A REALISTIC AND ACCURATE MODEL FOR CALCULATING FOOT RESISTANCE ABOVE GROUNDING SYSTEMS BURIED IN LAYERED EARTH
(0) This paper shows that errors can occur when the widely used IEEE Standard 80 method is used to carry out safety calculations in grounding designs assuming that the surface layer thickness, on which the foot rests, is small compared to the foot dimensions. This paper presents a more realistic foot model located above a grounding system buried in multi-layer soils to account for real soil conditions such as ground conductors’ proximity, surface layer thickness and seasonal variations during conditions where a thin surface layer exhibits a lower resistivity value that the rest of the surface layer. A detailed parametric analysis based on the accurate modeling of the entire earth-gridfoot system is described. The computation results revealed that for soil types with low resistivity top layers over high resistivity layers, the foot resistances computed by IEEE Standard 80 can be larger than the true values by as much as 1300％ causing unnecessary conservative results. When foot resistances are computed with the presence of the grounding system conductors, the foot resistance is reduced, as expected. For the cases studied, the presence of the grounding system reduces the foot resistance by as much as 23％. A case study is presented to examine touch and step voltages at a substation in northern climates accounting for seasonal variations. The safety analysis shows that the worst case scenario occurs during early spring season when the soil is partially thawed. The study shows that by accurately computing the foot resistance accounting for the early spring thawed conditions, the tolerable touch voltage limit is higher due to the increase in foot resistance. In this case earth surface potentials were computed while accounting for this thin wet surface layer.
Foot resistance IEEE Standard 80 multilayer soil electric safety soil resistivity
Sharon Tee Farid P. Dawalibi
国际会议
The International Conference on Electrical Engineering 2009(2009 电机工程国际会议)
沈阳
英文
1-6
2009-07-05（万方平台首次上网日期，不代表论文的发表时间）