| With the development of power system it becomes more impotent to reduce the loss of power network. People give attention to optimal reactive power gradually. The target of common optimal reactive power is economy. When the structure of power network becomes more and more complex and the demands of load increase rapidly,the accidents about security happen frequently. This will refer to security which is the most impotent thing for the whole power network; therefore, it is necessary for optimal reactive power to consider both economy and security.The thesis makes a brief overview of the history and current status of the research on volt/var control. The methods of volt/var control and their advantage and disadvantage are introduced. The theory of optimal reactive power is discussed. Algorithm of optimal reactive power and its advantage and disadvantage are analyzed. The research about security and the index of security are introduced.In order to make the power system more secures and economic, the security is added into object function of the optimal reactive power to combine with the economy. The hierarchical reactive power optimization considering security on area is proposed. Power network can be divided into upper grade and lower grade. Different index of security assessment is considered in each grade according its characteristic to indicate the secure state of this grade. The grades are divided to many areas and sub areas. Because of the different characteristic in each area and sub area, their values of the security index are different; the index of security assessment is calculated in each region and is used in security object function to complete the optimal reactive power.Different formula of security assessment can be used in different grade to quantize the state of security; hence the hierarchical reactive power optimization considering security on area is composed. The effectiveness of the optimal reactive power in this thesis is verified by sample.
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