The Research Of Small Current Single Phase To Earth Fault Selection In Small Current Grounding System Based On Wavelet Analysis

Non-ground neutral or by the arc suppression coil grounding way arewidely used in our country’s6to35kv power network, this kind of powerdistribution system is called the small current grounding system. In thissystem, the probability of single-phase ground fault is relatively large.Timely and accurately select fault line is of great significance to improvepower supply reliability. The small current grounding system has a veryimportant advantage that the current after single phase to ground is verysmall. But this became a very adverse factor for fault line selection. Theweak ground current tends to be annihilated by noise. Until now, there isnot a very perfect theory for line selection. With the distributionautomation’s level improvement, the further research for this problem isalso becoming more and more urgent.To the question of single-phase earth fault line selection in smallcurrent grounding system, this paper reviewed the existing method, andthen points out their shortcomings and insufficiency. Analysis the neutralindirectly grounding system, neutral the arc suppression coil groundingsystem and neutral the high resistance grounded system’s transient andsteady state characteristics when happen single-phase ground fault.Explicited the research direction that using transient to select fault line.Wavelet analysis as a new signal processing tools, can analyze thesignal in time domain and frequency domain at the same time, superior tothe traditional Fourier transform. It will have a broad application prospectin electric power system’s transient signal processing. This paper studiesthe wavelet theory and wavelet packet analysis theory, based on waveletpacket analysis, proposed a line selection method which uses the faulttransient amount. This method makes full use of the transient zerosequence current and zero sequence voltage, theory foundationimprovement. Using the simulink toolkit built a simple distributionnetwork model which has five lines. Simulated the single-phase groundfault in neutral indirectly grounding system and neutral the arcsuppression coil grounding system. Through change the neutral pointgrounding way, switching angle and grounding resistance in simulation to test the effect of the fault line selection method which is proposed thispaper. The result shows that this algorithm is accurate and reliable.