Study on lightning simulation model of transmission lines with characteristic of flow dispersion in soil

Lightning is the main reason that endangers the safety and reliability of transmission line, and impulse grounding resistance is the main factor that affects the lightning withstand level of line. The common calculation method of impulse grounding resistance multiplying power frequency resistance by impulse coefficient is widely accepted in simulation model, and assumes that it is constant. However, based on a number of experiments has approved that the impulse grounding resistance should be time varying under the effects of impulse characteristic of flow dispersion in soil. This paper proposed a new simulation model with time varying impulse coefficient. Firstly, time-difference voltage is obtained from calculating the voltage difference by using time varying or constant impulse coefficient between two ends of the impulse grounding resistance. Then the resistance model is revised by adding the parameter, and the flashover criterion also is updated. Finally, a new EMTP simulation model with characteristic of flow dispersion in soil is built.