Research On Fault Line Selection Of Small Current Grounding Power System Based On Matlab/Simulink

The characteristic of small current grounding system is that the fault current is small, it is unnecessary to remove the system fault immediately, so the power supply reliability is relatively high, therefore the small current grounding way is widely used in the domestic low voltage distribution network neutral point. However, the characteristics of small current grounding system also lead to failure of fault line selection, due to its fault signal is small, the ability to resist noise is poorer, so it is difficult to extract the characteristic signal during the failure moment of small current grounding system, it is hard to find out the fault line accurately. With the rise of the distribution network automation level, people require better power quality and power system reliability. For fear of occurrences of the grounding fault of the other two phases during the period of single-phase grounding fault, the single-phase fault must be eliminated timely. So the fault line selection of small current system's single-phase grounding fault is particularly important. Even through the reliable methods to select the fault line of the small current grounding system are widely studied at home and abroad and a variety of line selection methods have been proposed, they are not so satisfactory. To study out the efficient, accurate and reliable methods to select the fault line of single-phase grounding fault is imminent.However, the characteristics of modern power system are, ultra-high voltage,large capacity, cross-regional, and the distribution network is a very complex network contains many different voltage grades, including transformers, power distribution lines, and power loads. No matter from the point of view of the hardware or the system security, it is difficult to meet the experimental conditions of electric power scientific research experiments. So the stability of power system and fault analysis are often inseparable from the simulation research, and the current simulation research of the small current grounding system is mainly concentrated on the test of specific line selection methods.In order to find out a more effective method of line selection, firstly, this thesis makes a brief introduction of all kinds of neutral point connection mode of the power system and does an analysis of the small current grounding system in three different basic principles and makes a comprehensive comparison of parameters of these operating ways of neutral point. Secondly, the thesis builds simple simulation models to study of the typical characteristic of single-phase earth fault in small current grounding system. Then enumerate the various existing line selection methods and analyzes their basic principle, advantages and disadvantages one by one, as this thesis mainly focuses on line selection methods based on the theory of wavelet, and analyzes it in detail. Finally, this thesis sets up a small current grounding system containing multi loop simulation model using Matlab/Simulink simulation software package. Setting up parameters of the simulation model and does simulation and analysis for the first half wave method and line selection method based on wavelet analysis theory. According to the simulation results, the main problems of line selection method based on wavelet analysis and its development direction in the future are proposed.