At present, there are many production lines in China capable of producing ultra-high voltage cross-linked cables of 110KV or more. The metal jackets of each plant are not identical in structure. Different metal sleeves have their own characteristics. The user must first have a comprehensive understanding and understanding of the performance of the metal sleeves and choose according to their own conditions. The benevolent sees the person and the wise sees the wisdom. This article explains the performance and characteristics of various types of metal sleeves. This article only serves as a guide for jade, and Xi's power supply system can introduce the experience of using different metal sheath cables to make the manufacturing department understand the user's viewpoints and needs.
1. Types of metal sleeves Metal sleeves have two major functions: (1) Waterproofing: Prevents XLPE insulation from coming into contact with moisture to produce water trees. Metal sleeves are radial waterproof layers of cables; (2) Can withstand zero-sequence short-circuit current thermal stability Good sex. According to the production process can be divided into three categories: extrusion package seamless metal sleeve, longitudinal weld metal sleeve and integrated jacket. The materials used are lead, aluminum, copper and stainless steel. The type, manufacture, structure and characteristics of the metal sleeve are as follows:
Metal sleeve type manufacturing and structural features Seamless lead sleeves are continuously pressed by a lead extruder to extrude seamless seamless lead lead. The chemical properties are stable and corrosion-resistant.
The seamless corrugated lead sleeve is made of continuous or discontinuous aluminum machine to squeeze aluminum sleeves and rolled corrugated cables with light weight. The chemical properties of aluminum are more active. After the outer sheath is damaged, the aluminum sleeve is easy to perforate and the outside diameter is large.
Welded corrugated aluminum-clad aluminum coils are welded and then rolled up with the welder, but with longitudinal welds.
Welds Corrugated copper bushings Welded steel coils Welded after welding Welded with longitudinal welds, Large outside diameter.
Welded corrugated stainless steel stainless steel plate wrap welder welds with longitudinal seams after welding. The thermal stability capacity is lower than that of the wave vertical bushes, and the outer diameter is larger.
Composite sheathed aluminum foil PE compound film longitudinal cover coil hot air welding cable Light weight, aluminum foil for waterproof layer, with copper wire shield to meet the thermal stability.
The above 6 kinds of metal sleeves all have a good radial waterproof layer, but the intrinsic quality, application characteristics and manufacturing costs vary. At present, there are productions in addition to corrugated copper jackets and stainless steel jackets. The performance of the four types of products produced in China is described below.
2. Aluminium bushings At present, large companies that can manufacture lead-sleeved cross-linked cables in China have the ability to produce lead bushes with continuous lead presses. Lead-sleeved cross-linked cables have a tight internal structure, good longitudinal water resistance, good chemical stability against corrosion, and a disadvantage of heavy weight.
The melting temperature of the lead alloy is about 300°C, and the extrusion temperature of the die press of the lead press is 260°C. The lead sleeve manufactured on the lead screw continuous press is a continuous lead pipe without ash, seamless, and smooth inner wall. The creep performance of lead is good. When the structure size is designed, there is no need to leave a gap between the lead sleeve and the core. When the cross-linked insulation expands, it can expand the lead sleeve and the insulation surface is still smooth. Since the coefficient of expansion of crosslinked insulation is about one order of magnitude greater than that of metal, there must be sufficient expansion clearance within each type of corrugated metal jacket. If there is no gap or the gap is not large enough, after the insulation is expanded, it will leave ripples on the insulation surface, which will affect the electrical performance of the cable. After 20 thermal cycles in the type test, if the surface of the cable core is corrugated, the impact margin of the cable is not high. As the lead sleeve inner wall does not require design clearance, the structure is tighter. Therefore, the longitudinal waterproof performance of lead-sleeved cross-linked wires is better than that of any corrugated metal sheathed cable.
The resistance coefficient of lead is 7.8 times that of aluminum. The lead sleeve must meet the short-circuit thermal stability requirements in the technical conditions. The cross section of the lead sleeve must be much larger than that of the aluminum sleeve. The short-circuit thermal stability indicators of all power supply systems are much larger than actual ones, mainly because the zero-sequence short-circuit duration is too long, but only a few cycles actually occur. This indicator is set by the system and there is no right for cable technicians to change. Shanghai in the 220KV project requires 50KA 2 seconds, the use of lead sets of cable to be added under the lead sleeve copper shield, use corrugated aluminum sleeve to be thickened. In the 85 years of introduction, there was a project where foreign thickened corrugated aluminum sheathed oil-filled cables were mated with domestically-manufactured lead-sleeving oil-filled cables (without copper shields). The foreign manufacturer said: “If there is a short-circuit lead-sleeved cable, The lead sleeve will melt.†Actually, domestic super high pressure lead sleeve oil-filled cables and lead-set cross-linked cables used in the past since the 1970s have not experienced lead sleeve melting failure. The main reason is that the short circuit capacity of the current system is not so large, and the short circuit duration cannot reach 2 seconds. The current major power supply systems have compiled the “Provisions of Certain Technical Principles of the Power Gridâ€, in which the duration of the single-phase short-circuit current required for metal sheaths or metal shields of 110 kV or higher power cables is not to be less than 0.2 second (in Shanghai Power Grid). For example). Execution of this technical condition will make the metal sheath structure of the ultra-high cable reasonable, which will help reduce the cost of the cable.
The lead sleeve produced by the screw-type continuous lead press was selected. There was no problem of blisters on the lead sleeve due to the inclusion of the lead sleeve. Screw lead presses take lead extrusions from the bottom of the melting lead furnace. The proportion of lead oxides and various impurities is much smaller than that of lead, and they will float on the surface of molten lead and cannot be squeezed onto the cable. Even though the hydraulic press discontinuous pressure lead machine can produce high-quality lead sleeves, the key is the production process. There are hundreds of kilometers of single-lead leaded oil-filled cables in the Shanghai power system, most of which are produced in Shanghai. The lead bushes produced by hydraulic press discontinuous pressure lead machines account for a large proportion of these cables in more than 20 years of operation. There has been no failure of lead bush leakage. The key to product quality lies in process management and factory equipment. The radial water-blocking function of the lead sleeve is not only inferior to that of the aluminum sleeve, but also better than that of the aluminum sleeve.
The same specifications of the ultra-high voltage lead sheath cable are much heavier than the aluminum sheath cable, generally speaking it is required to weigh 60% to 90%. At present, the laying of ultra-high voltage cables is no longer a construction method for people. The side pressure of the cable must be strictly controlled during laying. Only the winding Yang machine plus the crawler belt conveyor can be used to control the laying tension and control the cable side pressure. When using laying machinery construction, the difference between the weight of the lead bush and the aluminum bush has become insignificant. In the construction, we must design some machinery and equipment to reduce labor intensity due to local conditions, overcome some difficulties during construction, and get a safe operation return in the future operation. In the event that the outer sheath is damaged after running, the lead sleeve will resist corrosion and the metal sleeve will not perforate quickly to cause water ingress. Lead-sleeving cross-linked cables are more flexible than aluminum-sheathed cross-linked cables, and lead-sleeved cables can be easily lead-free during joint operations.
The proportion of lead is 11.34 which is 4.2 times that of aluminum. The cost of lead-lead materials is much larger than that of aluminum sheaths. Take 110KV 1 x 630 square millimeter wire as an example to make a comparison: lead sleeve thickness is 4mm, aluminum sleeve is 2mm; in each lead sheath cable, the weight of lead is 7.5 times that of aluminum sheathed cable. Calculated according to the market price in the same period of 1999, the price per ton of lead raw materials is 34% of that of aluminum, while the lead cost of lead in lead sets is 2.5 times that of aluminum. If the requirements for short-circuit duration in the technical conditions are too long, copper shields must be added to the thermal stability of the lead sleeve design, which will result in a greater difference in raw material costs between the two metal sleeves. In the bidding competition, if manufacturers of lead-sleeved cross-linked cables participate in the competition with the aluminum-sheathed cross-connected cable at the same unit price or slightly higher price of the aluminum-sheathed cross-connected cable, it is cost-effective for the user.
Lead-set cross-linked cables are not replaced by aluminum-sheathed cross-connected cables. Each cable in the land has its own characteristics and advantages and disadvantages. It is preferable to choose the lead-jacketed cable in the direct burial and laying of the pipe. Submarine high-voltage cross-linked cables must be made of lead sheaths, and the probability of external force damage such as the anchorage of the cable is very high. Once the sheath is damaged, it is difficult to repair. If the aluminum sheathed submarine cable is damaged by external forces, the main insulation and the metal sheath are still intact, but the aluminum sheath will soon perforate in seawater and will inevitably reduce the service life. This is the reason why submarine cables do not use aluminum sleeves.
3. The biggest advantage of seamless corrugated aluminum sleeve corrugated aluminum sheathed cables is their light weight and short-circuit thermal stability. In systems where the short-circuit current is slightly longer, the standard aluminum sleeve can meet the requirements. For example, if the thermal stability is not enough in the calculation, the aluminum sleeve can be less thickened to meet the technical requirements, without using an additional copper shield. Lead sets are simple. Aluminum sleeves extruded with aluminum presses have good mechanical properties and tightness.
The weight of the aluminum sheathed cable is much lighter than that of the lead sheath. It is much easier than the lead sheathing cable when manoeuvring, lifting, boring, and moving cables in the laying process.
The corrugated aluminum sheath structure was developed in the sixties and seventies, when the high-voltage cables were mainly oil-filled cables. The use of corrugated aluminum sleeves in oil-filled cable designs has many advantages: the absence of a radial reinforcement belt for lead sleeves; the spiral corrugations constitute outer oil passages to significantly reduce the transient pressure drop of the oil-filled cable, allowing it to be placed in the circuit design. The length of the long oil supply section can reduce the number of stoppers; the aluminum price at that time is much lower than the current price, and the ratio of lead to copper is also much cheaper. Therefore, replacing lead sleeves with corrugated aluminum sheaths in land-based oil-filled cables in some countries has great economic and technological benefits. However, corrugated aluminum sets of cross-over cables spiral corrugated cable does not have a longitudinal water blocking function, in the wire design if it can also longitudinally block water and reduce the gap will reduce the electrical performance, seems to lose out.
The atomic number of aluminum in the periodic table is 13 and lead is 82. Aluminum is a very active chemical metal. During the operation, external force damages damage to the outer sheath or the outer sheath is broken on the bracket, and the aluminum sheath is quickly corroded and permeated to cause water ingress.
The melting point of aluminum is 658°C, and the temperature of the die holder when the aluminum press is extruded is about 500°C. The extrusion temperature of the lead sleeve is much higher than that of the lead sleeve. For this purpose, a copper wire braided glass ribbon or a semi-conductive resistance tape should be provided inside the aluminum sheath to prevent the insulation shield from being burned. Aluminum presses have continuous and discontinuous presses. Discontinuous aluminum alloy ingots have to be stopped for a period of time, which is not very beneficial for cross-linking cable cores. Although the old and new aluminum ingots can be combined into one body in the aluminum press machine, there are still joints on the surface of the aluminum sheath, but there is no effect on the strength of the aluminum sheath. It should be said that continuous is better than discontinuous.
Pressing aluminum machine is a high cost of precision equipment, aluminum pressure jacket production process and process is also more complex, aluminum machine production aluminum sleeve energy consumption and higher labor costs, metal sleeve production costs will be higher.
The allowable side pressure of the cable is related to the insulation type, not depending on the type of metal sheath. The data recommended by some authoritative manuals abroad is shown in the table below. Although the compressive strength of the corrugated aluminum pipe is higher than that of the lead pipe, the tension of the cable during laying is on the conductor core. The lateral pressure at the bend is transmitted from the conductor to the insulation, the metal sheath and the sheath, and the thrust is received by the corner pulley. . One of the most susceptible to mechanical forces is insulation, and it is reasonable to determine the side pressure that a cable can withstand by its resistance to insulation.
Cable type allowed side pressure (N/m)
Oil-paper insulated cable extruded insulation cable 3000
3000
Aluminium jacket cables have a lot of interest in installation. Light weight is the most popular point for laying workers, but its softness is not as good as lead sleeves. The outer end of the high-voltage cross-linked aluminum sleeve laid down from the cable tray must be straightened with a straightener to be pulled. In the laying process, the lateral pressure and traction of the wire are controlled by a winch and a drawer belt conveyor. Therefore, the traction at the end is not large. After the cable passes through the bend, the aluminum cable is not easy to straighten out on the turn. Not as good as lead-sleeving cable. In the installation of various types of accessories, aluminum sheathing can not be directly lead-bismuth, first on the surface of aluminum tin plated tin alloy and antimony lead to lead after the lead. Beryllium at the bottom of the lead requires a high level of skill for the personnel. Few helium will cause water to enter the cable. In a large-scale project, the amount of work required to terminate the wire and install the traction end of the wire is very large, and it is particularly useful in laying pipes. Aluminum sheath cables are not welcomed by joint workers.
4. Seam corrugated aluminum exposed weld aluminum sleeve is wrapped by aluminum plate and then welded by argon arc welding machine. The cost of the argon arc welding machine cannot be compared with the expensive aluminum press. After the equipment is low, the cost of repayment, depreciation, and other costs of entering the product will be less. The production and energy consumption of the weld aluminum sleeve are lower than that of the seamless aluminum sleeve. The low production cost of the weld aluminum sleeve is its greatest feature.
The melting point of aluminum is 658°C, and the melting processing temperature of aluminum is about 700 to 750°C. The arc temperature is even higher. In the welding process, the aluminum plate on the two sides of the weld will cause changes in the metallographic structure of the aluminum after it is heated, making the mechanical properties of the aluminum sleeve uneven over the circumference. In the laying of traction in the stress will produce a concentrated deformation. This phenomenon has occurred in actual projects. Two-circuit 110KV XLPE cable is laid in a certain project. One time is a seamless aluminum sleeve, and the other is a welded aluminum sleeve. Using the same construction method, the seamless round shape is good and the seamed aluminum sleeve is deformed. It is elliptical, which reflects the difference in the intrinsic quality of the two cables. The deformation of the cable during laying is related to the pressure on the control side. Before laying, calculate the tension and side pressure in sections and adopt appropriate measures. The wire will not be deformed.
Because of the great difference in expansion coefficient of the raw materials, the branch cable has complicated its thermo-mechanical properties. The weld temperature is about 700°C, and the aluminum sleeve on the opposite side of the weld is at a very low temperature. The crosslinked insulation is subjected to a non-uniform heating process. The cable is heated from the inside to the outside during the operation. When the aluminum sleeve is pressed or the lead sleeve is pressed, it is from the outside heat to the inside. It is a uniform symmetrical heating process. The uneven heating process of the weld aluminum sleeve during the production process makes the thermal mechanical properties in the cable more complex. Welded aluminum sleeves can only be welded on one side. This is the thinnest welding method in the welding process. In the standard, the strength of the weld seam is evaluated at 90% (54MP2) of the soft aluminum tensile strength.
The design of the weld aluminum sleeve often uses the reduction of clearance to achieve the purpose of longitudinal water resistance of the cable. As mentioned above, this will reduce the impact margin and will not be worth the loss. In addition to filling the water within 5 minutes in the longitudinal water blocking test, the actual working conditions should be simulated in the water injection process. If the cable is penetrated by a cable trench or working hole filled with water, a split hole will be formed in the metal sleeve. The water will infiltrate into the two sides immediately and will not allow the water to expand with an initial expansion process. In addition, if the gap is too small, it will cause the difficulty of stripping the aluminum sleeve when the attachment is installed, and it will not be welcomed by the joint workers.
Compared with the seamless aluminum sleeve, the weld aluminum sleeve has its own characteristics in addition to the common characteristics of the aluminum sleeve. Welded aluminum sleeve is an effective radial waterproof layer, but its internal quality is different from that of seamless aluminum sleeve and the production cost is different. There should be a difference in price. Generally speaking, the spread between the two can reach a two-digit percentage. The specific spread can find a reasonable price in the introduction of market competition mechanism.
5. Corrugated corrugated aluminum sheath corrugation and process problems have been studied in the country, and there are no provisions in the newly formulated standards. The differences between plants are not small. In recent years, many countries have introduced corrugated aluminum sheathed cables. Its appearance, waveform, wavelength and amplitude and other parameters and its relationship with the outer diameter of the cable core are for reference and reference. After doing some research, it can be used as the basis for formulating user standards or bidding technical documents. In addition, similar problems are allowed for bending radius and side pressure.
Waveforms The spiral corrugations commonly used in cross-linked cables have the disadvantage of non-blocking water performance. Ring-shaped (also called bamboo-shaped) corrugated is more suitable for cross-linked cables and Kieby-spiral, and it is easier to prevent longitudinal penetration of moisture.
Before the corrugation shape of the aluminum sheath is not finalized, the longitudinal tensile strength of the aluminum sheath should be used to monitor the quality of embossing.
6. The comprehensive sheathed composite sheathed cross-connected cable has the characteristics of light weight, small size, and low cost, and can be used in a system with a small zero-sequence short-circuit capacity; a copper wire shield is required in a system with a large short-circuit capacity, which has an advantage in cost. There are fewer exceptions. The domestically-made 110KV cross-linked cable was first used in Hangzhou and has a good track record since 1992. In the first phase of the subway project, Shanghai introduced such cables from Germany into the lines for direct burial and platooning. The water-repelling layer of German products uses water-swollen powder instead of water-blocking.
Radial water-blocking with integrated sheathed metal foil is an effective water-blocking layer. Its resistance to external damage and corrosion resistance after perforation of the outer sheath is fragile. The integrated sheath has the advantage of low cost in tunnels and pipelines with low probability of external damage. The light weight of the hydropower station's high drop project also has its own unique features.
7. Conclusions (1) Various metal sheaths have their own characteristics and can all be used as radial water blocking layers for ultra-high voltage cross-linked cables. Different metal sheaths have their own characteristics. Each has its applicability. When selecting the structure of the metal sleeve, the use conditions, construction habits and operating experience of each should be selected according to local conditions;
(2) In different cable structures and production processes, generally speaking, seamless metal sleeves are better than seams, and continuous ones are better than discontinuous ones;
(3) The internal quality of the cable is different and the production cost is different. There should be a significant difference in the cable price.
(4) The quality of the cable is determined by the overall quality of the components such as the conductor, the shield, the insulation, the metal sheath and the outer sheath, and the quality of the metal sheath is only one part.
1. Types of metal sleeves Metal sleeves have two major functions: (1) Waterproofing: Prevents XLPE insulation from coming into contact with moisture to produce water trees. Metal sleeves are radial waterproof layers of cables; (2) Can withstand zero-sequence short-circuit current thermal stability Good sex. According to the production process can be divided into three categories: extrusion package seamless metal sleeve, longitudinal weld metal sleeve and integrated jacket. The materials used are lead, aluminum, copper and stainless steel. The type, manufacture, structure and characteristics of the metal sleeve are as follows:
Metal sleeve type manufacturing and structural features Seamless lead sleeves are continuously pressed by a lead extruder to extrude seamless seamless lead lead. The chemical properties are stable and corrosion-resistant.
The seamless corrugated lead sleeve is made of continuous or discontinuous aluminum machine to squeeze aluminum sleeves and rolled corrugated cables with light weight. The chemical properties of aluminum are more active. After the outer sheath is damaged, the aluminum sleeve is easy to perforate and the outside diameter is large.
Welded corrugated aluminum-clad aluminum coils are welded and then rolled up with the welder, but with longitudinal welds.
Welds Corrugated copper bushings Welded steel coils Welded after welding Welded with longitudinal welds, Large outside diameter.
Welded corrugated stainless steel stainless steel plate wrap welder welds with longitudinal seams after welding. The thermal stability capacity is lower than that of the wave vertical bushes, and the outer diameter is larger.
Composite sheathed aluminum foil PE compound film longitudinal cover coil hot air welding cable Light weight, aluminum foil for waterproof layer, with copper wire shield to meet the thermal stability.
The above 6 kinds of metal sleeves all have a good radial waterproof layer, but the intrinsic quality, application characteristics and manufacturing costs vary. At present, there are productions in addition to corrugated copper jackets and stainless steel jackets. The performance of the four types of products produced in China is described below.
2. Aluminium bushings At present, large companies that can manufacture lead-sleeved cross-linked cables in China have the ability to produce lead bushes with continuous lead presses. Lead-sleeved cross-linked cables have a tight internal structure, good longitudinal water resistance, good chemical stability against corrosion, and a disadvantage of heavy weight.
The melting temperature of the lead alloy is about 300°C, and the extrusion temperature of the die press of the lead press is 260°C. The lead sleeve manufactured on the lead screw continuous press is a continuous lead pipe without ash, seamless, and smooth inner wall. The creep performance of lead is good. When the structure size is designed, there is no need to leave a gap between the lead sleeve and the core. When the cross-linked insulation expands, it can expand the lead sleeve and the insulation surface is still smooth. Since the coefficient of expansion of crosslinked insulation is about one order of magnitude greater than that of metal, there must be sufficient expansion clearance within each type of corrugated metal jacket. If there is no gap or the gap is not large enough, after the insulation is expanded, it will leave ripples on the insulation surface, which will affect the electrical performance of the cable. After 20 thermal cycles in the type test, if the surface of the cable core is corrugated, the impact margin of the cable is not high. As the lead sleeve inner wall does not require design clearance, the structure is tighter. Therefore, the longitudinal waterproof performance of lead-sleeved cross-linked wires is better than that of any corrugated metal sheathed cable.
The resistance coefficient of lead is 7.8 times that of aluminum. The lead sleeve must meet the short-circuit thermal stability requirements in the technical conditions. The cross section of the lead sleeve must be much larger than that of the aluminum sleeve. The short-circuit thermal stability indicators of all power supply systems are much larger than actual ones, mainly because the zero-sequence short-circuit duration is too long, but only a few cycles actually occur. This indicator is set by the system and there is no right for cable technicians to change. Shanghai in the 220KV project requires 50KA 2 seconds, the use of lead sets of cable to be added under the lead sleeve copper shield, use corrugated aluminum sleeve to be thickened. In the 85 years of introduction, there was a project where foreign thickened corrugated aluminum sheathed oil-filled cables were mated with domestically-manufactured lead-sleeving oil-filled cables (without copper shields). The foreign manufacturer said: “If there is a short-circuit lead-sleeved cable, The lead sleeve will melt.†Actually, domestic super high pressure lead sleeve oil-filled cables and lead-set cross-linked cables used in the past since the 1970s have not experienced lead sleeve melting failure. The main reason is that the short circuit capacity of the current system is not so large, and the short circuit duration cannot reach 2 seconds. The current major power supply systems have compiled the “Provisions of Certain Technical Principles of the Power Gridâ€, in which the duration of the single-phase short-circuit current required for metal sheaths or metal shields of 110 kV or higher power cables is not to be less than 0.2 second (in Shanghai Power Grid). For example). Execution of this technical condition will make the metal sheath structure of the ultra-high cable reasonable, which will help reduce the cost of the cable.
The lead sleeve produced by the screw-type continuous lead press was selected. There was no problem of blisters on the lead sleeve due to the inclusion of the lead sleeve. Screw lead presses take lead extrusions from the bottom of the melting lead furnace. The proportion of lead oxides and various impurities is much smaller than that of lead, and they will float on the surface of molten lead and cannot be squeezed onto the cable. Even though the hydraulic press discontinuous pressure lead machine can produce high-quality lead sleeves, the key is the production process. There are hundreds of kilometers of single-lead leaded oil-filled cables in the Shanghai power system, most of which are produced in Shanghai. The lead bushes produced by hydraulic press discontinuous pressure lead machines account for a large proportion of these cables in more than 20 years of operation. There has been no failure of lead bush leakage. The key to product quality lies in process management and factory equipment. The radial water-blocking function of the lead sleeve is not only inferior to that of the aluminum sleeve, but also better than that of the aluminum sleeve.
The same specifications of the ultra-high voltage lead sheath cable are much heavier than the aluminum sheath cable, generally speaking it is required to weigh 60% to 90%. At present, the laying of ultra-high voltage cables is no longer a construction method for people. The side pressure of the cable must be strictly controlled during laying. Only the winding Yang machine plus the crawler belt conveyor can be used to control the laying tension and control the cable side pressure. When using laying machinery construction, the difference between the weight of the lead bush and the aluminum bush has become insignificant. In the construction, we must design some machinery and equipment to reduce labor intensity due to local conditions, overcome some difficulties during construction, and get a safe operation return in the future operation. In the event that the outer sheath is damaged after running, the lead sleeve will resist corrosion and the metal sleeve will not perforate quickly to cause water ingress. Lead-sleeving cross-linked cables are more flexible than aluminum-sheathed cross-linked cables, and lead-sleeved cables can be easily lead-free during joint operations.
The proportion of lead is 11.34 which is 4.2 times that of aluminum. The cost of lead-lead materials is much larger than that of aluminum sheaths. Take 110KV 1 x 630 square millimeter wire as an example to make a comparison: lead sleeve thickness is 4mm, aluminum sleeve is 2mm; in each lead sheath cable, the weight of lead is 7.5 times that of aluminum sheathed cable. Calculated according to the market price in the same period of 1999, the price per ton of lead raw materials is 34% of that of aluminum, while the lead cost of lead in lead sets is 2.5 times that of aluminum. If the requirements for short-circuit duration in the technical conditions are too long, copper shields must be added to the thermal stability of the lead sleeve design, which will result in a greater difference in raw material costs between the two metal sleeves. In the bidding competition, if manufacturers of lead-sleeved cross-linked cables participate in the competition with the aluminum-sheathed cross-connected cable at the same unit price or slightly higher price of the aluminum-sheathed cross-connected cable, it is cost-effective for the user.
Lead-set cross-linked cables are not replaced by aluminum-sheathed cross-connected cables. Each cable in the land has its own characteristics and advantages and disadvantages. It is preferable to choose the lead-jacketed cable in the direct burial and laying of the pipe. Submarine high-voltage cross-linked cables must be made of lead sheaths, and the probability of external force damage such as the anchorage of the cable is very high. Once the sheath is damaged, it is difficult to repair. If the aluminum sheathed submarine cable is damaged by external forces, the main insulation and the metal sheath are still intact, but the aluminum sheath will soon perforate in seawater and will inevitably reduce the service life. This is the reason why submarine cables do not use aluminum sleeves.
3. The biggest advantage of seamless corrugated aluminum sleeve corrugated aluminum sheathed cables is their light weight and short-circuit thermal stability. In systems where the short-circuit current is slightly longer, the standard aluminum sleeve can meet the requirements. For example, if the thermal stability is not enough in the calculation, the aluminum sleeve can be less thickened to meet the technical requirements, without using an additional copper shield. Lead sets are simple. Aluminum sleeves extruded with aluminum presses have good mechanical properties and tightness.
The weight of the aluminum sheathed cable is much lighter than that of the lead sheath. It is much easier than the lead sheathing cable when manoeuvring, lifting, boring, and moving cables in the laying process.
The corrugated aluminum sheath structure was developed in the sixties and seventies, when the high-voltage cables were mainly oil-filled cables. The use of corrugated aluminum sleeves in oil-filled cable designs has many advantages: the absence of a radial reinforcement belt for lead sleeves; the spiral corrugations constitute outer oil passages to significantly reduce the transient pressure drop of the oil-filled cable, allowing it to be placed in the circuit design. The length of the long oil supply section can reduce the number of stoppers; the aluminum price at that time is much lower than the current price, and the ratio of lead to copper is also much cheaper. Therefore, replacing lead sleeves with corrugated aluminum sheaths in land-based oil-filled cables in some countries has great economic and technological benefits. However, corrugated aluminum sets of cross-over cables spiral corrugated cable does not have a longitudinal water blocking function, in the wire design if it can also longitudinally block water and reduce the gap will reduce the electrical performance, seems to lose out.
The atomic number of aluminum in the periodic table is 13 and lead is 82. Aluminum is a very active chemical metal. During the operation, external force damages damage to the outer sheath or the outer sheath is broken on the bracket, and the aluminum sheath is quickly corroded and permeated to cause water ingress.
The melting point of aluminum is 658°C, and the temperature of the die holder when the aluminum press is extruded is about 500°C. The extrusion temperature of the lead sleeve is much higher than that of the lead sleeve. For this purpose, a copper wire braided glass ribbon or a semi-conductive resistance tape should be provided inside the aluminum sheath to prevent the insulation shield from being burned. Aluminum presses have continuous and discontinuous presses. Discontinuous aluminum alloy ingots have to be stopped for a period of time, which is not very beneficial for cross-linking cable cores. Although the old and new aluminum ingots can be combined into one body in the aluminum press machine, there are still joints on the surface of the aluminum sheath, but there is no effect on the strength of the aluminum sheath. It should be said that continuous is better than discontinuous.
Pressing aluminum machine is a high cost of precision equipment, aluminum pressure jacket production process and process is also more complex, aluminum machine production aluminum sleeve energy consumption and higher labor costs, metal sleeve production costs will be higher.
The allowable side pressure of the cable is related to the insulation type, not depending on the type of metal sheath. The data recommended by some authoritative manuals abroad is shown in the table below. Although the compressive strength of the corrugated aluminum pipe is higher than that of the lead pipe, the tension of the cable during laying is on the conductor core. The lateral pressure at the bend is transmitted from the conductor to the insulation, the metal sheath and the sheath, and the thrust is received by the corner pulley. . One of the most susceptible to mechanical forces is insulation, and it is reasonable to determine the side pressure that a cable can withstand by its resistance to insulation.
Cable type allowed side pressure (N/m)
Oil-paper insulated cable extruded insulation cable 3000
3000
Aluminium jacket cables have a lot of interest in installation. Light weight is the most popular point for laying workers, but its softness is not as good as lead sleeves. The outer end of the high-voltage cross-linked aluminum sleeve laid down from the cable tray must be straightened with a straightener to be pulled. In the laying process, the lateral pressure and traction of the wire are controlled by a winch and a drawer belt conveyor. Therefore, the traction at the end is not large. After the cable passes through the bend, the aluminum cable is not easy to straighten out on the turn. Not as good as lead-sleeving cable. In the installation of various types of accessories, aluminum sheathing can not be directly lead-bismuth, first on the surface of aluminum tin plated tin alloy and antimony lead to lead after the lead. Beryllium at the bottom of the lead requires a high level of skill for the personnel. Few helium will cause water to enter the cable. In a large-scale project, the amount of work required to terminate the wire and install the traction end of the wire is very large, and it is particularly useful in laying pipes. Aluminum sheath cables are not welcomed by joint workers.
4. Seam corrugated aluminum exposed weld aluminum sleeve is wrapped by aluminum plate and then welded by argon arc welding machine. The cost of the argon arc welding machine cannot be compared with the expensive aluminum press. After the equipment is low, the cost of repayment, depreciation, and other costs of entering the product will be less. The production and energy consumption of the weld aluminum sleeve are lower than that of the seamless aluminum sleeve. The low production cost of the weld aluminum sleeve is its greatest feature.
The melting point of aluminum is 658°C, and the melting processing temperature of aluminum is about 700 to 750°C. The arc temperature is even higher. In the welding process, the aluminum plate on the two sides of the weld will cause changes in the metallographic structure of the aluminum after it is heated, making the mechanical properties of the aluminum sleeve uneven over the circumference. In the laying of traction in the stress will produce a concentrated deformation. This phenomenon has occurred in actual projects. Two-circuit 110KV XLPE cable is laid in a certain project. One time is a seamless aluminum sleeve, and the other is a welded aluminum sleeve. Using the same construction method, the seamless round shape is good and the seamed aluminum sleeve is deformed. It is elliptical, which reflects the difference in the intrinsic quality of the two cables. The deformation of the cable during laying is related to the pressure on the control side. Before laying, calculate the tension and side pressure in sections and adopt appropriate measures. The wire will not be deformed.
Because of the great difference in expansion coefficient of the raw materials, the branch cable has complicated its thermo-mechanical properties. The weld temperature is about 700°C, and the aluminum sleeve on the opposite side of the weld is at a very low temperature. The crosslinked insulation is subjected to a non-uniform heating process. The cable is heated from the inside to the outside during the operation. When the aluminum sleeve is pressed or the lead sleeve is pressed, it is from the outside heat to the inside. It is a uniform symmetrical heating process. The uneven heating process of the weld aluminum sleeve during the production process makes the thermal mechanical properties in the cable more complex. Welded aluminum sleeves can only be welded on one side. This is the thinnest welding method in the welding process. In the standard, the strength of the weld seam is evaluated at 90% (54MP2) of the soft aluminum tensile strength.
The design of the weld aluminum sleeve often uses the reduction of clearance to achieve the purpose of longitudinal water resistance of the cable. As mentioned above, this will reduce the impact margin and will not be worth the loss. In addition to filling the water within 5 minutes in the longitudinal water blocking test, the actual working conditions should be simulated in the water injection process. If the cable is penetrated by a cable trench or working hole filled with water, a split hole will be formed in the metal sleeve. The water will infiltrate into the two sides immediately and will not allow the water to expand with an initial expansion process. In addition, if the gap is too small, it will cause the difficulty of stripping the aluminum sleeve when the attachment is installed, and it will not be welcomed by the joint workers.
Compared with the seamless aluminum sleeve, the weld aluminum sleeve has its own characteristics in addition to the common characteristics of the aluminum sleeve. Welded aluminum sleeve is an effective radial waterproof layer, but its internal quality is different from that of seamless aluminum sleeve and the production cost is different. There should be a difference in price. Generally speaking, the spread between the two can reach a two-digit percentage. The specific spread can find a reasonable price in the introduction of market competition mechanism.
5. Corrugated corrugated aluminum sheath corrugation and process problems have been studied in the country, and there are no provisions in the newly formulated standards. The differences between plants are not small. In recent years, many countries have introduced corrugated aluminum sheathed cables. Its appearance, waveform, wavelength and amplitude and other parameters and its relationship with the outer diameter of the cable core are for reference and reference. After doing some research, it can be used as the basis for formulating user standards or bidding technical documents. In addition, similar problems are allowed for bending radius and side pressure.
Waveforms The spiral corrugations commonly used in cross-linked cables have the disadvantage of non-blocking water performance. Ring-shaped (also called bamboo-shaped) corrugated is more suitable for cross-linked cables and Kieby-spiral, and it is easier to prevent longitudinal penetration of moisture.
Before the corrugation shape of the aluminum sheath is not finalized, the longitudinal tensile strength of the aluminum sheath should be used to monitor the quality of embossing.
6. The comprehensive sheathed composite sheathed cross-connected cable has the characteristics of light weight, small size, and low cost, and can be used in a system with a small zero-sequence short-circuit capacity; a copper wire shield is required in a system with a large short-circuit capacity, which has an advantage in cost. There are fewer exceptions. The domestically-made 110KV cross-linked cable was first used in Hangzhou and has a good track record since 1992. In the first phase of the subway project, Shanghai introduced such cables from Germany into the lines for direct burial and platooning. The water-repelling layer of German products uses water-swollen powder instead of water-blocking.
Radial water-blocking with integrated sheathed metal foil is an effective water-blocking layer. Its resistance to external damage and corrosion resistance after perforation of the outer sheath is fragile. The integrated sheath has the advantage of low cost in tunnels and pipelines with low probability of external damage. The light weight of the hydropower station's high drop project also has its own unique features.
7. Conclusions (1) Various metal sheaths have their own characteristics and can all be used as radial water blocking layers for ultra-high voltage cross-linked cables. Different metal sheaths have their own characteristics. Each has its applicability. When selecting the structure of the metal sleeve, the use conditions, construction habits and operating experience of each should be selected according to local conditions;
(2) In different cable structures and production processes, generally speaking, seamless metal sleeves are better than seams, and continuous ones are better than discontinuous ones;
(3) The internal quality of the cable is different and the production cost is different. There should be a significant difference in the cable price.
(4) The quality of the cable is determined by the overall quality of the components such as the conductor, the shield, the insulation, the metal sheath and the outer sheath, and the quality of the metal sheath is only one part.
The Shielded Cable is a cable that is resistant to external electromagnetic interference formed by a transmission cable plus a shield.
Most of the shielding layers of such cables are woven into a mesh metal wire or a metal film, and there are many different ways of single shielding and multiple shielding. Single shielding refers to a single shielding mesh or shielding film in which one or more wires can be wrapped. The multi-shielding method is a plurality of shielding nets, and the shielding films are all in one cable. Some are used to isolate electromagnetic interference between wires, and some are double-layer shields used to enhance the shielding effect. The mechanism of the shielding is to ground the shield to isolate the externally induced inductive voltage of the conductor.
Shielded Cable
Shielded Cable,Shielded Usb Cable,Double Shielded Ethernet Cable,Control Signal Cable
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