Study On Impact Characteristics Of Typical Soils In Yunnan And Analysis Its Spark Discharge

The soil is the decisive factor of the grounding system,in recent years,domestic and foreign scholars carry out a lot of research works on the impedance characteristic of soil.Most of them used sand instead of soil,but ignored the abnormal structure which may lead to differences conductivity in soil.In this paper,through the experiment,the comparative study of the impact conductivity of Yunnan red clay and fine sand is done.And the effect of soil matrix structure on its impact characteristics is proposed.We increase the impact test of different specifications grounding structure in the clay environment,to explore the characteristics of spark discharge of clay.Finally,we analyze the lightning impulse waveform’s effect on grounding electrode grounding resistance combined with the problems in the process of test,to provide theoretical support for unified simplified impact test.Firstly,In this paper,we analyze the conductive mechanism of different matrix structural soil,and set the soil impact experiment platform to study the soil impact properties which affected by different matrix structure by experimental way.Experimental results show that:as for non agglomerated matrix structure of the soil,under the same water content,the soil impact resistivity,critical breakdown strength and breakdown delay time increases with the soil particle size;When soil matrix structure is agglomerated,it’s impulse characteristics does not conform to the rules which non agglomerated has.And under the same water content,the conductivity of the red clay is weaker than sandy soil with uniform particle size.Draw a conclusion that using fine sand alternative soil to carry impact characteristics research of soils is one-sided.Secondly,carrying out different specifications and structure grounding impact test in clay environment,we can get lots of results.Around the shorter grounding electrode,the soil spark discharge is stronger especially than the impulse voltage injected at the end.The influence of grounding angle on soil spark discharge effect is small.The box type grounding electrode can make voltage uniform,and when the box length increases,the surrounding soil’s spark discharge effect will weaken.The smaller surface area of the grounding electrode,the easier soil spark discharge occur.And in the grounding steel used in certain length,box type grounding is better than box + ray type grounding electrode.As for the box + ray type grounding electrode,increase the box length is better than increase the length of ray to reduce the grounding resistance.Finally,we study the grounding sample parameters which affected by different impulse waveform and polarity.And the basis of above rules is analyzed from quantity of electricity,continuity and spark discharge.Experimental results show that:The impact grounding resistance decreases 5%with the time of wave front is reduced by 50%,or the half wave time is reduced by 50%;When the impact polarity is only changed,the impulse grounding resistance under the positive electrode impact is smaller than that of the negative impact,and the maximum decrease is 10%;In ground impact experiment,the impact effect of current waveform control and voltage waveform control is consistent,that is,the increase of voltage or current wave energy of wave crest area will make the slight fall of impact resistance.