Research On Detection And Protection Method Of Distribution Network

To ensure the safe operation of the distribution network and realize distribution automation, fault detection and protection of distribution network are important components.Thought the theory of fault line selection has been more mature, problem still confuses us since those methods cannot solve the problem of the detection of low correct rate; what's more, high impedance fault detection is also a problem need to be solved, so researching for this problem is still in its infancy in domestic. The paper analyzes begin fault detection and protection methods, puts forward the method of fault line selection method in small current grounding system and high impedance fault identification.When the single-phase grounding fault happens in the small current grounding system,the transient grounding fault current will contain the whole system's fault characteristics. The main component of the transient phase current of health line is capacitive current to ground,considering the effect of the inductance that resist in the system, the differential current of the health feeder is so small that the waveform between its phase current and zero sequence current's transient information shows significant irrelevant, while the waveform of the fault line shows a significant correlation. Taking advantage of this feature of small current system when there occurs the signal-phase fault, which can be detected by the approximation ratio of the three phase bus voltage through wave transformed, the use of correlation analysis and comparison of each line's transient information differential current and zero sequence current correlation can select out the fault line correctly. The model of an 10 kV distribution network has been built in this paper by MATLAB/SIMULINK, simulation verify the correctness and effectiveness of the method under different fault lines, position, grounding resistance and nature of fault.When the high impedance fault happens in distribution network, the grounding resistance will exhibit the characteristics of non-linear, time-variant and high value, the fault current is small and unstable, the spectrum components is so complex that it is difficult to detect.Time-frequency distribution characteristics of the high impedance fault, low impedance fault and non fault disturbance such as capacitor switching have been analyzed. Since the time-frequency distribution of zero sequence current among fault feeder and other health feeder has a significant difference, there presents a high impedance fault detection method based on the time-frequency correlation. Firstly, generalized S transform has been used to analyze the time-frequency distribution of zero sequence current of each feeder, here obtains its time- frequency amplitude matrix, and the time-frequency energy matrix has been definedon this basis; Secondly, count the relevance among each time-frequency energy matrix and the faulty feeder has the minimum correlation coefficient; Finally, analyzing correlation of the zero-sequence current among each section to determine the fault section. The simulation shows the proposed method can reliably and accurately identify and distinguish high impedance faults, low impedance faults and disturbances caused by capacitor switching under different feeder, grounding point and resistance values, which can work well in detecting and locating the fault in distribution network.