The Design Of Small Current Grounding Line Selection And Its RTDs Simulation Research

In China,medium and low voltage(3~66kV)distribution network mostly adopts two small current grounding methods in which the neutral point is not grounded and the arc suppression coil is grounded.In distribution network,grounding faults occur frequently,of which singlephase grounding fault accounts for 80%.If not handled in time,it will easily cause phase-tophase short circuit,which will expand the accident and affect the reliability of power supply.At the same time,ensuring the safety of life is the primary task of power grid operation and management.Distribution network is distributed in densely populated areas and human activity areas,which is prone to electric shock accidents.In recent years,the death rate of electric shock occurred in medium and low voltage distribution network in China accounts for about 95%.When single-phase grounding fault occurs in distribution network,the small current line selection device can achieve rapid line selection and fault removal.Therefore,the standard design and stable operation of low current line selection device are of great significance to improve the automation level of power system operation,eliminate hidden dangers of personal safety and avoid the expansion of accidents caused by grounding overvoltage.In this paper,the steady-state process and transient process of single-phase ground fault in small current grounding system are analyzed firstly,and the basic characteristics of single-phase grounding fault in small current system are studied.Combined with the actual operation of the grid,aiming at the problems of imperfect function and low accuracy of the small current grounding line selection device,the function of line selection of the device is further optimally designed and studied,and the post acceleration and tripping-switching functions are put forward and realized.The designed function enables the small current line selection device to remove the fault line automatically,accurately and quickly under the conditions of a line reclosing in a permanent fault,a trip line selection failure,and high resistance grounding fault.Then,a unified operation management method is developed for the new type of small current line selection device,so that the small current line selection device can be unified,standardized,and ordered in operation.On the basis of the above,the RTDS(Real Time Digital Simulation)simulation model of the small current grounding line selection system is established and connected with the actual grounding line selection device to form a closed-loop real-time simulation test system.Experiments on different kinds of grounding faults in small current grounding system are carried out to test the correctness of the new type of grounding device,which provides important technical guidance for the engineering implementation of grounding device.