Soaring! Today’s copper price rises for 3 consecutive years! Up to 80000!

Today’s copper price

CCMN spot copper price: 77050 yuan / ton, up 2770 yuan / ton

                                 

Chile bill affects supply, copper may rise sharply on the 10th

Abstract: the prospect of economic restart in Europe and the United States is optimistic. Copper revenue rose nearly 3% every other week, reaching a record high. Chile’s tax increase bill will affect copper output, and renewable energy will promote consumption growth. Today, copper is expected to rise sharply.Huaxing ACSR Cable.
[copper futures market] with the acceleration of vaccine promotion, the prospects of economic restart in Europe and the United States are more optimistic. Every other week, Luntong continued to be strong and set a new record high. The latest closing price was $10413 / T, up 297 or 2.94%. The trading volume was 23447, up 9877, and the position was 328659, up 1073. On Friday night, Shanghai copper jumped to open high, and the latest closing price of the main monthly 2106 contract was 75720 yuan / ton, up 1570 yuan, or 2.12%.
London Metal Exchange (LME) reported its latest inventory of 126725 tons on May 7, a decrease of 4025 tons or 3.08% compared with the previous trading day.
Copper stocks in the previous period increased by 8603 tons to 208473 tons last week, after a slight decline for two consecutive weeks. Chile’s lower house of Parliament has passed a bill that includes a floating tax on copper sales based on copper price fluctuations. Industry analysts believe that the bill will at least delay Chile’s new copper production capacity projects. The CEO of Glencore believes that the copper price needs to grow to 15000 yuan to promote new supply, and the development of renewable energy will promote consumption growth for a long time. Today’s spot copper price is expected to rise sharply.

Working principle and characteristics of radiation cross-linked wire and cable

1. Explanation of the principle of irradiation:
Irradiation cross-linking is to use the high-energy electron beam generated by the electron accelerator to bombard the insulating layer and the sheath to break the polymer chain, and each broken point becomes a free radical. Free radicals are unstable and must be recombined with each other. After recombination, the original chain molecular structure becomes a three-dimensional network molecular structure to form crosslinks.
Second, the characteristics of radiation cross-linked low-smoke halogen-free wire and aaac cable
1. Large current carrying capacity; after radiation cross-linked cable, after high-energy electron beam irradiation, the molecular structure of the material changes from linear to three-dimensional network molecular structure, and the temperature resistance level is increased from non-crosslinked 70℃ to 90℃, 105 ℃, 125℃, 135℃, or even 150℃, the current carrying capacity of cables of the same specification is increased by 15-50%.
2. The insulation resistance is large; because the radiation cross-linked cable avoids the use of hydroxide as a flame retardant, it prevents pre-cross-linking during cross-linking and the insulation resistance drop due to the absorption of moisture in the air by the insulating layer. Thereby ensuring the insulation resistance value.


3. Long service life and strong overload capacity; due to the high temperature resistance grade and high aging temperature of the radiation crosslinked polyolefin material, the service life of the cable during the cycle of heating is extended.
4. Environmental protection and safety; since the materials used in the abc cables are all halogen-free environmentally friendly materials, the combustion characteristics of the cables meet environmental protection requirements.


5. Product quality temperature: The quality of traditional warm water cross-linked cables is affected by water temperature, preparation process, cross-linking additives and other factors, and the quality is unstable. The quality of irradiated cross-linked cables depends on the radiation dose of the electron beam. The radiation dose is controlled by a computer, and there are no human factors, so the quality is stable.
Irradiation cross-linked low-smoke halogen-free flame-retardant wires and cables are difficult to catch fire and have the ability to prevent or delay the spread of flames. They have strong overload capacity and once caught fire, they have halogen-free, low-smoke, non-toxic, and non-corrosive characteristics. Used in high-rise buildings, hotels, hospitals, subways, nuclear power plants, tunnels, power plants, ore, petroleum, chemical industries, etc.

Cable quality defects and troubleshooting methods

The degree of crosslinking (hot extension) is unqualified
If the degree of cross-linking fails to meet the standard, the thermal-mechanical properties of the aac cable are unqualified and cannot meet the requirement of 90°C working temperature.
The reasons for the unqualified cross-linking degree are the unqualified formula and the improper type and ratio of the compounding agent. The formula should be adjusted to solve the problem; the second is the improper vulcanization process, such as low air pressure, fast line speed, high cooling water level and other factors.
The solution is to first find out what is the reason, which may be one or several reasons at the same time, and eliminate the reasons.


Unqualified structure and appearance
(1) The thinnest point of the insulating layer thickness is lower than the minimum value specified in the standard, or the average thickness is lower than the nominal value. The reasons for the unqualified insulation thickness are the fast line speed, the small amount of glue from the extruder, and the improper selection of molds.
The solution is to reduce the linear speed or increase the speed of the extruder and adjust the size of the die.
(2) Eccentricity
The reason for the eccentricity is that the mold is not adjusted or the suspension control has changed after the recruitment is adjusted.
The solution is to control the drape as stable as possible during driving.
Bamboo-shaped
The reason for the appearance of the bamboo-shaped outside of the cable is electrical and mechanical systems that cause the traction speed to be unstable. The second is that the core is too small, or the outer diameter of the acsr conductor full form is uneven.
The troubleshooting method is to check the mechanical and electrical system and eliminate the fault. Properly adjust the size of the core, control the outer diameter of the suburbs and counties to be as uniform as possible, and the stranded wire that exceeds the process regulations can be used.


Scratches on the surface
(1) The cable touches the upper or lower wall or foreign matter in the vulcanizing tube. Therefore, it is required to adjust the degree of suspension, try to make the wire core move in the middle of the cross-linked tube, and find foreign matter, and clean it in time.
(2) There is burnt on the outer edge of the mold sleeve. The solution is to adjust the temperature of the mold sleeve when starting the car to prevent overheating. Once it is found to be burnt, it should be stopped immediately to remove it, or it will not get better by itself.
Impurity
Most of the impurities in insulating materials and semi-insulating materials are brought in during mixing and during the feeding process of the extruder. Strict attention should be paid to the cleanliness of materials during operation to prevent the mixing of external impurities. Another kind of impurity is scorching lumps, its existence affects the performance and service life of the abc cable, so the temperature is strictly controlled during mixing and extrusion to prevent the occurrence of scorching.


bubble
There may be two reasons for bubbles generated in insulation, one is caused during extrusion. The solution is to select appropriate molds. There are bubbles in the shielding layer. The main reason is that there is moisture in the material. It should be dried before extrusion. The second is insufficient cooling. At this time, the following will appear. A circle of bubbles will appear on the circumference equidistant from the core.
The elimination method is to strengthen the cooling, raise the water level and lower the temperature of the cooling water.
Unqualified cable performance
(1) Unqualified free discharge and dielectric loss
The causes of dissociation discharge and dielectric loss unqualified are very complicated, and they are shielded from the outside. Whether the insulation contains bubbles and impurities is closely related to the performance of the raw materials. The elimination method is to keep the raw materials clean and strictly follow the production process.
(2) Cable insulation breakdown
The main cause of cable insulation breakdown is the mixing of insulating materials and external damage. Due to strict avoidance of external damage, the mixing of impurities should be avoided as much as possible. The semi-finished products are strictly managed to prevent stumbling.
(3) Cushion breakdown
The main reason for the cushion layer breakdown is the steel with burrs, curling, and puncture the cushion. The method of elimination is the use of different quality requirements of the steel belt. The cushion shall be made of plastic tape with a higher hardness, and it shall be ensured The thickness of the cushion.

The basic process flow of plastic wire and cable manufacturing

1. Copper and aluminum monofilament drawing
Commonly used copper and aluminum rods for wires and cables, at room temperature, use a wire drawing machine to pass through one or several stretch die holes to reduce the cross-section, increase the length, and increase the strength. Wire drawing is the first process of various wire and abc cable companies, and the main process parameter of wire drawing is die matching technology.
2. Monofilament annealing
Copper and aluminum monofilaments are heated to a certain temperature to recrystallize the toughness of the monofilament and reduce the strength of the monofilament to meet the requirements of the wire and cable for the conductive core. The key to the annealing process is to prevent the oxidation of the copper wire.


3. Stranding of conductors
In order to improve the flexibility of the wire and cable and facilitate the laying and installation, the conductive core is made of multiple monofilaments twisted. From the stranding form of the conductive core, it can be divided into regular stranding and irregular stranding. Irregular stranding is divided into bundle stranding, concentric twisting, special stranding and so on. In order to reduce the occupied area of ​​the wire and reduce the geometric size of the cable, the compacted form is adopted while the acsr conductor size is twisted, so that the ordinary circle is transformed into a semicircle, sector shape, tile shape and compacted circle. This kind of conductor is mainly used in power cables.


4. Insulated extrusion plastic wires and cables mainly use extruded solid insulation layer, the main technical requirements of plastic insulation extrusion:
4.1. Eccentricity: The deviation value of the extruded insulation thickness is an important indicator of the level of the extrusion process. Most of the product structure dimensions and deviation values ​​are clearly specified in the standard.
4.2. Smoothness: The surface of the extruded insulating layer must be smooth, and there must be no poor quality problems such as surface roughness, burnt, and impurities
4.3. Density: The cross-section of the extruded insulation layer should be dense and strong, and no pinholes visible to the naked eye are allowed to prevent the existence of air bubbles.
5. Cable
For multi-core cables, in order to ensure the degree of forming and reduce the appearance of the cable, it is generally necessary to twist them into a circle. The stranding mechanism is similar to that of conductor stranding. Because the stranding pitch diameter is larger, most of them adopt the non-back-twisting method. Technical requirements for cable formation: First, to prevent twisting of the cable caused by the overturning of the special-shaped insulated core; second, to prevent the insulation layer from being scratched. Most of the cables are completed with the completion of the other two processes at the same time: one is filling to ensure the roundness and stability of the cable after the cable is formed; the other is binding to ensure that the cable core is not loose.


6. Inner sheath
In order to protect the insulated core from being damaged by the armor, it is necessary to properly protect the insulating layer. The inner protective layer is divided into: extruded inner protective layer (isolation sleeve) and wrapped inner protective layer (cushion layer). The wrapping cushion layer replaces the lashing tape and the cable forming process is carried out simultaneously.
7. Armoured
For cables laid underground, they may be subjected to certain positive pressure during work, and an inner steel tape armored structure can be selected. Cable laying in occasions with both positive pressure and tension (such as in water, vertical shafts or soil with a large drop), the structure type with inner steel wire armor should be selected.
8. Outer sheath
The outer sheath is the structural part that protects the insulating layer of the wire and cable from environmental factors. The main function of the outer sheath is to improve the mechanical strength of the wire and cable, prevent chemical corrosion, moisture, waterproof, and prevent the cable from burning. According to the different requirements of the cable, the plastic sheath is directly extruded by the extruder.

Advantages of copper-clad aluminum power cable

1.DC resistivity. The resistivity of copper clad aluminum wire is larger than that of pure copper wire, about 1.5 times that of pure copper wire. When the cathode value is the same, the weight of copper clad aluminum wire is about 1/2 of that of pure copper wire. According to the calculation of the skin effect, when the high frequency is above 5MHz, compared with the acsr conductor of the same cross section, its resistivity is the same. In the use of power cables with a frequency of 50 Hz, the skin effect and proximity effect of copper conductors gradually become prominent above 150mm2. At the same time, due to the continuous development of science and technology, high-order harmonic currents and energy will be injected into the power supply system. , The high-order harmonic voltage of the corresponding frequency is generated on the impedance of the system, causing the voltage waveform to be distorted, increasing the loss of the power supply system, and increasing the heat of the conductor; in addition, the cable amplifies the harmonics and generates overvoltage at the joint. Damage to the cable head. The use of copper-clad aluminum conductors can reduce the AC impedance (resistance) generated by high-order harmonics. In other applications, by increasing the volume of copper in the copper-clad aluminum monofilament and corresponding technological measures, the copper-clad aluminum/copper composite conductor is within the upper limit of the outer diameter of the existing conductor of the same specification and meets the conductor’s DC resistance requirement.
Connection method. The use of copper-clad abc conductors can meet the habit of product selection, design, use, installation, etc. of wires and cables that will be continued for many years, and it is also beneficial to the pressing and tin welding of the cable terminals.

2.Reduce AC resistance. AC resistance is the main basis for the current carrying capacity. According to the principle of skin effect, the current per unit area on the surface of a single wire is larger than the current per unit area of ​​the center of the wire, that is, the center of a large cross-section conductor In the area of ​​a circle formed by the same conductor, the current passing through the center of the circle is smaller than that of the circle. Therefore, it is the most reasonable and economical to use different metals for the center conductor and the circumferential conductor. In addition to the DC resistance and the skin effect, the AC resistance index also has the proximity effect. Compared with the copper conductor with the same DC resistance, after the copper composite conductor is used, the aluminum is in the center of the aac conductor and the copper is on the outer edge; In the composite conductor, the inner layer is copper-clad aluminum and the outer layer is pure copper. Aluminum is not sensitive to the skin effect and proximity effect of copper. At the same time, the copper composite conductor will increase the total cross-section of the conductor by a part, so it also increases the conductor. The surface area of ​​the cable improves the heat dissipation conditions of the cable and increases the heat dissipation area. The thermal conductivity of aluminum is similar to that of copper. Under the same material cost condition, the AC resistance index is much more economical.

3.It has good corrosion resistance: aluminum is more corrosive than copper, but because the copper-clad aluminum material has been completely metallurgized, aluminum is completely covered by copper and will not be in contact with water or air. It can fully achieve the same performance as copper. Copper-clad aluminum/copper composite conductors are also more useful to prevent the cable from being corroded, bruised, or due to tight pressure, poor soldering, and poor contact between the conductor and the terminal, heating and causing the copper layer to fall off and copper and aluminum. A potential difference is formed between metals, which accelerates galvanic corrosion and causes the hidden danger of burning at the end of the cable. For aluminum conductors, especially in coastal areas, the chloride ions contained in the salt spray in the atmosphere will condense on the surface of aluminum, which will easily cause local corrosion around impurities and defects on the surface, forming holes, cracks and micro-batteries, and aggravate the damage of aluminum conductors. corrosion.
4.Low cost and light weight. Compared with the copper core cable with the same technical index, the copper clad aluminum conductor cable can save more than 40% of the cost, and the copper clad aluminum/copper composite conductor cable can save more than 20% of the cost. The proportion of copper clad aluminum wire is only 37%-40% of pure copper wire. When the wire diameter and weight are equal, its length is 2.5 times that of pure copper wire.
5.Good weldability. The copper-clad aluminum wire is concentrically coated with a layer of pure copper, so it has the same solderability as pure copper wire and is convenient for production.

Various types of cables

Because cables are used in many different environments, they look very different in appearance. But regardless of any cable type, they are used as a conductor for signal transmission. These acsr conductor size also have different quality performances in transmitting different signals. Except for some special applications, the cables currently used for audio and video transmission are mainly single wires, twisted pairs, coaxial wires and optical fibers.


1.1. Single wire
A single wire is the most basic type of cable (such as a wire). It consists of one or a group of wires surrounded by a plastic protective layer. This kind of cable is commonly used to transmit low-frequency signals, such as power, audio, and computer ID code.
1.2. Twisted pair
Twisted pair is a general term. There are no restrictions on the number of wires and the type of twisting, but there are only two types in the structure of the cable: twisted pair with shielded net (STP: ShieldedTwistedPair) and without shielded net Twisted pair (UTP: UunshieldedTwistedPair). Twisted-pair cables are commonly used in telecommunications, the Internet, and professional audio. This aaac conductor full form is composed of two or more independent and mutually insulated cables that are continuously twisted. Two of the cables that are twisted to each other are called a group. , The transmission impedance is generally 100_, and the diameter of a single wire is between 20AWG (American wireline standard: 0.91mm) and 24AWG (0.61mm). Twisted pair is a relatively inexpensive cable. Each set of wires has the same anti-interference ability, which can effectively suppress external electromagnetic interference (EMI) and effectively shield the transmission signal from electromagnetic interference to the outside world.
UTP cables are most commonly used in telecommunications transmission and computer network environments. According to the type of twisting, they are divided into five, super five and six types of cables. Generally, they can reach a transmission rate of 100Mbps (100 million bits per second). The STP cable adds a layer of woven metal mesh or tin foil to the periphery of the wire group, which is more conducive to improving the signal and suppressing the impact of external radio waves. The metal shell of each connector of the STP cable must maintain good contact with the shielding net.

1.3. Coaxial cable
Coaxial cable (Coaxial) is a composite composed of two conductors. The center wire of the coaxial cable is used to transmit signals. The metal shielding net plays two roles: one is to provide current for the signal as a common ground wire for the signal. The second is as a shielding net for the signal, which suppresses the interference of electromagnetic noise on the signal. The center wire and the shielding net are between the semi-foamed polypropylene insulation layer. The insulation layer determines the transmission characteristics of the aac cable and effectively protects the wires in the middle.
Coaxial cables are widely used in audio, video or radio frequency transmission, and the transmission impedance is generally 75_, which has become the standard impedance of video (in the early days, 50_ impedance characteristics were also used for video transmission). High-quality standard coaxial cables are generally more expensive than twisted pairs because of the reliable physical characteristics of coaxial cables, which can provide excellent audio and video performance. The frequency and resolution of the signal and the effective transmission distance of the cable play a decisive role in the audio and video system.


1.4. Optical fiber
Optical fiber cable (OpticCable) is the best choice for long-distance signal transmission. Optical fiber transmission is a technical method based on photoelectric conversion instead of electronic transmission. The simple principle of optical fiber transmission is: the analog electric signal is transmitted to the optical transmitter, and the input voltage signal is converted into a current signal through the signal buffer circuit and the driving circuit, and the light-emitting tube or laser is driven. In this way, the input electrical signal is converted into an optical signal, which is coupled into the optical fiber through precise optical alignment and guidance.
After the optical signal is transmitted through the optical fiber, at the receiving end the optical signal is converted into the original electron source by a wavelength-matched photodiode, and then output after being amplified by a low-noise linear amplifier.
Optical fiber signal transmission avoids many shortcomings of traditional cable transmission, and has many advantages that cable transmission can’t match; Excellent anti-electromagnetic interference: In long-distance cable transmission, the cable itself is a huge antenna, which picks up electromagnetic signals in the surrounding space. , Especially in the display system, this kind of interference signal shows the granular noise that cannot be eliminated in the image display. The core of the fiber optic cable is glass, and it transmits optical signals, which is not easily interfered by external electromagnetic waves.
Very small volume: Most optical fibers are as thick as human hair.
Very low attenuation: Because the optical fiber transmission is completed by the glass conduit, there is no signal attenuation caused by the cable resistance and capacitive reactance. The optical fiber greatly improves the transmission bandwidth and transmission distance. High security of optical fiber: The signal content transmitted by optical fiber is not easy to be eavesdropped on.
Although optical fiber seems to be the ultimate method of signal transmission, there are some disadvantages;
Higher prices: optical cables, transmitters, and receivers are expensive
High labor: In the process of arranging and routing optical cables, a lot of human resources and special tools are required. Although the transmission loss of the optical signal in the optical fiber is very low, the attenuation of the signal by the electro-optical and photoelectric conversion at the transmitting end and the receiving end is very severe. Therefore, to ensure no insertion loss transmission, it is necessary to add a high-gain multi-stage amplifier to the transmission, and to ensure that the circuit can work stably.

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

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

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

Several reasons for cable aging

The most direct cause of wire and cable aging failure is the breakdown of the insulation due to degradation. There are many factors that lead to the reduction of conductive insulation. According to actual operating experience, it can be summed up as the following situations.

1) Reasons for cable aging: external force damage. Judging from the operation analysis in recent years, especially in the high-speed economic development of Haipudong, a considerable number of cable failures are now caused by mechanical damage. For example, non-standard construction during cable laying and installation can easily cause mechanical damage; civil construction on directly buried cables can also easily damage cables in operation. l Sometimes if the damage is not serious, it will take months or even years to cause the damaged part to be completely broken down and cause a failure. Sometimes the damage is serious and a short-circuit fault may occur, which directly affects the safe production of the electric power and the power user.

2) Reasons for cable aging: insulation is damp. This situation is also very common, and generally occurs at the cable joints in direct burial or piping. For example: unqualified cable joints and joints made in humid weather conditions will cause the joints to enter water or water vapor. For a long time, water branches will form under the action of the electric field, which will gradually damage the insulation strength of the power cable and cause failure.

3) Reasons for cable aging: chemical corrosion. The cable is directly buried in the area with acid and alkali, which will often cause the cable armor, lead skin or outer protective layer to be corroded. The protective layer suffers from chemical corrosion or electrolytic corrosion for a long time, which causes the protective layer to fail and reduce the insulation. The cable is faulty. Chemical: the unit’s cable corrosion is quite serious

4) Reasons for cable aging: long-term overload operation. Overload operation, due to the thermal effect of the current, the conductor will inevitably heat up when the load current passes through the cable. At the same time, the skin effect of the charge, the eddy current loss of the steel armor, and the insulation loss will also generate additional heat, which will increase the cable temperature. During long-term overload operation, excessively high temperature will accelerate the aging of the insulation, and even breakdown of the insulation. Especially in the hot summer, the temperature rise of the cable often leads to the first breakdown of the weak insulation of the cable, so in the summer, there are more cable faults.

 

5) Reasons for cable aging: cable connector failure. Cable joints are the weakest link in the cable line. Cable joint failures caused by direct faults (poor construction) by personnel often occur. In the process of making cable joints, if there are original nets such as insufficient joint crimping, insufficient heating, etc., the insulation of the cable head will be reduced, which may cause an accident.

6) Reasons for cable aging: environment and temperature. The external environment and heat source of the cable can also cause the cable to overheat, insulation breakdown, and even explosion and fire.

If you want to buy a cable, you can send us Huaxing Wire and Cable for consultation

Requirements of Power Cable Cross Section

Power cable section
The selection of power cable conductor cross-section should meet the following requirements:
1 The temperature of the cable bare conductor under the action of the maximum operating current shall not exceed the allowable value of the service life of the cable. Cable conductor work of continuous working loop
The temperature should meet the requirements of Appendix A of this code.
2 The temperature of the cable conductor under the action of the maximum short-circuit current and short-circuit time shall comply with the provisions of Appendix A of this code.
3 The voltage drop of the connected circuit under the maximum operating current shall not exceed the allowable value of the circuit.
4 In addition to meeting the requirements of paragraphs 1 to 3 above, the cross-section of power cables of 10kV and below should be based on the initial investment of the cable and the operation during its service life.
The principle selection of comprehensive cost economy. The selection method of economical current cross-section for power cables of 10kV and below should comply with the regulations in Appendix B of this code.
5 The minimum cross-section of multi-core power cable conductors, copper conductors should not be less than 2.5mm2, and all aluminum conductors should not be less than 4mm2.
6 For cables laid underwater, when the conductor is required to withstand the tensile force and is reasonable, the cross section can be selected according to the tensile requirements.

Commonly used cables of 10kV and below shall determine the allowable minimum cross-section of the cable conductor at 100% continuous working current, which should meet the requirements of Appendix C and Appendix D of this code. The current carrying capacity shall be greater than The working current of the loop.
1 Difference in ambient temperature.
2 The difference in soil thermal resistance coefficient when directly buried.
3 The influence of multiple parallel cables.
4 The influence of sunlight on outdoor overhead laying without shading.

Except for the conditions specified in Article 3.7.2 of this code, when the cable determines the minimum allowable cross-section of the cable conductor at 100% continuous working current, it shall be verified by calculation or test, and the calculation content or parameter selection shall meet the following requirements:
1 Non-coaxial cables used in power supply circuit cables with higher harmonic loads or intermediate frequency load circuits should be included in the skin effect and the increase in proximity effect
And other additional heating effects.
2 For single-core high-voltage cables that are cross-connected and grounded, when the three sections in the unit system are of unequal length, the effect of the additional loss and heating of the metal layer should be included.
3 The cables laid in the protective tube shall be included in the influence of thermal resistance; the cables with different holes in the pipe shall also be included in the influence of mutual heating factors.
4 Cables laid in closed, semi-enclosed or ventilated refractory trough boxes should be included in the heat resistance of the type of material and the thickness and size of the box.
The impact of increased resistance.
5 When the thickness of the fireproof coating, tape and other covering layer applied on the cable is greater than 1.5mm, the thermal resistance should be included.
6 When the cable in the trench is buried with sand and there is no regular water supplement, a thermal resistance coefficient greater than 2.0K·m/W should be selected according to the sand quality to include the influence on the increase of the thermal resistance of the cable.

When calculating the continuous allowable current-carrying capacity of the cable whose conductor working temperature is greater than 70℃, the following requirements should be met:
1 When a large number of such cables are laid in tunnels and shafts without mechanical ventilation, the impact on environmental temperature rise should be included.
2 Cables are directly buried in dry or moist soil. Except for the implementation of soil replacement treatment to avoid water migration, the soil thermal resistance coefficient is not
It should be less than 2.0K·m/W.

Control Cable and Its Metal Shield

1 The current and voltage of dual protection, as well as the two systems that need to enhance reliability, such as DC power supply and trip control loop, should use separate control cables.

2 In the following cases, the same control cable should not be used together:
1 Weak current signal, control circuit and strong current signal, control circuit.
2 Low-level signal and high-level signal loop.
3 Weak current control circuit of each phase of AC circuit breaker split-phase operation.
3 Each pair of round-trip wires of the weak current circuit should belong to the same control cable.
4 The phase wire and neutral wire of each group of secondary windings of current transformer and voltage transformer should be arranged in the same cable.
5 The control cables of strong current loops may not contain metal shields, except for those located in high-voltage power distribution devices or close to and parallel to high-voltage power cables and need to suppress interference.
6 The control cables of weak current signals and control circuits should have metal shields when they are located in an environment affected by interference and do not have effective anti-interference measures.7 The selection of the metal shielding type of the control cable should be included in the comprehensive interference suppression measures based on the possible electrical interference impact, and should meet the requirements for reducing interference or overvoltage, and should meet the following requirements:1 For the weak current control cables of power distribution devices above 110kV, general shielding or double-layer general shielding should be used.
2 The control cable used for the current, voltage and signal contacts of integrated circuit and microcomputer protection should be shielded.
3 The shield selection of the signal loop control cable of the computer monitoring system shall meet the following requirements:
1) Switch signal, general shield can be used.
2) For high-level analog signals, a pair of twisted cores should be used for general shielding, and a pair of twisted cores for separate shielding can also be used when necessary.
3) For low-level analog signals or pulse signals, it is advisable to use a pair of twisted cores and separate shields, and if necessary, a pair of twisted cores and a composite general shield can also be used.

4 In other cases, the appropriate shielding type should be selected according to factors such as electromagnetic induction, electrostatic induction and ground potential rise.
5 When the cable has steel armor or metal sheath,such as SWA cable , its shielding function should be fully utilized.
8 For control cables that need to reduce electrical interference, a grounded spare core can be added, and it should be grounded at one point on the side of the control room.
9 The grounding method of the metal shield of the control cable shall meet the following requirements:
1 The analog signal loop control cable shielding layer of the computer monitoring system shall not form two or more points of grounding, and shall be grounded at one point in a centralized manner.
2 The cable shielding layer of the current, voltage and signal of the integrated circuit and microcomputer protection shall be grounded at the same time as the switch placement place and the control room.


3 For the shielding layer of control cables other than the above, when the electromagnetic induction interference is large, two points should be grounded; when the electrostatic induction interference is large,
One point grounding can be used.
For double shielding or composite general shielding, it is advisable to use one or two grounding points for the inner and outer shields respectively.
4 In the choice of two-point grounding, the shielding layer should not be melted under the action of transient current.
10 The conductor cross-section of the strong current control loop should not be less than 1.5mm2, and the weak current control loop should not be less than 0.5mm2.