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during first ten years of the 21st century, the pace of power construction in china is unprecedented, and electric power installed capacity rapidly increases to 800,000,000 kw at present from 320,000,000 kw in 2000. especially during the period of “the eleventh five-year plan”, the newly added electric power installed capacity in china reaches 430,000,000 kw, and completes 50 years of total electric power installed capacity for 5 years. the newly added installed capacity every year exceeds national installed capacity of theuk.

however, at the same time of rapid development of power source construction, the problems of focusing much on power source construction but less on power grid construction existing in the power industry for a long time is not completely solved. because the construction of power grid lags behind, a series of new problems and contradictions are caused. for example, the acceleration of the construction of thermal power station outrages the originally tense transportation bottleneck. at power consumption peaks, stocks of thermal coal of many power plants inchinaare in urgent need, and “urgent need for coal” is common. the hydropower in southwest china and wind power in northwest china have to abandon water and wind due to resistance to transmission, the development of clean renewable energy is obstructed.

as this is the beginning year of the “the twelfth five-year plan”, can these problems exposed during “the eleventh five-year plan” be fundamentally solved during “the twelfth five-year plan”? the related expert in electric power told us that these problems would become history with the acceleration of construction of ehv power grid.

 “the twelfth five-year plan” for ehv construction may accelerate

on january 6, 2011, national development and reform commission approved the expansion project of ehv ac experimental demonstration project. this project is planned to be put into operation within this year, and the transmission capacity after expansion will be expanded to 5 million kw. this expansion project has become the beginning project of ehv construction inchinaduring the period of “the twelfth five-year plan”.

just 20 days apart, on january 26, state grid corporation of china announced that the demonstration project would be built within 5 years to largely promote the study on ±1100kv ehv dc, thus to provide support for large energy base with transmission distance over 2400km.

at the beginning of the “the twelfth five-year plan”, ehv construction began intensely.

it is forecast by relevant department that during the period of “the twelfth five-year plan”, the power demand in china will continue to keep rapid growth momentum. the average annual growth rate will reach over 8%, and average annual power installed capacity increases by nearly 100,000,000 kw. at the end of “the twelfth five-year plan”, the electric power installed capacity inchinais expected to reach approx. 1.44 billion kw. in order to guarantee energy needs, china will accelerate the construction of large hydropower bases in basins such as coal power bases, jinsha river, yalong river, dadu river of shanxi, shaanxi, ningxia, mongolia and xinjiang, as well as various 10-million kw level wind power bases such as xinjiang, gansu, inner mongolia, jilin, hebei and jiangsu. by 2015, the transmission scale of above coal-fired power, hydropower, and wind power will reach approx. 150 million kw, 50 million kw and 60 million kw respectively.

for such large-capacity and long-distance cross-regional power transmission, it is necessary to solve the bottleneck in power grid transmission, and the development of ehv has become the uppermost priority in power grid construction during “the twelfth five-year plan”.

state grid corporation of china puts forward in “the twelfth five-year plan” that china will construct “three vertical and three horizontal” ehv backbone network frame connecting large energy base with main load center, and 13 dc transmission projects (including 10 ehv dc projects), to form the large-scale energy allocation pattern of “west-to-east electricity transmission” and “north-south electricity transmission”. by 2015, the strong smart grid with information, automated and interactive features has been almost built with ehv power grid as backbone network frame and with coordinated development of multi-level power grids, to form three large synchronous power grids-“north china, central china and east china”, northwest china, and northeast china, making resource allocation capability, economic operation efficiency, security level, science and technology level and smart level of the state grid comprehensively improved.

during the period of “the twelfth five-year plan”, china will compressively welcome the ehv era.

why is ehv?

so-called ehv power grid refers to the power transmission network of ac 1000kv, dc ±800kv and above, and its biggest feature is long-distance, large-capacity and low-loss power transmission. it is estimated that the transmission capacity of 1000kv ac ehv transmission lines exceeds 5,000,000kw, nearly 5 times that of 500kv uhv ac transmission lines. the transmission capacity of ±800kv dc ehv reaches 7,000,000kw, 2.4 times the transmission capacity of ±500kv uhv dc lines.

the reason why ehv is selected as the key technology for solving the bottleneck in the power grid in china is the decision made aiming at specific national conditions of china.

as explained by bai jianhua, vice chief economist of state grid energy research institute and director of energy strategy and planning research institute, 76% of coal resources in china are distributed in north and northwest china, and 80% of hydropower resources are distributed in southwest china. wind energy and solar energy resources in most of land are distributed in northwest china. at the same time, over 70% of energy needs are centralized in central china and east china. the distance from energy base to load center is between 1000 and 3000km.

such layout provides two choices: the one is to build power station in center area of load, and the other is to transmit power after building power station in center area of energy.

the development of large-scale power source in center area of load is obviously constrained by various factors. for example, coal transportation problem and environmental capacity problem, etc.. moreover, the construction of thermal power can rely on coal transportation, while hydropower and wind power cannot be realized because they are impossible to transport like water and wind. on the one hand, large-scale construction of power source point is impossible; on the other hand, valuable clean energy such as hydro-energy and wind energy is puzzling. it is visible that the idea of building large-scale power source in the load center is not feasible.

thus, building power source in west china and north china with rich energy resources, and transporting the power to the load center become the only choice.

so, can the existing power grid realize such power transportation? the expert in power grid told us it is impossible. because the transmission capacity of 500kv uhv transmission line is small at present, and the more important is that long-distance transmission cannot be realized.

thus, experts in power grid point out that ehv power grid with large-capacity, long-distance and low-loss transmission has become the uppermost priority in power grid construction during “the twelfth five-year plan”, which is the best choice.

xue yusheng, the academician of chinese academy of engineering, believes that ehv not only has the capability of large-capacity and long-distance transfer of energy, but also can relieve the transportation pressure, improve economic benefits and promote the development of clean energy.

first, from optimal allocation of resources, as the energy strategy in china moves westward, the distance from large energy base to energy consumption center is farther and farther, and the scale of energy transportation is larger and larger. based on traditional transportation methods such as railway, highway, shipping and pipeline, increasing the transportation capacity of power grid is a choice for relieving transportation pressure. with 1000kv ehv demonstration project that has been put into operation as an example, it can transport 2 million kw of power everyday at present, reaching 5 million kw after reconstruction. this is equal to transportation of 25,000t-60,000t of raw coal from shanxi to hubei everyday. hubei media said this is equal to sending a gezhouba hydropower station to hubei.

from economic benefits, the price of thermal power in west china and north china is 200 yuan/tons for standard coal. the coal is loaded in the local area, and transported to qinghuangdao port through highway and railway, and then transported to east china through sea and highway. the price of thermal power increases over 1000 yuan/tons for standard coal. after conversion, the fuel cost of electricity per kwh reaches approx. 0.3 yuan. after building pithead plant in coal-producing area, the fuel cost is only 0.09 yuan/kwh. the power of pithead plant is transported to load center in central china and east china through ehv, excluding the cost of power transmission link, the electricity price is still less than 0.06-0.13 yuan/kwh of average electricity price of local coal.

ehv is necessary for supporting the development of clean energy. only ehv can solve the large-scale consumption of power generation of clean energy. some time ago, the problem of wind power sun-seeker in inner mongolia was widely concerned. in fact, wind power inchinais mainly centralized in “three north” area, and the local consumption space is very limited. the further development of wind power needs expansion of the consumption range of wind power objectively, and large wind power must be integrated into power grid. the strong power grid can significantly the consumption capacity of wind power. ehv power grid will constitute large-capacity and long-distance energy transportation channel inchina. it is estimated that if wind power is only consumed within the province, the exploitable scale of wind power all over the country will be 50 million kw in 2020. through transmission and expansion of consumption capacity of clean energy by ehv network interconnection, the national development scale of wind power may reach above 100,000,000 kw.

can ehv be established?

although there are various benefits above, after all, ehv is a new technology in the power system, which has no experience in business operation in the world. ehv was once defined by cigre as “immature technology”. moreover, if the voltage class of power grid is higher, the coverage is larger, and the hidden danger of the security is larger. the long-distance power grid is easy to suffer natural disasters such as typhoon, rainstorm and lightning strike. therefore, is the security of ehv guaranteed? facing various difficulties such as there is no mature technology at home and abroad, nor existing equipment, can we build ehv power grid?

xue yusheng, the academician of chinese academy of engineering told us after successful operation and stable operation of 1000kv southeast shanxi-nanyang-jingmen ehv ac experimental demonstration project and xiangjiaba-shanghai ±800kv dc demonstration project, we have confidence and ability to construct ehv.

according to the introduction of state grid corporation of china, new technology, new materials and new process are widely used in two large ehv demonstration projects, to successfully solve the difficulties such as large-span construction, bulk transportation, centralized installation and commissioning of a large number of new equipment. the construction tasks are completed for 28 months and 30 months respectively, which are successfully put into operation for one time. at present, safe and stable operations for 853 days and 212 days are respectively realized, and expected objectives such as security, quality, schedule and environmental protection of the project are realized, which provide valuable experience for large-scale construction of ehv in the future.

for example, for the security of power grid, sun xin, the director of ehv construction department of state grid corporation of china stresses that, “the security of ehv is guaranteed. since ehv ac transmission demonstration project is put into operation for two years, double-direction, full-voltage and large-capacity power transmission is realized, withstanding the test of bad conditions such as thunderstorms, winds, high and low temperatures. the measured transmission loss rate is 1.7%, approx. 1/3 that of 500kv project. various performance indexes are completely in line with the design requirement.”

lu qiang, the academician of chinese academy of sciences, expressed that assuming that a certain ehv line suffers a large interference fault, can a large ac synchronous system keep safe and stable? we carry out the simulation experiments in 500-600 conditions, and the answer is that security and stability are guaranteed by a series of innovative technologies.

aiming at the situation that there is no existing technology, equipment or standard at home and abroad, state grid corporation of china takes the development of ehv as the major project of technological innovation. before proposal of idea and comprehensive initiation, the company has invested huge capital to build four test bases (ehv ac, dc, high-elevation and engineering mechanics) and two r&d centers (large power grid simulation, and dc complete sets of equipment design), to form the experimental research system of power grid with complete functions and international leading comprehensive indexes. during the past few years, state grid corporation of china has completed 310 researches on major and key technology around ehv project, solved various world-class difficulties such as overvoltage and insulation coordination, design of external insulation, control of electromagnetic environment, system integration, safe operation and control of large power grid, gradually grasped the core technology of ehv transmission, and realized successful application in the experimental project.

the construction of ehv plays a more obvious role in promoting domestic equipment manufacturing industry. all equipment for three large domestic ehv experimental projects is provided by domestic enterprises. the localization rate of the projects reaches approx. 95%, and the localization rate of the equipment reaches approx. 91%. through the experimental project, the domestic equipment manufacturing industry is trained, and scientific and technological r&d strength is largely improved. for example, jiangsu shemar electric co., ltd. has successfully solved the world-class difficulty of ehv insulators. the chairman ma bin said that the performance of the international initiative ehv 1000kv hollow composite insulators that we have invested nearly 100 million yuan in r&d reaches the international advanced level, while the price is only 1/3 that of foreign products.

the relevant person of state grid corporation of china told the reporter full of confidence that with the scale construction of ehv project, major equipment and materials manufacturing technology are gradually mature, and engineering construction technology is increasingly improved. the scale effect is prominent, level of construction cost is further reduced, and the technical economy will be fully reflected.

the success in ehv in china has driven the development of ehv technology in the world. two international meetings of ehv transmission technology held successively in 2006 and 2009 make the world recognize the development situation of ehv inchina. at present, countries such asindia,brazil, theunited statesandrussiaare actively studying and promoting ehv power transmission, and actively seeking the cooperation with state grid corporation ofchina. the minister steven chu of united states department of energy considers the innovation of ehv inchinaas the challenge to technology leadership of theunited states.

at present, the development of ehv power grid is started, and the spring of ehv construction is coming. some expert believes that we should face all kinds of difficulties, and try to make such advanced technology benefit the country and the people. (ran yongping, yao lei)