Small Current Grounding System Based On Matlab, Automatic Line Selection Simulation Study

Indirectly grounded power system is widely used in medial and low voltage distribution networks in the world (including the neutral point is not grounded, by the Petersen-coil or by high resistors), which is benefit to improve the reliability of power system, because its characters that fault current is low and the system can continue to provide power to load while single-phase ground fault occurs. There isn't existed an effective method to select the fault line nowadays, which has been an important task for the relay protection researchers of power system. It is difficult to detect the signals while single-phase ground fault occurs, because the fault current is small and the electricity arc is instability. With the research and development of power automation, it has become more and more important to verdict the fault line correctly and promptly by auto-mechanism.This article firstly introduces the neutral point connection mode of power system, analyzes the fundamental principle and its function characteristics of the three modes, and compares the parameters of each mode synthetically. On the basis of analyzing the transient and steady electric parameters in indirectly grounded power system while single-phase ground fault occurs in detail, summarizes the most fashionable protection schemes for single-phase ground fault briefly. Each scheme' s basic principle and limitation was also shown. Particularly discusses the zero-sequence current comparative scheme, zero-sequence power scheme, fifth harmonic scheme and the "signal input" method in detail. Analyzes their principles, merit compared with other schemes, problems still exist and their practical applications. Furthermore, an unify simulated model of indirectly grounded power system is established in this paper, set equal line parameters and simulation parameters, based on the principles of the above four selecting line methods with the Simulink package of Matlab. Presents the simulation results and the waves of primary parameters. Finally, points out the main problems of the auto-selection fault line methods and theirs development orientation in the future.