Causes of blackening of copper wire of heavy rubber sheathed flexible cable

2.1 catalytic aging of copper is an important reason for rubber hair adhesion
The experiment of the former Soviet Union Institute of AAAC Cable science proved that copper infiltrated into the insulating rubber from the contact with rubber during vulcanization, and the thickness of 1.0-2.0mm contained 0.009-0.0027% copper. As we all know, trace copper has a great damage to rubber, that is, heavy metal is the catalytic aging of rubber. During the process of insulation vulcanization, qiulanm precipitates some free sulfur to react with copper to form active copper containing groups: CH3 ■ ch2-ch-c-ch2- ■ ■ SS ■ ■ cucu, when aging, weak s-s-bond breaks, forming active copper containing base: cu-s-, which acts with rubber, and acts with oxygen, breaks down long bond molecules of rubber, making rubber soft and sticky, which is a combination of low molecular chain. The French Academy of rubber also pointed out that if there are harmful metals in rubber, such as copper, manganese and other heavy metal salts, the rubber viscosity will occur regardless of the type of promoter.

2.2 sulfur migration to the surface of insulating rubber and copper wire in rubber sheath cable
The possibility of sulfur diffusion in cable sheath rubber was confirmed by the use of radioisotope by former Soviet scientists. The diffusion coefficient of free sulfur is about 10-6cm2 / s at 130-150 ℃ in the vulcanized rubber based on natural rubber. In the continuous vulcanization factory, when vulcanizing sheath rubber, the temperature is between 185-200 ℃, and the diffusion coefficient is greater. Because of the diffusion of free sulfur in rubber sheath, the structure of the colum rubber is changed, and the polysulfide bond may be formed. These polysulfide compounds migrate through chemical decomposition and chemical combination, namely “chemical diffusion”. Due to the migration, not only the structure of the insulating rubber can be changed, the heat resistance of the rubber can be reduced, but the reaction between sulfur and copper surface will result in copper sulfide and cuprous sulfide, which leads to the blackening of copper wire. In turn, copper sulfide and cuprous sulfide accelerate the aging of rubber, and lead to the occurrence of adhesion.

3. Reasons for processing technology
3.1 reasons for processing rubber
In the insulation formula based on the combination of natural rubber and SBR, the plastic of rubber needs to be improved by plastic refining. In order to produce, some factories use internal mixer to improve plasticity by adding a small amount of chemical plasticizer, accelerator M. If the temperature of plastic refining and rubber filtration are not well controlled, high temperature above 140 ℃ appears. When the raw rubber is put on the opening mill, it passes through the drum slowly. Because the rubber is affected by hot oxygen and accelerator M, it will be found that the rubber surface seems to be coated with oil. In fact, rubber molecules are more serious in promoting the chain breaking under the promotion of chemical plasticizer, A relatively soft and sticky rubber with smaller molecular weight was produced.
Although the rubber was mixed with SBR and then mixed with insulating rubber, these small molecular weight natural rubber were evenly dispersed in the rubber. After the rubber was extruded on the copper wire for continuous vulcanization, there might be no problem at that time, but a hidden danger was buried for the rubber copper ABC Cables. That is, the local copper wire sticking phenomenon will appear in the first place for these small molecular weight natural rubber.

The process of adding vulcanizing agent and accelerator to insulating rubber is also very important. Some small factories add vulcanizing agent on the mixer, that is, pour the pot containing vulcanizate into the middle of the drum, with many in the middle, and less on both sides. When the vulcanizate into rubber, the number of turning triangle was less, which would make the vulcanizate distributed unevenly in the rubber. In this way, copper wire blackening is easy to appear in many places with vulcanizing agent when extrusion is continuous vulcanization. In the blackening place for a long time, the phenomenon of rubber adhesive copper wire will appear.
3.2 reasons for vulcanization of insulating rubber
In order to pursue the production, some enterprises only have 60 meters long continuous vulcanization tubes, 1.3mpa steam pressure, and the vulcanization speed is 120 m / min. thus, the residence time of insulating rubber in the pipe is only 30 seconds. Rubber itself is a bad conductor of heat. The surface temperature of the insulating core is more than 190 ℃, and when the temperature is transferred to the inner rubber contacting with copper wire, it is also absorbed by copper wire. When the copper wire is heated to close to the inner rubber temperature, the vulcanized rubber wire core has been discharged from the vulcanizing tube. So the temperature of the inner rubber is relatively low, about 170 ℃, and the vulcanization tube will be left only a few seconds. When it enters the cooling and winding, the insulation rubber will not be vulcanized enough.
In order to achieve sufficient vulcanization, the amount of promoter TMTD (as vulcanizing agent) is up to 3.4%. The excess of vulcanizing agent also releases more free sulfur during the curing process. Besides the crosslinking rubber molecules, there are also excess free sulfur. This is the reason why the copper wire surface is blackened.
In short, it is still difficult to solve the problem of copper wire blackening. Every process from copper wire to rubber should be taken seriously to achieve better results. The key to the problem is the choice of rubber species and the adoption of vulcanization system. The solution to this problem needs to go through the test of time.

How to measure the temperature of cable terminal tail contact?

The contact resistance of the tail wire contact of AAAC Cable terminal (especially outdoor, sometimes connected by copper aluminum two different metals) will increase under the influence of long-term load and fault current, which will lead to overheating. When the line fails, the fault current flows through the contact, which will burn the contact. Measuring the contact temperature under the condition of no power failure, that is, to conduct live temperature measurement (preferably when the load is large), is an effective measure to monitor and check the contact condition. There are three main methods to check the contact temperature.


(1) Paste the temperature wax sheet: the temperature wax sheet is divided into three types: 60 ℃, 70 ℃ and 80 ℃, and are respectively expressed in different colors, and the commonly used ones are yellow, green and red. The temperature range can only be roughly checked by using the temperature wax plate. The reaction time is slow and the paste is not convenient. It is less used at present.
(2) Discoloration thermometer: this kind of color change thermometer is a surface measuring tool. It was used to monitor the temperature of heating working parts during welding in shipbuilding industry. It is used to indicate temperature according to the color changing characteristics of pigment in the pen at a certain temperature. The temperature measurement is quick and easy to use. Generally, the one with lower temperature can be selected for ABC Cable line. For example, the color changing temperature pen with color change temperature of 70 ℃ is selected, and it is marked as the original color. If the temperature is more than 70 ℃, it will become lake blue. The price of this color change thermometer is also cheaper. The temperature measurement reaction is fast (only 1-2s), and it is convenient to use.


(3) Infrared thermometer and thermal imager: the temperature wax plate and the color change thermometer shall be directly contacted with the live equipment, and the insulation rod shall be used for operation. Infrared thermometers and thermal imagers can measure temperature outside the measured point, so they are safe and reliable, and their measurement accuracy is much higher than the above two. The commonly used infrared thermometers or thermal imagers generally adopt portable type. See Fig. 9-4 and Fig. 9-5. The measuring distance is 5m, 10m, 100m, or even larger. The thermal imager can display the image of temperature distribution, and can store the image data in disk or computer, with good effect. But the price of this instrument is relatively expensive, and special personnel shall be responsible for the use and maintenance.

Differences in use of brass, phosphor copper and red copper

Pure copper is a purplish red metal, commonly known as “red copper”, “red copper” or “red copper”. Pure copper is ductile. Pure copper, the size of a drop of ACSR Cable, can be drawn into two kilometers of filaments or rolled into almost transparent foil larger than a bed. The most valuable property of pure copper is its excellent conductivity, second only to silver in all metals, so it has become the “leading role” of the electrical industry.

Pure copper is more widely used than pure iron. Every year, 50% of copper is electrolyzed and purified into pure copper for electrical industry. The pure copper mentioned here is really very pure, with a copper content of more than 99.95%. A very small amount of impurities, especially phosphorus, arsenic, aluminum, will greatly reduce the conductivity of copper. The oxygen content in copper (easily mixed with a small amount of oxygen in copper smelting) has a great influence on the conductivity, so the copper used in electrical industry must be oxygen free copper. In addition, lead, antimony, bismuth and other impurities will make copper crystal can not be combined, resulting in hot brittleness, also affect the processing of pure copper.
This kind of pure copper with high purity is usually refined by electrolysis: the Impure Copper (crude copper) is used as anode, the pure copper as cathode, and the copper sulfate solution as electrolyte. When the current passes through, the Impure Copper on the anode gradually melts, and the pure copper gradually precipitates on the cathode. Copper thus refined; The purity can reach 99.99%.
Red copper is a relatively pure copper, generally can be considered as pure copper, conductivity, plasticity are better, but the strength, hardness is poor.
Properties and uses of brass
Brass is a kind of copper containing other alloy components. Its price is cheaper than that of red copper. Its conductivity and plasticity are worse than that of red copper, but its strength and hardness are higher.
Brass is an alloy of copper and zinc. The simplest brass is copper zinc binary alloy, which is called simple brass or ordinary brass. The higher the content of zinc in brass, the higher the strength and the lower the plasticity. The zinc content of brass used in industry is not more than 45%. No matter how high the zinc content is, brittleness will occur and the alloy properties will deteriorate.
Adding 1% tin to brass can significantly improve the corrosion resistance of brass in seawater and marine atmosphere, so it is called “Navy brass”. Tin can improve the machinability of brass. Lead yellow copper is what we usually call easy to cut national standard copper. The main purpose of adding lead is to improve the machinability and wear resistance, but lead has little effect on the strength of brass. Carved copper is also a kind of lead brass. Most brasses have good color, processability and ductility, and are easy to be electroplated or coated.
In industry and civil use, different materials are selected according to different use characteristics. If make electric wire, requirement is softer, red copper is better. If the connection piece is made, brass is often used for the screw.
Properties and uses of bronze

It originally refers to copper tin alloy. Later, except brass and Cupronickel, all copper alloys are called bronze, and are often preceded by the name of the first major additive element. Tin bronze has good castability, antifriction and mechanical properties, and is suitable for manufacturing bearings, worm gears and gears. Lead bronze is widely used in modern engines and grinding machines. Aluminum bronze has high strength, good wear resistance and corrosion resistance. It is used for casting high load gears, shaft sleeves, marine propellers, etc. Beryllium bronze and phosphor bronze have high elastic limit and good conductivity. They are suitable for manufacturing precision springs and electrical contact elements. Beryllium bronze is also used to manufacture non sparking tools used in coal mines and oil depots.
Properties and uses of white copper
Copper alloy with nickel as the main additive. Copper nickel binary alloy is called ordinary white copper; Copper alloy with manganese, iron, zinc, aluminum and other elements is called complex copper. Industrial white copper can be divided into structural white copper and electrical white copper. The structural white copper is characterized by good mechanical properties, corrosion resistance and beautiful color. This kind of white copper is widely used in manufacturing precision machinery, chemical machinery and ship components. Electrical white copper generally has good thermoelectric properties. Manganin, constantan and Kaotong are white manganin copper with different manganese contents. They are used to manufacture precision electrical instruments, varistors, precision resistors, strain gauges and thermocouples.

How to distinguish red copper, brass, bronze and white copper
White copper, brass, red copper (also known as “red copper”) and bronze (cyan gray or grayish yellow) are distinguished from each other in color, among which white copper and brass are very easy to distinguish; It is difficult to distinguish red copper from pure copper (impurity < 1%) and bronze (about 5% of other alloy components). Before oxidation, the color of red copper is brighter than that of bronze, and the bronze is slightly cyan or yellow and dark; After oxidation, red copper turns black, while bronze turns Turquoise or chocolate.

How to prevent and control pests on cable lines?

For direct buried ACSR Cable laying, in addition to preventing external mechanical damage, there is another kind of external damage from insects, such as termites. South China is located in the subtropical zone with humid climate, which is suitable for termite breeding. Termites will damage the lead sheath of the cable, causing the insulation damp after the lead sheath is perforated. In the areas where termite activities are more frequent, the special sheathed cable with termite resistance should be selected for the cable line design. If termite breeding is found near the cable line that has been put into operation, it should immediately report to the local termite control department for termite control, and adopt centralized trapping and prevention measures.

reference:
[1] Shi Chuanqing, chief editor. Question and answer of power cable installation and operation technology

What is the valve performance of the sheath protector?

In order to ensure that the sheath insulation will not be damaged under the action of lightning overvoltage and switching overvoltage, the sheath protector should be used. The ball gap protector was used in the early stage, but its disadvantage was that its surface was burnt by power frequency afterflow after each action. This type is not only heavy maintenance, but also unreliable. At present, zinc oxide, a non-linear resistor, is widely used in sheath protectors.
under normal operation, the current flowing through the sheath protector is microampere, so as to ensure the reliable operation of the AAC Cable.


Function of cable sheath Protector:
1. Limit the power frequency induced voltage in the metal sheath of ACSR Cable line.
In the normal working state of the cable line, the high-voltage cable sheath protector presents a high resistance state, which cuts off the power frequency induced current circuit in the cable metal sheath.
2. The power frequency and impulse overvoltage in the metal sheath of cable line can be reduced rapidly.
When grounding fault, lightning over-voltage or internal over-voltage occurs in the cable line, which leads to high over-voltage in the metal sheath, the sheath protector presents a low resistance conduction state, which makes the fault current quickly pour into the earth through the protector.


Selection of cable sheath Protector:
1. The residual voltage under the action of the possible maximum impulse current shall not be greater than the value of [impulse withstand voltage of cable sheath] – (37.5kv for 110kV cable) divided by 1.4 (included in the insulation coordination coefficient).
2. The possible maximum power frequency overvoltage shall be able to withstand without breakdown or damage under the action of 5S.
3. The protector shall not be damaged after 20 times cumulative action of the maximum possible impulse current.
Regular inspection and maintenance of cable sheath Protector:
Regularly measure the DC reference voltage of cable sheath protector at 1mA and the leakage current at 0.75 times of the reference voltage, especially after the system failure.

Operation and maintenance of protective layer protector

In order to reduce the induced overvoltage of the metal sheath of single core AAAC Cable lines of 110kV and above, a protective layer protector should be installed between the ungrounded end of the metal sheath and the earth.

In case of system trip or line lightning stroke, special patrol shall be conducted for cable sheath protector.
The valve plate of protective layer protector may be damaged during power frequency overvoltage. The damage degree of the valve plate is related to the overvoltage of the protective layer. If the valve plate is damaged, it should be replaced.

At present, zinc oxide sheath protector is widely used in high voltage ABC Cable lines, and its residual work ratio is 2.5 ~ 4.0. Insulation resistance monitoring should be carried out for sheath protector, which can usually be tested at 500V / min.
The cross transposition box should be cleaned once a year, and the underground transposition box should also be checked for ponding.

Why measure the surface temperature of the cable in operation?

The temperature of the cable is closely related to the load, but only checking the load can not ensure that the AAAC Cable is not overheated
(1) the thermal resistance coefficient and side-by-side correction coefficient used in calculating the allowable ampacity of cables may be different from the actual situation.
(2) when choosing cables to determine conductor cross-sectional area, designers may lack sufficient information about the laying conditions and surrounding environment of the whole line.
(3) newly built and rebuilt power lines or thermal pipelines have an impact on the original surrounding environment and heat dissipation conditions.


(4) the excessive density of cables greatly exceeds the regulations of design and operation departments. In addition to measuring the load frequently, the operation Department must also check the actual temperature of the cable surface to determine whether the AAC Cable is overheated. The inspection shall be carried out at the maximum load and the section with the worst heat dissipation condition (generally not less than 10m). Thermocouple or pressure thermometer can be used for measuring instrument. The pressure thermometer is easy to install. Two temperature measuring points shall be installed at each measuring point. When measuring the temperature of the cable, the temperature of the surrounding environment should be measured at the same time, but it must be noted that the temperature measuring point of the surrounding environment should be kept a certain distance from the cable (generally 3M away), and there is no influence of external heat source.
On site detection method
During infrared detection, the cable should be live running for more than 24 hours, and try to remove or avoid the shelter between the cable and the thermometer, such as glass window, door or cover plate, etc; It is necessary to measure all parts of the cable line to avoid missing the measuring parts; It is best to carry out the test in the peak load state of the equipment, generally no less than 30% of the rated load. The infrared detection of the arrester connected with the cable terminal can refer to the requirements of DL / t664.
a) The emissivity of the tested equipment should be selected correctly, especially considering the influence of metal material oxidation on the selection of emissivity. For the selection of emissivity, please refer to Appendix B; Generally, 0.9 for metal conductor and 0.92 for insulator;


b) If the safety distance is allowed, the infrared instrument should be close to the equipment under test as far as possible, so that the equipment under test can fill the field of view of the whole instrument, so as to improve the resolution and temperature measurement accuracy of the instrument to the surface details of the equipment under test. If necessary, medium and long focal length lenses should be used; Generally, medium and long focal length lenses are used for outdoor terminal detection;
c) The compensation parameters such as atmospheric temperature, relative humidity and measurement distance are input and corrected, and the appropriate temperature range is selected;
d) Generally, the infrared thermal imager is used to scan all the tested parts, focusing on the cable terminal and intermediate connector, cross interconnect box, grounding box, metal sleeve grounding point and other parts. After finding the abnormal parts of the thermal image, the abnormal parts and the key tested equipment are measured in detail;
e) In order to measure temperature accurately or track conveniently, several different directions and angles should be set in advance to determine the best detection position and mark it for future retest, so as to improve the comparability and work efficiency;
f) Record the actual load current and voltage of the tested equipment, the temperature of the tested object and the temperature value of the environmental reference body according to the format of Appendix C.

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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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