Choose the wire and cable, quickly identify the type!

The main function of wire and cable is to transmit electric energy, signal and realize electromagnetic conversion. The transmission of electric power, such as power cable, overhead line, etc., is the same as shaft ABC Cable, and the wire with electromagnetic conversion is like paint wrapped wire. If you choose a wire or cable, you need to quickly identify the type and type to select the right cable to use.

According to the number of transmission lines of each other with each other which are fixed together, the insulated wires can be divided into single core wires and multi-core wires. Multi core wires can also fix multiple single core wires in one insulating sheath. The multi-core wires in the same sheath can be as many as 24 cores. The parallel multi-core line is indicated by “B”, and the twisted multi-core wire is indicated by “s”.
Insulated wires can be divided into single wire and multi-core wire according to the stock number of each transmission line. Generally, the insulated wires above 6 square mm are all multi-core wires. The insulated wires with 6 square mm and below can be single wires and can also be multi-core wires. We call the single wire of 6 square mm and the following as hard wire, and multi-core wire is called copper wire.
Hard wire is indicated by “B” and copper wire is indicated by “R”. The common insulating materials of ACSR Cable are polyethylene and high pressure polyethylene. The “V” of PE indicates that “Y” is used for high-pressure polyethylene.

Bv copper core polyethylene insulated wire; BLV aluminum core polyethylene insulated wire; BVV copper core polyethylene insulation layer polyethylene protective cable; Blvv aluminum core polyethylene insulation layer polyethylene protective cable; BVR copper core polyethylene insulation copper wire;
RV copper core polyethylene insulation layer is installed with copper wire; RVB copper core polyethylene insulation layer flat electrode connecting wire copper wire; BVS copper core polyethylene insulation layer twisted copper wire; RVV copper core polyethylene insulation layer polyethylene wire sheath copper wire;
BYR high voltage polyethylene insulated soft cable; Byvr high voltage polyethylene insulation layer polyethylene wire sheath copper wire; Ry high voltage polyethylene insulated copper wire; RYV high voltage polyethylene insulation layer polyethylene wire sheath copper wire;
BVVB copper core polyethylene insulation layer polyethylene protective wire sleeve flat cable; BLVVB aluminum core polyethylene insulation layer polyethylene protective wire sleeve flat cable; Bv-105 copper core high temperature resistant 105 ℃ polyethylene insulated wire.

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What are the three rules for selecting wires and cables

The application of wire and cable in life is essential. What people pay more attention to is the quality of wires and cables, but the types of cables are also various. The more kinds, the more difficult it is to choose. Many people don’t know how to choose the right wires and cables to use, which leads to problems. To teach you how to choose the right wires and cables
Nowadays, more and more ACSR Cable lines are used in distribution lines, but it is very important to choose the cable type. Combined with the actual work, the paper simply discusses the application scope and selection of 10kV cable lines. First, it is necessary to determine where the cable is applied, where the cable passes, the load nature, capacity, etc. to select the cable.

1、 Application scope of wire and cable line: the place where the power equipment is clustered, prosperous area, important section, major roads, urban planning and urban environment with special requirements. In the area of serious pollution and corrosion which is difficult to solve, the reliability of power supply is high or the users with important load are required, key scenic spots, high load density urban center areas, new residential areas and high-rise buildings with large building area are built.
2、 Selection of wires and cables: determine the section according to the long-term allowable current carrying capacity, select the cable section according to short circuit thermal stability, select the cable section according to the voltage drop of the connecting circuit, check the section according to the mechanical strength, and select the section of neutral wire (n), protective ground wire (PE), protective grounding neutral line (pen).

3、 Correction of the current carrying capacity of electric wires and cables: long-term allowable current carrying temperature correction of cables, soil correction of long-term allowable current carrying capacity of cables, long-term allowable current carrying capacity correction for directly buried and parallel laying power cables, and correction of carrying capacity of 10kV and below cables laying through pipes.ç

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How to select cable label

AAAC Cable label is an identification mark used in field installation and after maintenance.
The purpose of cable identification is
Ensure the organization and correctness of installation
And the convenience of maintenance and inspection later.
This paper is to share the purpose, characteristics and how to choose cable label for you.

Application and characteristics of cable identification
In a line system, it is impossible for the operation and maintenance personnel to memorize a wide range of equipment and lines. In order to make sure that they do not miss in the inspection, it is necessary to manage the line identification. After marking each line, it shall be sorted and summarized and posted in a conspicuous position. In the future, it can be done without omission if the inspection is carried out in strict accordance with the project requirements.
Cable identification system can not only provide correct guarantee for the operation and maintenance personnel to carry out correct daily maintenance and abnormal accident handling, but also provide help for the later generations. Even if the new personnel are employed, as long as the identification is followed, there will be no misoperation.
How to select ACSR Cable label
Mark before or after the terminal is completed
Cable identification card: 1. It can be used before or after the terminal connection. 2. The content is clear. The label is completely wrapped around the cable.
Heat shrinkable cable identification pipe: 1. It can only be used before the terminal is connected, and is sheathed on the wire through the open end of the wire. 2. Before heat shrinking or splicing, the label can be replaced randomly. 3. After the terminal is jacketed, the sleeve will become a permanent mark which can withstand the bad environment. And it’s low cost.
What is the diameter of the cable
The diameter of the cable determines the type, length, or diameter of the sleeve to be identified. Cable identification card is widely used in large square cable, large logarithmic cable and outdoor optical cable. The heat shrinkable label tube is widely used on the small square secondary small line. Identification cards can be used for various cables of different diameters.
What environment will cable labels be placed in
Factors to consider include:
1. Is there any contact with oil, water, chemicals or solvents?
2. Is flame retardant required?
3. Does the state have any special or other provisions on this?
4. Is it used in clean or other environments? Even in the harsh environment, the heat transfer printing, industrial grade printing quality, has strong anti pollution, in fact, the print content is also “anti oil pollution”.

Do you plan to print or buy pre processed logo yourself?
Purchase cable identification
1. There are a variety of preprint content available for selection;
2. If the demand is large, it can provide customized preprint content;
3. There are various kinds of marks such as card and sleeve type, which can be selected, convenient to use and convenient for transportation;
4. It is suitable for various applications.
Print logo by yourself
1. Print various content as needed (even if you print very little);
2. There are various label and label sleeve materials for portable printer, heat transfer printer and computer printer;
3. Suitable for printing longer characters;
4. And have the label size suitable for different applications.

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Radiation crosslinked cables and materials

1. development of crosslinking technology
In 1952, Charles by invented crosslinked polyethylene insulation by using radiation energy to trade polyethylene into polyethylene in a nuclear reactor test;
In 1957, Ge first made cross-linked ACSR Cable in cable industry by using peroxide (DCP) as chemical crosslinking reagent on the basis of the above principles;
In the late 1960s, Dow Corning invented silane crosslinking technology, and has developed to date

2. radiation crosslinking process of cable
There are three kinds of production processes: two-step one-step copolymerization and ethylene silane copolymerization.
The two-step technology is the first developed technology. The secondary method has less investment and low cost, but it is easy to bring impurities, so it can only be used in the manufacture of low-voltage cable. It has little requirements for equipment and can be completed on conventional extrusion equipment;
The one-step process of grafting reaction and adding condensation catalyst was combined to extrude the cable in one step to reduce the pollution opportunity of impurities, which is suitable for the manufacture of medium and low voltage power cables. But the technology is difficult, and it needs special extruder, and the investment is bigger than one-step;
In the copolymerization, silane copolymers are reacted in PE reactor, which improves the electrical insulation performance of crosslinked PE significantly, and is more suitable for medium and low voltage AAAC Cables besides the manufacture of low voltage cables. Reply to “cable”, and check for more related articles
3. requirements for materials of irradiation cable
Irradiation cable shall be processed three times
a) Material modification to get cable material
b) Cable sheath plastic
c) To withstand the attack of high energy particles
The environment of irradiation cable
High temperature, possibly oil pollution, other harsh environment

4. irradiation crosslinking of polymer materials
5. Application of irradiation crosslinking cable
Various connecting wires and installation wires commonly used in buildings are copper wires wrapped in insulation layer, which are used for low voltage electrical equipment and lighting devices. This wire is commonly known as “laying wires”.
Electrical installation line, but the application field of electrical installation line is more extensive, and the requirements for cables are different in different application occasions. In some cases, the diameter of the line is relatively thin, which belongs to the commonly known “electronic line”.
Radiation crosslinking cable is also needed in the lead-up flexible wire of motor winding
Car and locomotive lines
Marine and petroleum platform cables
Overhead insulated cable
Locomotive navigation aids light cable
New energy cable (photovoltaic, wind, charging pile)
Other special occasions (aerospace, nuclear)

6. Standard and quality control of irradiation crosslinking cable and materials
1. gel content
Gel content is an important index of cross-linking degree of surface materials. Generally, linear polymer materials can be dissolved in some solvents under certain conditions, but the crosslinked network structure is not soluble in any solvent. Based on this principle, gel content can be obtained. It is the most direct and simple method to characterize the degree of crosslinking of polymers. The cross linked polymer with known weight was put into Soxhlet extractor and refluxing with suitable solvent for a certain time. After being removed, the gel content was obtained by vacuum drying and weighing.
2. thermal extension
Although the gel indicates that the degree of crosslinking of polymers is more accurate, but the operation is rather cumbersome, it is often tested in the cable industry to determine the degree of cross-linking after the thermal elongation of the material coated by the radiation. After applying 0.2MPa tensile force at 200 ℃ for 15min, the elongation is less than 175%. After the sample is taken out of the heat aging box and cooled, the permanent thermal deformation is less than 15%, which means the cross-linking is qualified.
3. thermal aging
The temperature grades of crosslinked cable materials in JB / t10436-2004 are 90 ℃, 105 ℃, 125 ℃, 150 ℃, and the aging time is 168 hours, but the aging temperature is 121 ℃, 136 ℃, 158 ℃, 180 ℃ respectively

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What should be paid attention to when storing wire and cable reel?

Attention should be paid to the following points when storing and transporting wires and AAAC Cables on shelves:
1、 In storage, first of all, it is forbidden to contact with acidic, alkaline and corrosive substances and store them separately. Insulated wires and cables should be stored in a dry and ventilated warehouse. The suitable temperature in the warehouse is 5-30 degrees, and the relative humidity should not exceed 75%. The glass on the warehouse window should be painted with white paint to avoid direct sunlight and premature aging of insulation layer.

2、 There shall be no harmful gas that can damage the insulation layer or corrode the conductor metal around the wire and cable storage place.
3、 Avoid storage in open air to prevent accidental damage.
4、 Small quantities of wires can be stacked in the shelf, and the stack height should be 5-10 rolls. Large quantities of wires can be stacked into plum blossom style ventilated round stacks. Single core wire and cable can be appropriately high code; The stack height is 2 meters in spring and winter and 1.5 meters in summer and autumn. When stacking, the pallet should be padded with sleepers, and the sleepers should be paved with planks, and two layers of moisture-proof paper should be added, and good ventilation should be maintained. During the storage of wires and cables, they should be stacked once every three months, and the upper and lower layers should be replaced to prevent long-term compression and deformation of the lower layer. Always check whether the sealing package of wires and cables is intact during storage.
5、 The storage life of wires and ACSR Cables shall be subject to the date of production. Generally, the storage life shall not exceed one and a half years, and the longest shall not exceed two years. Pay attention to the change of temperature and humidity in the process of storage, and take cooling measures immediately if the temperature in the warehouse exceeds 30 ℃. If the relative humidity reaches 75% for 3 consecutive days, desiccant or other measures should be taken to absorb moisture.

6、 It is strictly forbidden to drop wires and cables from high places during transportation, so as to avoid cracking of insulation layer and sheath layer, damaging the electrical and mechanical properties of wires and cables.
7、 During hoisting operation, it is strictly forbidden to hoist multiple coils of wires and cables at the same time. On vehicles, ships and other means of transport, wires and cables must be laid flat and properly fixed to prevent collision or overturning and damage to the outer or internal structure of wires and cables.

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Cable fault detection and search method, you should understand

For direct short circuit or broken cable fault, the multimeter can be used to measure and judge directly; For non direct short circuit cable fault and grounding AAC Cable fault, the insulation resistance between cores or insulation resistance between cores to ground can be measured by megohmmeter, and the type of cable fault can be judged according to the resistance value. The following describes the method of cable fault finding:
Zero potential method
The zero potential method is also called potential comparison method. It is suitable for short cable core to ground fault. The application of this method is simple and accurate, and does not need precise instruments and complicated calculation. The measurement principle is as follows: parallel the cable fault core with the same length of comparison wire, when the voltage VE is applied at both ends of B and C, it is equivalent to connecting the power supply at both ends of two parallel uniform resistance wires. At this time, the potential difference between any point on one resistance wire and the corresponding point on the other resistance wire must be zero, otherwise, the two points with zero potential difference must be the corresponding points. Because the negative pole of the microvolt meter is grounded and equipotential with the cable fault point, the point when the positive pole of the microvolt meter moves to zero on the comparison wire is equipotential with the cable fault point, that is, the corresponding point of the cable fault point. S is a single-phase knife switch, e is a 6e battery or four No. 1 dry batteries, and G is a DC microvolt meter
1) First, connect battery e to B and C phase core wires, and then lay a comparison wire s with the same length as the fault cable on the ground. The wire shall be bare copper wire or bare aluminum wire with equal cross section and no intermediate joint.
2) The negative pole of the microvolt meter shall be grounded, and the positive pole shall be connected with a long flexible wire. The other end of the wire shall be fully contacted when sliding on the laid comparison wire.
3) Close the knife switch s, slide the end of the flexible wire on the comparison wire, and the position when the microvolt meter indicates zero is the position of the ACSR Cable fault point.

High voltage bridge method
High voltage bridge method is to measure the DC resistance value of the cable core with double arm bridge, and then accurately measure the actual length of the cable, and calculate the cable fault point according to the positive proportional relationship between the cable length and resistance. This method is suitable for direct short circuit between cable cores or short circuit point contact resistance less than 1 Ω Generally, the judgment error is not more than 3m, and the contact resistance is greater than 1 Ω The method of high voltage burn through can be used to reduce the resistance to 1 Ω Next, measure according to this method. When measuring the circuit, first measure the resistance R1 between core a and B, R1 = 2RX + R, where Rx is the resistance value of a phase or B phase to the cable fault point, only the contact resistance of short contact. Then move the bridge to the other end of the cable and measure the DC resistance value R2 between A1 and B1 core wire, then R2 = 2R (l-x) r, R (l-x) is the resistance value of one phase from A1 phase or B1 phase core wire to the cable fault point. After measuring R1 and R2, short circuit B1 and C1 according to the circuit shown in Fig. 3, and measure the DC resistance value between B and C two-phase core wires, then 1 / 2 of the organization is the resistance value of each phase core wire, expressed by RL, RL = RX R (l-x), from which the contact resistance value of the fault point can be obtained: r = R1 r2-2rl table. Therefore, the resistance value of core wires on both sides of the fault point can be expressed by the following formula: RX = (r1-r) / 2, R(L-X)=(R2-R)/2。 After Rx, R (l-x) and RL are determined, the distance X or (l-x): x = (Rx / RL) l, (l-x) = (R (L-2) at the end of the cable, the capacitance current IA1, IB2 and IC3 of each phase core are measured to check the capacitance ratio between the core and the broken core, and the approximate point of the broken distance can be judged preliminarily.
3) According to the capacitance calculation formula C = I / (2) Π When the positive voltage U and frequency f are constant, C is proportional to I. Because f (frequency) of power frequency voltage is constant, the ratio of capacitance current is the ratio of capacitance as long as the applied voltage is constant. If the total length of the cable is l and the distance between the broken point of the core is x, then IA / ic = L / X and x = (IC / IA) L. In the process of measurement, as long as the voltage remains unchanged, the reading of ammeter is accurate and the total length of cable is accurate, the measurement error is relatively small.
Sound measurement
The so-called sound measurement method is based on the sound of fault cable discharge, which is more effective for the flashover discharge of high voltage cable core to insulation layer. The equipment used in this method is DC withstand voltage testing machine. TB is the high voltage test transformer, C is the high voltage capacitor, VE is the high voltage rectifier silicon stack, R is the current limiting resistance, q is the discharge ball gap, l is the cable core. When the capacitor C is charged to a certain voltage value, the ball gap discharges the cable fault core wire, and the cable core wire discharges the insulation layer at the cable fault location, producing “Zi, Zi” spark discharge sound. For the open laying cable, it can be found directly by hearing. If it is buried cable, it is necessary to determine and mark the cable direction first. When searching, put the pickup close to the ground and move slowly along the direction of the cable. When the “Zi, Zi” discharge sound is the largest, this is the cable fault point. It is necessary to pay attention to safety when using this method, and special personnel should be set up at the end of test equipment and cable. The cable fault locator produced by our company can not only measure the sound, but also detect the magnetic signal. The signal strength is visually displayed synchronously, which can locate the cable fault point faster and more accurately.

Japan plans to build its largest submarine cable

According to foreign media reports, in order to improve the environment for transmitting a large amount of electricity generated by renewable energy to the capital circle and Kansai consumer areas, Japan’s Ministry of economy, industry and other countries are exploring ways to enhance the transmission network by laying the largest submarine cable in China. The route connecting Hokkaido and Kanto and the route from Kyushu to China and Shikoku are very likely. The government has proposed to achieve the goal of net zero emission of greenhouse gases by 2050, and strive to achieve it through the leap forward expansion of renewable energy.

The Ministry of economy and industry began to discuss the adjustment of the national power supply wide area operation promotion organization (wide area organization) in March this year summarized the discussion plan. The government has positioned offshore wind power generation as the core of renewable energy in the future. The coastal areas of Hokkaido and Kyushu have many suitable places for stable wind, and efforts will be made to deliver power to urban areas.

The capacity of the line from Hokkaido to Kanto is 8-12 million KW, which is about 10 times of the 900000 kW transmission line connecting Hokkaido and Honshu. This paper discusses the submarine ACSR Cable as the largest capacity of transmission line in China. For the route, several options are considered, such as connecting to the Kanto region through the Pacific Ocean or the sea of Japan, and connecting to the northeast region.

According to the analysis, the distance of the line will reach nearly 1000 km. There are only two submarine cables connecting dozens of kilometers in Japan, which will be the longest one. Compared with the common AC power transmission line, the submarine cable transmits power by the DC mode with less loss.

As for the route from Kyushu To Kansai, new submarine cables (with capacity of 1.4-2.8 million KW) connecting Kyushu to China and submarine cables (with capacity of 700000-2.8 million KW) connecting Kyushu to Shikoku will be considered. In addition, the transmission equipment connecting the East Japan border with the West Japan border will be strengthened.

So far, the power giant has focused on connecting the company’s nuclear power plants, large thermal power plants and consumer areas within its jurisdiction to build a transmission network. It was pointed out that, together with the small capacity of transmission equipment in interconnected areas, it constituted an obstacle to the realization of renewable energy projects far away from consumption areas. The submarine cables under discussion are connected to or across the jurisdiction. If completed, it will achieve the change of transmission network appearance.

Huge construction costs are needed to strengthen the transmission network. Wide area agencies intend to curb costs as much as possible, and it is said that submarine cables cost 100 million to 180 million yen per kilometer (about 6.01 million to 10.81 million yuan). If the connection between Hokkaido and Kanto requires at least hundreds of billions of yen in construction costs, it may lead to a rise in electricity charges.

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Discussion on cable process: cable forming

1、 What is cable formation
Definition of cable forming: the process of twisting multiple insulated cores into AAC Cables according to certain rules.
2、 The role of cable forming in cable production
Cable forming is one of the important processes in the production of multi-core cables. The three core, four core (one core is the ground wire) and five core (one core is the ground wire and the other is the neutral wire) of the three-phase power supply is commonly used for power cables. The number of control cable cores is more (more than 2 cores to 61 cores). During the cable forming process, several insulated cores are twisted together according to certain rules, The process of forming a multi-core cable. In addition to the stranding, the process of cable forming includes filling of the gap between the cores of the insulated wires, wrapping and shielding on the core after the cable forming.
When forming cables, the twisted form of insulation core adopts concentric normal stranding. If the diameter of the insulated core is identical, it is called symmetrical cable forming. If the diameter of the insulation core is different, the cable formation is called asymmetric cable formation. In order to avoid the influence of torsional stress on the core during the process of cable forming, the cable forming machine with the torsion device or bow shaped cable forming machine is used for the cable forming of circular insulated core to conduct the twisting and twisting.
3、 The way of cable forming
There are two ways to twist the strand and the cable, one is to twist back and the other is not to twist.
The rewinding and twisting is that the cable tray frame equipped with the setting out plate keeps the setting out plate at all times horizontal position when the machine rotates by means of the special device (the torsion device) on it. When the cable is formed, the insulation core is only subjected to the bending action, but does not twist. The back twisting is often used in the process of forming the circular insulated core. The core has no rebound stress after the cable forming, which can ensure the accuracy of the roundness and diameter of the cable.
The non twisted twisted cable is mostly used for the formation of fan-shaped lines. After the compression of the die, it becomes plastic deformation, thus eliminating the original torsional stress and ensuring the round after the cable is formed.

4、 Cable forming direction and pitch diameter ratio

The cable forming direction is generally right. The confirmation of cable forming direction is in the direction of ACSR Cable core forward, if the cage turns left, it is right direction, otherwise, otherwise, it is opposite.
The ratio of cable pitch diameter is different according to different types of cables. The circular core insulated by cross-linked polyethylene is hard and the diameter of cable forming is larger, with a disk of 30-40; The pitch diameter ratio of PVC insulated power cable is 30-40, and that of sector line is 40-50; The diameter ratio of the cable core of plastic insulated control cable is specified in the national standard, and generally it shall not be more than 16-20.
5、 Stranding coefficient and twist rate
In a pitch of the cable forming, the ratio of the actual length of the insulation core to the length of the pitch of the cable is called the stranding coefficient (k=l/h);
The stranding rate is the ratio between the difference between the actual length of the insulating core and the length of the cable forming pitch and the length of the formed pitch within a cable forming pitch λ=( L-H)/H × 100%
It is convenient to adopt the coefficient K, and the K value is always greater than 1. Thus, the actual value of K is increased by one K value for the single insulated core after the cable forming. The resistance of the core is proportional to the core, that is, the resistance of the core is also increased by a k value. If the insulation resistance is inversely proportional to the length of the insulating core, the insulation resistance of each core will be reduced by a k value. From the angle of reducing the core resistance and increasing the insulation resistance value, it is hoped that the smaller the coefficient of cable winding is, the better.
The ratio of the cable formation to pitch ratio is inversely proportional to the square of the pitch ratio. Therefore, the smaller the pitch ratio, the greater the coefficient of the cable formation, the greater the amount of insulating core material is, otherwise, from the perspective of saving the material consumption, the smaller the coefficient of cable formation is, the better.
6、 Wrapping process
The production process of wrapping all kinds of metal or non-metallic materials on the core or core of the guide cable is covered with the specified pitch spiral in the form of ribbon or wire.
7、 Non armored cable wrapping
In order to prevent the cable core from deformation after the cable forming and to prevent the adhesion with sheath, the insulating core shall be wound with the wrapping layer while forming and filling on the cable forming machine. For the non armored plastic insulated cable, the 1-2-layer non-woven fabric belt is usually wrapped by covering (the first layer or two layers are used for the specific purpose, and the principle of cable forming and tightening is adopted), The covering size is 10% – 15% of the bandwidth, and the wrapping angle is 25% °~ forty ° Within the scope.

8、 Armouring of cables
Steel belt armored cable is mainly suitable for underground direct burial, and can bear certain mechanical pressure; Steel wire armored cable is mainly suitable for laying with drop or vertical, and can bear large mechanical tension. Armored cable is mainly divided into steel strip armor and steel wire armour, and their combination armouring mode.
If there is shielding material (including unified shielding) on the core of the steel belt armored cable, the cable core shall be replaced by the extruded insulating sleeve instead of the inner layer. If the insulation core has no metal shielding layer, the inner layer of the insulation wire can be extruded or wrapped. The inner layer of the wrapping is generally PVC or PE and other similar strip.
Generally, the steel wire armored cable adopts the extruded inner layer.
For the model of armored cable, such as yjv22, there will be two numbers, the first number is the armor Code: generally, there are 2, 3 and 4 numbers:
2 – indicates double layer steel belt armor
3 – indicates the thin steel wire armouring
4 – indicates the thick steel wire armouring
The steel strip thickness and copper clearance of armored cable, wire diameter and clearance of steel wire armored cable shall meet the relevant standards.

Technical problems in power cable insulation detection

1. It is not suitable to adopt AC voltage withstand test, but DC voltage withstand test
High voltage electrical equipment is generally tested by AC withstand voltage test for its main insulation withstand voltage strength, while power cable is often limited by the capacity of test equipment due to its large capacitance, so it is difficult to carry out power frequency AC withstand voltage test. In addition, the AC withstand voltage test may produce free discharge in the hole of oil paper insulated cable and damage the cable. The insulation strength of the cable damaged by the same high AC voltage is much greater than that of DC voltage. Therefore, DC withstand voltage test has become a common method to check the insulation performance of cables. DC withstand voltage test, small equipment capacity, high voltage. Under the action of DC voltage, the voltage in the insulation of the power cable is distributed according to the resistance. When the power cable has defects, the voltage will be mainly applied to the parts related to the defects to make the defects more easily exposed, which can not be achieved by AC withstand voltage test.

2. During DC voltage withstand test, negative polarity connection must be adopted
Generally, when conducting DC withstand voltage test, only pay attention to whether the wiring is correct, and ignore the problem of voltage polarity. The DC breakdown strength of ACSR Cable is related to the voltage polarity. If the cable core is connected to the positive pole, under the action of electric field, the moisture in the cable insulation layer will penetrate and move to the lead skin with weak electric field. As a result, the defects are not easy to find, and the breakdown voltage is 10% higher than that when the cable core is connected to the negative pole. Therefore, the negative connection should be used for DC withstand voltage test of power cable.
3. Influence of temperature on DC withstand voltage test
The insulation resistance of cable decreases with the increase of temperature and increases with the decrease of temperature, just like other high-voltage apparatus; The leakage current increases with the increase of temperature and decreases with the decrease of temperature. It can be seen that temperature has a great influence on the test data. It is very important to convert the test data according to the recorded temperature. If the power cable is cut off for a long time, the actual temperature of the cable should be recorded during the insulation test. The cable test is usually done after several hours of power failure. At this time, the temperature of the cable core is close to the soil temperature. Because the test time is relatively fixed every year, the soil temperature generally has no great difference, but the test data can not be converted according to the recorded outdoor temperature, but should be calculated according to the soil temperature. The temperature of different places is also different. The outdoor temperature of the cable placed in the open air is subject to the outdoor temperature, and the water temperature of the cable placed in the water is subject to the recorded water temperature. For the cable just cut off, the core temperature of the cable should be tested. The voltage distribution between the cable core and the lead sheath depends on the insulation resistance, so the temperature of the cable core and the lead sheath has a great influence on the voltage distribution. When the temperature difference is small, the voltage shared by the insulation near the cable core is higher than that near the lead sheath; If the temperature difference is large, the insulation resistance near the cable core will decrease due to the increase of temperature, and the voltage shared by the insulation resistance near the cable core will decrease, which may be smaller than that near the lead skin. Therefore, it is easy to find the insulation defects near the cable core in the cold state, and it is easy to find the insulation defects near the lead skin in the hot state.

4. During DC withstand voltage test, the cable must be fully discharged
The capacitance of power cable is very large. After DC withstand voltage test, the energy of residual charge is still relatively large, which directly affects the measurement of insulation resistance and absorption ratio. If the discharge time of the cable is short after the first DC withstand voltage test and the residual charge is not discharged completely, the charging current and absorption current will decrease compared with the first time, so the phenomenon of false increase of insulation resistance and decrease of absorption ratio will appear.
In addition, insulation resistance test immediately after DC withstand voltage test will produce false phenomenon of insulation resistance decrease and absorption ratio increase. This is mainly caused by the opposite polarity of the connection voltage of the megohmmeter measuring the insulation resistance and the DC withstand voltage. In the DC withstand voltage test of cable, if the discharge is not sufficient, measure the insulation resistance immediately, then the insulation resistance meter needs to output a lot of charge to neutralize the residual charge in the cable, resulting in false reduction of insulation resistance. Because the DC withstand voltage test time is generally 5min, the discharge time of cable after DC withstand voltage test should be more than 5min. The longer the cable is, the longer the discharge time is. After insulation resistance test, the discharge time is longer than the charging time.
5. During DC withstand voltage test, it must be shielded
When DC withstand voltage and DC leakage tests are carried out on power cables, the stray current caused by equipment has a great influence on the test results because the test voltage is higher and the leakage current of cables with good insulation is smaller. In order to eliminate the influence of stray current on the test results, the microammeter is connected to the high voltage side, and the high voltage lead and the microammeter are shielded. Because the micro ammeter is connected to the high-voltage circuit and the high-voltage lead and micro ammeter are shielded, the influence of the corona of the high-voltage lead and the stray current of the test equipment on the test results can be eliminated, and the accuracy of the test results is high. This kind of wiring can be used for the cable sheath with or without insulation to the ground.

Tuopu electric, a professional manufacturer of DC high-voltage generator, thinks that under harsh environmental conditions, the leakage current on the cable surface is large, so that the test data can not reflect the real situation of insulation. This method can completely eliminate the influence of the surface leakage at both ends of the cable, and can measure the real leakage current data of the cable insulation.

Electric vehicle high voltage cable performance requirements and standards

1、 Overview
With the rising of international crude oil price, the whole society pays more attention to the environmental deterioration and global warming, and the tax tilt and policy support of governments, which promotes the market share of alternative energy, especially electric vehicles, to increase all over the world.
Electric vehicles mainly include three types, namely pure electric vehicles, hybrid vehicles and fuel cell vehicles.
Pure electric vehicle and fuel cell vehicle are driven by an electric motor. Hybrid electric vehicles are supported by motors when the efficiency of internal combustion engines is not high under acceleration and low speed conditions.
Their common feature is to use up to 600V or higher drive voltage, involving wiring, they all have the same basic requirements, both in EMI (electromagnetic interference) protection system safe transmission of high current and voltage.
As a high voltage acsr cable, it is used to connect high voltage battery, inverter, air conditioning compressor, three-phase generator and motor to realize the transmission of power and electricity.
The basic principles of electric vehicles seem to be simple. But in-depth analysis, the manufacturers of the system are facing a series of challenges to overcome.
New technical requirements are put forward for the items of high voltage cable, such as flexibility, shielding, safety and size of electric vehicle, because these will affect the wiring of components with high current and high voltage. In the face of different technical points of each possible power system, different special requirements are put forward for the components needed.
It is necessary to note that the high voltage system of electric vehicles is not a typical high-voltage system. The relevant terms such as “high voltage” and “high current” must be limited to the scope of the automotive field, compared with the low-voltage system of conventional vehicles.
In other fields, reference systems adopt totally different standards, such as the definition of high voltage in the power field, which starts at thousands of volts.
2、 Requirements for high voltage cable of electric vehicle
The innovative electric vehicle design presents new challenges to high voltage cables and system components, which cannot fully adopt the existing solutions. The specific requirements are analyzed as follows.
1. voltage
The basic difference between the cable and the conventional vehicle is that the structure needs to be designed at 600 V rated voltage, and if used on commercial vehicles and buses, the rated voltage can be up to 1000 V. By contrast, it’s even higher. The cables used in vehicles powered by internal combustion engines are designed to have a rated voltage of 60 v.
Power generated by the system (P = u × 1) The high voltage can reduce the power loss in the transmission system (pls= I2) without change due to the use of lower current × R)2. current
Because the cables connect the battery, inverter and motor, the high voltage cable needs to transmit high current. According to the power requirements of system components, the current can reach 250A to 450A. It is difficult to find such a high current in conventional drive vehicles.

3. Temperature
The result of high current transmission results in high power consumption and heating of components. Therefore, the high voltage cable is designed to bear higher temperature. At present, it can be seen that there is a trend of further increase in temperature requirements.
In contrast, the current vehicle usually uses a cable rated at 105 ° C, as long as it is not used in the engine compartment or other areas with high temperature resistance. High voltage cables of electric vehicles are usually higher than this temperature, such as 125 ℃ or 150 ℃.
If the routing in electric vehicles is unfavorable, the host plant will even put forward higher requirements for high temperature resistance. Such as exhaust pipe, motor front, battery back, etc.
4. working life
The automotive industry usually has a design life of 3000 hours for cables of specified temperature grade. In recognized cable standards (e.g. ISO 6722, ISO 14572), this value is usually used for long-term aging tests. The special requirements of customers in high voltage applications may exceed 3000 hours, and the cumulative operating time at the specified temperature can reach 12000 hours.
5. shielding effect
The high voltage aaac cable itself does not need to be shielded, because it does not transmit data as coaxial cable, but it is necessary to prevent or reduce the high frequency radiation generated by switching power supply in the system to be induced to the surrounding parts through the cable.
Unlike fuel driven vehicles, it is necessary to control the three-phase alternating current of the motor of the electric vehicle. The sinusoidal voltage with energy is equivalent to the square wave pulse signal with different frequencies. Because of the steep edge of high frequency pulse, it will generate strong energy harmonic emission to the surrounding area.
EMI problem can be solved by using appropriate shielding method. In some cases, different shielding types are needed to meet different requirements of shielding effect.
6. flexibility
The challenge for the development of hybrid vehicles in many cases is that the existing series of platforms originally designed only to load gasoline engines and its components into more electrical components. Even if wiring is not considered, the space constraints can be predicted.
In addition, space is required for cables and connectors to pass through routing. The usual consequence is the bending radius that leads to tension.
Because of the inherent design of conventional cables, high bending force is difficult to overcome. In order to solve this problem, high flexibility and toughness of high voltage cable is very important. Only flexible design can be easily realized through vehicle routing.
7. bending resistance
If the motor is located near the moving part of the vehicle and then causes continuous vibration of the connected high voltage cable, it requires that it be designed to withstand high cyclic bending to ensure good bending endurance.
8. identification
Because of the increased application risk caused by high voltage, various standards define that high voltage cables must be visually different from ordinary vehicle cables, and the designated surface must be bright orange.
Warning content and special marks can also be printed, such as “caution! High voltage 600V “, high voltage lightning sign, etc.
3、 The standardization status of electric vehicle cable
In view of the challenges and requirements of the high voltage cables used in the electric vehicle, it is necessary to establish new cable standards to meet the needs of suppliers, harness plants and host plants.
The international organization for Standardization (iso/tc 22/sc 3/wg4) of the electrical and electronic sub Technical Committee of the Technical Committee on road vehicles of the international organization for standardization is carrying out this work.
As can be seen on ISO 6722, revisions have been made based on the common 60 V cable standards to meet the requirements of 600V cables. Because most of its requirements are still very common, but often do not consider the special design of high voltage cable. Similar revisions have been made to ISO 14572.
At present, standardization of high voltage cable with voltage higher than 600V is a task of each working group. The standard number is ISO 17195.
SAE will adjust the current high voltage (600 V rating) specification SAE j1654 requirements for high voltage cables and cover rated voltages from 600 to 1000 V. The newly created standard SAE j2840 will be defined as shielded type cables.
LV is a common purchasing specification of five major German auto companies. At present, LV 216 is a high voltage cable standard for electric vehicles with rated voltage of 600 v. It covers shielded cables with single core and multi-core.
The national automobile industry standard of high voltage shielded cable in China is under development, and its rated voltage will reach 1000 V.
4、 The structure design of high voltage cable for electric vehicle
Standard products and very specific requirements are difficult to define. The purpose of this paper is to solve the basic design ideas and overcome the challenges mentioned above by applying advanced high voltage cable structure principle.

1. conductor design
The flexibility of high voltage cable is mostly determined by the design of conductor. That’s why high voltage cables use special conductors with a large number of very small diameter monofilament. A certain number of single wires are twisted first, then concentric rewind is carried out to form the soft conductor required by high voltage cable.
Another advantage of the number of roots is better bending resistance. The short pitch of the strand can also improve the bending life of the high voltage cable.
2. insulation materials
The selection of insulation materials mainly considers the heat resistance requirements and mechanical strength. Compared with the standard battery cable, the soft materials can be selected reasonably to keep the specially designed stranded conductor flexible.
3. cable formation
When the cable is multi-core, it is usually necessary to twist the core. In order to make up for the deformation caused by the twisted high voltage cable core, the so-called twisted special equipment is needed. In this process, the special strand machine is equipped with a set-up plate which rotates in reverse direction relative to the direction of stranding. This is necessary to prevent the deformation tension of the cable.
According to the structure of cable, filling is usually used to ensure the high concentricity of shielded cable, and finally to obtain a satisfactory high voltage cable. The use of wrapping tape in the stranded cable core can keep the cable flexible.
4. shielding
Due to EMC requirements, the braided shielding is made up of several copper wires. Tin plated copper wire can make it more powerful to resist environmental effects such as oxidation. The design is flexible with fine copper wire
Shielding requires a coverage of more than 90% to overcome the EMI problem described earlier.
Different shielding effects need, woven shielding can be combined with other shielding, such as aluminum plastic to meet the film. The shield can be wrapped with a layer of non-woven fabric to ensure that the sheath is easily peeled off during assembly.
5. sheath
As with the insulation of the core, the sheath material is selected according to the requirements of heat and mechanical properties. Environmental properties such as resistance to liquids and wear are also important for sheath due to direct contact. These characteristics are mainly determined by the type of sheath material selected, and to some extent, are affected by the design of sheath structure.
If special requirements, such as overcoming the wear of the installation vehicle environment, require increased wear resistance, this should be considered when selecting materials. Usually, test equipment is used to simulate the reality to verify these characteristics.
Choosing a softer material benefits from flexibility, which can lead to lower wear resistance of high voltage cables.
The extruded jacket shall be a bright orange as specified in the relevant specifications and special high pressure warning marks can be added as specified.