Why should the length of power cable be reserved?

It is very difficult to repair and replace600V 90°C XLPE ACWU90 AC90 Cable, especially when the middle section is in trouble, because the cable is laid in the open, the bridge, the buried, the cable trench and the pipe. So in the cable laying is required to reserve. Not only in the cable trench in the feeder, but also to reserve the end; if it is tube or cable trench laying, in the middle of the maintenance wells to reserve a certain length.

Advantages: When the power cable is connected to the feeder circuit or equipment, the copper nose needs to be pressed and the outer protective layer of the cable needs to be removed And the distribution cabinet, control cabinet itself is also relatively easy to affect the cable, so the cable in both ends need to reserve a certain length to deal with the subsequent maintenance.

Otherwise, it will be difficult to deal with the problem in the figure below. The advantage of the reserved maintenance well: When the power cable is laid secretly, a maintenance well must be set up at a certain distance, which is mainly used to deal with the inspection and repair of the fault in the middle part ofPVC XLPE Insulated Power Cable 25mm² ~ 400mm². If a section is damaged by external forces or problems, the amount reserved in the manhole can be used nearby, making maintenance convenient and time-saving. Otherwise, it is very difficult to deal with the following problem.

Other benefits: due to the general cable laying path is generally more complex, often need to turn bend, calculation of cable length can not be accurate, appropriate length can also be reserved for laying a variety of special circumstances.

Cable maintenance tips

Everyone knows that everything will deteriorate after being used for a long time, and the same goes for wires. WhenAerial Bundled Cable (ABC) HD 626 S1 Standard is aging for household or commercial use, it is easy to cause danger if it continues to be used, and timely inspection can eliminate potential safety hazards. But how to detect wire aging in time requires some tricks.
The wire is mainly insulated by the outer layer of sheath. After a long time, it will be corroded by corrosive gas, and the insulation performance will gradually decrease. It will gradually age and become hard, become brittle or fall off, and then it will not be insulated. In fact, the direct cause of the aging failure of the wire and cable is the breakdown of the insulation due to the degradation.
1. “Check the appearance along the wire, darkening and hard cracks are seen. Bending the wire with both hands for insulation, stiff and cracked skin.” It means to observe the insulation layer along the wire. If the color of the insulation layer is found to be tarnished, darkened, or changed Hard, cracked, and partially peeled off.


When the insulated conductor is bent with both hands, the wire is stiff, even the insulation layer is cracked, the insulation layer falls off, etc., which shows that the wire has experienced different degrees of aging and severe aging.
2. “Accurate method to measure insulation, megohm is not low. The humidity value in rainy days can be small, and the value can be less than half.” It means that the insulation resistance meter can be used to measure the insulation of electrical circuits to determine the insulation status of the circuit more accurately.


3. If the wires cannot be replaced in time, you can also choose to use good internal materials to reduce hidden dangers. Once the insulation of the sheath of the wire casing is damaged, the possibility of fire will increase. The length of time for causing a disaster has a lot to do with the quality of the oxygen barrier. The newly produced diamond mud ceramic silica gel with silicone rubber as the base material by Shanghai Tengruina Chemical Technology Co., Ltd. has good high temperature resistance, fire resistance and fire resistance. The effective prevention and control of fire sources is to prevent fires to a certain extent. avoid lost. If there is a fire around the line, the shell of diamond mud ceramic silicon rubber can also ensure that it will not melt or drip in the flame, which effectively protects the normal use of the line and avoids explosions.
Finally, the editor still has a small reminder: the wire is aging, and the wire needs to be replaced in time. Don’t have a fluke mentality. The diamond mud oxygen barrier can only reduce the possibility of fire. Once a fire occurs, it will affect manpower, material resources and financial resources. The losses should not be underestimated!

What effect does the cable sheath have on the PVC Sheath Flexible Cable ?

The sheath is the “skin” of the wire and cable and the appearance that people look directly at. It must be smooth and round, uniform in color, not eccentric, not damaged, free of impurities, free of bubbles, and not flattened, twisted, etc., except In addition to being unsightly, the thickness of the sheath also has a certain impact on the quality of H05VV-F H03VV-F PVC Insulated cable.

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  1. Reduce service life
    After the cable is laid, it will be energized for a long time, which will generate heat. The allowable working temperature of the conductor is 70℃. The long-term use temperature of polyvinyl chloride should not exceed 65℃. If it is summer, the working temperature will rise, and these temperatures will pass outside. When the sheath is emitted, the thickness of the sheath increases, and the heat energy is difficult to dissipate, which will affect the service life of the cable. Due to the heat of PVC, the insulation layer will undergo a series of physical and chemical changes and lose its original excellent performance. , Resulting in a significant decrease in insulation performance, and even a short circuit, affecting the normal operation of the unit.
  2. Material performance defects
    The performance of the material is not reflected by the thickness. According to the requirements of the GB8815-2002 standard, if one of its indicators does not meet the standard, the flame-retardant PVC material, its oxygen index is lower than 30.
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  1. There are problems with the cable structure
    Conductor, insulation layer, and braid density are strictly controlled in accordance with the requirements of the standard. If the outer diameter of the cable is normal but the sheath is too thick, it is very likely that other structures are cutting corners.
  2. Increase the difficulty of cable laying
    At present, cable laying is mainly based on bridges or pipes. Many companies are implementing tight cable requirements and small outer diameters. There can be gaps during the laying process to dissipate heat and ensure that the outer sheath of PVC cable is not damaged. Otherwise, the construction unit and Cable laying brings difficulties.
    To sum up, the thickness of the sheath should be strictly controlled in accordance with the standard, which not only saves resources, reduces material consumption, and increases profits for the enterprise, but also ensures the quality of the cable and creates high-quality and low-cost products.

the advantages of overhead insulated cables

The Aerial Bundled Cable series products are composed of pressed copper, aluminum (aluminum alloy) conductors, inner shielding layer, weather-resistant insulating material and outer shielding layer. They have both the power transmission characteristics of power cables and the strong mechanical properties of overhead cables. Compared with bare wires, this product has the advantages of small laying spacing, high safety and reliability, and excellent resistance to atmospheric aging
  1. Uses of overhead insulated cables Overhead insulated cable products are a new series of products for power transmission through overhead transmission lines, and are preferred for power grid construction and transformation of 10kV transmission lines. It is the most suitable series of products for line maintenance and safety. Soft copper core products are suitable for the lower leads of transformers.
  2. Overhead cable implementation standards
  3. 1KV overhead insulated cable: GB12527-90 is equivalent to the International Electrotechnical Commission IEC60502, IEC227;
  4. 10KV overhead insulated cable: GB14049-93 is equivalent to the International Electrotechnical Commission IEC60502. Overhead insulated cable Third, the characteristics of (ABC) HD 626 S1 Standard
  5. Rated voltage: 0.6/1KV, 10KV;
  6. The long-term allowable working temperature of the cable: 70°C for PVC insulation and 90°C for XLPE insulation.
  1. When short-circuited (the longest time is no more than 5 seconds), the maximum temperature of the cable: 160°C for PVC insulation, 150°C for high-density polyethylene insulation, and 250°C for cross-linked polyethylene insulation;
  2. The ambient temperature during cable laying is not lower than -20℃;
  3. Allowable bending radius of cable: (1) Cables with rated voltage below 1KV: cable outer diameter (D) less than 25mm should not be less than 4D, cable outer diameter (D) of 25mm and above, should not be less than 6D;
  1. (2) The rated voltage of 10KV cable should not be less than 20 (D+d). Where: D—the actual outer diameter of the cable, d—the actual outer diameter of the cable conductor. Overhead fixed laying of soft copper core products is used for transformer down-conductor; when laying cables, a certain distance between cables and trees should be considered, and frequent contact between cables and trees is allowed during cable operation. For overhead fixed laying and cable erection, a certain distance between the cable and the tree should be considered, and frequent contact between the cable and the tree is allowed when the cable is running. Overhead fixed laying; When installing cables, consider keeping a certain distance between cables and trees. When cables are running, only short-term contact between cables and trees is allowed.

Analysis of commonly used PVC materials for wire and cable sheath

Commonly used plastics for wires and cables include polyethylene, cross-linked polyethylene, polyvinyl chloride, polypropylene, polyolefin, fluoroplastics, nylon, etc.
Polyethylene is currently the most widely used plastic with the largest consumption. From the data in the table, it can be seen that polyethylene has low meson loss, high resistivity, high breakdown field strength, good weather resistance and manufacturability. It is currently the best electrical Insulation Materials. However, due to its low operating temperature, it is mainly used as insulation for communication cables. Medium-density and high-density polyethylene have high strength and hardness, and their water permeability is low, and they are mostly used as cable sheaths. However, polyethylene has the biggest disadvantage, that is, it is easy to burn and has strong black smoke, so its application brings many hidden dangers to the environment.
Cross-linked polyethylene is an excellent thermosetting insulating material formed by adding a cross-linking agent to low-density polyethylene. On the basis of inheriting many excellent properties of polyethylene, it has improved mechanical properties, weather resistance and allowable working temperature, thus becoming the best insulation material for power cables.
Due to the different crosslinking agents added, different crosslinking processes are formed. At present, there are three kinds of chemical crosslinking, warm water crosslinking, and radiation crosslinking that are most used. Chemical crosslinking is mainly used for medium and high voltage cables (such as 10KV and above); warm water crosslinking and radiation crosslinking are mainly used for low voltage cables (1kV and below).
The insulation conductor performance of cross-linked polyethylene is closely related to its purity. The insulation of high-voltage and ultra-high voltage cables above 35KV must be made of ultra-clean cross-linked polyethylene, which not only requires high purity of raw materials, but also requires high cleanliness of cross-linking process equipment and environment, and the process is stable and reliable.
It should be particularly pointed out that the insulation properties of polyethylene and cross-linked polyethylene have a “quirk”, that is, they are suitable for AC insulation, not DC insulation, especially DC high voltage will reduce their insulation life. Therefore, the insulation of DC cables is mostly rubber insulation or oil-paper insulation. Furthermore, polyethylene and cross-linked polyethylene insulation have “waterphobia”, and their breakdown is often related to the presence of water, that is, “water branches” are formed under high voltage, leading to insulation damage. Therefore, when polyethylene and cross-linked polyethylene are used for the insulation of high-voltage and ultra-high-voltage cables, they are particularly “water-proof” during their processing, storage and transportation, and insulation extrusion, and there should be a water-blocking structure outside the cable insulation shield, such as metal jacket.
Compared with polyethylene, polyvinyl chloride and paper insulation, one of the biggest advantages of cross-linked polyethylene insulation is that the working temperature is increased by 20°C, which improves the safety of the cable and reduces the input cost of the cable. For example, when the line flow is the same (such as 300A), the cross-sectional area of ​​the copper conductor of the polyethylene or PVC insulated cable (such as the YV type or VV type) needs 120mm2, while the cross-linked polyethylene insulation tape male basketball copper conductor cross-sectional area only needs 70mm2 is sufficient. It can be seen how remarkable the advantages of cross-linked polyethylene insulated cables are.
Polyvinyl chloride has good physical and mechanical properties and excellent process performance. It is the most used plastic in the 20th century. It is also the main insulation material and sheath material for low-voltage wires and cables. But entering the 21st century, PVC will gradually shrink or even fade out in the cable market. There are two reasons for this. On the one hand, people’s safety awareness has increased and they hope to adopt halogen-free materials, so many halogen-free materials have emerged. There is no doubt that it will become the new favorite of the 21st century cable industry and squeeze the market. On the other hand, PVC has five weaknesses: one is its high density, which is about 1.5 times that of cross-linked polyethylene, and its insulation cost is high; the other is its low working temperature; and the third is its higher dielectric loss than cross-linked polyethylene. One hundred times higher; fourth, poor cold resistance (brittle at -15 degrees); fifth, toxic gas (HCL) is released during combustion. In recent years, the mechanical properties, electrical heating properties, and insulation resistance of cross-linked polyvinyl chloride developed in recent years have been greatly improved. Some small cross-section cables have been introduced into the market by irradiation technology, and they have been used in equipment and installation wires, high-voltage lead wires, automotive wires and building wiring. Application, but its shortcoming of halogen cannot be changed.
Fluoroplastics are widely used in wires and cables due to their high working temperature, small medium, insulation, weather resistance, acid and alkali resistance, oil resistance, and good flame retardancy. Among them, polyperfluoroethylene propylene is particularly popular due to its good manufacturability. But it is expensive, and users have to think twice.
Low-smoke halogen-free polyolefin is a new type of cable sheathing material that has not been developed in the 20th century. Its greatest advantage is its flame retardancy, low smoke and non-toxic gas during combustion, and it is increasingly widely used in important public buildings.

Different influencing factors, the degree of cross-linking of cross-linked cables is also different

Cross-linked cable is the abbreviation of cross-linked polyethylene insulated cable. It is composed of conductor, insulating material, internal and external semi-conductive material, sheath material, shielded copper tape, armored steel tape/steel wire, inner lining, isolation sleeve, filling material, etc. Part of the cable. Different components have their own usage requirements and characteristics. For example, XLPE insulated cables are the insulating medium material of XLPE, and the temperature resistance can reach 90°C. Therefore, the XLPE insulated cables cannot Compared with the advantages, it has simple structure, light weight, good heat resistance, strong load capacity, non-melting, chemical resistance, and high mechanical strength. It is mostly used in power transmission and distribution lines with power frequency AC voltage of 500KV and below.
In order to improve the temperature resistance of polyethylene, chemical or physical methods are usually used to make it into a body-shaped molecular structure. This is called cross-linking, which is the basic principle of cross-linking. So, do you know what is the degree of cross-linking of cross-linked cables? The following is an introduction to the factors that affect the degree of cross-linking of cross-linked cables for your reference.
1. Temperature
The temperature here not only refers to the working temperature of the cross-linked cable during cross-linking, but also includes the extrusion temperature. Specifically, it is:
(1) The cross-linking process is completed in the heating section of the vulcanized tube. Therefore, when other factors remain unchanged, the higher the temperature of the vulcanized tube, the higher the degree of cross-linking of the cross-linked cable. This is a certain point. Generally speaking, considering various factors, the temperature of the vulcanized tube for dry cross-linking should be around 290~310℃, otherwise the cross-linking degree of the cross-linked cable during cross-linking will be affected and will be greatly changed. Small, it is not a good thing for the use of cross-linked cables.
(2) Extrusion temperature. Because the cross-linked cable is processed, an extruder is required. If the cross-linking degree of the cross-linked cable is suitable, it is necessary to use a suitable extrusion temperature during the processing of the extruder, and the extrusion temperature may be related to the formula of the raw material, so this requires The material is fully plasticized without pre-crosslinking.
2. Linear speed during crosslinking
Obviously, the higher the line speed, the higher the production efficiency, but the degree of crosslinking will be lower. Therefore, when crosslinking, the line speed should be suitable. The line speed will be affected by factors such as rated voltage, cable specifications, cooling water temperature and water level, vulcanizing tube, etc. The larger the cable cross section, the greater the amount of glue required from the extruder, so the line speed cannot be too fast; The higher the temperature and the longer the pipeline, the faster the line speed; the higher the voltage, the thicker the insulation and the slower the crosslinking speed…
Well, the above is an introduction to the factors that affect the degree of cross-linking of cross-linked cables. I hope everyone can understand, and then cross-link correctly according to actual conditions and requirements.

What are the common types of aluminum alloy cables

Aluminum alloy cable (abbreviation: alloy cable) is different from the traditional copper core cable. This aluminum alloy cable uses high elongation aluminum alloy material. The pure aluminum is added with iron and other materials, and undergoes a compact stranding process and special Annealing treatment can “squeeze” the voids in the alloy aluminum to reduce the cross-sectional area, so that the cable has better flexibility. The safety performance of this kind of aluminum alloy cable is also better than that of copper core cable. When its surface is in contact with air, it can form a thin and strong oxide layer, which can withstand various corrosions. Even when overloaded or overheated for a long time, the stability of the connection can be guaranteed. To achieve the same electrical performance, the direct purchase cost of aluminum alloy cables is 40% lower than that of copper cables, and the general construction and installation costs can be saved by more than 20%.

1.Aluminum alloy (STABILOY) non-armored AC-XLPE insulated PVC sheathed cable:
AC-XLPE insulated PVC sheathed cable, aluminum alloy non-armoured cable is made of conductor, the cross-section specification is from 10mm² to 400mm², the core is grade compressed strand type, which fully complies with CSA C22.2 NO.38 about ACM alloy conductor Standards, also in line with the latest editions of GB 12706.1 and IEC 60502.1.
Aluminum alloy (non-armoured cables use cross-linked polyethylene insulation with a working temperature of 90℃ and black PVC outer sheath, which have a very wide range of applications where no armored mechanical protection is required. They can be used in non-combustible buildings, such as Feeder lines for lighting, sockets and other equipment in office buildings, hotels, shopping malls and factories.

Aluminum alloy cable is an aluminum alloy conductor specially developed for construction application cables. The safety performance, electrical performance, and mechanical performance of aluminum alloy cables have been tested by the China Quality Certification Center and the National Wire and Cable Quality Supervision and Inspection Center, and all meet the requirements of China’s National Standards (GB). Aluminum alloy cables have been successfully used in North America for more than 30 years and are advanced and mature technologies and products.

2.Self-locking armored cable:
ACWU90 is a highly flexible self-locking aluminum armored, PVC outer sheath, 90℃ cross-linked polyethylene waterproof insulated single-core or multi-core cable, with an equipotential bonding bare conductor. Because of the FT4 grade PVC outer sheath, ACWU90 can be directly laid and buried in the ground, and is suitable for corrosive environments and non-combustible buildings. ACWU90 reduces the construction difficulty and labor cost caused by pipeline wiring.


The alloy cable has been assembled in the factory with a highly flexible self-locking armor and a sealed PVC outer sheath. There is no need for pipelines and accessories and manual procedures such as intensive drawing, buckling and pipe threading. ACWU90 has passed the CSA certification and can be used in open or dark wiring in dry and humid environments, as well as in the first-level hazardous environment in zone 1 and 2, as well as the second and third-level hazardous environments. Laying method: Brackets, ladders, trays and cable clamps can be used for indoor laying. Outdoors can be directly buried, cable trench, cable tunnel and other methods. ACWU90 is equipped with calibration marks per meter to accurately determine the cable length.


Aluminum alloy cable, ACWU90 multi-core cable is made of conductor, and the cross-section specification ranges from 10mm² to 400mm². It is fully compliant with IEC 60502.1 and GB 12706.1 standards, and can also provide various specifications of low-smoke and halogen-free products according to customer requirements. Both AC90 and ACWU90 can be used as user incoming cables. The self-locking armored technology used makes the cables more flexible and easier to install than conventional armored cables. In fixed installation, the bending radius of the self-locking armored cable can be only 6 times the outer diameter of the cable.

3AC90 type multi-core aluminum alloy self-locking armored aluminum alloy cable:
AC90 is a highly flexible self-locking aluminum armored, 90℃ cross-linked polyethylene insulated single-core or multi-core cable, with an equipotential bonding bare conductor. The AC90 cable is assembled in the factory with high-flexibility self-locking armor, without the need for pipelines and accessories, and manual procedures such as intensive drawing, buckling and pipe threading.
AC90 type has been used in non-combustible buildings, such as office buildings, hotels, shopping malls and factories in the lighting, sockets and other equipment feeder lines, can be used as users on the ground and in dry environments as the incoming cable. AC90 can be installed on the cable tray (perforated tray, non-perforated tray and ladder frame), and can also be laid along the wall and the top by using a bracket or a cable clamp.
AC90 multi-core cables are made of conductors, with cross-sectional specifications ranging from 10mm² to 400mm². It has passed CSA certification and can be used for open or dark wiring in a non-humid environment, and has the same performance as pipeline laying. AC90 is a flame-retardant Class A, low-smoke and halogen-free type, which fully complies with the standards of IEC 60754, GB17650.1 and IEC 60502.1\GB 12706.1.

 

Precautions for testing cross-linked cables

In recent years, silane cross-linked polyethylene cable material (hereinafter referred to as XLPE) has become the leading material for low-voltage cross-linked cable insulation because of its simple manufacturing equipment, mature technology, convenient operation, and low overall cost.

At present, the commonly used XLPE is the two-step XLPE. When the cable factory produces the insulated core, the polyethylene (PE) grafted with silane and the catalyst masterbatch are mixed in a certain proportion and extruded in a common extruder. Then complete the cross-linking in hot water or steam; the other one-step method XLPE is made by the cable material manufacturer, which mixes all the raw materials together by a special method according to the ratio, and the cable factory directly completes the grafting and grafting in one step in the extruder. Extrude the insulated core, and then complete the cross-linking under natural conditions. The common point of these two types of XLPE is that no special extrusion equipment is needed and the cross-linking process is relatively simple. As long as the raw materials and process conditions meet the requirements, it can be made into an insoluble and infusible thermosetting plastic. Compared with thermoplastic PE, its heat-resistant deformation and mechanical properties at high temperature, environmental stress cracking, aging resistance, chemical resistance, etc. have been improved or improved, while the electrical properties remain basically unchanged, and the long-term work of the cable The temperature is increased from the original 70°C to 90°C, thereby improving the short-term current withstand capability of the cable. In summary, XLPE low-voltage cables have become the main products of cable manufacturers in recent years.

As a third-party inspection agency, this type of cable is also increasing year by year. How to accurately provide the test results of the thermal extension and aging performance of this type of product? Inspectors are faced with some special circumstances. The following is an analysis:

First, the problem of abnormal thermal extension of XLPE insulation. When testing, the author often finds that the elongation rate of XLPE cable insulation under load in the 200℃ thermal extension test greatly exceeds the requirements specified in the standard, or the sample is put into the oven and melted in a short time. If the test is repeated immediately with the original sample, The reproducibility of the results is very good. According to the routine, as long as the test method is correct and the sampling is correct, a conclusion can be drawn based on the test results. However, for XLPE, this may be a great risk. Because the cross-linking process of ACWU90 AC90 Cable is a slow chemical change process related to temperature, humidity, time, insulation thickness and other factors, especially the naturally cross-linked XLPE insulation material is affected by the above factors to complete the cross-linking. There will be a big difference in time, and it is entirely possible that the natural cross-linking has not been completed within the prescribed test period. Once the natural cross-linking is completed over time, its performance may meet the requirements of national standards. For such situations, the author believes that under the premise of reflecting the current situation of the sample, we should not rush to determine, but should provide the sample with a condition to promote crosslinking-soaking in hot water at 90°C±2°C Do the hot extension test after 4 to 5 hours. Practice has proved that the test results at this time can be used as a basis for judgment. It is worth mentioning that individual manufacturers are pursuing commercial profits one-sidedly, using the similar characteristics of PE and XLPE to pretend to be XLPE, and PE will not produce cross-linking changes no matter what conditions are provided to promote cross-linking. In terms of performance, it does not meet the requirements of XLPE at all, which is the same as the fact that stones cannot hatch chicks. This requires inspectors to have the ability to identify true and false, good and bad XLPE. In fact, through observation and work accumulation, we can distinguish whether the tested sample is under-crosslinked, inferior XLPE, or PE is used according to the fusing time and fusing point after the sample is placed in the oven. However, as a third-party inspector, you cannot draw conclusions based on experience alone, and must make judgments based on real data.

Second, the problem of the change rate of XLPE heat aging test exceeding the standard. When testing, if you get the sample, prepare it immediately, and put it in the oven for aging as usual, the tensile strength and elongation at break will often exceed the standard after aging, and you must be cautious in judging this result. This phenomenon is not entirely caused by poor aging performance, it may be because XLPE has not been completely cross-linked (from the time curve of XLPE cable material thermal extension with warm water placement, it can be seen that when the thermal extension is qualified, it does not represent the sample Completely cross-linked), and after being placed in the aging box, XLPE is still completing its cross-linking process, which leads to an increase in tensile strength, a decrease in elongation at break, and the final rate of change exceeds the standard. Due to the long time to complete the aging, it will be troublesome to discover the problem once the test is over. Therefore, it is necessary to thoroughly crosslink the sample before performing the aging test.

In summary, it can be seen that special factors should be considered to determine the thermal elongation and thermal aging performance of XLPE. Personnel engaged in third-party inspections can neither make a hasty conclusion on the results of the test, because doing so involves the risk of misjudging qualified products as unqualified; nor can they avoid these two tests because it is difficult to draw conclusions. This may cause substandard products or counterfeit products to be missed. Therefore, it is necessary to exclude the possibility that the sample has not been cross-linked or completely cross-linked before performing the above two tests. We advocate the use of scientific and reasonable test methods to provide fair and reliable test results.

Treatment method of polyethylene insulated power cable damp and water

In urban power grid renovation projects, cables, especially polyethylene insulated power cables, have been widely used. However, due to the particularity of the cable, there are special requirements for the installation, operation and maintenance of the cable. Moisture or water in the cable reduces the insulation resistance of the cable, which is a few important aspects that cause operation accidents in the cable line.


Causes and hazards of cables being damp
(1) When XLPE insulated cable  is shipped from the factory, both ends of the cable are sealed with plastic sealing sleeves. However, after a section of the cable is used according to the actual situation at the construction site, the remaining part is simply wrapped with plastic cloth to wrap the fracture. Placed in the open air and poorly sealed, over time, water vapor will inevitably seep into the cable.
(2) During cable laying, it is necessary to cross roads, bridges and culverts frequently. Due to weather or other reasons, a lot of water often accumulates in the cable trench. During the laying process, it is inevitable that the cable head will be immersed in water. , Because the plastic cloth is not tightly wrapped or damaged, water enters the cable; in addition, the outer sheath or even the steel armor is sometimes scratched when pulling and piercing the pipe. This phenomenon is particularly prominent when using mechanical traction.


(3) After the cable is laid, the cable head cannot be made in time due to the constraints of the site construction conditions, so that the unsealed cable fracture is exposed to the air for a long time, or even immersed in water, causing a large amount of water vapor to enter the cable.
(4) In the process of making cable heads (including terminal heads and intermediate joints), due to the negligence of the construction personnel, the newly processed cable ends sometimes accidentally fall into the stagnant water on site.


(5) In the normal operation of the cable, if breakdowns such as breakdown occur due to some reason, the water in the cable trench will enter the cable along the fault point; in civil construction, especially when large construction machinery is used It is not uncommon for cables to be damaged or broken down due to various human factors on construction sites in China. When such an accident occurs, the cable insulation is severely damaged, and water can enter the cable.
After the cable enters the water, under the action of the electric field, the aging phenomenon will occur, and finally the cable will break down.

Analysis of XLPE ACWU90 AC90 Cable Waterproof Structure

Cable waterproof structure type:
For XLPE ACWU90 AC90 Cable, there are usually the following waterproof structures:
1. For single-core cables, wrap a semiconducting resistance hose on the insulation shield of the cable, wrap a common water blocking tape outside the metal shield, and then squeeze the outer sheath. The outer sheath material can be ordinary For PVC, HDPE material with radial water blocking function can also be used, depending on other performance requirements of the cable. For three-core cables, in order to ensure the full contact of the metal shield, only the single-conductance resistance hose is wrapped outside the insulating shield, and the water blocking tape is no longer wrapped outside the metal shield. Water blocking filling, inner lining and outer sheath materials are the same as those described in single-core cables.


2. The aluminum-plastic composite tape layer is longitudinally wrapped inside the outer sheath or inner lining layer as a waterproof layer.
3. Squeeze the HDPE outer sheath directly on the outside of the cable.

Cable waterproof structure type:
For XLPE insulated power cables, there are usually the following waterproof structures:
1. For single-core cables, wrap a semiconducting resistance hose on the insulation shield of the cable, wrap a common water blocking tape outside the metal shield, and then squeeze the outer sheath. The outer sheath material can be ordinary For PVC, HDPE material with radial water blocking function can also be used, depending on other performance requirements of the cable. For three-core cables, in order to ensure the full contact of the metal shield, only the single-conductance resistance hose is wrapped outside the insulating shield, and the water blocking tape is no longer wrapped outside the metal shield. Water blocking filling, inner lining and outer sheath materials are the same as those described in single-core cables.


2. The aluminum-plastic composite tape layer is longitudinally wrapped inside the outer sheath or inner lining layer as a waterproof layer.
3. Squeeze the HDPE outer sheath directly on the outside of the cable.
For PVC XLPE Insulated Power Cable, the metal sheath is mainly used to make the cable meet the waterproof requirements. The most important feature of the metal sheath is that it is completely impermeable, so the cable with the metal sheath has very good radial water blocking performance. The main types of metal sheaths are: hot-pressed aluminum sleeve, hot-pressed lead sleeve, welded corrugated aluminum sleeve, welded corrugated steel sleeve, and cold drawn metal sleeve.


Cable waterproof form:
Cable waterproofing methods are generally divided into longitudinal water blocking and radial water resistance. Water blocking yarn, water blocking powder and water blocking tape are commonly used in longitudinal water blocking. Their water blocking mechanism is that these materials contain a material that can swell in contact with water. When water flows from the cable end or from the sheath After entering the defect, this material will quickly expand with water to prevent further diffusion of water along the longitudinal direction of the cable, thus achieving the purpose of longitudinal waterproofing of the cable. Radial water resistance is mainly achieved by extruding HDPE non-metallic sheath or hot pressing, welding, and cold drawing metal sheath.
Cable waterproof test basis:
The cable waterproof test method, the cable longitudinal water resistance performance can be tested and judged by the IEC 60502-1997 ANNEX D (normative) or GB/T 12706.2-2002 Appendix D (standard catalog) water permeability test; and the cable radial water resistance Performance, currently is mainly determined by indirect methods, such as checking whether the HDPE non-metal sheath or non-metal sheath is defective. If these sheaths are determined to be intact, then the cable is considered to have good radial water resistance. performance. However, many users of this method have raised some questions, caused some disputes, and lacked convincing power. Therefore, cable manufacturers and users now urgently need a test method to determine the radial water blocking performance of the cable. This can avoid disputes between manufacturers and users about the cable’s radial water blocking performance due to the lack of a radial water blocking test method.