Several Power Transmission Backbone Schemes

Transcription

1 Proceedings of the 14 th International Middle East Power Systems Conference (MEPCON 10), Cairo University, Egypt, December 19-21, 2010, Paper ID 182. Several Power Transmission Backbone Schemes Yutian Liu, Dong Yang and Hong Chen School of Electrical Engineering Shandong University Jingshi Road, Jinan, , China & 1 Abstract - Considerable activities have been carried out in US and EU to formulate and promote the vision for the evolution of electricity networks. However, the majority of these activities just focused on the distribution system and demand side, while the big picture of power transmission backbone in the future is still unclear. Several power transmission backbone schemes in the future are introduced or proposed in this paper, including asynchronous interconnected power grid of US Grid 2030, the Europe, Middle East and North Africa Supergird and a vision of China wide-area renewable energies power grid, as well as ultra-high voltage power grids of China and India. This work is expected to provide a primary discussion on the conceptual design of future transmission framework. Index Terms - Power transmission backbone, renewable energies, transmission capacity, ultra-high voltage grid. I. INTRODUCTION Efficient transmission and distribution of electricity is a fundamental requirement for providing citizens, societies and economies with essential energy resources. Whilst current electricity networks presently have fulfilled their functions effectively, more of the same will not be sufficient to meet current challenges and policy imperatives. In this context, considerable activities have been carried out in US and EU to formulate and promote the vision for the evolution of electricity networks [1]-[6], such as SmartGrid, IntelliGrid, FutureGrid, etc. However, the majority of these activities just focused on the distribution system and demand side, while the big picture of power transmission backbone in the future is still unclear [7]. The needs to reduce the large-scale blackout risk, integrate more sustainable generation resources and meet growing electricity demands, presents major challenges. These are more important and urgent than ever before to drive the existing transmission backbone to satisfy the opportunities and challenges of the future. Therefore, the transmission backbone of the 21 st century must attach the smart features, which are mainly, 1) self-healing: enabling the electricity network reconfigure itself dynamically and quickly to recover from deliberate attacks, natural disasters or network components failures; 2) accessible: granting connection access to all network users, particularly for renewable power sources and high efficiency generation with zero or low carbon emissions; 3) efficient: improving the transmission capability as fully as This work was supported in part by Key Science and Technology Project of State Grid Corporation of China under Grant SGKJ[2009]12. possible to meet increased consumer demands without adding new infrastructures. Several power transmission backbone schemes in the future are introduced or proposed in this paper, which is expected to provide a pre-construction for the conceptual design of future transmission framework. The paper is organized as follows. Asynchronous interconnected power grid of US Grid 2030 will be discussed in Section II. Section III will introduce the Europe, Middle East and North Africa Supergird, then propose a vision of China wide-area renewable energies power grid. Ultra-high voltage power grids of China and India will be demonstrated in section IV. Further discussions and conclusions will be given in section V. II. ASYNCHRONOUS INTERCONNECTED POWER GRID For now, US Grid comprises Western, Eastern and Texas synchronous systems, each of that has the free network structure and is interconnected with other two through DC links. What is called the free network structure has no hierarchy, no partition and no tie lines, in which massive power is transmitted through the complex network. Since 1965, 21 blackouts with more than 8GW power losses each have occurred all over the world, including 6 times in US Grid. The free network structure, in essence, is just the reason why accidental faults possibly trigger load transfer and chain reaction, then lead to angle oscillation and voltage collapse, finally split the whole and pose the blackout. According to American vision for electricity s second 100 years, a transmission backbone from the Pacific coast to the Atlantic coast, north to Canada and south to Mexico will be built by 2030 as shown in Fig. 1 [8]. This conceptual design will integrate mass energy storage, high temperature superconductivity and advanced DC transmission technologies to form a backbone network with double DC lines [9], [10]. The nation-wide backbone like a pentagon has the ability to balance power supply and demand in the wide area, where season, weather and other differences are available to provide complementary effects. Below the backbone, local distribution grids, mini-grids and micro-grids are interconnected with each other through radial DC lines, thus realizing the hierarchy and partition, reducing the blackout scope and improving the emergency support. The vision of US Grid 2030 is proposed on the background of massive equipments aging, transmission bottlenecks emerging and frequent blackouts occurring. If the vision comes into truth, 3 former synchronous systems will be divided into more small-scale district grids that are isolated, controlled and mutual supported through DC links, thoroughly 377

2 ending up with the free network structure in US Grid over a century. renewable energies distribution in the expanse covering Europe, Middle East and North Africa. Fig. 1. Transmission backbone of US Grid 2030 III. WIDE-AREA RENEWABLE ENERGIES POWER GRID A. Europe, Middle East and North Africa Supergrid In January 2010, 9 European countries along the North Sea jointly launched plans for a clean energy supergrid in the north of Europe to integrate wind power, solar power, hydropower and other renewable energies. According to European recent planning, the capacity of off-shore wind power in the North Sea exceeds 100GW, about 10% of Europe s entire electricity demands. Norway hydropower with the scale of 30GW, as a giant battery for clean energies, will be available to store massive off-shore wind power in the North Sea and fulfill system peak load and frequency regulation. On the basis of European vision for electricity networks of 2050, the North Sea Supergrid will be combined with the large solar power project, which Germany started in the Sahara Desert in October The supergrid is to be gradually expanded into a wider area covering Europe, Middle East and North Africa as shown in Fig. 2 [11], [12]. By 2050, the large solar power project in the desert, so called Concentrating Solar Thermal Power + Seawater Desalination, is expected to transmit 50~200GW power to Europe. The North Sea Supergrid will be constructed with thousands kilometers of submarine cables [13]. The transmission distance of solar power in the Middle East and North Africa sent to European load center is about 1500~3000km. Due to HVDC transmission advantages in underwater cables greater than 30km as well as overhead lines greater than 600km, the EU-MENA (Europe, Middle East and North Africa) Supergrid will introduce novel HVDC technologies to build the backbone network. As a product of Europe coping with energy crisis and CO 2 emissions, the EU-MENA Supergrid is specialized for renewable energies transmission. In brief, stable and reliable power is to be generated through the EU-MENA Supergrid balancing Fig. 2. Transmission backbone of EU-MENA Supergrid 2050 B. A Vision of China Renewable Energies Power Grid According to preliminary estimate, China will have a total installed capacity of 2400GW by 2050, approximate 30% of which from non-water renewable energies. The planning and pre-construction for several 10-million-kW wind power bases have been carried out. By 2050, the large-scale wind power sent from the northwest, North China and northeast region will reach the 100-million-kW level, including 12.7GW in Jiuquan, Gansu, 20GW in Hami, Xinjiang, 20GW in the west of Inner Mongolia, 30GW in the east of Inner Mongolia and 10GW in the north of Hebei. Supposed that every 30km 2 desert area can be allocated for 1GW installed capacity of solar power, 0.85 million km 2 desert area in China will quite satisfy the need for solar power. The demonstration and planning for several 10-million-kW solar power bases in Xinjiang, Qinghai, Gansu, Inner Mongolia and other regions rich in solar power resources have been conducted. By 2050, the large-scale solar power sent from the north and northwest region will also reach the 100-million-kW level. There is no change in the inverse distribution of energy resources and load demands after the strategic adjustments of China energy structure. The remarkable weakness of new energies lies in unstable and intermittent power supplies. How to safely deliver the large-scale wind and solar power will become the key challenge in the future. To solve its scale access to conventional networks, abundant energy storage installations, such as pumped storage power stations and combustion gas turbine power stations, must be added at great expense, which will greatly drag the development of new energies. If a wide-area renewable energies power grid can be built to integrate wind power in the north, solar power in the desert and hydropower in the upper reaches of the Yellow River, the intermittence and instability of new energies will be relieved depending on energy resources complementarities in the expanse, thereby reducing the investments of energy storage installations to a large extent. Therefore, a vision of 378

3 China renewable energies power grid is proposed in this paper as shown in Fig. 3. Phase I, new energies will be transmitted to load centers hundreds to thousands kilometers away through UHVDC lines in a point-to-point way. The impacts of intermittent energies on receiving-end systems are able to be weakened with the integration of wind power, solar power and energy storage. Phase II, the established point-to-point UHVDC lines will be expanded into a multi-terminal DC backbone network covering Xinjiang, Qinghai, Gansu, Inner Mongolia and other northern regions. In recent years, novel DC transmission technologies have the rapid developments [14]-[16], for example, VSC-HVDC with the advantage of multi-terminal DC interconnection has been put into operation in Japan and US. Due to the capacity constraints of fully-controlled switching devices, the existing VSC-HVDC cannot replace conventional HVDC in the long-distance large-capacity transmission. Accordingly, its voltage level and transmission capacity are to be further improved. and Southern Grid is interconnected with other parts through DC lines or DC back-to-backs. India s energy resources are mainly distributed in the east and northeast, where coal and water power are in the majority, besides, wind and solar power are in plenty. However, most load centers and densely populated areas are located in the north, south and west. Therefore, Indian vision for electricity networks will focus on east-to-west power transmission as well as north-to-south power transmission. By 2025, India will have a total installed capacity of 800GW and power sent from Eastern and Northeast Grid will increase to the scale of 90GW. According to Indian planning, the nation-wide 1200kV AC and ±800kV DC transmission backbone, coupled with 765kV AC and ±500kV DC grid, will be built as shown in Fig. 4 [18]. Whatever, India UHV Grid is the very backbone network in which the huge-scale DC power from Eastern and Northeast Grid is expected to safely land. Fig. 3. The vision of China renewable energies power grid By 2020, the installed capacity of hydropower stations in the upper reaches of the Yellow River will increase to 14GW and 31 pumped storage power stations with 14.2GW will be equipped in the northwest [17], which can be used for new energies storage in scale. In February 2007, China ventured a strategic planning that would deliver a good amount of seawater from the Bohai Sea to the desert belt. According to preliminary estimate, this seawater pumped project requires the installed capacity of 20GW. Supposed that the pumping loads are fully supplied by China wide-area renewable energies power grid, east-to-west seawater transmission project with the irregular pumping will become a giant battery for the intermittent energies. Besides, distributed electric vehicle charging stations in the receiving-end system can also be used to regulate system peak load. IV. ULTRA-HIGH VOLTAGE POWER GRID A. India Ultra-high Voltage Grid At present, Indian transmission backbone consists of Northern, Southern, Western, Eastern and Northeast Grid. Northern and Northeast Grid are synchronous interconnected Fig. 4. Indian UHV Grid in the planning year of 2025 B. China Ultra-high Voltage Grid China has the inverse distribution of energy resources and load demands. More than 70% of coal resources and most non-water renewable energies are in Inner Mongolia, Shanxi, Shaanxi, Gansu, Xinjiang and other northern areas. More than 80% of water resources are in Sichuan, Yunnan, Tibet and other southwest areas. However, two-thirds of energy demands are located in the east and middle. SGCC (State Grid Corporation of China) proposes that China will construct 4 large-scale synchronous power grids in the future [19], comprising North China Central China East China Grid, Northeast Grid, Northwest Grid and Southern Grid. By 2020, a UHV transmission backbone will be built in North China Central China East China Grid as shown in Fig. 5. Northeast Grid, Northwest Grid and Southern Grid are respectively interconnected with the UHV grid through DC lines or DC back-to-backs. 379

4 Since 2004, China has made great progress in the planning and construction of the UHV grid. In January 2009, the first UHVAC project, Jindongnan-Nanyang-Jingmen double lines, was put into commercial operation, which marks essential breakthroughs in 1000kV UHVAC transmission techniques and equipment manufacture. UHV/EHV DC transmission projects of ±660kV Ningdong-Shandong line, ±800kV Jinping-Sunan line, ±800kV Yunnan-Guangdong line and ±800kV Xiangjiaba-Shanghai line are presently in construction or put into monopole operation. In the future, with the large scale of more than 700GW [20], well damping characteristics and great impact resistance, China UHV Grid has the ability to provide a strong supporting framework for tens of planning UHV/EHV DC lines of nearly 300GW from northern and western sending-ends. Fig. 5. North China, Central China and East China UHV Grid in the planning year of 2020 The major source of foreign blackouts over 40 years lies in the free network structure that is uncontrolled and easy for load transfer. The chain reaction of UHV synchronous grid is difficult to control, that possibly leads to the large-scope blackout. Supporting the huge-scale DC power and reducing the blackout scope is a contradiction. The key is to make a balanced decision for dealing with the large-probability small-impact DC blocking and the small-probability large-impact blackout. Based on national conditions, China and India both regard UHV strong supporting framework in priority. Therefore, lowering the blackout risk of UHV power grid from structure planning is of significance. In summary, for one thing, EHV/HV loops should be promptly opened in order to avoid multi-level electromagnetic loops and UHV/EHV loops are necessarily opened in due time. For another, self-healing abilities for UHV synchronous grid should be improved, especially for flexible districting, active splitting and fast recovering, which are used to suppress cascading trips, thus reducing the blackout scope effectively. V. CONCLUSION Through primary discussion on several large-scale power transmission backbones in the future, some conclusions are derived as follows. 1) US Grid 2030 divides 3 former synchronous systems into more small parts that are isolated, controlled and mutual supported through DC links, thereby greatly lowering the large-scale blackout risk. 2) If a wide-area renewable energies power grid can be built, the intermittence and instability of new energies will be relieved depending on energy resources complementarities in the expanse, thus reducing the investments of energy storage installations to a large extent. 3) UHV grids in India and China have the ability to provide a strong supporting framework for the huge-scale UHVDC power. Meanwhile, to reduce the blackout scope for UHV grids is also necessary and challenging. This work will be helpful to draw the big picture of power transmission backbone in the future. REFERENCES [1] European Commission. European SmartGrids technology platform vision and strategy for Europe s electricity networks of the future. [Online]. Available: [2] Office of Electric Transmission and Distribution, United States Department of Energy. The smart grid: an introduction. [Online]. Available: Book_Single_Pages(1).pdf [3] EPRI. Profiling and mapping of intelligent grid R&D programs. [Online]. Available:

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