Simulation And Experimental Study On The Influence Factors Of Step Voltage After Grounding Fault In Distribution Line

All the time,the electric shock accidents caused by the grounding fault of the distribution network line happen frequently in China.With the increasing growth of the distribution network line length,it is inevitable that the distribution networks line pass through the highdensity crowded areas,which means that the hidden danger of the grounding fault is more and more prominent.The step voltage is the key parameter to characterize the damage degree of the electric shock.On one hand,it is affected by the distribution system structure.On the other hand,it is also closely related to the grounding environment and the state of the electric shock.Therefore,it is of great significance to establish the calculation model of step voltage under the combined influence of these factors,to study the distribution characteristics of step voltage and to put forward corresponding protective measures.Above all,this thesis derives the coupled model between grounding current and step voltage for different single-phase to ground faults in power system,and the model is calculated by the algorithm.The error values of the grounding current between the joint method and the professional power system simulation software are less than 3%.The error value of step voltage calculation between the coupled method and professional electromagnetic field simulation software are less than 5%.The error values of the step voltage between the coupled method and the experiment are less than 10%.All of these error values verify the correctness of the model.The coupled model solves the problem that the current grounding fault analysis needs to be manually switched back and forth in a number of professional calculation softwares in different fields,and realizes the consideration of the comprehensively influence among power system,human circuit and electromagnetic field in the ground.Besides,it solves the problem that the current calculation methods can’t solve the current and step voltage after the non-metallic grounding fault at the both ends of the single-phase broken line.The coupled model provides the basis for the subsequent step voltage impact analysis and protection under special working conditions.In addition,a simulation experiment platform of distribution network grounding fault is built.Then based on the experiment and simulation,the influence of different electric shock area,the depth of human foot into the soil,human impedance,the length and the buried depth of the grounding line are analyzed.Besides,the influence of different soil environmental parameters are studied through the coupled model.At the same time,based on the combination of the coupled model and the finite element software,the effects of different special grounding ways are considered,such as earthing device,concrete tower and both ends of the broken wire,and different soil environmental parameters.The characteristic analysis can provide reference and basis for further step voltage risk assessment and protection research.Furthermore,in order to study the distribution line grounding fault in farmland,the resistivity of farmland soil model under the influence of water infiltration was established through the typical clay moisture content and soil resistivity test experiments.The effects of different grounding state,water level and saturation layer thickness of farmland were studied.Finally,the step voltage risk reduction protection was studied for the direct earth fault of distribution network,the earth fault of grounding device and the earth fault of concrete tower.