Research On Neutral Grounding In Medium-Voltage Power Grid Of Tianjin

Grounded mode of power system related to technical, economic, security and other various aspects is one of the foundations of security and stability operation of the system. It is of great significance to the security and economic operation of the power system. With the growing capacity and increasing voltage levels of the current distribution network, the original neutral point grounded mode has become increasingly unable to meet the requirements for the development of the power system. Therefore, it is necessary to fundamentally research better grounded mode of the neutral point and, solve the technical difficulties of all the modes so as to further enhance the security and economic operation of the network.This thesis deals with this problem, aiming to find the deficiency of existing method and probe for more effective criteria. At first, the grounding principles and basic characteristics of three kinds of grounded mode (ungrounded, grounded through a resistance, compensated grounded) currently used in medium voltage network are analyzed in detail. The SimPowerSysterms toolbox of MATLAB are used to simulate the single-phase to earth fault to make quantitative analysis and comparison to the basic characteristics of medium voltage network with different grounded modes and approximately define the bound of every mode.In the course of operation, each neutral point grounded mode has its own problems that require attention. In this paper, the location of fault line with ungrounded and compensated grounded, the principle of the resistance selection and the cooperation of the relay protection are discussed in detail. At last, the operation test of a transformer substation with a neutral point grounded through a resistance validates the feasibility of this grounded mode.