Technical Progress in the Field of Power Transmission and Distribution Affects Electricity Environmental Protection

Yang Yong (Zhejiang Electric Power Test Institute, Hangzhou 310014, China). It is pointed out that in order to control the pollution of the power industry to the environment, in addition to increasing technological advances and capital investment in power supply, technological advances in the field of power transmission and distribution will also have a positive impact on China's power environmental protection business.

As the basic industry of the national economy, the power industry has achieved tremendous development while the country continues to increase investment. The installed capacity of thermal power continues to grow rapidly. At the same time, the emission of harmful gases such as C2, S2, and NOx from coal-fired power plants has also been growing at the same time, which has become a major source of air pollution in China. According to related data, if it is not controlled, it is expected that by the end of 2000, the S2 emissions from coal-fired power plants will reach the top of the world in terms of annual emissions of C2 in China. This will bring a series of environmental disasters such as large-area acid rain and accelerating climate warming.

In view of the severe air pollution situation, the state has increased its control. On April 3, 2000, the National People’s Congress passed a new law on the prevention and control of air pollution, which also imposed more stringent restrictions on the emission of harmful gases from coal-fired power plants. Therefore, in the future, the development of China's electric power industry must put environmental pollution prevention and control in a prominent position, and increase investment in electric power environmental protection. In addition to the expansion of installation of desulfurization equipment in coal-fired power plants, development of large-scale supercritical units, shutting down small thermal power, and implementation of clean coal power generation technologies, etc., a series of measures to control and reduce harmful emissions in power supply, transmission and distribution technologies Progress will also have a positive impact on power environmental protection.

1 Minimize the loss of power grids The power grid in China, especially urban and rural areas, has a weak foundation, and the power loss of power transmission and distribution systems is quite high. The average line loss rate of power grids in the power sector in the country is around 8%. Consider urban-rural distribution. The loss of the power grid, the total line loss rate of about 15%, and the developed countries, transmission and distribution line loss rate has been from about 10% in 1960, gradually reduced to the current 5% to 8%. Visible, and industrial countries In contrast, the line loss rate of China's power grid is quite high. The electrical energy provided for the depletion has added to the atmospheric pollution. Therefore, optimizing the operation of the power transmission and distribution system not only improves the economic efficiency of the power system operation, but also reduces the power generation capacity for the loss of the power transmission and distribution system, which indirectly effectively reduces the emission of harmful gases such as C2 and S2. .

1.1 Vigorously promote the power-saving transformer The transformer is an indispensable power device for power transmission, and also the largest electrical loss in the power transmission and distribution system. Its loss accounts for about 10% of the total power generation, accounting for the loss of the power transmission and distribution system. 50%. With the advancement of power transmission and distribution technologies, the loss of transformers has shown a sharp decline. In 1998, the state stated that it was required to phase out high-loss old transformers and replace it with a low-loss, energy-saving S9 transformer. In recent years, foreign countries have begun to promote the use of energy-saving amorphous alloy distribution transformers, which replace amorphous silicon alloy cold-rolled silicon steel sheet, so that its no-load loss significantly reduced. Analysis of prototypes of 160, 200, 315, and 500 kVA prototypes manufactured by transformer factories in Shangchang, Foshan, and Baoji shows that the no-load loss of amorphous alloy transformers is about 75% lower than that of S9 transformers. Has been put into production abroad, the United States has millions of amorphous transformers used on the Internet, the country also has more than 3,000 units put into operation.

Large-scale distribution transformers, if the overall promotion of the use of amorphous transformers, the effect of reducing consumption will be very significant. According to statistics, more than 200,000 units of distribution transformers are produced each year in the country. If they are replaced by amorphous transformers, the reduction in losses is equivalent to the emission of 1.3 million tons of CO2 to the atmosphere, SO22.3 million tons, and NO x 1040 tons. Therefore, amorphous transformers are It is called a green power plant without a generator. The price of amorphous transformers is about 1.3 times that of S9 transformers, but it is estimated that the extra purchase costs can be recovered from the saved electricity charges in about three years. Therefore, to rationally use resources and protect the ecological environment, efforts should be made to promote the use of amorphous transformers.

1.2 Other Measures to Reduce Line Loss The transmission line system, especially the urban-rural distribution network, has a large line loss rate, which is related to low investment in power grid construction, aging of facilities, and backward management. As far as China’s current situation is concerned, there is considerable potential for reducing line losses.

The main measures are: actively carry out scientific and technological innovation, accelerate the implementation of distribution network automation, adjust and optimize the distribution network through the control of the load switch of the ring network, and realize the entire control through the control of the capacitor and the distribution transformer with on-load voltage regulation. The reactive power/voltage control of the distribution network eventually achieves the goal of reducing network losses.

Strengthen power management, resolutely plug measurement loopholes, and effectively prevent and crack down on power theft. Actively develop anti-tampering technologies to improve and improve users' metering devices to achieve accurate metering and anti-tampering functions.

Realize load monitoring and remote meter reading.

Replace thin wires, balance three-phase loads, add reactive power compensation, and increase the power factor of the user. At present, the natural power factor of household appliances in China is only about 0.7. At the same time, small industrial and commercial users connected to low-voltage power grids do not have power factor assessments and means for detecting power factors. This is an important reason for low-voltage power line losses.

2 The impact of technical progress of the transmission system on environmental protection 2.1 Construction of ultra-high voltage lines to create the conditions for the transmission of clean energy In the national strategy for the development of the western region, the development of hydropower resources in the western region will be actively pursued to realize the transmission of power from the west to the east. Replacing the coal-fired power plants in the east with inexpensive, clean, pollution-free western hydropower has a profound impact on China's environmental protection undertakings. The Xiludu and Xiangjiaba hydropower projects under construction in the western part of China and the large-scale and extra-large hydropower bases planned for the western region in the future have installed capacity of several GW and several tens of GW or more, and the distance to the east is more than 1000km. The transfer of these powers to the Eastern Load Center is not only to meet the electricity needs but also to protect the environment. The existing 500 kV voltage transmission line (economic transmission capacity 1GW, transmission distance 300 ~ 500km) has been difficult to meet this requirement.

In addition to more high-voltage direct current (HVDC) transmission, the exchange of UHV power transmission as the backbone grid of the West-East electricity transmission should be considered as one of the major solutions. Taking a transmission line with a transmission capacity of 10 GW for 1 000 km as an example, the comparison of the number of loops with different transmission voltages and the width of the occupied corridors is shown in Table 1. It can be seen from Table 1 that the number of circuits using UHV transmission is greatly reduced. In terms of line cost, the cost of a 750kV line is 90% of a 1000kV line. The cost of the line is only 500kV at 66%. The 1000kV transmission loss is 1/2 of 750kV, which is 1/5 of 50CkV. Visible, UHV transmission is either It has a great advantage in terms of the line occupancy corridor width, cost, or operating costs.

From a worldwide perspective, 750kV transmission has more than 20 years of operational experience and the technology is relatively mature. During the “10th Five-Year Plan” period, China will first construct an UHV power transmission line with a voltage level of 75CkV in the northwest power grid. The research work for the development of the UHV transmission at a voltage level of 1 000kV should also be carried out gradually. UHV transmission can save land resources and line corridors, better realize the strategic goal of West-to-East power transmission, and effectively solve the problem of environmental pollution in load centers in eastern China.

Table 1 Comparison of loops and occupancy corridors for different AC transmission voltages Transmission voltage/kV loop number Occupation Corridor width/m Note Transmission distance is 100Ckm Transmission capacity is 10 GW/. 2.2 Actively develop HVDC technology HVDC commercial The operation has been in operation for nearly 50 years. With the development of power electronics, computers, optical fibers and other technologies, the advantages of HVDC in long-distance large-capacity transmission are even more apparent.

Line loss can be reduced by more than 50% compared to AC transmission. As the HVDC transmission technology has matured, it will play an important role in reducing emissions from coal-fired power plants in the east by sending electricity from West to East.

To protect the environment, we must vigorously develop renewable non-pollution energy sources, such as runoff small hydropower, wind power generation, tidal power generation, solar power generation, geothermal power generation, etc., and gradually increase their proportion in power generation. However, these power supplies often have small capacity, unstable operating conditions, and large losses due to AC transmission. In recent years, there has emerged a light-duty HVDC transmission technology that uses high power gates to shut off thyristors, which overcomes the limitation that traditional HVDC receivers must provide sufficient reactive power, and is particularly suitable for connecting small-scale distributed power supplies to large power grids. See its basic structure. Utilizing light DC transmission technology, these non-polluting renewable power sources, fuel cells with low greenhouse gas emissions, micro-turbine and other distributed power sources can be connected to the large power grid, and the role of these environmentally friendly energy sources can be brought into full play, adding them to energy consumption. The proportion in China will correspondingly reduce the power generation of coal-fired power plants and further reduce atmospheric pollution.

The main wiring diagram of the light-duty HVDC power transmission system China's Zhejiang Zhoushan submarine HVDC transmission project consisting of all domestically produced equipment and the introduction of the 500kV Ge-Nan HVDC transmission project have all gained valuable experience in equipment digestion, absorption, operation and maintenance. . At present, the single-pole project with a capacity of 1800MW and 500kV Tianyiguang has been put into operation, and the DC transmission project in the Three Gorges and Changzhou is under construction. However, compared with the international advanced level, there is still a large gap in the manufacture of HVDC transmission equipment. There are not many HVDC transmission projects actually put into operation. This requires more investment in equipment manufacturing, design, operation, etc., to expand the scope of application of DC transmission.

2.3 The role of flexible AC transmission technology in environmental protection In order to improve the static stability of the power grid under fault conditions, the power system must maintain 15% to 20% of the accident backup capacity during normal operation; the transmission line is limited by the natural transmission power. But can not further increase the transmission capacity, plus outlet corridor will have an impact on the environment; environmental protection requires the load center away from the power supply, but the load center lacks reactive and voltage support, the characteristics of transient voltage instability is more prominent; the existing transmission system circulation The presence of power often causes power bypass and power backflow, which will lead to a large amount of power loss and transmission capacity of the power transmission system. Large power grid interconnection can reduce the power backup capacity, but the security and stability issues become more prominent as the system interconnection increases. , limiting the scale of the interconnected power grid. These transmission system problems related to the environmental protection of electricity are difficult to solve by traditional control methods.

The emergence of FACTS technology based on power electronics technology has made it possible to solve these problems. For example, the main component of FACTS, the TCSC, uses thyristor control to smoothly adjust the reactance value of the transmission line series compensation device over a relatively large range, so as to improve the stability of the power system and expand the transmission of transmission lines. Power, flexible control of power flow in the grid, etc. For another example, a line parallel compensator-STATCOM using FACTS technology maintains the stability of the line voltage by interacting with the reactive power of the system. Its function is similar to that of a camera, but there is no rotating part and the response speed is Extremely fast is an effective tool for suppressing system voltage fluctuations and improving system stability, especially voltage stability. The Unified Power Flow Controller (UPFC) integrates the functions of series compensation to control the line voltage, impedance, and phase, thus achieving various functions such as controlling power flow, damping oscillation, and improving system stability. China's application of FACTS technology has also made considerable progress. The 2CMvarSTATCOM jointly developed by Henan Provincial Electric Power Bureau and Tsinghua University has been successfully put into operation. The ongoing TCSC application research of Northeast Yiyi Feng and Hua Dongyang Yihuai 50CkV transmission lines has also made great progress.

From the viewpoint of power environmental protection, the primary system of STATCOM devices can increase the transmission capacity of West-to-East power transmission, reduce the number of transmission lines, increase the scale of the interconnected power grid, and reduce the use of standby systems to maintain stability. The power supply capacity reduces the power consumption of the power grid, improves the stability after the load is removed from the power supply, and is conducive to the protection of the environment.

3 Strengthen the storage capacity of the power grid and reduce the standby capacity of the system With the rapid development of the national economy, the improvement of the people’s living standards and the rapid spread of household appliances, the peak-to-valley difference of the power grid is increasing, and the main source of power for the power grid is coal-fired. The peak shaving capacity of the power plant is not good. For this reason, the power grid has to expand its power supply capacity. As the system's capacity for peak load adjustment and accident emergency backup, the capacity of the unit can account for 10% to 15% of the total capacity. Large-scale changes in unit load also increase coal consumption, which aggravates coal-fired power plants. Atmospheric pollution. Therefore, strengthening the peak-shaving capability of the system is not only the need for peaking and filling of the grid, the emergency of accidents, and the need for economic operations, but also the need to reduce the environmental pollution of coal-fired power plants.

Pumped storage is the main means to strengthen the storage capacity of the power grid. In recent years, the construction of pumped-storage power stations in China has developed rapidly. The world’s largest capacity 2.4 million kW Guangzhou pumped storage power station, 1.8 million kW Zhejiang Norushi Ping pumped storage power station, and 800,000 kW Beijing Ming Tombs Pumped storage power stations and other large and medium-sized pumped storage power stations have been put into operation one after another, enabling a group of fossil-fired power plants that originally served as peaking tasks to be decommissioned, correspondingly reducing the reserve capacity of the power grid, and the environmental benefits to society are obvious. China has built about 5.57 million kW pumped-storage power stations, accounting for 1.9% of the country's installed capacity of power generation, accounting for 5% of the world's capacity for pumped-storage power stations built and under construction, with a relatively small proportion. There are many pumped and stored energy resources available in China, and this precious resource should be reasonably developed and utilized as soon as possible. In particular, the southeastern coastal areas are both the center of load and the strict control of environmental protection, and it is necessary to speed up the construction of pumped storage power stations in order to optimize Power structure to protect the environment.

In addition to pumped-storage power plants, the development of superconducting superconducting reserves using superconducting technology has also made significant breakthroughs. A typical system for superconducting energy storage sees.

Under normal circumstances, the power of the power grid is converted into direct current by a high-power electronic converter, and the magnetic field is injected into the superconducting coil to be stored in the magnetic field in the form of electromagnetic energy. When the energy is released, the electromagnetic energy is converted into alternating current power. The release rate is very fast, usually only a few ms. Because the DC resistance of the superconducting coil is almost zero, there is no loss of energy storage and the conversion efficiency is as high as 95%. In contrast, the conversion efficiency of pumped storage Only about 70%. Therefore, the superconducting energy storage has the characteristics of high speed, high conversion efficiency, and freedom from construction site limitations compared with other energy storage forms such as pumped storage, battery storage, and flywheel energy storage. As a result, the supersonic energy storage system replaces the reserve Peak power has great potential for development. Now, the development of superconducting energy storage has entered the practical stage of engineering. The United States has put small superconducting energy storage devices into operation. Some of the world’s major industrial countries have invested a lot of money to invest in superconducting technology research. China should also strengthen scientific and technological research in this area so that it can improve Environmental services.

4 Conclusion Power environmental protection issues have become increasingly prominent, environmental pollution has become a constraint factor for the sustainable development of China's power industry, in addition to increasing scientific and technological progress and capital investment in power, in the field of power transmission and distribution, the development and application of energy-saving transmission and distribution Advanced power system technologies such as equipment, FACTS technology, high-voltage direct current transmission technology, and grid energy storage technology will undoubtedly greatly reduce the loss of the power grid, reduce the peaking capacity of the power grid and spare capacity for accidents, promote the use of renewable energy, and ensure that the western region is cheap Clean hydro energy sources are continuously sent to the eastern load center, which in turn reduces the demand for coal-fired power generation, reduces the total emission of harmful gases from coal-fired power plants, and better protects the environment.

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