| The main fault type of the distribution network is single-phase grounding faults,of which arc grounding faults are the majority.With the rapid development of urban power grids and the widespread use of cable lines,the leakage current of the distribution network lines to the ground has become larger and larger,thus greatly increasing the probability of failure.The traditional arc suppression coil grounding system can no longer achieve the purpose of reliable arc suppression.Long-term operation of the system with faults will greatly threaten personal safety and equipment safety.In order to deeply compensate the ground current,this paper theoretically analyzes the fault characteristics and ground current expressions of a single-phase ground fault,and analyzes the adaptability of the traditional active voltage arc suppression method and the active current arc suppression method.By demonstrating the law of system parameters in flexible grounding mode,a flexible grounding arc suppression method based on closed-loop control of system ground admittance parameters is proposed.The current is injected through the active inverter to make the system admittance value after the fault equal to the system admittance value before the fault,so as to realize deep compensation for the ground current.In order to obtain the zero sequence parameters of the system,a parameter measurement method based on the zero-sequence voltage closed loop is proposed.Considering the threephase parameter imbalance in the system,the parameter measurement method is optimized.The influence of unbalanced current on the neutral point voltage is theoretically analyzed,and a compensation method for unbalanced current is proposed,which fundamentally solves the problem of unbalanced system zero-sequence parameters.The effectiveness of the method proposed in this paper is verified by digital simulation.For disconnection faults,mathematical models of disconnection faults are not grounded,disconnected and grounded on the power supply side,and disconnected and grounded on the load side.The changes of neutral point offset voltage,bus phase voltage,and phase voltage after a fault in various situations are derived with the changes of system parameters,disconnection degree,and grounding resistance.The reason why the traditional phase selection method based on voltage drop has greatly reduced the success rate in disconnection faults is pointed out.A single-phase fault phase selection method based on signal current injection is proposed,which solves the problem of phase selection under disconnection faults.The digital simulation verifies the accuracy of the voltage relationship under the disconnection fault,and the fault phase selection method obtains a higher accuracy rate in the case of non-high resistance grounding.Based on the energy balance theory,the arc equation under the traditional arc model is derived.According to the characteristics of the distribution network,the arc model is optimized to adapt to the single-phase grounding of the distribution network under a smaller current.Due to the non-linear characteristics of the arc,the ground current contains more harmonic components.Through the multi-frequency admittance method,the harmonic components in the ground current are used to construct the characteristic multi-frequency admittance vector index.According to the direction of the vector index,which has the characteristics of distinguishing between faulty lines and non-faulty lines,effective fault line selection is carried out.In order to make the difference between the faulty line and the non-faulty line more obvious,the principal component analysis method is used to replace the fixed weight method for weight selection,which effectively distinguishes the faulty line from the non-faulty line.The digital simulation verifies the influence of the parameters of the arc mathematical model on the arc,and verifies that the characteristic multi-frequency admittance has a higher line selection accuracy under the arc ground fault.In order to further verify the effectiveness of the proposed method,a set of 10 k V distribution network dynamic model experiment simulation platform was built to verify the method described in this paper.Experimental results show that the closed-loop flexible grounding technology based on zero-sequence admittance parameters can effectively compensate the ground residual current and make it reach the standard of fault elimination.The fault phase selection method based on signal injection achieves a high accuracy rate in the case of a non-high resistance ground fault.Finally,a brief summary of the full paper is given. |
