Study on distribution characteristics of surface potential in extra-high GIS

Extra-high (EHV) transmission system has the characteristics of high voltage and large capacity, and a high amplitude current will be generated through the grounding line and ground net when failure occurs. Step voltage caused by the diffusion of fault current in soil is an important parameter affecting the normal operation of the system. The calculation and analysis of the step voltage in IEEE Std 80-2000 standard is rough, unable to reflect the soil surface potential distribution in substation comprehensively. This paper present an algorithm combined transmission line theorem and finite element analysis to calculate the electric potential distribution accurately, getting the attenuation law of surface potential and the step voltage. Analysis shows that the soil surface electric potential is well-distributed in normal operation and the step voltage is very small, only a dozen volt; The potential value can achieve kilovolt during short trouble and there will be a great attenuation within one meter; Soil resistivity, earth current amplitude and buried depth of ground net are the important factors influencing the surface potential distribution and step voltage.