Cable types

How many rumors do you know about wires and cables?

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The rapid development of the Internet age has not only brought convenience to everyone’s life, but also brought new challenges to our social management. In particular, we have seen the rapid spread of rumors. I believe you can distinguish many rumors, but how many rumors about wires and AAAC Cables have you heard? Can you identify it in time?


If the square of the wire is not enough, it will not be qualified?
not always! For many people, this is already a “common sense” existence, but is this really the case? With the improvement of conductor material production process and scientific and technological progress, the advanced production process of oxygen free copper has been widely used. The resistivity of copper conductor material is enough to ensure that the copper wire less than the nominal diameter can meet the requirements of DC resistance of corresponding specifications, while the conductor of wire and cable has strict requirements on the resistivity of conductor, for example, The DC resistance of 25 mm2 copper core conductor specified in the standard at 20 ° is not greater than 0.727 Ω / km (the second stranded conductor), so the conductor is qualified as long as it is not greater than this value.
Flame retardant ABC Cables will not burn?
wrong! Flame retardant of flame-retardant wire and cable refers to that when a wire and cable fire accident occurs, it can block and delay the diffusion and spread of flame along the wire and cable, and minimize the expansion of fire range of wire and cable. This type of cable has the characteristics of self extinguishing after fire. Fire resistant wire and cable refers to that in the case of wire and cable fire accident, the wire and cable product can adhere to the normal operation for a certain time under the condition that the external flame is still burning, maintain the integrity of wire and cable lines and maintain the normal operation of line equipment.
Will wires and cables have radiation?
Wires and cables do have radiation. However, the fact is that all live things have radiation. For example, 220V wires also have radiation, but the radiation is very small and basically negligible. Moreover, the radiation of wires is much lower than that of mobile phones. If you are really afraid of wire radiation, it is recommended to throw away the mobile phones first. If you are afraid of the magnetic field generated by wires and cables and think that the magnetic field will cause any harm to the human body, the geomagnetic field is even more terrible. Therefore, I think that “radiation from wires will damage health” is just groundless, and I think too much.


The thicker the cable insulation, the better?
No, too thick cable insulation will increase the difficulty of AAC Cable laying. At present, cable laying is mainly bridge or through pipe. Now many enterprises are implementing cable requirements, with tight cable requirements and small outer diameter. There can be gaps in the laying process to emit heat energy to ensure that the outer sheath of the cable is not damaged. Otherwise, it will bring some difficulties to the construction unit and cable laying. In summer, the working temperature will rise, and these temperatures will be emitted through the outer protective layer. The thickness of the sheath increases, and the heat energy is difficult to be emitted, which will affect the service life of the cable. Due to the thermal action of PVC, a series of physical and chemical changes will occur in the insulating layer, losing the original excellent performance, resulting in obvious decline in the insulating performance and even short circuit, Therefore, when selecting the cable, the thickness of the cable must be moderate.
The laying of water and electricity shall be horizontal and vertical
unnecessary! Although the water and electricity wires laid horizontally and vertically look very good, there are really many hidden dangers! Firstly, the material cost of the wire pipe is much higher than that of other laying methods. Secondly, because it is 90 degrees horizontally and vertically, it is easy to get stuck when threading the wire in the later stage! So as long as it complies with the specifications, how convenient it is to lay it!


In addition to the above, there are numerous rumors about wires and cables: wires and cables are cheap, so selling cables makes a lot of money; Wires of the same quality can certainly be bought at a cheaper price; The copper conductor used in wires and cables is not so high; Wires and cables will leak electricity in rainy days, which is unsafe.
Although some are rumors, it’s not too much to say that wires and cables are lifelines. We should be more careful when buying. Only by selecting manufacturers, products and national standard products can we use them at ease.

What are the measures to speed up cable fault repair?

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The speed of cable fault repair directly affects the economic benefits and social image of cable operation Department, and it is also an important symbol to measure the comprehensive management level of AAC Cable operation Department. The repair of cable fault, from receiving the cable fault repair order, checking data, measuring faults, finding fault points, troubleshooting, repairing faults to restoring power transmission, requires the cooperation of all departments. In case of problems or delay in a certain department or construction link, the speed of cable fault repair will be affected. In order to speed up cable fault repair, the following measures are taken:
(1) establish an efficient fault emergency repair command system, and be responsible for commanding emergency repair and coordination of various departments. According to the number of AAAC Cable faults, a fault emergency repair command center or a fault emergency repair dispatching center can be set up.

(2) provide reliable and effective communication equipment to enable the command center to obtain the repair information in time, maintain smooth communication with the emergency repair site, and the material and logistics departments can understand the information of the emergency repair site in time.
(3) formulate a standardized emergency repair software package, and clarify the standard process of emergency repair and the work standards of each department.
(4) provide a skilled emergency repair team and establish a 24-hour emergency repair duty system.

(5) advanced and fast means of transportation shall be equipped. All departments undertaking ABC Cable fault repair shall be equipped with engineering rescue vehicles approved by the government traffic management department.
(6) provide sufficient and orderly accident spare parts and effective and fast means of transportation.
(7) make public commitments to the society and accept social supervision.
Note: in addition, due to the sharp increase in the scale of cables and channels, perfect basic information (especially channel location information and joint location information), experienced skilled personnel and effective fault finding equipment are also the key elements to speed up cable fault repair.

How to avoid being trapped when buying household cables?

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Cable is a relatively insignificant raw material in home decoration, but it is closely related to everyone’s daily life and involves the problem of safe power consumption in daily life. Therefore, when purchasing AAAC Cable, we should pay special attention to avoid buying fake and shoddy goods. Here is a detailed description of how to price the cable and what key points should be paid close attention to when purchasing.

How much does a meter of cable cost
At this stage, the price of wires on the market is very unstable. The price of wires depends on the price fluctuation of copper. The more expensive copper is, the more expensive cable is. Moreover, the price of different well-known brands will also vary. Generally, the price of 4 square meters is about 230 yuan for one roll (100 meters long), and that of 2.5 square meters is 140 yuan for one roll (100 meters long), 1.5 is 85 yuan a roll (100 meters long). This price is for reference only. The actual price is based on the local specific price.
Cable selection is an important link
1. Length
Pay attention to the length. Some people will find that the number of meters on the ACSR Cable line they buy is 100 meters. However, it should be noted that there is a meter mark, but in the middle part, some black chambers of Commerce count less than 10 meters. For example, after 30 meters, they gradually mark 40 meters.
2. Copper quality
The true red copper of the cable is a reddish color, while brass turns yellow. In addition, red copper is relatively soft and brass is relatively hard. It is not too much to fake brass at this stage.
3. PVC material
Pay attention when selecting cables. Many people will make copper core wires very standard, but they are fake and shoddy products on PVC materials.

4. CCC product certification certificate
The cable line shall be marked with CCC product certification certificate as far as possible. Since the cable goods are compulsory identity certification goods in China, all machinery manufacturing industries shall obtain CCC product certification certificate verified by China electric welder product quality certification Research Association as far as possible. In addition, the cable is associated with safe power consumption, and the quality of the cable will damage everyone’s asset and capital security. Therefore, we must select the cable products with CCC product certification certificate.
5. Product certificate
Check whether the AAC Cable is marked with product certificate, specification and model, test, production and manufacturing date, enterprise name, production and processing place, telephone, etc. This is the product produced by reliable manufacturers. Everyone should understand it correctly when buying.

What are the effects of temperature on cable selection?

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Whether our colleagues in electrical design or factory electrical maintenance can not open the topic of cable selection, we often see that the AAC Cable selection size of the same equipment under the same power will be different in the work, some may be less than one or two levels, and some friends may be confused by which right? Why do you choose different? Today we will learn how to choose the cable and how to consider it from? What is the effect of temperature on the selection of cables?


1、 Cable selection
(1) Select cable according to temperature rise
We all know that when the conductor passes through the load current, the temperature of the conductor will rise, the conductor has insulation layer, and the conductor temperature shall not exceed the maximum temperature allowed for a long time by the conductor insulation, and the conductor will be damaged after exceeding.
(2) According to mechanical strength
When laying, the conductor has a minimum section allowed according to the laying mode and the distance between the support point and the distance.
(3) Select according to economic conditions
That is, choose the most economical way.
(4) Select by line voltage drop
We all know that when the current passes through the conductor, the voltage drop will be generated in the line due to the existence of line impedance. If the voltage drop is too large, the voltage at the end of the line, that is, the load end is too low, which will cause the equipment to fail to work or affect the equipment life. Therefore, it is required that the voltage drop cannot be too large, so the cable section should be selected reasonably.

(5) Cable selection shall meet the requirements of load protection
When the circuit is in fault, the protective device should act according to the specified time, whether it can operate reliably or not has a great relationship with the cable section. Therefore, we should consider the requirements of reliable action when choosing the ACSR Cable.
(6) Select cable according to the requirements of thermal stability
In case of failure of cable or electrical equipment, the cable shall meet the requirements of thermal stability, and the size of cable section shall be considered in order to meet this requirement. The maximum cross section is the final result by combining the above conditions.

What are the cable maintenance items?

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1. Manhole and drainage pipe
(1) water samples were taken for chemical analysis.
(2) remove the water in the well and remove the sludge.
(3) paint the iron parts such as cable bracket and hook.

(4) check the well cover and ventilation, and check the well body for settlement and cracks.
(5) dredge the spare pipe hole.

(6) check the condition of ACSR Cables and joints in the manhole to see if there is any oil leakage, whether the insulation gasket on the bracket is in good condition and whether the grounding is good.
(7) check the circuit name plate.
(8) check whether there is electric erosion, and measure the potential and current distribution of cables in the manhole.
2. Cable trench and tunnel
(1) check whether the door lock is normal and whether the access is smooth.
(2) check whether there is water seepage and ponding in the tunnel, remove the ponding and repair the leakage.

(3) check whether the ABC Cable bracket falls.
(4) check whether the insulation gasket between the metal sheath of the cable and connector and the bracket is intact, and whether there is any damage on the bracket; Whether the bracket has fallen off.
(5) check whether the fireproof tape, coating, blocking material and fireproof box are in good condition, whether the fireproof equipment and ventilation equipment are perfect and normal, and record the room temperature.

(6) check whether the grounding condition is good, and measure the grounding resistance if necessary.

(7) clean cable trench and tunnel.
(8) check the cable and cable joint for oil leakage.
(9) check cable tunnel lighting.

How to measure the temperature of cable terminal tail contact?

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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.

What is the content of periodic test for high voltage cable?

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“Power cable operation regulation” stipulates that under the condition of not losing normal oil pressure, it is not necessary to conduct DC withstand voltage test regularly for high voltage oil filled AAAC Cable. As long as the oil pressure is normal and the dielectric loss and breakdown strength of oil are qualified, it can be considered that the cable insulation is reliable. Therefore, oil filled cable should be tested regularly to measure its dielectric loss and breakdown strength. The test period is generally sampled one year after putting into operation. If the results of two consecutive tests do not change, the test period can be gradually extended. In addition to the oil sample test, the following tests should also be carried out.


1. Measure the insulation resistance of outer sheath
the outer sheath of oil filled cable not only insulates the metal sheath from the ground, but also has anti-corrosion effect on the lead sheath and reinforcing tape. The insulation resistance of the sheath of oil filled cable shall be measured once a year by insulation resistance meter or other methods to check the integrity of the sheath insulation and the degree of water seepage. The high pressure oil filled cable is under the positive oil pressure, and the moisture in the air cannot invade people. Periodic measurement of outer sheath insulation can find out the early mild damage of sheath. When measuring the insulation of protective layer, the transposition bar and protector on transposition board in cross interconnection box shall be disassembled, and the insulation resistance of protective layer shall be measured by sections. Long lines shall be measured with electric insulation resistance meter.


2. Measure the grounding resistance
in the sheath grounding system with two ends grounded, one end grounded or cross interconnection connection, the value of grounding resistance will affect the operation of the protector. GEOX type grounding resistance measuring instrument can be used to measure the grounding resistance of the cable sheath connected with the grounding electrode or the grounding connecting line of the protector.
3. Measure the DC resistance of conductor
by measuring the DC resistance of the conductor and comparing it with the test values in previous years, we can check the change of the contact resistance between the outgoing stem or connecting pipe and the cable core, and judge whether the conductor connection is good.

Why measure the surface temperature of the cable in operation?

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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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Factors affecting insulation resistance of wires and cables

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Small insulation resistance is often encountered in AAC Cable production, which is affected by many factors. In fact, there are four main factors that have a great influence on the coefficient of insulation resistance.

1、 The influence of temperature
With the increase of temperature, the insulation resistance coefficient decreases. This is due to the increase of thermal motion and the increase of ion production and migration. Under the action of voltage, the conduction current formed by ion motion increases and the insulation resistance decreases.
The theory and practice show that the insulation resistance coefficient decreases exponentially with the increase of temperature, and the conductivity increases exponentially with the increase of temperature.
2、 Influence of electric field intensity
When the electric field strength is relatively low, the mobility of ions increases in proportion with the increase of electric field strength. The ionic current and electric field strength follow Ohm’s law. When the electric field intensity is relatively high, with the increase of electric field intensity, the mobility of ions gradually changes from linear relationship to exponential relationship. When the electric field is close to breakdown, a large number of electrons will migrate and the insulation resistance coefficient will be greatly reduced.
The withstand voltage test voltage of various wire and ACSR Cable products specified in the standard is in the stage of ion mobility increasing in proportion to the electric field strength, so the influence of electric field strength on the insulation resistance coefficient cannot be reflected. The effect of electric field on the insulation resistance coefficient is obviously reflected when the sample is subjected to breakdown test.


3、 Influence of humidity
Due to the large conductivity of water, the size of water molecules is much smaller than that of polymer molecules. Under the action of heat, the polymer macromolecules and the constituent chain move relatively, so that water molecules can easily penetrate into the polymer, increase the conductive ions in the polymer, and reduce the insulation resistance.
The standard specifies the immersion test of various wires and cables. For example, the rubber specimen is immersed in water for 24 hours before the insulation resistance is measured. The purpose is to meet the influence of moisture and water on electrical performance during use.
Insulation resistance is one of the main electrical properties of insulating materials, and it is also an important index of wire and cable products or materials. Generally, the insulation resistance should not be lower than a certain value. If the insulation resistance value is too low, the leakage current along the wire and cable line will inevitably increase, resulting in the waste of electric energy. At the same time, electric energy will be turned into heat energy to prepare for thermal breakdown and increase the possibility of thermal breakdown.
4、 Influence of material purity
The impurity mixed into the material increases the conductive particles in the material and reduces the insulation resistance. Therefore, the insulation resistance of a certain rubber plastic material will reflect the purity of the material and verify whether it meets the standard.
In the process of wire and cable production, the process does not strictly comply with the operating procedures, mixed impurities and materials Blister due to moisture, insulation core deviation or outer diameter size is less than the standard, insulation delamination or crack, insulation scratch, etc., It will reduce the insulation resistance of the product.
Therefore, in order to check the insulation resistance, it is necessary to check whether there are any problems in the process operation. During the use of wires and cables, measuring the change of insulation resistance can also check the insulation damage and prevent accidents.

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High voltage cable intelligent anti breaking system

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01
Project background

If the city grid is given life, the AAAC Cable is his blood vessel, which injects the energy of the power grid.
However, with the development, the construction frequency is high, which leads to the explosion of the risk of cable external force damage. Please see, this is the scene after the cable has been destroyed. Then, once the underground cable is damaged by the external force of construction machinery, it may cause chain reaction and lead to large-scale power failure.
If the power outage occurs in hospitals, transportation hub, government agencies and other important places, how much loss will be suffered to the people’s lives and property, and the indirect economic losses caused by the power failure are immeasurable; On the other hand, cable damage may also lead to the construction of personnel casualties. In view of this, it is urgent to prevent external damage!


Traditional cable inspection mainly relies on manual field inspection, which makes it difficult to find out the cable external breakage due to various mechanical construction on the ACSR Cable path in time and accurately. There are few operation and maintenance personnel, and the inspection mode mainly depends on the drawing and oral communication to confirm the cable location. Inspection efficiency is low and maintenance cost is high.

02
Function and characteristics of the scheme

With the national policy support for the digital transformation of state-owned enterprises and the promotion and application of 5g technology, our team seized the opportunity to break through the bottleneck, combined smart IOT technology with cable anti-external breaking work organically, and independently developed “intelligent brain – high voltage cable intelligent external breaking system based on artificial intelligence”.


Function 1
The full time visual monitoring device is applied to improve the real-time visibility of the equipment channel. The visual monitoring device is installed on the smart light pole in key cable channels and construction intensive areas, which can automatically identify the hidden dangers outside the cable channels such as large construction machinery.
The real-time data collected by camera is compared with the hidden danger image database of cable channel, and all kinds of external damage hazards on cable channel are automatically studied and identified.
At the same time, the system has the ability of autonomous learning, and with the deep use of the system, the recognition efficiency is improved.
Function 2
The fiber vibration technology is applied to improve the state perception of the equipment. The abnormal vibration caused by external force is automatically captured, and the warning is given before the external force endangers the power cable. According to the external vibration of optical fiber, the external force failure signal is automatically identified and the location of the hidden danger of external failure is accurately located.


Function 3
The application of “four-dimensional” visualization technology can enhance the visual operation and maintenance capability of underground cables. Realize the operation and maintenance personnel to stereoscopic view the cable lines and auxiliary facilities in VR form on site through PDA terminal, and guide the accurate operation.

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