Grounding Failure Detection Based On Wavelets Method In Resonant Grounded Power Distribution System

Neutral non-grounded and Petersen-coil grounded systems are also called neutral un-effectual grounded system (NUGS), and they are widely used in 35 kV power distribution network in China. It is the single phase to earth fault that takes place in the distribution system with most probability, accounted for 80 percent of the system fault.But the different kinds of grounding methods and random disturbance is predominant influence in faulty line selection. To date, there is still a lack of a more reliable fault line detection method device for detecting earth fault line and a more accurate device, the problem of fault line detection for single-phase-to-earth fault would threaten the power supply reliability.For this reason, this thesis introduce the principles of various available methods of fault line selection and their traits,and the advantages and disadvantages of methods of fault line selection were analyzed and compared.Analysis and study the transient process after single-phase-to-ground fault. The results of analysis show that transient currents is much larger than steady currents, the neutral point grounding method is unacted on transient currents. On this foundation we introduce the wavelet analysis, wavelet analysis is the most outstanding research achievements of mathematics , that is a kind of time-frequency analysis method. After researching wavelet analysis character, we can raise four principles that the choice wavelet function in single-phase ground fault. Base on Sampling frequency , it selects the special frequency band, the singularity detection with db wavelet packet is employed to obtain the polarities and magnitudes of the abrupt of current , and through comparing the polarities and magnitudes the fault circuit can be determined.This thesis introduces a novel fault circuit selecting method, which utilizes Matlab 7.0 to build 35 kV Distribution Network simulation models, and then utilizes wavelets transform to obtain useful fault transient components. In the simulation, parameters such as grounding position, switch angle, grounding resistance, grounding distance, are all taken into consideration. After Simulation experiment, this method is proved correctly and can be carried out simply, as well as its good practicality prospect.