor is wrapped outside the cable core. It can be N wire (neutral wire), PE wire (protective earth), or PEN (neutral wire and protective earth shared), and the material is copper Wire or copper tape, or copper wire plus copper tape. The carrying surface is the same or half of the electric phase core
- In the structure, the N wire is in the cable core, and the neutral wire is wrapped around the cable core as a PE wire. The neutral wire can be copper wire or copper wire plus copper tape. The cross section is half of the cable phase core
- In the structure, the N wire is wrapped outside the copper core, and the PE wire composed of copper wire is wrapped outside the N wire, and the copper wire is composed of copper tape to form a double-layer shielding structure. The cross-section is the same as the phase core of the cable.
Advantages of the same-core conductor and shielded neutral power cable
- When transmitting power, it will not cause interference to surrounding electrical equipment; it also eliminates the influence of external electromagnetic interference on electrical equipment connected to this cable
- It can avoid breakdown or damage caused by strong lightning electromagnetic effect voltage, and improve the lightning protection effect and reliability of high-rise buildings
- It can improve the sensitivity of the overcurrent protection device at the head end of the line, so that the cable and the electrical equipment connected to it can be effectively protected
- It has low and uniform forward (reverse) sequence and zero sequence impedance, which is conducive to improving the quality of copper electricity
- TN-C and TN-C-S system power supply suitable for coreless cables
- It can eliminate the ground fault caused by the insulation breakdown of one phase as soon as possible
- Convenient processing, high flexibility and easy construction
- Can reduce costs