| In China, energy resources and energy consumption are not in equilibrium. The regions with abundant energy resources are very far from the developed areas. Geographically speaking, the energy is distributed more in the north but less in the south, and more in the west but less in the east. The southwest hydropower base and the northwest coal-power stations are 800 to 3000km from the mid east region. To meet the power demands from the social development and people's livelihood in the future, objectively, it is supported to realize the optimized allocation of the energy in very large scale through a strong power grid. Since the current 500kV power grids are limited for long distance and large volume power transmission, it is very hard for the western hydropower base and the north coal-power base to transmit power with high effiency to the central and eastern region. Therefore, a large number of coal-power projects have to be installed, which tightens the situation of coal supply, transportation and environmental protection, lowering the efficiency of energy configuration.Therefore, to secure the harmony between China's energy and the development of economy and society, it is necessary to build long-distance, great capacity and low loss UHV power transmission system. It will help the intensive development of the large-scale coal-power, hydropower and nuclear generation bases and it will help to optimize the energy production and consumption configuration; it will help the western regions to change the energy advantage into economy benefits, so as to promote the harmonious development of the regional economy; it will also help to improve the framework of the power grid and enhance the safety of the power grid; it will help to decrease the cost for the construction of power grid, to save land resources, to relieve the pressure of transportaion and environmental protection, to improve the management effieciency and promote the construction of energy-saving and environment-friendly society. The development of the UHV power grids goes with the actual situation of China; it is a great strategy for the sustainable development of the power industry; it is very imporamant for the overall construction of a well-off society and a harmonious society; it will also promote the development of electricity power industry of the world. Based on the preliminary research achievements, the UHV grid plan is formed and a scheme is proposed to build the north, central and east China UHV AC synchronous electric grid and realize large capacity transmission with super long distance through UHV DC in this dissertation. The main contributions of dissertation include the following.(1) Several main factors influencing the transmission capability of UHV AC lines have been discussed, including the synchronous stability, voltage and reactive power control, series compensation and shunt compensation. The short circuit ratio for AC transmission system is proposed in this dissertation, which accurately describes the influence of the two end systems upon the transmission capability. From the above analysis, a set of curves reflecting the relationship between the transmission capability and the transmission distance has been developed, which can be used in electric power system planning and design. On the other hand, through the analysis of the simplified AC/DC interconnected system model, the transmission capabilities of UHV DC systems connected to weak AC systems have been studied in detail. The concepts and their computation algorithm of the maximum power curve, the maximum available power, the critical short circuit ratio and the boundary short circuit ratio are discussed. The strength classification of the connected AC systems according to the critical short circuit ration and the boundary short circuir ratio is proposed in this dissertation.(2) 2/3 of China's exploitable hydro resource lie in Sichuan, Tibet and Yunnan, which indicates that most hydro-units will be located in southwest regions. 2/3 of China's coal resource lie in Shanxi, Shaanxi, Inner Mongolia and Ningxia, and most planned coal-units will be located in northwest regions. However, 2/3 of electricity demand is at the east of Beijing-Guangzhou railway. Therefore, the converse distribution of resources and demand decides that mass energy devilery from west to east is necessary in China. UHV AC technique is adopted to deliver electricity form Northwest coal-base to North China, Central China and East China demand centers; both UHV AC and DC techniques are used to deliver electricity form Southwest hydro-base to Central China and East China demand centers, which naturally assemble a national UHV AC grid that binds the coal-base, the hydro-base and the demand centers together. The power flows take a picture that stream form north to south or from west to east.(3) On the basis of analyzing the future situation of power flows in China and considering the developing plan of domestic power grids, a scheme for the structure and construction of UHV power grids around the time period from 2010 to 2020 is proposed. It is researched whether if the security and stability performance of UHV grid could meet the requirement of power system security and stability criteria of China. Power system security and stability analysis include: power system power flow ans static state security analysis, transient stability, dynamic stability, influence of serious faults on system stability, reasonable operation schemes and control measures of UHVAC, as well as influence between UHVAC and UHVDC transmission system and system security on both sides, reactive power balance and voltage regulation, short-circuit current, etc. In a word, the development of UHV transmission has obvious economic benefit ans social benefit. It is in line with the requirement of economical development, clean development and safe development and is thus the inevitable road for the sustainable development of China's electric power industry.(4) Currently, most of our nation's power grids are interconnected. There are four major nationwide synchronous grids, which are Northeast-North-Center China, East China, Northwest China, and South China grids. In the planned future synchronous power grid, the Northeast-North-Center China grid will be adjusted to North-Center-East China grid, and using UHV grid as backbone, four major synchronous grids, which are North-Center-East China, Northwest China, Northeast China and South China grids, will be formed. Interconnected UHV synchronous grids have such benefits as long-distance and large capacity power transmission; facilitating hydro and thermo power supplementation among large areas and drainage areas; provide grid support for optimum resource allocation; avoiding dynamic stability problems that exits in 500kV AC lines when connecting large grids; solving 500kV grid short-circuit current over limit problem.
|
PDF Full Text Request