Research On Single-phase Grounding Protection Technology For Low Resistance Grounding System

With the rapid development of the domestic economy,the demand for electricity continues to increase,and cable lines are used in large quantities in the distribution network,resulting in a sharp increase in system capacitance current.Some developed cities in China have changed the original distribution network grounding mode to the low resistance grounding method.At present,the mainstream of single-phase grounding protection for low resistance grounding systems is zero-sequence over-current protection.When other lines have a ground fault,the zero-sequence over-current protection of this line is set to prevent misoperation,and the setting value is set according to the capacitance current flowing through the line in the area when the metal ground fault occurs outside the line,so action current of the zero sequence over-current protection is relatively large.Therefore,a grounding protection problem is caused,that is,when a high-resistance ground fault occurs,since the fault current is relatively small,the fault current is smaller than the zero-sequence over-current protection setting value,and the grounding protection is likely to be rejected.At the same time,the arc grounding fault also affects the stability of the distribution network to a certain extent.In view of the above-mentioned high resistance ground fault problem of low resistance grounding system,the grounding protection technology of the low resistance grounding system is studied.Studying the zero sequence current and phase current abrupt of high resistance ground fault in small-resistance grounding system,the RMS value characteristics of zero-sequence current and break-variable of phase current are theoretically analyzed and studied.The waveform characteristics of the zero-sequence current and break-variable of phase current are studied by using the ground fault field test data of a real-type experimental field,and the similarity characteristics of the zero-sequence current and the break-variable of phase current are obtained.After the ground fault feature is quantified by mathematical method,the construction method of the ground fault feature matrix is studied.The effective values of the zero sequence current and the break-variable of the phase current after the fault are calculated,and the ratio of the zero sequence current is obtained as well as and the phase current abrupt,and the magnitude characteristics of the effective value are quantitatively analyzed.Based on the fractal theory that can strongly analyze nonlinear objects,the fractal dimension of zero sequence current and phase current abrupt is calculated,and their similarity characteristics are quantified.Study the principle of arc generation,based on energy balance theory,the Mayr arc model is built using Matlab/Simulink simulation software to simulate arc ground faults.At the same time,the distribution network model of 10 kV low resistance grounding system is constructed,and the grounding faults and arc grounding faults of different transition resistances are simulated to obtain simulation data.According to the construction method of the ground fault characteristic matrix,the ground fault feature matrix is constructed by using the simulation data.The K-means clustering analysis method is used to analyze the ground fault feature matrix and get the cluster center of the fault cluster and the non-fault cluster,The grounding protection technology of small resistance grounding system based on fractal theory and cluster analysis is proposed.The method is validated by using the true test data.The results show that the method has better applicability to high-resistance ground faults.The resistance to resistance is theoretically up to 2000 ?.