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What Is an All Aluminum Conductor (AAC) and Where Is It Used? Discover what an All Aluminum Conductor (AAC) is and its key applications in power transmission and distribution. Learn how AAC conductors offer excellent conductivity, lightweight design, and corrosion resistance. Explore their uses in urban networks and short-span power lines with Dynamic Cables Limited.
Advantages of High Voltage Transmission
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.
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.
The difference between multimode fiber and single mode fiber
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.
Single-mode fiber uses a solid-state laser as the light source; multimode fiber uses light-emitting diodes as the light source; single-mode fiber has a wide transmission frequency and long transmission distance, but because it requires a laser source, the cost is high; multimode fiber has low transmission speed and short distance , but its cost is relatively low; single-mode fiber has a small core diameter and dispersion, allowing only one mode of transmission; multi-mode fiber has a large core diameter and dispersion, allowing hundreds of modes of transmission.
High voltage 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.
However, the transmission voltage cannot be increased blindly. The higher the transmission voltage is, the more stringent the requirements for the materials used in the construction of transmission overhead lines will be, and the higher the cost of the line will be. Therefore, it is necessary to proceed from the specific actual situation to ensure that the transmission line can not only reduce power loss, but also save construction investment. High-voltage transmission can reduce the loss of electric power, but from the perspective of power generation, the generator cannot generate a high voltage of 220 kV, because the generator needs to generate such a high voltage, and its materials, structure, and safe operation and production are all important. There are almost insurmountable difficulties. From the perspective of electricity consumption, the vast majority of electrical equipment cannot operate under high voltage. This determines that a series of power transformers are used to increase or decrease the voltage from power generation, transmission to power consumption. The electricity generated from a large hydropower station is sent to the user through the transmission line, and the voltage needs to be changed five times in the middle (one rise, four drops). For small and medium-sized power stations, the number of intermediate voltage conversions is less, which depends on the specific conditions such as the voltage emitted by the TV and the distance of the transmission line.
The reason why high voltage is used for long-distance power transmission
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.
The difference between HVDC and AC transmission
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.
DC transmission is suitable for the following occasions: Long-distance high-power transmission; submarine cable power transmission; communication between AC systems with different frequencies or the same frequency running asynchronously; using underground cables to supply power to large cities; when AC systems are interconnected or the distribution network is increased, it is used as a device for limiting short-circuit current One of the measures; cooperate with the transmission of new energy.
Classification of coaxial cables
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.
Broadband coaxial cable Coaxial cable systems that use finite television cables for analog signal transmission are known as broadband coaxial cables. The word "broadband" comes from the telephony industry and refers to a frequency band wider than 4kHz. However, in computer networking, "broadband cable" refers to any cable network that uses analog signals for transmission. Since the broadband network uses standard cable TV technology, the usable frequency band is as high as 300MHz (often to 450MHz); due to the use of analog signals, an electronic device needs to be placed at the interface to convert the bit stream entering the network into an analog signal, and Convert the output signal of the network into a bit stream. The broadband system is divided into multiple channels, and TV broadcasting usually occupies a 6MHz channel. Each channel can be used for analog TV, CD quality sound (1.4Mb/s) or 3Mb/s digital bit stream. TV and data can be mixed on one cable.
multimode fiber
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.
Multi Mode Fiber (Multi Mode Fiber): The central glass core is relatively thick (50 or 62.5 μm), which can transmit multiple modes of light. However, its intermodal dispersion is relatively large, which limits the frequency of digital signal transmission, and it will be more serious with the increase of distance. For example: 600MB/KM optical fiber has only 300MB bandwidth at 2KM. Therefore, the transmission distance of multimode fiber is relatively short, generally only a few kilometers. Multimode fiber: There are hundreds of modes transmitted in multimode fiber, and the propagation constant and group velocity of each mode are different, so that the bandwidth of the fiber is narrow, the dispersion is large, and the loss is also large. It is only suitable for medium and short distances and small capacity. Fiber optic communication system.
