Research On The Retrofit Technology Of Small Resistance Grounding Mode In Medium Voltage Distribution Network

Every kind of grounding method has its special application conditions.Most of the distribution networks in China adopt the form of small current grounding.However,due to the rapid development of the city,many serious problems have been exposed successively.It is one of the solutions to change these distribution networks to small resistance grounding mode.At the same time,the reform scheme is studied in this paper.In this paper,the application status of neutral grounding at home and abroad is described,and three grounding modes,which are ungrounded,and the electrical properties of three grounding modes are analyzed when single-phase grounding fault occurs.In the process of reconstruction,the selection of grounding resistance and relay protection are studied.Then the value range of limiting grounding resistance value is considered from the point of view of system technology and safety.Then the function between device cost and grounding resistance value is constructed to define the grounding resistance value with the lowest cost as the target.The optimization scheme is given for the protection of the main equipment.The fault trip rate model is constructed according to the different kinds of lines,and then after the detailed analysis of the grid structure and automation degree,the indexes related to the reliability of power supply are calculated,and then the goal of technical evaluation is realized.Finally,the whole life cycle cost model is constructed,and the economy of the reconstruction scheme is evaluated.