To study the effect of surface massive soil on the property of a grounding grid and optimize the grounding performance

the software CDEGS is used to simulate the secondary peak of step voltage generated by the surface massive soil.The effects of the surface massive soil parameters

such as the soil length L

the edge gradient tang

and the resistivity p

on the secondary peak voltage are analyzed.Then

a grounding simulation test system is established

the application method of agar gel is improved

and the feasibility of simulating surface massive soil with agar gel is verified.The influences of the resistivity and soil scale on the secondary peak of step voltage is simulated

and the results show that:1)the large area of surface massive soil with low resistivity can reduce the grounding resistance

and cause the secondary peak of step voltage outside the substation at the same time;2)this secondary peak has obvious negative relation with the soil length and the resistivity;3)the larger the scale of the massive soil

the more significant the reduction of the secondary voltage peak via changing the soil resistivity.So in actual construction of substation

the edge of earthwork should be processed to form a smaller slope to reduce actual work amount and save investment.