abc cables

Typical failure of overhead cable line

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1. Common faults of empty overhead  cable lines
1. Overhead line failure
①Short circuit and damage of wires. The reasons that cause short circuit and damage to the wire are:
a. The distance between the wires and wires is small, and the flatness of the three-phase wires is different. It is very easy to cause color collision and short circuit when the wind blows, and the wires are burned.
b. Tree technology and internal metal objects falling on the line; accidentally touching the line when the crane is working also cause the wire to be short-circuited and damaged.
c. Long-term erosion by harmful substances in the surrounding environment, with a reasonable cross-section reduction. The damage to the wire is not very serious, and the method of laying wire maintenance can be considered as appropriate to solve it.
2. The wire connector is overheated. The reasons that lead to the over-temperature of the wire connector are:
a. The load current of the wire exceeds the larger specified value of the wire cross section.
b. The quality of the construction work of the wire connector is not good.
c. The circuit has been blown by rain and wind for a long time, and air oxidation and erosion have become more and more serious: the resistance of the connector loop increases: the hazard is hot. Department is
If the wire is overheated, you can try to reduce the load. Monitor the operation again, and allocate and solve it according to the development trend.

2. ABC Cable line failure
In terms of conditions, common cable faults include mechanical equipment damage, lead (aluminum) cracking, bursting, environmental pollution of terminal equipment heads, explosion of terminal equipment heads or intermediate connectors, insulation penetration, and metal material protection wire Common faults such as sleeve erosion holes. For this reason, common cable faults include damage by external force, chemical corrosion or electric erosion, lightning strikes, water immersion, improper construction of plant diseases and insect pests ↓Improper maintenance and other common faults. Common cable faults and avoiding methods are as follows:
① Water seepage of the plastic cable: Once the plastic is invaded by water, it is very easy to cause embrittlement of the insulation layer, especially when the temperature of the conductor is high, the infiltration and embrittlement caused by the water in the conductor is more serious. Therefore, no water seepage is allowed in the transportation, storage, laying and operation of plastic cables.
②Cable overload operation: The safety factor of cable operation is not so much related to the current carrying capacity of the cable. Overloading may increase the failure rate of the cable, and at the same time, it will continue to reduce the service life of the cable. The cable damage caused by overload is mainly in the following aspects:
a leads to the destruction of the wire contacts;
b. Speed ​​up the embrittlement of the insulation layer of the cable maintenance;
c. Make the lead bag of the cable swell and even crack, such as the fatigue, cracking, and cracking of the lead bag caused by the long-term overload of the cable with poor quality of production and poor installation standards;
d. The cable terminal equipment head is swollen and cracked by the bituminous insulating rubber.
③Destroyed by external force: Some of the safety accidents of the cable itself are caused by the destruction of mechanical equipment under external force. According to the investigation, the damage of mechanical equipment caused by external force caused by improper municipal management methods and improper construction of the project is about It accounts for 50% of cable safety accidents. Therefore, when cables are transported, hoisted, and laid through regenerated buildings, care must be taken to avoid the harm of external forces. During the construction of the surrounding engineering of the cable line, it is necessary to remind the construction workers to pay attention to this point and implement safeguard measures when necessary.
④Environmental pollution of the waterproof casing of the cable terminal equipment head: The key method is to clean the waterproof casing on time, and it is best to carry out complete cleaning under the power-off standard: in the area with serious pollution, the waterproof casing of the cable terminal equipment head should be coated Stain-resistant architectural coatings, or moderately improve the flame retardant grade of waterproof casing.
⑤The water seepage of the outdoor terminal equipment head explodes: mainly because of unreasonable operation and maintenance, the condensed water of the terminal equipment head will accumulate in the cable head, and finally cause the insulation layer to penetrate back and cause an explosion.
⑥The cable’s middle connector exploded: most of the cases were caused by the over-loading of the insulating rubber in the connector box and the shell swelling, or the poor conductor connection caused the connector to overheat and explode.
⑦The inspection of outdoor cable terminal equipment head has the following aspects:
a. Whether the waterproof casing at the end of the cable is cracked, and whether the electrode connecting wire clamp of the grounding wire of the transformer is heated:
b. Whether the insulating glue in the cable terminal equipment head becomes soft, overflows, lacks, and whether there is moisture on the surface:
c. Whether each sealing part of the cable terminal equipment head leaks oil;
d. Is the wire connector good?

Cable quality defects and troubleshooting methods

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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

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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.

Factors Affecting Cable Performance and Placement in Wiring

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Factors affecting Aerial Bundled Cable (ABC) SANS 1418 Standard and placement in the wiring six factors affecting cable performance:

  • Ultraviolet (UV)– Do not use cables without UV protection in direct sunlight.
  • Heat — The temperature of the cable in the metal tube or groove is very high, and many polymeric materials will degrade their service life at this temperature.
  • Water — moisture in a twisted-pair cable on a LAN can increase the capacitance of the cable, thereby reducing the impedance and causing near-end crosstalk problems.
  • Mechanical damage (repair cost)– Cable repair is very expensive and requires at least two terminations at each break point.
  • Grounding — If the shielding of the cable needs to be grounded, the appropriate standards must be complied with.
  • Total length of routing (not just between buildings)– Outdoor LAN twisted pair cables are used between buildings and the total length is limited to 90 meters. For 100Mbps or 1000Mbps networks, the paved distance cannot exceed this limit. If the laying distance is between 100 meters and 300 meters, optical cable should be chosen.

Is the cable placed in:

1.Under the eaves. 4/0 Aluminum Cable can only be used when they are not directly exposed to sunlight or ultra-high temperatures. Standard LAN cables are recommended.

  1. Exterior wall. Avoid direct sunlight exposure to the wall and man-made damage.
  2. In pipes (plastic or metal).If in pipes, pay attention to the damage of plastic pipes and the heat conduction of metal pipes.
  3. Hanging applications/overhead cables. Consider cable sag and pressure. What kind of binding do you plan to use? Whether the cable is exposed to direct sunlight.

  1. It is directly laid in the underground cable trench, which is the least controlled environment. The installation of cable trench should be checked regularly for dryness or humidity.
  2. Underground pipes. In order to facilitate future upgrades, cable replacement and isolation from surface pressure and surrounding environment, auxiliary pipe isolation, auxiliary pipe is a better method. But don’t expect the pipes to stay dry forever, which will affect the type of cable you choose.

Cable Quality Defects and Their Elimination Methods

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The crosslinking degree (thermal elongation) is not acceptable

If the crosslinking degree is not up to the standard, the thermal and mechanical properties of the cable are not qualified and can not meet the requirements of the working temperature of 90℃. The reasons for the unqualified crosslinking degree are as follows: first, the formula is unqualified, and the type and proportion of the complex agent is improper, so the formula should be adjusted to solve the problem; Two is the vulcanization process is not appropriate, such as the pressure is too low, the line speed is fast, the cooling water level is high, The solution is to first find out what the reason is, it may be one or several reasons exist at the same time, and eliminate the reasons.

Disqualified structure and appearance

(1) The thinnest point of insulation 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 high linear speed, small amount of extruder, improper selection of mold, etc.

The solution is to reduce the linear speed or extruder speed, 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 being collected and adjusted.

The solution is to keep the drape as stable as possible during driving.

The cable outside the bamboo joint is caused by the electrical, mechanical system causes the traction speed is not stable, the second is the die core is too small, or the conductor outside diameter is not uniform.

The elimination method is to check the mechanical, electrical system, troubleshooting. Properly adjust the size of the core, control the outer diameter of suburban counties as uniform as possible, more than the process requirements of the strand can be used.

Surface scratch

(1) the ACSR conductor encounters the upper or lower wall or foreign body in the vulcanized pipe. Therefore, it is required to adjust the suspension degree, try to make the wire core move in the middle of the crosslinked pipe, and clean it up in time when foreign bodies are found.

(2) there is burnt material on the outer edge of die sleeve. The solution is to adjust the temperature of the mold sleeve when starting the car to prevent overheating. Once burnt, it should be stopped immediately, or it will not get better by itself.

impurities

Most of the impurities in insulating material and semi-insulating material are brought into the process of mixing and extruder feeding. During the operation, strict attention should be paid to the cleaning of the material to prevent external impurities from mixing. Another impurity is coke pimp, its existence affects the performance and service life of the cable, so the temperature is strictly controlled when mixing and extrusion, to prevent the occurrence of coke phenomenon.

Air bubbles

There are two possible causes of air bubbles in insulation. One is caused by extrusion. The solution is to choose the right mold. The shielding layer has bubbles, the main reason is that there is water in the material, before extrusion should be dry, two is not sufficient cooling, then there will be as follows, in the isometric circumference of the line core appears a circle of bubbles.

The elimination method is to strengthen cooling, rise the water level and lower the temperature of cooling water.

(1) Cable performance is not up to standard

Disqualification of free discharge and dielectric loss

Free discharge and dielectric loss unqualified causes are very complex, it has to do with external shielding. Whether the insulation contains bubbles and impurities, and the properties of raw materials are closely related. Elimination method is to keep raw materials clean, strictly according to the process of production.

(2) cable insulation breakdown

Cable insulation breakdown is mainly caused by the insulation material mixed with impurities and external damage. Due to the strict avoidance of external damage, impurities should be avoided as far as possible. Semi-finished products should be strictly managed to prevent tripping and bruising.

(3) cushion breakdown

The main reason for the breakdown of the cushion is that the steel has burr, roll edge and puncture the cushion. The method to eliminate the steel strip is not equal to the unqualified quality requirements. The cushion is made of plastic belt with greater hardness, and the thickness of the cushion should be ensured.

Plastic Extrusion and Traction Speed of Cable Technology

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The rate of plastic extrusion

According to the flow rate analysis of the viscous fluid in the material conveying and homogenizing section of the ABC conductor,  the flow rate of the plastic (that is, the extrusion speed) is proportional to the screw speed, and the screw speed is an important operating variable to characterize the extrusion speed in the extrusion process because of the convenience of adjustment. Therefore, in general, increasing the screw speed is an important means to improve the production capacity of modern plastic extruder and realize high-speed extrusion. But the analysis of the plastic melting length shows that the increase of the screw speed, on the one hand, increases the viscous dissipation heat due to the enhanced shear effect; On the other hand, in the absence of head pressure control, the screw speed increases, the flow rate increases, and the material stays in the machine time is shortened. Moreover, the influence of the latter is more than that of the former, and the normal extrusion process will be destroyed due to the extension of the melt length to the homogenizing section. Therefore, it is necessary to increase the screw speed to improve the extrusion speed, but also to increase the heating temperature or use the control of the head pressure to achieve the purpose.

Plastic extrusion speed or the quality of plasticizing is related to the use of plastic material and temperature control, the plasticizing temperature of various plastics is different. If you want to quickly extrude plastic, only the material is good, the temperature is appropriate, to achieve. In addition, the extrusion speed is closely related to the extrusion thickness. In the normal extrusion process, the amount of glue is large and the extrusion speed is slow. On the contrary, the extrusion speed is fast, on the premise of ensuring the quality, the extrusion speed can be appropriately improved.

Traction speed

Extruded products are dragged through the machine head by traction device, in order to ensure the quality of products, the traction speed is required to be uniform and stable, in coordination with the screw speed, to ensure the uniformity of extrusion thickness and outer diameter of products. If the traction speed is not stable, the extrusion layer is easy to form bamboo joints, and the extrusion thickness is large when the traction speed is too slow, and the phenomenon of glue stacking or empty pipe occurs. When the traction speed is too fast, it is easy to cause extruding and thinning, or even the phenomenon of degumming and leakage. Therefore, in the normal extrusion process, we must control the traction speed.

International Advanced Level of Environmental Protection Wire and Cable Indicators

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Environmental protection wire refers to the material is environmental protection wire.

The material includes insulating material, conductor material and shielding material. Insulation such as PVC, irradiated cross-linked PVC (XL-PVC), irradiated cross-linked polyethylene (XL-PE), low smoke free (Halogen-free), silicone rubber, Teflon Telflon and so on. The environmental protection of insulation materials is mainly the EU’s RoHS environmental protection directive and the EU’s environmental regulations on children’s toys do not contain 6P (Non-6P), that is, does not contain phthalates. Now the most environmentally friendly is low smoke halogen-free, does not contain halogen elements.

The most common conductor material is copper. Copper has bare copper (brass, red copper), tinned copper, silver-plated copper wire, etc., which are essentially copper, but the surface is plated with other substances. Now there are copper – coated aluminum and copper – coated steel conductors on the market. If the electrical performance requirements are high, copper is the best. The environmental protection of conductors is mainly required to be free of heavy metals (RoHS).

Environmental protection cable means that it does not contain lead, cadmium, hexavalent chromium, mercury and other heavy metals, and does not contain brominated flame retardants. The environmental protection performance of the cable is tested by SGS recognized testing institutions, and it is in line with the European Union Environmental Protection Directive (ROSH) and higher than its index requirements. No harmful halogen gas, no corrosive gas, less fever when burning, no pollution of soil wires and cables.

Main technical indicators:

  1. Rated voltage: 450/750V and below
  2. The maximum permissible operating temperature of the conductor shall not exceed 70 ℃, 90 ℃ and 125℃ respectively.
  3. Cable combustion smoke density in line with GB/T 17651-1998 (equivalent to IEC1043) standard requirements, light transmittance ≥60%.
  4. Cable halogen acid content test conforms to GB/T 17650-1998 (equivalent to IEC 754-2) standard requirements.

(1) PH ≥4.3

(2) Conductivity ≤10μs/mm

  1. The flame retardant performance of the cable conforms to the requirements of GB/T 12666-1990.

6.Toxicity index of cable ≤3.

National Standard Cable

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In today’s wire and cable market, product quality levels are uneven, and production companies are mixed. Many Party A simply uses price as the procurement standard, which breeds a market for substandard products. So that when users are faced with different prices of “national standard cables”, they will be at a loss, not knowing how to identify and buy national standard cables. Today’s article mainly introduces the standards and identification of national standard cables. What kind of cables are produced in accordance with national standards? How to distinguish and distinguish cables of different qualities? What kind of quality is “enterprise standard/non-standard”, “market national standard” and “protected resistance national standard”? No matter you are selling cables , Or purchasing, I believe it will be helpful to you.

What is Aerial Bundled Cable (ABC) HD 626 S1 Standard

The national standard cable, literally understood, is the wire and cable produced in strict accordance with the national standard. my country has clear regulations on the appearance, mechanical strength, insulation of the sheath, pressure resistance, wire resistance and other aspects of the cable. Different types of cables have different national standards, mainly as follows:

Irradiation cross-linked power cable (0.6/1KV) executive standard: GB/T12706.1-2008

Medium voltage cross-linked cable (6/6KV-26/35KV) executive standard: GB/T12706.2-2008

High voltage cross-linked cable (64/110KV) executive standard: GB/T 11017-[/B]2002

Control cable (450/750V) executive standard: GB9330-88

Aluminum stranded wire and steel core aluminum stranded wire (0.6/1KV) executive standard: GB/T 1179-1999

How to identify the (ABC) SANS 1418 Standard

  1. It depends on

See if there is a quality system certification; see if the certificate is standardized; see if there is a factory name, site, inspection stamp, and date of production; see if there are trademarks, specifications, voltages, etc. printed on the wires. It also depends on the cross-section of the copper core of the wire. The high-quality copper is bright in color and soft in color, otherwise it is inferior.

  1. Try

It is recommended to bend a wire head repeatedly by hand. Anything with soft hand feeling, good fatigue resistance, elastic plastic or rubber hand feeling and no cracks on the wire insulator is the best product.

  1. Weighing

Good quality wires are generally within the specified weight range. For example, the commonly used plastic insulated single-strand copper core wire with a cross-sectional area of ​​1.5mm² has a weight of 1.8~1.9 kg per 100 meters; a 2.5mm² plastic insulated single-strand copper core wire has a weight of 3~3.1 kg per 100 meters; poor quality The weight of the wire is insufficient, or the length is not enough, or the copper core of the wire is too much impurity

  1. Look at copper

The copper core of the qualified copper core wire should be purple-red, shiny, and soft to the touch.

The fake and inferior copper core wires are purple-black, yellowish or white, with many impurities, poor mechanical strength, poor toughness, and will break with a little force, and there are often broken wires in the wires.

When checking, you only need to peel off the wire 2cm, and rub a piece of white paper on the copper core. If there are black substances on the white paper, it means that there are more impurities in the copper core. In addition, the insulating layer of fake wires seems to be very thick, but in fact, most of them are made of recycled plastics. Over time, the insulating layer will age and cause leakage.

  1. Look at the price.

Due to the low production cost of counterfeit and shoddy wires, vendors often sell them at low prices under the guise of low prices and good quality when selling.

“Non-standard/enterprise standard/market national standard” and “protected resistance national standard”?

When many sales companies are asked whether they are national standard cables, they often hear words like “market national standard” and “resistance protection national standard”. Many people have a little understanding. What do these vague words mean?

National standard for resistance protection: The cable is used to energize, and the resistance value of the conductor directly affects the conductivity. If the conductor resistance is too large, the conductivity will be poor, and a large amount of heat will be generated when a large current passes, which will cause a fire. At the same time, due to the large resistance, heat will be generated and the power will be consumed inaction.

The resistance-protected cable is to ensure that the resistance value of the cable is in compliance with the national standard, but it does not guarantee that the component materials of the cable are produced in full accordance with the national standard, such as the number of conductor squares, insulation, and sheath. To put it bluntly, it means that the manufacturer can achieve safe use of cables under the premise of reducing material costs through various technological innovations (or means).

Note that two words are used here: innovation and means. Innovation refers to reducing costs through technological innovation, such as current aluminum alloy conductors, special-shaped conductors, etc., such cables reduce the price on the premise of ensuring safe use. Some manufacturers use some illegal means to reduce costs, such as using second-generation materials, reducing conductor purity, etc. Even if the resistance value of such a cable is within the standard range, its use is extremely unsafe. The cable must be checked again and again.

Wire and cable common sense questions and answers

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1. What are the requirements for cable piping?

Answer: (1) The distance from the top of the pipe to the ground is 0.2m in the workshop, 0.5m under the sidewalk, and 0.7m in general areas;

(2) Pipe pits should be installed at the change direction and branch, and pits should also be added when the length exceeds 30mm;

(3) The pit depth is not less than 0.8m, and the manhole diameter is not less than 0.7mm;

(4) The drain pipe should have a drainage slope of 0.5% to 1% inclined to the pit.

2. What are the requirements for the resistance of the cable conductor connection point?

Answer: The resistance of the connection point is required to be small and stable. The ratio of the resistance of the connection point to the conductor of the same length and the same cross-section should not be greater than 1 for the newly installed terminal head and intermediate head; This ratio should not be greater than 1.2.

3. What requirements should the design of cable joints and intermediate head meet?

Answer: The requirements that should be met are:

(1) High compressive strength and good conductor connection;

(2) High mechanical strength, low medium loss;

(3) Simple structure and strong sealing.

4. What is a cable fault? There are several common types?

Answer: Cable failure refers to the failure of the cable’s insulation breakdown during the preventive test or during the operation, which forces the aerial bundled cable 33-209 standard  to power out due to insulation breakdown, wire burnout, etc. Common faults include ground faults, short-circuit faults, disconnection faults, flashover faults and mixed faults.

5. How to deal with the single-phase ground fault of the cable line?

Answer: Generally speaking, the damage to the cable conductor is only partial. If it is a mechanical damage and the soil near the fault point is relatively dry, local repairs can generally be carried out and a fake connector is added, namely Without sawing the cable core, only the fault point is insulated and sealed.

6. What tests and inspections should be carried out on power cables before laying?

Answer: Before laying, check whether the type, specification and length of the cable meet the requirements and whether there is external force damage. Low-voltage cables use a 1000V megohmmeter to remotely measure the insulation resistance, and the resistance is generally not less than 10MΩ, and high-voltage cables are measured with a 2500V megger. The resistance is generally not less than 400MΩ.

7. What should be paid attention to when laying cables in the main workshop?

Answer: When laying cables in the main factory building, generally pay attention to:

(1) All control cables leading to the centralized control room should be laid overhead;

(2) 6KV cables should be laid in tunnels or pipes, and the high groundwater level can also be laid overhead or pipes;

(3) For 380V cables, tunnels, trenches or pipes should be used when the two ends of the cable are at zero meters. When one end of the equipment is on the top and the other is on the bottom, it can be partially overhead laid. When the local water level is high, it should be overhead.

8. Where are the inner and outer shielding layers of power cables? What material is used? What’s the effect?

Answer: In order to make the insulation layer and the cable conductor have better contact and eliminate the increase in the electric field strength of the conductor surface caused by the unevenness of the conductor surface, the conductor surface is generally covered with an inner shielding layer of metalized paper or semiconductor paper tape. In order to make the insulating layer and the metal sheath have better contact, generally the outer surface of the insulating layer is covered with an outer shielding layer. The material of the outer screen layer is the same as that of the inner screen layer, and sometimes copper tape or braided copper ribbon is tied outside.

9. Briefly describe the composition and performance of epoxy resin compound.

Answer: The epoxy resin compound is composed of epoxy resin added with hardener, filler, toughening agent and diluent. Has the following properties:

(1) Have sufficient mechanical strength;

(2) Excellent electrical performance;

(3) Stable electrical performance;

(4) It has sufficient adhesion to non-ferrous metals;

(5) Good corrosion resistance;

(6) When used outdoors, it is resistant to rain, light, and humidity.

Physical characteristics of aluminum alloy cables

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The advantage of aluminum alloy cable over ordinary cables is that under the same volume, the actual weight of aluminum alloy is about one-third of copper. According to this calculation, under the premise of meeting the same electrical conductivity, the length of the aluminum alloy cable with the same weight is twice that of the copper cable. Therefore, the weight of the aluminum alloy cable is about half of the copper cable at the same current carrying capacity. The use of aluminum alloy cables instead of copper cables can reduce the weight of the aerial bundled cable ASTM b231, reduce the installation cost, reduce the wear of the equipment and the cable, and make the installation work easier.

Aluminum alloy power cable is a new type of material power cable created by advanced technologies such as AA-8000 series aluminum alloy material as the conductor, using special pressing technology, annealing treatment, and chain armoring technology.

The difference between aluminum alloy cables and ordinary cables: aluminum alloy cables use AA-8000 series aluminum alloy conductors, while ordinary cables use copper or pure aluminum as cable conductors.

Tensile strength and elongation

Compared with pure aluminum conductors, aluminum alloy conductors have greatly improved tensile strength due to the addition of special ingredients and special processing techniques, and the elongation rate has increased to 30%, making it safer and more reliable to use.

Thermal expansion coefficient

The coefficient of thermal expansion is used to calculate the dimensional change of the material when the temperature changes. The coefficient of thermal expansion of aluminum alloy is equivalent to that of copper. Aluminum connectors have been reliably used for copper and aluminum conductors for many years, and most of the electrical connectors used today are made of aluminum, which is especially suitable for aluminum alloys. So the expansion and contraction of the aluminum alloy conductor and the connector are exactly the same.

Strong weight bearing capacity

Aluminum alloy improves the tensile strength of pure aluminum. Aluminum alloy cables can support a weight of 4000 meters, while copper cables can only support 2750 meters. This advantage is particularly prominent when wiring large-span buildings (such as stadiums).

Armour characteristics

Most commonly used armored aerial bundled cables(abc) b230 standard in China are armored with steel tape, with low security level. When subjected to external destructive forces, their resistance is poor, which is easy to cause breakdown, and the weight is heavy, the installation cost is quite high, and the corrosion resistance is poor. The service life is not long. The metal interlocking armored cable we developed according to American standards uses aluminum alloy tape interlocking armor. The interlocking structure between the layers ensures that the cable can withstand the strong destructive force from the outside, even if the cable is subjected to greater pressure The cable is not easy to be punctured under the impact force, which improves the safety performance. At the same time, the armored structure isolates the cable from the outside world. Even in the event of a fire, the armored layer improves the flame-retardant and fire-resistant level of the cable and reduces the risk of fire. Compared with the steel tape armored structure, the aluminum alloy tape armored structure is lighter in weight and convenient to lay. It can be installed without bridges and can reduce installation costs by 20% to 40%. Different outer sheath layers can be selected according to different places of use, which makes the use of armored cables more extensive.