The advantages of copper core cable and aluminum core cable are compared

Copper core cables have more advantages than aluminum core cables:

1. Low resistivity: the resistivity of aluminum core aerial bundled cable BS 7870 is about 1.68 times higher than that of copper core cable.

2. Good ductility: the ductility of copper alloy is 20-40%, the ductility of electrical copper is more than 30%, while aluminum alloy is only 18%.

3. High strength: the allowable stress at room temperature, copper is 7~28% higher than aluminum. Especially the stress at high temperature, the difference between the two is even greater.

4. Anti-fatigue: Aluminum is easy to break after repeated bending, while copper is not easy. In terms of elasticity index, copper is also about 1.7-1.8 times higher than aluminum.

5. Good stability and corrosion resistance: The copper core is resistant to oxidation and corrosion, while the aluminum core is susceptible to oxidation and corrosion.

6. Large current carrying capacity: Due to the low resistivity, the copper core cable of the same cross section is about 30% higher than the allowable current carrying capacity (the maximum current that can pass) of the aluminum core cable.

7. Low voltage loss: Due to the low resistivity of the copper core cable, the same current flows in the same section. The voltage drop of the copper core cable is small. Therefore, the same transmission distance can ensure higher voltage quality; in other words, under the allowable voltage drop condition, the copper core cable can reach a longer distance, that is, the power supply coverage area is large, which is beneficial to network planning and reduces The number of power supply points.

8. Low heating temperature: Under the same current, the copper core cable with the same cross section has much smaller heat than the aluminum core cable, which makes the operation safer.

9. Low energy consumption: Due to the low electrical resistivity of copper, it is obvious that copper cables have low power loss compared to aluminum cables. This is conducive to improving the utilization rate of power generation and protecting the environment.

10. Anti-oxidation and corrosion resistance: The performance of the connector of the copper aerial bundled cable(ABC) B231 is stable, and there will be no accidents due to oxidation. When the connector of aluminum core cable is unstable, the contact resistance will increase due to oxidation and heat will cause accidents. Therefore, the accident rate is much greater than that of copper core cables.

11. Convenient construction: The copper core is flexible and the allowable bend radius is small, so it is convenient to bend and easy to pass through; the copper core is fatigue-resistant, repeated bending is not easy to break, so the wiring is convenient; the copper core has high mechanical strength and can withstand relatively The large mechanical pulling force brings great convenience to construction and laying, and also creates conditions for mechanized construction.

12. Cheap price: Copper pole is 3.5 times the price of aluminum pole, and the proportion of copper is 3.3 times that of aluminum. Therefore, aluminum core cables are much cheaper than copper core cables, and are suitable for low-cost projects or temporary electricity use.

13. The cable is very light: the weight of the aluminum core cable is 40% of the copper core cable, and the construction and transportation costs are low.

14. Anti-oxidation and corrosion resistance: Aluminum quickly reacts with oxygen in the air to form an oxide film, which can prevent further oxidation. Therefore, aluminum wire is a necessary material for high-voltage, large-section, and large-span overhead power transmission.

Although aluminum core cables are cheap, copper cables have outstanding advantages in cable power supply, especially in the field of underground cable power supply. The underground power supply using copper core cables has the characteristics of low accident rate, corrosion resistance, high reliability, and convenient construction and maintenance. This is why copper abc cables are mainly used in underground power supply in China.

Three problems with cable insulation

It can be seen from the structure of the cross-linked polyethylene cable that there is a layer of outer semiconductor and copper shielding outside the main insulation layer of the cable. If this layer of outer semiconductor layer and copper shielding does not exist in the cable, then the core and core of the three-core cable Will an insulation breakdown occur during the period?

In the three-core cable terminal head, there must be a small section of the cable whose outer semiconductor and copper shielding layer have been stripped off, so is this small section of cable a weak link?
Can you overcome this problem by stripping less of the semiconductor and copper shielding layer (preserving the longer outer semiconductor and copper shielding layer as much as possible)? What is the disadvantage of keeping the longer outer semiconductor and copper shielding layer? The so-called “shielding” in the cable structure is essentially a measure to improve the electric field distribution. The cable conductor is formed by twisting multiple wires. An air gap is easily formed between it and the insulating layer. The surface of the conductor is not smooth, which will cause electric field concentration.Add a shielding layer of semi-conductive material on the surface of the conductor, which is equipotential with the shielded conductor and in good contact with the insulating layer, so as to avoid partial discharge between the conductor and the insulating layer. This layer of shielding is the inner shielding layer; Similarly, there may also be gaps at the contact between the insulating surface and the sheath, which is a factor causing partial discharge. Therefore, a shielding layer of semi-conductive material is added to the surface of the insulating layer. It has good contact with the shielded insulating layer and is in contact with the metal shield. The sheath is equipotential, so as to avoid partial discharge between the insulating layer and the sheath. This layer of shielding is the outer shielding layer; for extruded insulated cables without metal sheaths, in addition to the semi-conductive shielding layer, copper tape must be added Or the metal shielding layer wrapped with copper wire, the role of this metal shielding layer is to pass capacitive current during normal operation; when the system is short-circuited, it acts as a channel for short-circuit current and also plays a role in shielding the electric field.

It can be seen that if this outer semiconductor layer and copper shield do not exist in the ABC cable, the possibility of insulation breakdown between the core and the core of the three-core cable is very high. The main purpose of stripping off a small section of the shielding layer when making cable terminations or connectors is to ensure the creepage distance of the high voltage to the ground. The stress on the shielding fracture is very concentrated, which is a weak link! Appropriate measures must be taken for stress treatment. (Use stress cone or stress tube, etc.)

The length of the shielding layer is stripped to ensure the creepage distance; the basis is to enhance the creepage resistance of the insulating surface. Excessive stripping of the shielding layer will increase the difficulty of construction, and it is completely unnecessary to increase the cost of cable accessories.

Medium and low voltage cable accessories are currently used more products

The main types of products that are currently used for medium and low voltage cable accessories are heat shrinkable accessories, prefabricated accessories, and cold shrinkable accessories. They have the following characteristics:

1. Heat shrinkable accessories

The material used is generally a blend of polyethylene, ethylene-vinyl acetate (EVA), and ethylene-propylene rubber. This kind of product mainly uses stress tube to deal with the problem of electric stress concentration. That is, the parameter control method is used to relieve the electric field stress concentration. The main advantages are light weight, easy installation, good performance and low price.

The stress tube is a kind of heat-shrinkable tube with special electrical parameters with moderate volume resistivity (1010-1012Ωcm) and large dielectric constant (20-25). The electrical parameters are used to force the stress at the abc cable insulation and shielding fracture to evacuate. The stress tubes are more evenly distributed. This technology is generally used in cable accessories of 35kV and below. Because the stress tube will heat up when the voltage level is high and cannot work reliably.

The key technical issues in its use are:

To ensure that the electrical parameters of the stress tube must reach the values ​​specified in the above-mentioned standards, it can work reliably. In addition, attention should be paid to filling the air gap at the fracture of the cable insulation semi-conductive layer with silicone grease to eliminate gas and achieve the purpose of reducing partial discharge. Cross-linked cables will shrink greatly during operation due to poor internal stress handling, so when installing accessories, pay attention to the stress tube and the insulation shield to cover not less than 20mm to prevent the stress tube from separating from the insulation shield during shrinkage. Due to the small elasticity of heat-shrinkable accessories, air gaps may occur at the interface during thermal expansion and contraction during operation. Therefore, the sealing technology is very important to prevent moisture intrusion.

2. Prefabricated accessories

The material used is generally silicone rubber or ethylene propylene rubber. The geometric structure method is mainly used to deal with the stress concentration problem. Its main advantages are excellent material performance, easier and faster installation, installation without heating, good flexibility, and greatly improved interface performance. It is the main form adopted by low-voltage and high-voltage cables in recent years. The disadvantage lies in the high requirements for the outer diameter of the cable insulation layer. The usual interference is 2-5mm (that is, the outer diameter of the cable insulation is larger than the inner hole diameter of the cable accessory by 2-5mm). The interference is too small, and the cable The accessories will malfunction; the interference is too large, and the installation of the cable accessories is very difficult (high process requirements). Especially in the middle joint, the problem is prominent, the installation is not convenient, and it often becomes the point of failure. In addition, the price is more expensive.

The key technical issues in its use are:

The size of the accessory and the size of the cable to be installed must meet the specified requirements. In addition, it is necessary to use silicone grease to lubricate the interface to facilitate installation and fill the air gap of the interface. Prefabricated accessories generally rely on their own rubber elasticity to have a certain sealing effect, and sometimes sealants and elastic clamps can be used to enhance the sealing.

3. Cold shrinkable accessories

The material used is generally silicone rubber or ethylene propylene rubber. Cold-shrinkable accessories generally adopt geometric structure method and parameter control method to deal with the problem of electric stress concentration. The geometric structure method that uses the stress cone to relieve the concentrated electric field distribution is better than the product of the parameter control method.

Like prefabricated accessories, it has excellent material properties, can be installed without heating, and has good flexibility, which greatly improves the interface performance. Compared with prefabricated accessories, its advantage is that it is more convenient to install and only needs to be in the correct position. The installation can be completed by pulling out the inner lining core tube of the cable accessory. The material used is better than prefabricated accessories in terms of mechanical strength, and the requirements for the outer diameter of the cable insulation layer are not very high, as long as the inner diameter of the cable accessories is less than the outer diameter of the cable insulation 2mm (the data is like this, this The type attachment requires a deviation of 2~5mm (Editor) to fully meet the requirements. Therefore, the construction and installation of cold shrinkable accessories are more convenient.

Its biggest feature is that the installation process is more convenient and quicker. After the installation is in place, its working performance is the same as the prefabricated accessories.

The price is equivalent to that of prefabricated accessories, and slightly higher than heat shrinkable accessories. It is the most cost-effective product.

Application of XLPE cable in urban network

Actively develop the ABC cable distribution network to meet the needs of load growth and urban construction (improvement of the city appearance and reduction of land occupation). In recent years, with the extensive use of cables in urban network construction and transformation, cable failures have gradually increased.

It is an important task for electric power workers to discuss the problems that should be paid attention to in the use of cables in urban networks.

1. Analysis of common cable faults The most direct cause of cable faults is breakdown due to insulation degradation.

Analyze the causes of cable failures in recent years, mainly include:

(1) Overload operation. Long-term overload operation will cause the temperature of the power cable to rise and the insulation aging, which will lead to insulation breakdown.

(2) Construction quality. Electrical aspect: the construction process of the cable head fails to meet the requirements, the sealing of the cable head is poor, moisture invades the inside of the cable, and the insulation performance of the cable is reduced; protective measures are not taken when the cable is laid, the protective layer is damaged, and the insulation is reduced. In terms of civil engineering: poor drainage of pipe trenches in industrial wells, long-term soaking of cables in water, impairing the insulation strength; too small industrial wells, insufficient cable bending radius, and long-term extrusion.

(3) Damage by external force. Mainly, it was the brutal construction of machinery in municipal construction, digging wounds and cutting cables.

(4) Corrosion. The protective layer suffers from chemical corrosion or electric corrosion for a long time, which causes the protective layer to fail and the insulation decreases.

(5) The quality of the cable itself or the cable head accessories is poor, and the insulating glue dissolves and cracks, resulting in insulation degradation and accidents.

2. Response measures

(1) The design model should have a proper margin. On-site operating experience shows that for the important load cables that are continuously produced, a proper margin should be left in the design and selection. Although the investment is slightly larger, it can ultimately reduce cable failures and extend cable life.

(2) Laying methods should be adapted to local conditions. Different laying methods should be adopted for different areas. Commonly used laying methods are: direct buried laying, pipe laying, trench laying, laying in tunnels, etc. In urban areas and rainy and humid areas, direct burial should not be used; cable tunnels or cable wells should be used in areas where the number of cables is relatively concentrated; when trenches are not suitable, pipe laying methods can be used.

3) Choose good quality cables and cable head accessories. The quality of the cable is very important to prevent the deterioration of water branches. When choosing a cable, you should have a certain understanding of the production process and management of the cable, so that you can buy a good quality cable and lay the foundation for reducing failures. The quality problems of the cable head accessories will dissolve and crack the cable head insulation, causing the cable to be damp, the insulation drop, and cause accidents; in recent years, we have begun to adopt cold shrinkage on the cable heads and middle heads on both sides of the main cable (especially outdoors) Head craft. Because the processing and installation are more convenient, and it is easy to store and not easy to deform, the construction quality is less affected by human factors, so it is gradually promoted.

Cable quality defects and troubleshooting methods

The degree of crosslinking (hot extension) is unqualified
If the degree of cross-linking does not meet the standard, the thermal-mechanical properties of the 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 proportion of the compounding agent. The formula should be adjusted to solve it; 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 mold selection.
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, and the second is that the core is too small, or the conductor outer diameter 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 as uniform as possible, and the stranded wire that exceeds the process regulations can be used.
Surface scratches
(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 clean up in time if foreign matter is found.
(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.

Impurities
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 scorch, which affects the performance and service life of the cable. Therefore, 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 the 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 water 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 cooling, raise the water level and lower the temperature of the cooling water.
Unqualified ABC cable performance

(1) Unqualified free discharge and dielectric loss
The causes of dissociation discharge and dielectric loss unqualified are complex, 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 for the unqualified steel belt. The cushion shall be made of plastic tape with higher hardness, and ensure The thickness of the cushion.If you want to buy cables, you can learn about our Huaxing cables