Research On Single-phase Grounding Fault Differential Line Selection Method For Small Current Grounding System

China’s distribution network generally adopts small current grounding operation mode,and single-phase grounding fault is the multiple failure of this kind of grounding operation mode.Because the fault signal is weak,it is easy to be interfered by various complicated situations,and the transient quantity signal after the fault occurs.The extraction of features is very difficult,so the selection and location of faults has become a difficult point in relay protection research.With the development of living production,it is very important to quickly and accurately select the fault line and determine the fault location,especially for places with high safety requirements such as industrial and mining.Aiming at this,this paper proposes a line selection theory based on steady-state signal difference to solve the existing problems of the existing line selection method,which has important theoretical significance and practical value.Firstly,the paper analyzes the fault line selection and positioning methods of relatively mature small current grounding systems that have been proposed so far,and the applicable scope,advantages and disadvantages of these methods.At the same time,the small current grounding system is analyzed,including the neutral point ungrounded,the neutral point through the arc suppression coil grounding and the neutral point through the resistance grounding mode,the different characteristics of the zero sequence fault current when single phase ground fault occurs.Secondly,on the basis of summarizing the characteristics of fault current zero sequence current of different grounding methods,the principle of differential line selection based on neutral point compensation is proposed.The zero-sequence network of the system is changed by setting the neutral point,and the faulty line is judged according to the characteristics of the steady-state zero-sequence current at the time of failure.The characteristics of the steady-state fault signal difference before and after the neutral point are compensated under different compensation modes,and the fault criteria are summarized.Then,based on the principle of line selection,the criterion of fault interval location is proposed by using the mutual cooperation between line selection devices.At the same time,the variation of the grounding current of the fault point under the condition that the compensation neutral point is grounded by different compensation components is analyzed,and the compensation parameters are adjusted appropriately to meet the requirements of safety and sensitivity.Finally,the MATLAB/simulink software is used to simulate and simulate the principle of differential line selection.The simulations verify the correctness of the fault criterion under different compensation modes at the neutral point.At the same time,according to the simulation results,the neutral point compensation difference is proved.The reliability and sensitivity of thedynamic selection line and positioning principle,and then the 380 V distribution system model was built in the laboratory,and the zero-sequence current transformer was used to measure the difference between the steady-state fault components before and after the compensation of the neutral point.The experimental results also proved the theory.The correctness has theoretical guiding significance for the practical application of the line selection method in the future.