Research On Flexible Compensation Of Arc Suppression Coil And Fault Line Selection Technology In Medium Voltage Distribution Network

Distribution network connects transmission network and terminal users,and its fault handling level determines the reliability of power supply to a certain extent.Among the faults occurring in distribution network,the single-phase grounding fault accounts for a high proportion.Therefore,rapid arc elimination for transient grounding faults can greatly improve the reliability and security of power supply.The flexible operation mode of distribution network and the continuous improvement of the proportion of cable lines lead to the change of singlephase grounding fault current.As a result,the traditional fixed compensation method of arc suppression coil is difficult to ensure that the compensated ground current meets the requirements due to the inability to track the change of fault current in real time.The flexible compensation technology of arc suppression coil can realize the accurate compensation of the fundamental component of the capacitive current at the fault point by measuring the ground parameters of the system in real time and adjusting the inductance value of the arc suppression coil in operation,so as to promote the arc to go out and avoid further expansion of the fault.For permanent grounding faults,the fault line can be quickly and accurately selected and removed by fault line selection technology to ensure the normal operation of the healthy part of the power grid.The flexible compensation of arc suppression coil and fault line selection in medium voltage distribution network are important technical measures to reduce the harm degree of grounding fault,and play a very important role in improving the safety,economy and reliability of power supply in distribution network.In view of the problems existing in the flexible compensation of arc suppression coil and fault line selection,the main work of this paper is as follows:(1)The working principle of resonant grounding system is analyzed.Firstly,the arcextinguishing principle of resonant grounding is analyzed from two aspects:compensating grounding capacitive current and reducing the recovery speed of fault phase voltage.Then,the neutral displacement voltage of resonant grounding system during normal operation is analyzed,which provides a theoretical basis for the design of flexible compensation strategy of arc suppression coil.(2)The flexible compensation strategy of master-slave arc suppression coil is designed.Firstly,aiming at the problems existing in the signal injection method,a novel earth capacitance measuring method for distribution network based on direct signal-injection at neutral point is proposed,and the calculation formula of the earth capacitance is derived.According to the actual topology and parameters of the 10kV distribution network under the jurisdiction of a power supply company,a distribution network model is built in PSCAD/EMTDC simulation software,and the simulation and error analysis of the proposed measuring method are carried out.Then,the influence of asymmetry of system parameter on the direct measuring method is analyzed.A novel earth capacitance measuring method in distribution network based on adjusting single-phase additional resistor is proposed.The calculation formula of the earth capacitance is derived.And the simulation and error analysis are carried out by simulation model.Finally,a flexible compensation control strategy is proposed for the master-slave arc suppression coil based on switch switching,and the effectiveness of the proposed strategy is verified by the simulation model.(3)The method of line selection for single-phase grounding fault under flexible compensation technology is proposed.By analyzing the steady-state and transient characteristics of single-phase grounding fault under the flexible compensation of arc suppression coil,it is concluded that the steady-state fault characteristics cannot be used for fault line identification.Based on the characteristics of high similarity between the transient zero-sequence full current waveforms of the healthy lines and low similarity between the fault line and the healthy lines,and combined with the discrete Fréchet distance and the average discrete Fréchet distance,a grounding fault line selection method for distribution network based on the similarity of transient zero-sequence full current waveform is proposed.Finally,the accuracy of the proposed line selection method is verified based on the simulation data and the recorded data of manual fault test in Luohe real model proving ground.