Research On The Application Of Dynamic Grounding Device For Neutral Point Of Distribution Network

In order to meet the requirement of distribution network of both power supply reliability and power supply security,we have developed a dynamic grounding device for neutral point of distribution network.The device combines the advantages of arc suppression coil grounding mode and grounding resistance mode.When the instantaneous grounding fault occurs,the device works in the arc suppression coil grounding mode,and controls the residual current to make the arc extinguish,so that the system can resume normal operation.When permanent ground fault occurs,the device switch to the resistance grounding mode to quickly select the fault line and remove it.The development of the device has been completed.But before large-scale application,it is necessary to make further research on the dynamic switching time,setting of the grounding resistance value,the capacitance current measurement method,communication function,and so on,then improve the function of the device.The setting of device dynamic switching time is closely related to the critical arc blowout time of single-phase earth fault.Therefore,the article uses the single-phase earth fault arc extinguishing simulation experiment to get the arc blowout time in the different insulation level when the fault current is different,and then setting the dynamic switching time.In 10 k V simulation of distribution network,set up simulated single-phase grounding fault point,access the fuse near the insulator,through fuse arc,simulate the insulator flashover.Adjusting the fault point current,through the experimental method to get the arc extinguishing time of P-15,P-20 two kinds of typical pin type insulator in different fault current.Using statistical theory to analyze test data,get the arc blowout time of which the confidence level is 95%.Arc suppression coil grounded system by increasing the resistance grounding branch,toggle switch,and the corresponding controller can be transformed into dynamic grounding mode.The resistance grounding system can also be transformed into dynamic grounding method through increasing the arc suppression coil branch,toggle switch,and the corresponding controller.In addition,considering from many aspects like the select fault line,fault current limiting,inhibition of arc grounding overvoltage multiple,the grounding resistance value should be less than or equal to the system capacitance to earth.Through the PLC of the Modbus communication module,complete the Modbus communication design,realize the basic communication function,and then through the protocol converter to realize the communication requirements of different communication methods.By cutting in arc suppression coil bar series damping resistance,causing the change of arc suppression coil branch current and voltage,then collecting the current and voltage of arc suppression coil branch to calculate the capacitance current value of the system.The single-phase earth fault arc extinguishing test was carried out in 10 k V simulated distribution network in Luohe City,Henan province,and the arc extinguishing time of P-15,P-20 two kinds of typical pin type insulators in 13 A,16A,18 A,21A fault current under the95% confidence has gotten.Then depending on lines at different insulation level,setting the corresponding dynamic switching time.The advantages of dynamic grounding method is verified by means of simulation.The simulation results show that this capacitive current measuring method has higher precision.Designed Modbus communication based on S7-200 PLC,which laid a foundation for communication between different specifications.Through the research of this paper,the function of the distribution network neutral dynamic switching device has been further improved.