Method Of Medium And Low Voltage Network Based On Vulnerability Of Power Network Structure

City grid is an important part of power system as well as an important infrastructure for the city.With the rapid development of economic construction,urban electricity loads are growing rapidly,and the reliability requirements from users are getting higher and higher.These demands lead to more and more pressure on power enterprisesfor the reliability of the grid is not as expected and the efficiency of investment becomes very low.According to the characteristics of urban power grid,this paper puts forward a scientific index system and an evaluation method,which can provide effective decision support for planning and operation personnels,escort the safe and efficient operation of power grid,and ensure the development of power grid could maintain social harmony and stability.First,the idea of "seven steps" to construct the evaluation index system is introduced,under which guidance the evaluation index system of urban power structure fragility is established and the indicators are optimized.These indicators are classified according to their influencing factors and the evaluation index system of urban power structure vulnerability with a hierarchical structure is obtained.However,the number of evaluation indicators at the bottom is large.The dimensions of indicators are also different that will lead to confusion.The evaluation needs that indicators are dimensionless,so as to facilitate the unity of the system risk score.The evaluation indice at the bottom are divided into three categories with their respective specific scoring criteria.Secondly,this paper presents three methods to evaluate the structural vulnerability of urban power grids--the analytic hierarchy process,the artificial neural network and the method integrated from them.While these three methods have their own advantages and disadvantages,users should choose the method based on the situation and requirements.Finally,the author evaules the structural vulnerability of urban power grids in Yangquan City,Shanxi Province,and analyzes the results that suggesting the fragile points of the urban distribution network structure,which provides scientific and reasonable technical support for the urban distribution network planning.This method will be the basis of urban distribution network planning.