Substations have a large number of signal transmission cables beneath the ground. Both the insulation safety and signal reliability of the cables are affected severely by the electromagnetic field. Under high-amplitude impulsive currents

the dispersion of currents can cause soil discharge and thus cause unexpected distortions in an electromagnetic field. This paper focuses on the distortions of the electric field. In general

soil discharge channels occur in the vicinity of the independent rod. Closer development of the channel might enhance the electric field distribution and the potential surrounding the outer insulation of the cables (i.e. the surface potential on the cable). Therefore

this paper establishes a platform for observing the soil discharge channel and measuring the surface potential. Direction characteristic of the channel is extracted from the captured image of soil discharge channels and the surface potential is obtained by the measured coupling capacitive current on the shield experimentally. This paper also presents an improved model considering a dynamic growing discharge channel for the transient analysis of the grounding electrode. Study results show the surface potential increases as the discharge channel approaches the cable. To quantify this enhancement effect

the ratio of the highest to the lowest value of surface potential in different directions is taken as the multiple of the surface potential increase. The calculated multiples of the surface potential increase are in the range of 1 to 1.64 times under different conditions by the improved model. Therefore

taking the soil discharge channel into account is helpful to accurately analyze the impulsive interference of buried cables.