Cable Encyclopedia

AAC cable

Advantages of high voltage transmission: reduce power loss, and then improve transmission efficiency.

High voltage transmission is a method of transmitting the voltage output by a generator through a transformer used in a power plant. The reason for using this method of transmission is because under the same transmission power, the higher the voltage, the smaller the current. This way, high-voltage transmission can reduce the current during transmission, thereby reducing the heat loss caused by the current and reducing the material cost of long-distance transmission.

It can be seen from the S=root 3 UI that under the condition of transmitting the same power, the higher the voltage, the smaller the current. We know that the safe carrying capacity of the conductor is certain, and the higher the voltage, the more power the conductor transmits. Therefore, high-voltage transmission can improve transmission efficiency. Reason:

Address the limitations of high-capacity transmission on equipment manufacturing.

Reduce the transmission current and reduce losses.

AAC cable

The core diameters of multimode fiber and single-mode fiber are different. Although the cladding diameter of multimode fiber and single-mode fiber is the same, and the diameter is 125 μm, the core diameter of multimode fiber is much larger than that of single-mode fiber. The core diameter of single-mode fiber is generally 9 μm, while the core diameter of multimode fiber is generally 50 μm/62.5 μm.

MV ABC cable

In fiber optic communications, a single-mode fiber (SMF) is a fiber that directly transmits optical signals in the transverse mode. Single-mode fiber runs at a data rate of 100M/s or 1 G/s, and the transmission distance can reach at least 5 kilometers. Typically, single-mode fiber is used for long-distance signal transmission.

AAC cable

The electric energy sent from the power station is generally sent to various places where electricity is used through transmission lines. Different high voltages are used according to the distance of the power transmission distance. From the two aspects of reducing the power loss on the transmission line and saving the materials used in the transmission wire, high voltage or ultra-high voltage is required for long-distance transmission of electric energy.

MV ABC cable

Twisted pair (twisted pair, TP) is the most commonly used transmission medium in integrated wiring engineering. It is composed of two copper wires with an insulating protective layer. Two insulated copper wires are twisted together at a certain density, and the radio waves radiated by each wire during transmission will be offset by the radio waves emitted by the other wire, effectively reducing the degree of signal interference. The principle of twisted pair: Twisted-pair wires are generally made up of two 22-26 insulated copper wires wound with each other, and the name "twisted-pair wires" comes from this. Twisted pair wires are twisted from a pair of mutually insulated metal wires. In this way, not only can a part of the electromagnetic wave interference from the outside be resisted, but also the mutual interference between multiple pairs of twisted wires can be reduced. Twisting two insulated wires together, the interference signal acting on the two twisted wires is consistent (this interference signal is called a common mode signal), and the common mode can be used in the differential circuit of the receiving signal Signal elimination, thereby extracting the useful signal (differential mode signal). Twisted pair anti-interference, if there are two untwisted telephone lines, it means that ordinary lines are not resistant to external electromagnetic interference, and twisted pairs are called twisted pairs.

AAC cable

The reason for using high voltage for long-distance power transmission is as follows: The reason for using this method of power transmission is that under the same transmission power, according to the formula P=UI, the transmission current I must be reduced, while the transmission power P remains unchanged (large enough ), it is necessary to increase the transmission voltage U. The higher the voltage, the smaller the current, so that high-voltage power transmission can reduce the current during power transmission, thereby reducing the heat loss caused by the current and reducing the material cost of long-distance power transmission. According to Joule's law Q=I^2Rt, there are three ways to reduce the heat generation Q: one is to reduce the transmission time t, the other is to reduce the resistance R of the transmission line, and the third is to reduce the transmission current I. It can be seen that the third method is very effective: the current is reduced by half, and the lost electric energy is reduced to a quarter of the original. To reduce the loss of electric energy, the transmission current must be reduced. On the other hand, power transmission is to transmit electric energy, and the transmitted power must be large enough to be practical.Obviously, high pressure delivery is economical. After the high voltage is used to transmit electric energy to the power consumption area, the voltage needs to be lowered successively to return to the normal voltage. The electric energy sent from the power station is generally sent to various places where electricity is used through transmission lines. Different high voltages are used according to the distance of the power transmission distance. From the perspective of my country's power situation, when the power transmission distance is 200-300 kilometers, 220 kV is used for power transmission; when it is about 100 kilometers, it is 110 kV; 10 kV, 12 kV are used for ~20 kilometers, and some use 6300 volts. Lines with transmission voltages of 110 kV and 220 kV are called high-voltage transmission lines, lines with transmission voltages of 330, 550, and 750 kV are ultra-high voltage transmission lines, and lines with transmission voltages of 1000 kV are called It is called UHV transmission line.

AAC cable

High-voltage power transmission has both direct current and alternating current. The comparison between the two is as follows:

Compared with AC transmission, HVDC transmission has the following advantages: (1) When transmitting the same power, the line cost is low: AC transmission overhead lines usually use 3 conductors, while DC only needs 1 (unipolar) or 2 (bipolar) conductors. Therefore, DC transmission can save a lot of power transmission materials, and can also reduce a lot of transportation and installation costs. (2) Line active loss is small: Since the DC overhead line only uses 1 or 2 wires, the active loss is small, and it has a "space charge" effect, and its corona loss and radio interference are smaller than that of the AC overhead line. (3) Suitable for subsea power transmission: Under the same conditions of non-ferrous metals and insulating materials, the allowable working voltage of DC is about 3 times higher than that of AC. The power Pd delivered by a 2-core DC cable line is much greater than the power Pa delivered by a 3-core AC cable line. In operation, there is no magnetic induction loss. When used in DC, there is basically only the resistance loss of the core wire, and the aging of the insulation is much slower, and the service life is correspondingly longer. (4) System stability issues: In an AC transmission system, all synchronous generators connected to the power system must keep running synchronously. If a DC line is used to connect two AC systems, since the DC line has no reactance, the above-mentioned stability problem does not exist, that is to say, the DC transmission is not limited by the transmission distance.

(5) Can limit the short-circuit current of the system: When connecting two AC systems with AC transmission lines, due to the increase of system capacity, the short-circuit current will increase, which may exceed the breaking capacity of the original circuit breaker, which requires the replacement of a large number of equipment and increases a large amount of investment. When direct current transmission, there is no such problem. (6) Fast adjustment and reliable operation: DC transmission can easily and quickly adjust active power and realize power flow reversal through thyristor converters. If a bipolar line is used, when one pole fails, the other pole can still use the ground or water as a circuit to continue to deliver half of the power, which also improves the reliability of operation.

AAC cable

Baseband coaxial cable A coaxial cable has a hard copper wire as the core and is covered with a layer of insulating material. This layer of insulation is surrounded by a densely woven mesh of conductors that is covered with a layer of protective material. There are two widely used coaxial cables. One is a 50-ohm cable, which is used for digital transmission. It is also called a baseband coaxial cable because it is mostly used for baseband transmission; the other is a 75-ohm cable, which is used for analog transmission, which is the broadband coaxial cable to be discussed in the next section. This distinction is due to historical reasons, not technical reasons or manufacturers. This structure of coaxial cable makes it have high bandwidth and excellent noise suppression characteristics. The bandwidth of a coaxial cable depends on the length of the cable. A 1km cable can achieve a data transfer rate of 1Gb/s~2Gb/s. Longer cables can also be used, but at a reduced transmission rate or with an intermediate amplifier. At present, coaxial cables are largely replaced by optical fibers, but are still widely used in cable TV and some local area networks.

AAC cable

According to the transmission mode of light in the optical fiber, it can be divided into: single-mode optical fiber and multi-mode optical fiber. The core diameter of the multimode fiber is 50~62.5 μm, the outer diameter of the cladding is 125 μm, the core diameter of the single mode fiber is 8.3 μm, and the outer diameter of the cladding is 125 μm. The working wavelength of the optical fiber is short wavelength 0.85μm, long wavelength 1.31μm and 1.55μm. Optical fiber loss generally decreases as the wavelength increases. The loss of 0.85μm is 2.5dB/km, the loss of 1.31μm is 0.35dB/km, and the loss of 1.55μm is 0.20dB/km. This is the lowest loss of optical fiber. The wavelength is 1.65 Losses above μm tend to increase. Due to the absorption of OHˉ, there are loss peaks in the ranges of 0.90~1.30μm and 1.34~1.52μm, and these two ranges have not been fully utilized. Since the 1980s, single-mode fiber tends to be used more, and the long wavelength 1.31 μm is used first.

AAC cable

For short-distance networking, optical fibers have no advantage over network cables In long-distance data transmission, the advantages of optical fiber are obvious, and the speed is indeed very fast, which can reach the real gigabit level. However, at the distance of several meters between the computer and the router, the speed advantage of optical fiber cannot be brought into play. Even if we use optical fiber to form a small network for the computer and router, it can only reach the speed of ordinary network cables. The theoretical value of the transmission rate of the current Category 5e twisted pair network cable can also reach Gigabit. Although in actual use, this theoretical value cannot be reached, but about 300M can be easily achieved. And the bandwidth of our current mainstream home optical fiber is only 200M-300M. This speed has exceeded the conventional needs of an ordinary family. Remember the 10M of China Telecom a few years ago? A family use, not also more than enough. It can be seen that optical fiber has no advantage in short-distance networking.

2, the cost of optical fiber hardware configuration is too high. If we use optical fiber to network our home computers at close range, the optical fiber cable will not cost much, but other supporting hardware facilities for optical fiber networking are still a bit expensive. Since it is necessary to use optical fiber to form a network - to use optical fiber cables to connect the router and the computer, then ordinary routers will not work, and a dedicated optical fiber router with optical fiber outlets is required (ordinary optical modems only have optical fiber inlets) , the price of this type of router will not be too cheap, it is several times the price of ordinary routers. Since it is a fiber optic cable, the network card interface on the computer should also provide a fiber optic interface. For desktop fiber optic network cards, the cheapest one costs more than 500 yuan. If it is a notebook computer with an optical fiber interface, the price is not to mention. Just a rough calculation like this, the cost of fiber home networking is at least 1000-2000 yuan more than ordinary networking. For ordinary networking, the 5-meter twisted pair cable costs about 10 yuan, and the ordinary router costs about 200 yuan, which is the cost of ordinary networking.

AAC cable

Advantages:

Extremely wide frequency band and large communication capacity

Optical fiber has a much larger transmission bandwidth than copper wire or cable, and the modulation characteristics, modulation methods, and dispersion characteristics of optical fiber communication systems depend on the light source. For single wavelength fiber optic communication systems, the advantage of large fiber bandwidth cannot be fully utilized due to the electronic bottleneck effect of terminal devices. Usually, various complex technologies are used to increase the transmission capacity, especially the current dense wavelength division multiplexing technology, which greatly increases the transmission capacity of optical fibers. At present, the transmission rate of single wavelength fiber optic communication systems is generally between 2.5Gbps and 1OGbps.

Low loss and long relay distance

At present, the loss of commercial quartz optical fibers can be lower than 0-20dB/km, which is lower than the loss of any other transmission medium; If non quartz system ultra-low loss optical fibers are used in the future, the theoretical analysis shows that the loss can be reduced even lower. This means that fiber optic communication systems can span larger distances without relays; For a long-distance transmission line, the cost and complexity of the system can be greatly reduced due to the reduction in the number of relay stations.

Strong resistance to electromagnetic interference

The raw material of optical fiber is an insulator material made of quartz, which is not easily corroded and has good insulation. An important characteristic associated with it is the immunity of optical waveguide to electromagnetic interference. It is not subject to the interference of lightning in nature, changes in the ionosphere and sunspot activities, nor to the electromagnetic interference released by humans. It can also be erected in parallel with high-voltage transmission lines or composite with electrical conductors to form a composite optical cable. This is particularly advantageous for communication systems in the field of strong electricity, such as power transmission lines and electrified railways. Due to its ability to eliminate electromagnetic pulse effects, fiber optic transmission systems are particularly suitable for military applications.

Disadvantages:

(1) The texture is brittle and the mechanical strength is poor.

(2) The cutting and splicing of optical fibers require certain tools, equipment, and technology.

(3) Shunting and coupling are not flexible.

(4) The bending radius of fiber optic cables should not be too small (>20cm)

AAC cable

1) Transmission point modulus class The modulus of the transmission point is divided into single mode fiber (Single Mode Fiber) and multimode fiber (Multi Mode Fiber). The core diameter of single-mode fiber is very small, and it can only transmit in a single mode at a given working wavelength, with wide transmission frequency and large transmission capacity. Multimode fiber is an optical fiber that can simultaneously transmit in multiple modes at a given operating wavelength. Compared with single-mode fiber, the transmission performance of multimode fiber is poor.

MV ABC cable

Sheath: Indoor optical cables are generally made of polyethylene or flame-retardant polyethylene, and the appearance should be smooth, bright, flexible, and easy to peel off. The outer sheath of the optical cable with poor quality has poor finish, and it is easy to adhere to the tight sleeve and aramid fiber inside. The PE sheath of the outdoor optical cable should be made of high-quality black polyethylene. After the cable is formed, the sheath is flat, bright, uniform in thickness, and free of small bubbles. The outer sheath of inferior optical cables is generally produced with recycled materials, which can save a lot of cost. The outer sheath of such optical cables is not smooth. Because there are many impurities in the raw materials, the outer sheath of the optical cable made has many very small pits, which will crack and enter after a long time. water.

Optical fiber: Regular optical cable manufacturers generally use A-level fiber cores from major manufacturers. Some low-priced and inferior optical cables usually use C-level, D-level optical fibers and smuggled optical fibers from unknown sources. These optical fibers have a long delivery time due to their complicated sources. It has often become damp and discolored, and multimode fibers are often mixed with single-mode fibers. Generally, small factories lack necessary testing equipment and cannot make judgments on the quality of fibers. Because the naked eye cannot distinguish such optical fibers, the common problems encountered in construction are: narrow bandwidth and short transmission distance; uneven thickness, which cannot be connected with pigtails; optical fibers lack flexibility, and they will break when they are bent.

Reinforced steel wire: The steel wire of the outdoor optical cable of regular manufacturers is phosphating-treated, and the surface is gray. Such steel wire does not increase hydrogen loss after being cabled, does not rust, and has high strength. Inferior optical cables are generally replaced by thin iron wires or aluminum wires. The identification method is very easy-the appearance is white and can be bent at will when pinched in the hand. The optical cable produced by such steel wire has a large hydrogen loss, and after a long time, the two ends of the optical fiber box will rust and break.

Steel armor: regular production enterprises use double-sided anti-rust coating longitudinal wrapping steel strips, and inferior optical cables use ordinary iron sheets, usually only one side has been treated with anti-rust.

Loose tube: The loose tube for installing optical fiber in the optical cable should be made of PBT material. Such a tube has high strength, no deformation, and anti-aging. Inferior optical cables generally use PVC as the sleeve. The outer diameter of such a sleeve is very thin, and it will be flat when squeezed by hand, a bit like a drinking straw for us to drink.

Fiber paste: The fiber paste in the outdoor optical cable can prevent the oxidation of the optical fiber. Due to the moisture ingress, the fiber paste used in the inferior optical fiber is very little, which seriously affects the life of the optical fiber.

AAC cable

High-voltage transmission in order to reduce consumption and reduce costs. The reason why high-voltage transmission is used is that under the same transmission power, the higher the voltage, the smaller the current, so that high-voltage transmission can reduce the current during transmission, thereby reducing the heat loss caused by current and reducing the material cost of long-distance transmission.

AAC cable

Coaxial cables can be divided into thick coaxial cables and thin coaxial cables according to their diameters. Thick cables are suitable for relatively large local networks. Its standard distance is long and its reliability is high, because it does not need to cut the cables during installation. Therefore, the network access position of the computer can be flexibly adjusted according to the needs, but the transceiver cable must be installed in the thick cable network, which is difficult to install, so the overall cost is high. On the contrary, thin cable installation is relatively simple and low in cost, but because the cable needs to be cut off during the installation process, the basic network connector (BNC) must be installed on both ends, and then connected to both ends of the T-shaped connector, so when there are many connectors, it is easy to produce bad faults. hidden danger, which is one of the most common failures in running Ethernet.

MV ABC cable

The purpose of armored cables is to increase mechanical strength and prevent mechanical damage. Usually, the armor layer of armored cables needs to be grounded. Why do we need to ground both ends?

Because when the insulation of the cable is damaged, the armor layer will become charged. Armored cables have no interference issues, and our grounding purpose is safety. Grounding at both ends can reduce grounding resistance, increase fault current, and ensure more reliable electrical protection.

The specific analysis is as follows:

If the steel strip pierces a certain phase of insulation in the middle of the cable, and the outer protective layer is intact, the steel strip is in a charged state but cannot be detected, which is easy to cause an electric shock accident; If grounded, it can drive the protection device to trip.

Although the steel strip of the inner armored cable is not exposed, when the three-phase current is unbalanced, the armored layer may discharge due to the induced electromotive force, and in severe cases, the protective layer may be burned. When the armor layer is grounded, its potential with the ground is flattened, leading to discharge.

After grounding the copper tape shield as part of the core insulation shielding layer, it can not only equalize the potential of each core shielding layer, but also reduce the potential difference between the copper tape and the steel armor to avoid discharge.

AAC cable

Low voltage safety, not easy to cause personal injury. It can also be used in electric heating occasions, because the conductor heating requires a large current. Cause of low voltage

The distance from the power transformer is far away, and the thinner wires cause line loss and lower voltage.

When the power load is too heavy and exceeds the load capacity of the power transformer, the voltage will naturally become lower. What damage does low voltage cause? (1) Burn out the motor. If the voltage is too low by more than 10%, the current of the motor will increase and the temperature of the winding will increase. In severe cases, the mechanical equipment will stop or fail to start, and even burn the motor. (2) The lights are dimmed. If the voltage drops by 5%, the brightness of ordinary lamps will drop by 18%; if the voltage drops by 10%, the brightness will drop by 35%; if the voltage drops by 20%, the fluorescent lamp will not start. (3) Increased line loss. When a certain amount of electric energy is transmitted, the voltage decreases and the current increases accordingly, causing the line loss to increase. (4) Reduce the stability of the power system. As the voltage decreases, the limit capacity of line transmission is correspondingly reduced, thus reducing the stability, and voltage collapse accidents may occur if the voltage is too low. (5) The output of the generator is reduced. If the voltage drops by more than 5%, the output of the generator should be reduced accordingly. (6) The reduction in voltage will also reduce the capacity of power transmission and transformation equipment.

Low Voltage Hazard Analysis

If the voltage is too low, less than 80% of the system voltage (176V), some electrical appliances cannot be started, or cannot operate normally, and the self-heating is serious, which reduces the service life.

If the voltage is too low by more than 10%, the motor current will increase and the winding temperature will rise. In severe cases, the mechanical equipment will stop or fail to start, and even burn the motor.

If the voltage drops by 5%, the brightness of ordinary lamps will drop by 18%; if the voltage drops by 10%, the brightness will drop by 35%; if the voltage drops by 20%, the fluorescent lamp will not start.

Due to the reduction of voltage, the limit capacity of line transmission is correspondingly reduced, thus reducing the stability, and voltage collapse accidents may occur if the voltage is too low.