Analysis On Structure Of The UHV AC/DC Hybrid Grid In Hunan

Since Hunan province is lack of primary energy, not only can the UHV project provide more energy, but also reduce the shortage of power and alleviate the energy scarcity problem for Hunan, to which a great impact of security and stability on the current power system can also be cuased. How to keep the security and stability of grid is much important while Hunan power system accepts the UHV power. Because the network structure of power system is the decisive factor of system stability, a reasonable UHV construction sequence should be determined in the design stage in order to improve the reliability of the network structure as well as the level of system security and stability.After briefly describing the economic development of Hunan province and the status and characteristics of Hunan power grid, this thesis analyzes the main existing problems which mainly include:power shortage due to lack of primary energy, less reasonable power layout reasulting in the receiver system lack of support, larger ratio of hydropower increasing the difficulty of adjusting grid operation mode, increasing significantly input power from other provinces making the tie lines between provinces overloaded for a long time. Based on the power demand forecasting results of Hunan grid in2015, the power balance analysis without the UHV is performed, it is shown that power supply shortage will appear in2015. Therefore, construction of the UHV can eliminate this situation and thus reduce the power flow on the tie lines. Additionally, this thesis also analyzes the economy of the Hunan UHV project in both aspects of the operating efficiency and cost of electricity purchasing, and it is verified that the UHV is economical.According to the planning data of Hunan power grid in2015, two kinds of power grids, the grid with the UHVAC built firstly and the grid with the UHVDC built firstly, are modeled seperately by using the software of PSASP based on the typical load level in summer. Afterwards, the rationality of each power grid plan is evaluated in four aspects, such as power flow calculation, short circuit calculation, static security analysis and transient stability analysis. In addition, The solving measures are proposed by comparing and analyzing the main problems appearing in each power grid. With analyzing and comparing the calculation results of the two power grids, it is easily found that constructing UHVAC firstly is more conducive to the safre and stable operation of Hunan power grid and can also improve the transmission capacity of the tie lines.