Advantages of high temperature superconducting cable

Compared with traditional power cables, superconducting cables have the advantages of low loss, large transmission capacity, small ABC Cable volume and strong system security and stability. Cold insulated HTS cables have low mutual electromagnetic influence and thermal field influence, and have stable current carrying capacity. They have great development prospects in underground cable systems in densely populated big cities or specific high-capacity transmission applications. There are many underground pipe networks in big cities, various underground pipes (tunnels) are complex, and the space for cable laying is very limited. It is more and more difficult to install and lay traditional cables, and the installation and maintenance cost will be greatly increased. Using the existing pipe or cable tunnel and replacing the existing conventional cable with high temperature superconducting cable can double the transmission capacity of underground power grid and solve the contradiction between the increase of load and the limited underground space.

In terms of loss, the traditional cable transmission loss is mainly conductor loss, dielectric loss and shielding loss. Among them, for general land ACAR Cables, conductor loss accounts for about 95% of transmission loss. The loss of superconducting cable mainly includes: AC loss of cable conductor, Joule loss of cable terminal, heat leakage loss of superconducting cable insulation pipe, cable terminal and refrigeration system, loss of liquid nitrogen overcoming cycle resistance, etc. Considering the efficiency of refrigeration system, the operating loss of HTS cable is about 50% ~ 60% of that of conventional cable when transmitting electric energy of the same capacity.
The interconnection of large power grids is the trend of power development. With the interconnection of major power grids and the increase of power demand, the short-circuit current level of the system will further rise after short-circuit fault. How to solve the problem of fault current has attracted more and more attention of the power department. The transmission conductor of superconducting cable is superconducting material. Under normal working conditions, the transmission density of superconducting cable is large and the impedance is very low; In the case of power grid short-circuit fault and transmission current greater than the critical current of superconducting material, superconducting material will lose its superconducting ability, and the impedance of superconducting cable will be much greater than that of conventional copper conductor; When the fault is eliminated, the superconducting cable will restore its superconducting ability under normal working state. If the high temperature superconducting cable with certain structure and technology is used to replace the traditional cable, the power grid fault current level can be effectively reduced. The ability of superconducting cable to limit fault current is directly proportional to the cable length. Therefore, the large-scale superconducting transmission network composed of superconducting cables can not only improve the transmission capacity of the power grid and reduce the transmission loss of the power grid, but also improve its internal fault current limiting capacity and improve the safety and reliability of the whole power grid.

Internationally, the research and development process of HTS cable can be divided into the following three stages. The first stage is the preliminary exploration of HTS cable technology. With the development of bismuth (BI) high temperature superconducting tape technology, the research on high temperature superconducting cable has attracted extensive attention. The main contents of the research include: the research on the structure of superconducting AAAC Cable, including room temperature insulated (WD) high temperature superconducting cable, cold insulated (CD) high temperature superconducting cable, three-phase coaxial structure, three core in one structure, etc; Carry out research on electrical performance and transmission characteristics of superconducting cable. The second stage is the research and development of CD insulated HTS cable that can truly realize commercial application in the future. At the end of 1999, the 30m, three-phase, 12.5kv/1.25ka cold insulated HTS cable developed by southwire was connected to the grid, which has taken a solid step towards the practicability of HTS technology. The third stage is the demonstration project research of CD insulated HTS cable. In the past 10 years, the United States, Japan, South Korea, China, Germany and other countries have successively carried out a number of demonstration projects on CD insulated HTS cables.

When the traditional cable is running, the heat generated by the transmission loss is directly distributed to the surrounding environment, and its current carrying capacity is very sensitive to the external heat source. Generally, the current carrying capacity will decrease by 8% ~ 10% when the ambient temperature increases by 10 ℃. Therefore, intensive laying will lead to mutual heating of cables and sharp decline of current carrying capacity. According to the calculation, 2 × 4 rows of pipes, 3 × 3 rows of pipes and 4 × The current carrying capacity of traditional cables with dense 4-row pipes will be reduced by about 20%, 30% and 40% respectively. At the same time, because the traditional cable uses combustible organic materials as the main insulation, it is very easy to cause fire in case of failure. The outermost layer of CD insulated HTS cable is a composite vacuum insulation layer, which has good thermal insulation performance. The heat generated by the cable is taken away by circulating liquid nitrogen. Therefore, the thermal field of superconducting cable is relatively independent and the cable has stable current carrying capacity. At the same time, due to the good electromagnetic shielding function of CD insulated superconducting cable, it can completely shield the electromagnetic field generated by the cable conductor in theory, so it will not cause electromagnetic pollution to the environment. Due to these advantages, superconducting cables can be laid in dense ways such as underground pipes, which will not affect the operation of surrounding power equipment, and because it uses non combustible liquid nitrogen as refrigerant, it also eliminates the risk of fire.

Why are mineral insulated cables so hot?

In recent years, the city has developed rapidly
Subway, station, hospital, school, high-rise residence
Expansion of public facilities construction scale
The number of high-rise buildings surged
The demand for urban electricity is rising
Such a densely populated key area
In case of fire, the consequences are serious
In recent years, the fire spread trend in such places shows a similar pattern

According to the analysis of construction safety and fire protection experts
At present, there are still many cables selected for public facilities
No fire resistance
It is difficult to play its due role in fire
The law expressly stipulates that China’s civil construction law stipulates that in the code for fire protection design of construction projects, the fire protection system needs to use mineral insulated cables in order to pass the fire protection acceptance.
Under fire conditions, mineral insulated AAAC Cable can not only ensure the fire power supply within the fire duration (more than 180 minutes), but also will not delay combustion, produce smoke and secondary disasters, so as to win valuable time for fire rescue.
It can be said that mineral insulated cable is a special cable that must be used for fire protection in national important facility construction, large public areas, high-rise buildings and other places. Its fire resistance, durability, safety, reliability and economy can not be replaced by traditional power cable.
1、 Mineral insulated cable structure
Chengtiantai mineral insulated cable is a kind of cable that uses copper sheath to wrap copper conductor core wire and magnesium oxide powder as inorganic insulating material to isolate conductor and sheath (outer sheath is optional), forming a close whole with metal core and sheath.
Magnesium oxide is also a non combustible material, and will not produce toxic smoke or other harmful substances when encountering high temperature. Therefore, the cable with magnesium oxide as the insulator of copper core and copper sheath has good performance and many advantages.
2、 Performance and advantages of mineral insulated ACSR Cable
Chengtiantai mineral insulated cable mainly includes bbtrz (flexible mineral insulated fireproof cable) and yttw (flexible inorganic mineral insulated cable) series. It has the characteristics of good fire resistance, high temperature resistance, large current carrying capacity, waterproof, corrosion resistance, mechanical damage resistance, radiation resistance, electromagnetic compatibility and elegant appearance. At the same time, the cable will not emit any smoke under fire conditions Halogen and toxic and harmful gases.

1. Fire performance
Because mineral cables are all composed of inorganic substances, they will not cause fire, can not burn or support combustion, and will not produce toxic gases. Even if there is external flame combustion, the cable can still work normally. Mineral insulated cable is insulated with magnesium oxide, and the melting point of magnesium oxide is as high as 2800 ℃, which is difficult to burn easily. Therefore, the fire resistance of mineral insulated cable is excellent.
The test shows that the mineral insulated cable can run normally after burning in the flame with the temperature up to 800 ℃ – 900 ℃ for 2h; After burning under 1000 ℃ flame for 30 min, the cable is still intact and continues to operate normally.
2. High temperature resistant operation, large current carrying capacity
The normal service temperature of mineral insulated ACAR Cable can reach 250 ℃. Under special circumstances, the cable can maintain operation for a short time at a temperature close to the melting point of copper sheath. It is very suitable for laying in high temperature places, such as metallurgy, boiler, glass furnace, blast furnace and so on.
Its cut-off flow is much higher than that of other cables. Because magnesia powder has a better conductor coefficient than plastic, the cut-off flow is greater at the same working temperature. For lines above 16mm, one section can be reduced, and two sections can be reduced where people are not allowed to touch.
3. Waterproof, explosion-proof, high mechanical strength
The insulating layer of mineral insulated cable is processed by high-density compaction process, and then protected by seamless copper sheath. In the product standard, it must meet the three requirements of fire resistance, spray resistance and mechanical impact, and can withstand severe impact and mechanical damage. Therefore, it can not only prevent the infringement of water, moisture, oil and some chemical substances, but also apply to the connection of various explosion-proof equipment and equipment in places with explosion risk.
4. Overload protection
When the line is overloaded, the plastic cable will cause insulation heating or breakdown due to overcurrent or overvoltage. For mineral insulated cables, as long as the heating cannot reach the melting point temperature of copper, the cable will not be damaged. Even if the breakdown occurs instantaneously, the magnesium oxide at the breakdown point will not form carbide at high temperature. After the overload is cleared, the cable performance will not change and can still continue to be used normally.

5. The service life is longer and more safe and reliable
Since the structure of mineral insulated cable is composed of copper core and insulating sheath, which is a closed whole, it is difficult for the material to be aged due to the action of oxygen in the external air, which makes the overall service life of the cable longer (2-3 times the service life of ordinary cables). In addition, the characteristics of the copper sheath make the grounding of the cable better, Therefore, lightning protection and grounding measures are effectively realized, so as to ensure the safe and reliable operation of electrical lines.
Due to many excellent characteristics of mineral insulated cables, they have been successively adopted by many domestic electrical design codes or standards in recent years, and also used in many engineering projects in different industries. It can be expected that the use of mineral insulated cables in China will increase significantly in the next decade.

Harm of harmonics in power system

1. Hazards to distribution transformer:
For the distribution transformer with the wiring group of yyno, during the three-phase four wire system wiring, the third harmonic current generates harmonic voltage in the original and auxiliary windings of the distribution transformer and causes the neutral point voltage to rise. In addition, because the odd harmonics have the same phase, their phasors on the neutral line are superimposed, so that the phasors of the zero sequence current on the neutral line are superimposed. Therefore, the medium linearity is heated due to the harmonic current.
During three-phase three wire connection, the ACSR Cable sequence harmonic forms the neutral point voltage due to the same phase, which changes the phase voltage.
For the distribution transformer with dyno wiring group, the zero sequence harmonic current forms a circulating current in the winding to heat the distribution transformer winding and reduce the service life of the distribution transformer.
2. Hazards to power cables:
Due to the high frequency rise of harmonic number and the larger cross-sectional area of cable conductor, the skin effect is more obvious, resulting in the increase of AC resistance of conductor and the reduction of allowable current of cable. In addition, the resistance of the cable and the inductive reactance of the line are connected in series with the system, and the capacitor for improving the power factor and the capacitive reactance of the line are connected in parallel with the system. A certain value shows that the inductance and capacitance may vibrate.
3. Hazards to power capacitors:
When there are harmonics in the power grid, when the capacitor is input, the terminal voltage increases, the current passing through the capacitor increases, and the loss power of the capacitor increases. The capacitive reactance of the capacitor is inversely proportional to the frequency. The higher the frequency, the smaller the impedance. Therefore, the harmonic voltage can greatly increase the current of the capacitor. If the allowable conditions of the capacitor are exceeded, the capacitor will be overcurrent and overload, resulting in abnormal heating. Especially when the capacitor is put into the power grid with distorted voltage, it may also aggravate the harmonic of the power grid, that is, harmonic expansion. Partial discharge is induced in the medium. Due to the large voltage change rate and high partial discharge intensity, it can accelerate the aging of the insulating medium, so as to shorten the service life of the capacitor( Copyright) generally speaking, for every 10% increase in voltage, the service life of the capacitor will be shortened by about 1 / 2. When the harmonic is matched with the parameters of the capacitor, it will produce resonance and make the harmonic square. When the harmonic is serious, it will cause bulging, breakdown, group explosion and greater loss of the capacitor.
4. Damage to incandescent lamps:
Incandescent bulb is a widely used lighting fixture. Its life is closely related to the thermal effect of harmonics. The AAC Cable of distortion coefficient shortens the life of bulb, and changing the fundamental voltage has a greater impact than changing the distortion coefficient.

5. Damage to motor:
The damage of harmonic to motor is mainly caused by additional loss, mechanical vibration, noise and harmonic overvoltage.
The distorted wave can increase the magnetic saturation of the motor core, especially the magnetic saturation of the core clamp winding, and reduce the fundamental short-circuit impedance. It is generally believed that the magnitude of the Nth harmonic current of the three-phase asynchronous motor can be calculated by the following formula:
6. Impact on electric energy meter:
(1) mechanical watt hour meter is an inductive mechanism. When measuring electric energy, it can be divided into the following three situations:
① The distorted wave power supply provides linear load. At this time, the electric energy meter measures the fundamental wave electric energy and some harmonic electric energy, which will deteriorate the performance of user equipment. In this way, users not only suffer from harmonic pollution, but also pay more electricity charges.
② The sine wave power supply supplies the nonlinear load. At this time, the electric energy meter measures the fundamental wave electric energy minus part of the harmonic electric energy. This shows that users pollute the power grid and pay less electricity bills.
③ The distorted wave power supply supplies nonlinear loads, which is more complicated. The fundamental current flows to the load, while the harmonic current is not necessarily. It may flow to the load or to the power supply, depending on the specific situation. The most direct method is to measure with an instrument.
⑵ the electronic watt hour meter uses an integral circuit, whether the power grid provides harmonic current to the load or negative current
The harmonic current provided by the load to the power grid will be integrated and measured together, which will cause measurement error.
7. Hazards to low voltage switchgear:
For the circuit breaker for power distribution, the full electromagnetic circuit breaker is easy to be affected by the harmonic current, which increases the iron consumption and generates heat. At the same time, it is difficult to trip due to the influence on the electromagnet and eddy current, and the higher the harmonic number, the greater the influence; The thermal magnetic circuit breaker generates heat due to the skin effect of conductor and the increase of iron consumption, resulting in the reduction of rated current and tripping current; For electronic circuit breakers, harmonics should also reduce their rated current, especially for electronic circuit breakers that detect peak values. AAAC Cable can be seen that the above three distribution circuit breakers may misoperate due to harmonics.
For the leakage circuit breaker, because the harmonic will affect the leakage current, the circuit breaker may be abnormally heated and misoperate or refuse to operate. For electromagnetic contactors, the harmonic current increases the temperature rise of magnet components, and the increase of coil temperature reduces the rated current. For the relay, the current should also be reduced due to the influence of harmonic current. They may cause misoperation during operation.
8. Interference to weak current system equipment:
For weak current equipment such as computer network, communication, cable TV, alarm and building automation, harmonics in power system are coupled to these systems through electromagnetic induction, electrostatic induction and conduction to produce interference. The coupling strength of electromagnetic induction and electrostatic induction is directly proportional to the interference frequency, and the conduction is coupled through the common grounding. A large amount of unbalanced current flows into the grounding electrode to interfere with the weak current system.
9. Impact on communication lines:
Generally, the working frequency of audio channel is about 200-400hz, and many harmonics of power supply system are within this frequency range. Because the power levels of power lines and communication lines are very different, the harmonics in the power supply system will cause perceptible, sometimes even unacceptable interference noise.
10. Impact on rectifier, inverter and logic control circuit:
Rectifier devices and thyristor circuits are widely used in various electrical equipment, ranging from rectifier and inverter devices for DC transmission, DC power supply for urban trams, to frequency conversion equipment, television, microcomputer, AC regulated power supply, battery charger and uninterruptible power supply (UPS), On the one hand, these devices open and close different circuits according to a certain law, resulting in harmonic current injected into the power grid and become a harmonic source. On the other hand, the distorted waveform affects the normal operation of them and their loads. The distortion wave will cause the error of the control circuit, cause the ignition angular displacement, and the excessive current change rate and voltage change rate or overheating of the rectifier will cause equipment failure and damage to the rectifier components. These will bring harm to the converter. At the same time, the logic control circuit of some rectifier devices often leads to operation error due to distorted voltage.
11. Influence on fuse melt:
Overheating of the harmonic current in the melt will cause the displacement of its ampere second characteristic curve. Therefore, for the fault with low current, special attention should be paid to the selection of fuse to prevent accidental fusing and power failure, affecting the power supply.
12. Influence of harmonic skin effect:
The alternating current generates alternating magnetic flux through the conductor, and the alternating magnetic flux generates induced electromotive force with the conductor, so that the current density inside the conductor increases from the center to the outside along the conductor section, and the central current density is the smallest, which is commonly known as skin effect. Skin effect not only reduces the current carrying capacity of the conductor, but also increases the loss of the conductor, and this skin effect becomes more serious with the increase of current frequency. In general, the loss caused by skin effect is small at power frequency (50 Hz), while when the harmonic frequency is high, the loss and impact caused by skin effect such as harmonic with fifth harmonic frequency above 250 Hz are very significant. Therefore, the skin effect of harmonics should be considered when selecting conductors, and the conductor section should be increased appropriately.
13. Harmonics are also harmful to human body:
From the perspective of human physiology, when human cells are stimulated and excited, they will fluctuate rapidly or flip reversibly on the basis of cell membrane resting potential. If its frequency is close to the harmonic frequency, the electromagnetic radiation of power grid harmonic will directly affect human brain and heart.
Harm of harmonics to cables
As we all know, harmonic refers to the electric quantity whose frequency is an integral multiple of the fundamental wave contained in the current.
Generally, harmonic generation comes from three aspects: harmonic generation due to low quality of power generation, harmonic generation due to transmission and distribution system and harmonic generation due to electrical equipment. The third point is the main cause of harmonics, such as nonlinear loads, such as rectifier, switching power supply, UPS, frequency converter, inverter, etc. As shown in Figure 1, the harmonic generated by the equipment.

Figure 1 harmonics generated by equipment
The harmonics generated by the above three points have a serious impact on our electrical equipment. For the Xi’an Metro cable mentioned at the beginning of this article. Let’s focus on the harm of harmonics to cables.
Harmonic pollution will increase the dielectric loss, transmission loss, leakage current, temperature rise and partial discharge of dry-type cable, and increase the possibility of single-phase grounding fault.
Because the distributed capacitance of power cable can amplify the harmonic current, when the system load is low, the system voltage increases and the harmonic voltage increases accordingly. The higher the rated voltage level of the cable, the greater the risk of cable medium instability caused by harmonics, and the more prone to failure. As shown in Figure 2, it is cable combustion caused by harmonics.

Figure 2 cable combustion caused by harmonics
For the problem cables of Xi’an metro, the impact of harmonics will be more prominent. Unqualified cables and heating caused by harmonics are prone to accidents. This will be more serious in a relatively closed and crowded subway station. Of course, the problem with cable is not just about harmonics.
Therefore, for the safety of our transportation and other aspects, we should not only require from the transmission medium, but also check from the source of power quality. At this time, a device is needed to accurately capture and measure all parameters of power quality, and then analyze them to timely investigate possible potential safety hazards.

Mineral insulated cables in fire power distribution

Mineral insulated ACSR Cable, the full English name is mineral insulated cable, and the abbreviation is (MI) cable.
Due to its complex process, high production cost and much higher market price than conventional YJV and yjy cables, it was rarely used in China at the initial stage and was only used in important places with high requirements for safety conditions. Later, it was clearly required to be used under certain conditions due to the implementation of code for fire protection design of buildings gb50016-2014, which was widely popularized.
But for most engineers who do design, they often know to use it, but their understanding of it is not as good as YJV cable.
(1) Structural form
It is a kind of cable that uses copper sheath to wrap copper conductor core wire, and uses magnesium oxide powder as inorganic insulating material to isolate conductor and sheath (that is, magnesium oxide insulating layer is between core conductor and copper sheath). The outermost layer can select appropriate outer sheath as required.
See the following figure:

Mineral insulated (MI) cable
There is also a similar cable, which uses metal sheath instead of copper sheath to wrap conductor core wire and magnesium oxide insulation layer, which is called [mineral insulated metal sheathed cable].
(2) Performance and characteristics
1. Fire resistance
From the above structural form, mineral insulated cable does not contain organic materials, so it has the characteristics of non combustion, smokeless, non-toxic and fire resistance.
The melting point of copper is 1083 ℃, and the melting point of mineral insulating layer is above 1000 ℃, while the maximum temperature at the fire site of general civil buildings is below 1000 ℃. In this way, the copper sheath of the secondary layer can withstand the high temperature at the fire site.
The common fire-resistant cable, also known as organic insulated fire-resistant ACAR Cable, generally has a fire-resistant temperature of 750 ~ 800 ℃ for 90min. Therefore, the fire resistance of mineral insulated cable is quite excellent, and it is safe to use it in the fire area below the melting point of copper.
2. High temperature resistant operation
We know that the current carrying capacity and working temperature of the core are actually taken from the withstand temperature of the cable insulation layer. The higher the withstand temperature of the insulation layer, the greater the current carrying capacity.
Mineral insulated cable can withstand continuous working temperature up to 250 ℃ according to different application places. Under special circumstances, the AAAC Cable can maintain operation for a short time at a temperature close to the melting point of the copper sheath. It is very suitable for laying in high temperature places, such as metallurgy, boiler, glass furnace, blast furnace and so on.

3. Long life
The inorganic materials used in the insulating layer and sheath layer of mineral insulated cable can make it more stable and longer service life.
4. Waterproof, explosion-proof and high mechanical strength
The insulating layer of mineral insulated cable is processed by high-density compaction process, and then protected by seamless copper sheath. In the product standard, it must meet the three requirements of fire resistance, spray resistance and mechanical impact, and can withstand severe impact and mechanical damage.
(3) Classification and model
According to the cable structure, it can be divided into [rigid] and [flexible]. As the name suggests, rigid mineral insulated cables are very difficult to bend during construction and installation, while flexible cables are relatively easy to lay, and their structural profile
Rigid mineral insulated cable is marked as [BTT] type, and flexible mineral insulated cable is marked as [RTT] type.
National standard GB / T 13033-2007 rigid cable models: light load 500V bttq, bttvq, bttyq, heavy load 750V bttz, bttvz, bttyz. 500V and 750V here refer to the voltage between the core conductor and the sheath and between each conductor does not exceed 500V and 750V.
The models of flexible cables in the national standard GB / T 34926-2017 are rttz, rttyz and rttvz, and the voltage levels are 0.6/1kv or 450 / 750V.
The models of other flexible cables are named by each manufacturer. There are more than ten common types, such as bttrz, bbtrz, yttw, ng-a (btly), etc.
From the above, the national standard for rigid cables was promulgated and implemented very early, which has strong constraints on the products of various manufacturers and fixed product models; The flexible cable market was chaotic before the introduction of the national standard.

However, both rigid and flexible cables can pass the most stringent C, W and Z tests in the British Standard Code for fire resistance of cables bs6387.
Finally, for the engineering design and application of mineral insulated cables, there is a problem that everyone is concerned about, that is, as pointed out in article 10.1.10-3 of code for fire protection design of buildings gb50016-2014 (2018 Edition), mineral insulated non combustible cables should be used for fire distribution lines.

What is the reason for the problem of high voltage cable?

ACSR Cable is the bridge between power supply equipment and electrical equipment, which plays the role of transmitting electric energy. It is widely used, so faults often occur. The following briefly analyzes the causes of common problems of YJV high-voltage cable. According to the causes of faults, they are roughly divided into the following categories: Manufacturer’s manufacturing reasons, construction quality reasons, design reasons of design unit and external force damage.
1、 Reasons for construction quality there are many cases of high-voltage cable system failure caused by construction quality. The main reasons are as follows:
1. The site conditions are poor, the environment and process requirements of cables and joints are very high when they are manufactured in the factory, and the temperature, humidity and dust on the construction site are not easy to control.
2. During cable construction, small slip marks will inevitably be left on the insulation surface, and semi-conductive particles and sand particles on abrasive cloth may also be embedded in the insulation. In addition, moisture will be absorbed in the insulation due to insulation exposure in the air during joint construction, which will leave hidden dangers for long-term safe operation.

3. The installation did not strictly follow the process construction or the process regulations did not consider the possible problems.
4. DC withstand voltage test is adopted for completion acceptance, resulting in the formation of reverse electric field in the joint, resulting in insulation damage.
5. Due to poor sealing treatment. The intermediate joint must adopt the sealing structure of metal copper shell plus PE or PVC insulation and anti-corrosion coating, and the lead seal is dense during on-site construction, so as to effectively ensure the sealing and waterproof performance of the joint.
2、 The manufacturer’s manufacturing reasons are divided into cable body reasons, AAAC Cable joint reasons and cable grounding system reasons according to different parts.
1. Reasons for cable joint manufacturing high voltage cable joints used to be wrapped, molded, molded and other types, which requires a large amount of work to be made on site. Moreover, due to the limitations of on-site conditions and manufacturing process, there will inevitably be air gaps and impurities between insulating tape layers, so problems are easy to occur. The commonly used types in China are assembled type and prefabricated type. The cable joint is divided into cable terminal joint and cable intermediate joint. No matter what type of joint, the cable joint failure generally occurs at the fracture of cable insulation shield, because this is the part where the electrical stress is concentrated. The reasons for the cable joint failure due to manufacturing reasons include manufacturing defects of stress cone body, insulation filler problems, oil leakage of sealing ring and so on.

2. Cable grounding system cable grounding system includes cable grounding box, cable grounding protection box (with sheath protector), cable cross interconnection box, sheath protector, etc. The common problems are mainly due to the poor sealing of the box and the water inflow, resulting in multi-point grounding and excessive induced current of the metal sheath. In addition, unreasonable parameter selection or poor quality of sheath protector and unstable zinc oxide crystal are also easy to cause sheath protector damage.
3. The reasons for the manufacture of the cable body generally include insulation eccentricity, uneven insulation shield thickness, impurities in the insulation, protrusions in the internal and external shields, uneven crosslinking degree, cable moisture, poor sealing of the cable metal sheath, etc. some conditions are more serious, and faults may occur in the completion test or shortly after putting into operation, Most of them exist in the form of defects in the cable system, causing serious hidden dangers to the long-term safe operation of the ABC Cable.

How to avoid being trapped when buying household cables?

Cable is a relatively insignificant raw material in home decoration, but it is closely related to everyone’s daily life and involves the problem of safe power consumption in daily life. Therefore, when purchasing AAAC Cable, we should pay special attention to avoid buying fake and shoddy goods. Here is a detailed description of how to price the cable and what key points should be paid close attention to when purchasing.

How much does a meter of cable cost
At this stage, the price of wires on the market is very unstable. The price of wires depends on the price fluctuation of copper. The more expensive copper is, the more expensive cable is. Moreover, the price of different well-known brands will also vary. Generally, the price of 4 square meters is about 230 yuan for one roll (100 meters long), and that of 2.5 square meters is 140 yuan for one roll (100 meters long), 1.5 is 85 yuan a roll (100 meters long). This price is for reference only. The actual price is based on the local specific price.
Cable selection is an important link
1. Length
Pay attention to the length. Some people will find that the number of meters on the ACSR Cable line they buy is 100 meters. However, it should be noted that there is a meter mark, but in the middle part, some black chambers of Commerce count less than 10 meters. For example, after 30 meters, they gradually mark 40 meters.
2. Copper quality
The true red copper of the cable is a reddish color, while brass turns yellow. In addition, red copper is relatively soft and brass is relatively hard. It is not too much to fake brass at this stage.
3. PVC material
Pay attention when selecting cables. Many people will make copper core wires very standard, but they are fake and shoddy products on PVC materials.

4. CCC product certification certificate
The cable line shall be marked with CCC product certification certificate as far as possible. Since the cable goods are compulsory identity certification goods in China, all machinery manufacturing industries shall obtain CCC product certification certificate verified by China electric welder product quality certification Research Association as far as possible. In addition, the cable is associated with safe power consumption, and the quality of the cable will damage everyone’s asset and capital security. Therefore, we must select the cable products with CCC product certification certificate.
5. Product certificate
Check whether the AAC Cable is marked with product certificate, specification and model, test, production and manufacturing date, enterprise name, production and processing place, telephone, etc. This is the product produced by reliable manufacturers. Everyone should understand it correctly when buying.

How to distinguish the quality of aluminum alloy cables

Conductor, insulation and armored sheath are necessary for the composition of aluminum alloy cables. The quality of aluminum alloy cables mainly depends on the aluminum alloy conductor rods and cable insulation. Aluminum alloy cables have very good performance, corrosion resistance, and mechanical Performance, bending performance, flexibility, etc.
1. Aluminum alloy conductor rod
See if we can independently produce high-quality aluminum alloy conductor rods:
1. At present, there are not many manufacturers with independent aluminum alloy conductor production technology. They have aluminum alloy conductor rod production lines that can be continuously smelted, continuous casting, continuous casting and rolling. If they do not have independent aluminum alloy conductor rod production capacity, rely on Consignment processing, so-called secret smelting, or other aluminum alloy conductor rods purchased without a formal source not only cannot ensure the basic quality of aluminum alloy cables, but also cannot control the quality of the cables from the source.
2. In addition to the aluminum alloy conductor rod production line with smelting, continuous casting, continuous casting and rolling, it also depends on the size of the continuous casting billet section of its production line. The larger the section, the better the quality of the rolled aluminum alloy rod. Excellent, “good steel is made by hard work.” Excellent aluminum alloy conductor rods are the decisive factor for the electrical and mechanical properties of aluminum alloy cables. If you do not have high-quality aluminum alloy rods, no matter how drawing, stranding, cabling, armoring, etc., the subsequent processes cannot be changed The basic quality of its conductor.

2. Cable insulation
There are three things to look at with regard to insulation; cross-linking degree, stranded conductors, and conductor cable annealing:
1. Cross-linking degree: One of the advantages of aluminum alloy cables over copper cables is that all aluminum alloy cables are insulated with cross-linked polyethylene, and the operating temperature of the cable is 90 degrees. It is precisely because of the use of cross-linked polyethylene insulation that there is a problem of cross-linking degree. Regular professional aluminum alloy cable manufacturers should have a special cross-linking room.
2. Stranded conductor: Look at the conductor stranding technology and conductor stranding production line. At present, the stranded conductor equipment in the domestic cable industry is basically the same. The stranded conductor produced usually produces aluminum chips and burrs, which damage the insulation and affect the insulation. Effect, cause safety hazards and shorten insulation life. The advanced stranded conductor equipment is a sub-motor type, PLC program-controlled nano-technology conductor stranding equipment. Using this advanced process equipment, computer-controlled production programming, and innovative top-level nano-technology, the aluminum alloy conductors produced have no aluminum on the surface Chips, no burrs, no oil, no bumps, no scratches, no scratches, can effectively ensure that the cable insulation is free from any damage and destruction, and the service life of the product is much higher than that of similar products.
Third, the performance of aluminum alloy cables
1. Corrosion resistance: The corrosion resistance of pure aluminum is better than that of copper, but the corrosion resistance of aluminum alloy is better than that of pure aluminum, because the chemical elements such as rare earth added to aluminum alloy can increase the corrosion resistance of aluminum alloy, especially The performance of electrochemical corrosion resistance solves the long-term electrochemical corrosion problem of pure aluminum at the joint.
2. Mechanical properties: tensile strength and elongation. Compared with pure aluminum conductors, aluminum alloy conductors have added special ingredients and adopted special processing techniques to greatly improve the tensile strength, and the elongation rate is increased to 30%, making it safer and more reliable to use.
3. Bending performance: The bending performance of the aluminum core cable is very poor, and the bending is easy to break. The bending radius of the aluminum alloy power cable is 7 times the outer diameter of the cable, which is far better than the GB/T12706 “small bending when the cable is installed. 10 to 20 times the outer diameter of the cable specified in “Radius”.

4. Flexibility: As long as the pure aluminum cable is twisted at a certain angle for a few times, the conductor will crack or break, which is easy to cause accidents. The aluminum alloy power cable can withstand dozens of bends, eliminating the installation and use of pure aluminum cables in the past. The hidden dangers of accidents occurred during the process, which greatly improved the safety and reliability.
5. Aluminum alloy conductor is an emerging conductor material formed by adding rare earth, magnesium, copper, iron and other elements to pure aluminum through alloy technology. As we all know, after adding other alloying elements to aluminum, the electrical conductivity will decrease. However, through process control, the electrical conductivity can be restored to a level close to that of pure aluminum, making it have a current carrying capacity similar to that of pure aluminum.
6. Pure aluminum has poor creep resistance. The thermal expansion and contraction caused by power-on and power-off will cause a large amount of creep at the connection. After a long time, it will relax, and the contact resistance will increase and cause overheating, which is easy to cause accidents. The creep resistance of AA8000 series aluminum alloy is 300 of that of pure aluminum conductor, which greatly reduces the possibility of cable joint slack and improves the connection of conductors.

Commonly used aluminum alloy wire varieties and product advantages

The commonly used aluminum alloy wire varieties are as follows:
1. High-strength aluminum alloy wire
High-strength aluminum alloy wire is an aluminum alloy product with magnesium and silicon added to aluminum and processed to obtain sufficient strength, plasticity and electrical properties, deformation and heat treatment. It is the largest and most widely used aluminum alloy variety of aluminum alloy transmission lines. The electrical conductivity of high-strength aluminum alloy wire is 53% IACS, which is almost twice that of ordinary aluminum wire, and the single-wire strength of aluminum alloy is greater than 300Mpa. The strength of ordinary aluminum single wire is 150~170Mpa, and aluminum alloy wire has a greater advantage in strength.



2. Heat-resistant aluminum alloy wire
Heat-resistant aluminum alloys are classified into heat-resistant aluminum alloys with an electrical conductivity of 58% IACS and high-conductivity heat-resistant aluminum alloys in which yttrium is added to aluminum. Since the current carrying capacity of the wire used at 150°C can be increased by 61-69% than that of the wire used at 90°C, the heat-resistant aluminum alloy can be used as a compatible wire. The high-strength performance of high-strength heat-resistant aluminum alloy wire can improve its dynamic stability under short-circuit or overload conditions; its heat resistance can improve thermal stability. The super heat-resistant aluminum alloy and ultra-high heat-resistant aluminum alloy to be developed can further improve the current-carrying capacity and heat resistance of the wire, and further increase the long-term use temperature to 180°C, 210°C and 230°C.
Compared with traditional ACSR, high-strength aluminum alloy wire and heat-resistant low-resistance aluminum alloy wire have the following advantages:
(1) Under the same unit weight, the DC resistance of the aluminum alloy conductor is low. , The current capacity is large, the pulling force is large, the unit weight is larger than the pulling force;
(2) Compared with the condition of the same current-carrying capacity, aluminum alloy wire has the advantages of lighter weight, greater tensile force, and greater tensile force per weight. Aluminum alloy wire is a single material wire, easy to install and construct.
(3) The carrying hazard level of aluminum alloy conductors is low;
(4) The service life of ordinary steel core aluminum stranded wire is about 50 years, and the service life of aluminum alloy wire is more than 100 to 120 years.