| The neutral Non-effectively grounding operation is widely used in China’s Distribution Network, which includes Neutral point grounding and neutral grounding via arc suppression coil.As the requirement of urban planning in recent years, a large number of cable lines are accessed to distribution network, which makes the system capacitive current greatly increased. Therefore,the problem of fault line selection in cable-overhead hybrid line has been a hotspot issue in recent years.Firstly, this paper analyzes fault steady state and transient characteristics of the small current grounding system, and introduces distribution of the transient zero sequence current. A new method for fault line selection based on HHT and Fractal Correlation Dimension is proposed to avoid the fault line selection algorithm in a "wrong selection" and other issues, when different fault situations occur. Firstly the transient zero sequence before and after the 1/8 cycle of each line is decomposed with EMD to get its IMF components when single-phase grounding fault occurs. Extract the highest frequency of the IMF components for mutating detection, and select the fault line through comparing mutating polarity. By computing the instantaneous frequency and instantaneous amplitude of each IMF components and comparing with the free oscillation frequency of transient zero sequence current, the main components of the IMF can be selected and then reconstructed. In order to avoid the impact of current transformer, the fractal correlation dimensions are calculated with the reconstructed signal, the 1/8 cycle date of which is selected before and after the failure. The selective criterion is formed by comparing the size of the correlation dimension in the different embedding dimensions. Achieve correct location through the comprehensive decision-making of two kinds of route results. At last, simulating validation of the method, the simulation results show the effectiveness and the accuracy of this method. |
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