Analyze the relationship between smart grid and AC/DC UHV

Analyze the relationship between smart grid and AC/DC UHV

UHV DC UHV and AC UHV, their technical characteristics and their role in the grid are very different and cannot be confused. DC UHV is used for long-distance, large-capacity transmission, with obvious advantages in economy and technology. China's hydropower, wind power and solar energy resources are concentrated in the western region and there are long-distance transmission requirements. Therefore, UHV as an advanced transmission technology is an indispensable means to build a smart grid and realize the greening of China's power grid. This conclusion is clear and has long been consensus.
What is controversial is the exchange of UHV. The voltage level of the power grid continues to increase from low to high as the scale of the power grid expands. This is indeed a common road for the development of power grids in various countries over the past 100 years. Looking back at history, it is not difficult to see that the technical route of the traditional power grid is to solve the problems that arise in the development of the power grid by increasing the voltage level, so as to meet the economic and social demand for electricity. However, the development of things is not always a straight line. Some laws only play a role in one stage. The route to the development of the power grid by means of raising the voltage level is based on fossil energy, and energy development tends to become more concentrated. It can be said that it is the product of the second industrial revolution. When the new energy revolution, the third industrial revolution, rose in the world, the development of the power grid has actually broken away from this route and embarked on a new road to build a smart grid.
The American futurologist Jeremy ˙Rifkins, in his book The Third Industrial Revolution, introduced the insights of the American Institute of Electric Power experts on this issue. U.S. experts believe that the development of decentralized energy production in the smart grid may adopt a route similar to that of the computer industry. The mainframes will allow small and geographically dispersed desktops and laptops to be connected and fully integrated. Become a very flexible network. In the power industry, centralized power plants will continue to play an important role, but they will also require small, clean, decentralized power plants. Energy storage technology will support their development; and control and processing of complex interconnected systems The enormous amount of information and energy flow brought about by advanced electronic control technology is absolutely essential.
It can be said that relying on advanced information, control, energy storage, superconductivity and other new technologies, we focus on the development of clean and renewable energy sources in a small and decentralized way, focusing on the use of new management concepts and technological means to improve energy efficiency, and achieving energy efficiency. Sustained development is the development path of the modern power grid (ie, smart grid) demonstrated by the third industrial revolution. Since the distribution of renewable energy is relatively uniform, the result of decentralized development will make the layout of the power supply more reasonable; small power supplies and microgrids can directly access the distribution network and supply power to users at a lower voltage; especially for superconducting transmission technologies. The continuous progress and the increasing application in the project show that the voltage level of modern power grids will not only increase on the basis of ultra-high pressure, but will even gradually decrease.
The voltage level of the power grid developed from low to high during the second industrial revolution and no longer increased after entering the third industrial revolution. It also showed a trend of development from high to low. From the perspective of the entire development process, it is precisely The law of negation of negation in the development of things. The view that the grid will always develop in accordance with the law of increasing scale and higher and higher voltage levels is a metaphysical view that lacks dialectical thinking. The modern power grid no longer develops to AC UHV power grids, but also because of the following fatal shortcomings of AC UHVs:
1 The environment is expensive. Since the construction of AC UHV is to superimpose a 1000-kilovolt grid on top of the existing 500-kilovolt grid, after the power up to the grid is sent to the receiver, it must first be stepped down to 500 kilovolts and then to 220. KV grid, so it can not only replace the 500 kV substation and the corresponding 500 kV transmission line, it will also increase the voltage level of China's power grid from the existing 5 to 6 (that is, to become 0.4/10 /110/220/500/1000 kV), becoming the most voltage-level grid in the world. And the exchange of UHV noise, electromagnetic pollution to the environment is far more than ultra-high pressure, and its power transmission and transformation equipment are giants, and the required land area is also greater (about 80 meters high on the same tower with double-circuit UHV transmission line tower, The width of the corridor is about 70 meters; an AC UHV substation covers 9-20 hectares). Therefore, the construction of an exchange UHV power grid means that while the complexity of the power grid is increasing, an unsustainable environmental cost has to be paid for an additional layer of power grid (especially in the densely populated Sanhua region, the problem will become more pronounced).
2 Poor investment efficiency. AC UHV From a technical point of view, long-distance transmission is not as good as DC ultra-high voltage, and near-distance transmission is not as good as 500 kV, but investment is very large. It is a very low-cost solution. China Southern Power Grid compared the use of AC UHV schemes with the use of DC UHV plus AC 500 kV grid solutions, resulting in the former investment 600-1000 billion yuan more than the latter, about 1.3-1.5 times higher [5]. In three The construction of an exchange program for UHV synchronous power grids in the Chinese region is at least 300 billion yuan more investment than the construction of an asynchronous networked scheme that only uses UHV plus AC 500 kV grids. In addition to pushing up electricity prices, it also means that more steel, aluminum and cement will be consumed, and the production of these high-energy-consuming products will undoubtedly increase pollution to the environment.
3 Two-step boost, both increasing energy loss and reducing transmission capacity. In exchange for UHV power transmission, power supplies generally have to be first boosted and collected in a 500 kV substation and then boosted to an AC UHV power grid. Since there is basically no direct access to the generator set it is equipped with, the AC UHV power grid is actually a passive, empty shelf. This situation has never been seen in the development of other voltage levels. The highest-level voltage grid of the power grid is critical to ensure stable operation and power balance of the entire power grid. After it is formed, the generator capacity directly connected to it will not be less than 35%. For example, as of the end of 2012, China Southern Power Grid The capacity of the 500 kV power grid is 36.6% in Guangdong, 43.7% in Guangxi, 58.8% in Yunnan, and 50.6% in Guizhou; the capacity of Sichuan Power Grid accessing the 500 kV grid at the end of 2013 is approximately 47%. The step-up access to the power grid is a rather taboo practice in power system planning and design, because it will inevitably increase the system impedance, which not only leads to increased power consumption, but also limits the increase in transmission capacity. The emergence of this phenomenon shows from a side, along the traditional route of raising the voltage level, when going to the UHV, this road has nowhere to go.
Due to the above problems, combined with advances in DC transmission technology, large-capacity long-distance transmission of electricity has been achieved. Developed countries such as Europe, the United States, Russia, and Japan passed through the UHV technology research and experiment in the 1970s and 1980s. After the boom, the exchange of UHV was abandoned. In spite of its large scale, the European interconnected power grid has a maximum voltage of only 400 kilovolts (100 kilovolts below the 500 kilovolts commonly used in China's power grid), and will certainly not develop an exchange UHV in the future.
But even so they have a much higher share of renewable energy in the grid than in China. Germany's plan for 2020 renewable energy accounts for 35% of the total, 50% in 2030, and 80% in 2050. This shows that there is no correlation between the greening of the grid and the voltage level of the grid. The main ways to increase the proportion of renewable energy in the power grid are as follows: First, vigorously develop various energy storage technologies and continuously expand the scale of energy storage in the power grid; second, develop, enrich, and optimize grid peak-sharing measures, including storing and mobilizing demand response resources; It is to maximize the complementary operation of various renewable energy sources.
As for the problem of haze management, the construction of an exchange of UHV power grids will consume more steel, aluminum, and cement that could not be consumed, and the result is undoubtedly counterproductive. The strategy of electricity from afar depends mainly on DC UHV. However, this strategy alone is not enough. At the same time, we must implement the strategy of electricity from the side, that is, develop all available clean energy around us in a decentralized manner. Both sides must achieve the goal of effectively controlling haze.
The development direction of the world power grid shown by the third industrial revolution has determined that modern power grids can no longer take the old road of increasing the voltage level of the power grid. The higher the voltage level, the stronger the power grid. In fact, a variety of innovative renewable energy development and utilization technologies, distributed power microgrid technology, energy storage technology, superconducting transmission technology, multi-terminal DC technology, and other new technologies including shale gas development and nuclear fusion Energy technology is the negation of the exchange of UHV.
History has proved and will continue to prove that the exchange of UHV is a product of the traditional technological route, and it bears the mark of the second industrial revolution that cannot be erased. Although it has reached the technical peak of the traditional grid, it is just setting up a more eye-catching new landmark for the traditional grid. Today people can create conditions for it to continue to play an important role in the third industrial revolution, and it can also follow the trend to get it out of the stage of history. Cong hears it silently, and the bright one sees nothing. How does China's grid innovation go? The Chinese should have the wisdom to make the right choice.

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