Single-phase Ground Fault Line Selection Of Small Current Grounding System Based On Wavelet Analysis

Neutral non-effective grounded system is widely adopted in power distribution networks of 6~35kv in China , it also called small current grounded system, and the single-phase-to-earth fault happens most frequently in the system, almost 80% of all faults in the system. During occurrence of the fault, the voltage of the grounded phase down to zero and the voltage of the ungrounded phase up to the line voltage. Since the line voltage is still symmetrical under fault conditions, the systems can keep operating for two hours. However the fault line must be detected quickly to avoid more seriously fault and destroying devices. The fault line detection is a difficult problem, especially in the resonance-grounded power system, because the small fault current and arcing effect etc. So the research of the fault line detection is very necessary and valuable.This paper analyzes the steady and transient process of the small current grounded power system, especially details on the resonance-grounded power system. And introduces a novel fault line select method—adaptive magnitude and phase comparison utilizes fault transient components based on the wavelet transform method. The method utilizes fault transient components, for the transient components are much larger than the steady components.The transient signal is high frequency and unsteady, the Fourier transform cannot process this signal well. However the wavelet transform can process it prefect for its localization character in time and frequency domain. Therefore this paper processes the fault transient components based on the wavelet transform.The paper makes a model of the small current grounded system and simulates it. The result of the simulation proves that the method is correct and effective.