Research On Fault Location Method Of Single And Three-phase Hybrid Distribution System

In recent years, the national power grid company attached great importance to the development of the single-phase power distribution and application technology and promoted the application of single phase distribution transformers in urban and rural power grid continually. After adding the single phase distribution mode, the low voltage distribution system presents a pattern of single and three-phase hybrid power distribution. Single-phase distribution has the characteristic of small capacity, dense distribution points and short radius that lead to the more branches in single and three-phase hybrid distribution system. Its network structure becomes more complexity, and the fault location becomes more difficult. At present, study on the single and three-phase hybrid distribution system is still rarely. So based on the characteristics of the single and three-phase hybrid distribution system, this paper chooses suitable methods of line selection and fault location for study, and improves the shortage of the methods. The main contents are as follows:Research the method of line selection and fault location based on AC signal method. Analyze the influence of distribute capacitance and distribute inductance and to AC signal. Study the relationship between the effective location distance and fault grounding resistance, signal frequency with theoretical derivation and simulation Based on the characteristics of system added the single-phase power distribution. After adding the single-phase distribution, the length of the lOkV line increases, which lead to more outstanding effect of distribute capacitance. Aim at this problem we can cut off the fault line first, then find the fault point with the method that fixing fault segment with DC signal and fault position with AC signal. This method combines the convenient detection of AC signal method and the reliability of DC signal method effectively and achieves the complement of the two methods. Then build a model of single and three-phase hybrid distribution system based on MATLAB, and research the case of line selection and the method of fixing fault segment with DC signal and fault position with AC signal by simulation. The result shows that:the AC signal method has its applicability for line selection and fault location. The combination of the two signal methods improves the efficiency and precision of fault location.After adding the single-phase power distribution in the lOkV small current grounding system, the short circuit current will not increase. The line selection methods based on steady-state voltage and current are easy failure. In contrast, though the transient process time is short, the transient signal is rich in features which can be used to choose the line. Wavelet analysis can accurately handle the signals and is sensitive to transient mutation and weak change of signal, so I choose the wavelet analysis to extract the effective frequency band from transient signal to select the fault line. First, disposing the zero sequence voltage of the bus-bar with wavelet transform and using the wavelet transform modulus maxima to determine the fault occurring time. Then, disposing the zero sequence current of each line with wavelet transform and using the size and polarity of the wavelet transform modulus maxima to select fault line. Verified by simulation that this method breaks the limit of the fault ground resistance’s size and the neutral-point grounding way. It is sensitive and reliable and suitable for the Single and three-phase hybrid distribution system.Because of the discontinuity and the variety of the arcing fault, it is always a problem in fault line selection. In this paper, I studied a lot about the arcing fault of the small current grounding system. Through large number of simulation, I get that wavelet transform can handle the arcing fault effectively, and select the fault line accurately.At last, this paper proposes to combine the line selection method based on AC signal with it based on wavelet transform to reduce the failure rate of the line selection. The simulation proves that the improved method can work well.