Reducing the impulse grounding resistance of transmission line tower grounding system is the major measure to improve the lightning impulse withstand level and to ensure power system stability. For tower mainly adopts box with radiation grounding devices, this paper uses simulation experiments method based on similarity theory, researches the influence of radiation length, radiation angle and the proportion of box and radiation, branch length on the box with radiation grounding devices' impulse

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... characteristics in layer soil model. Results of the experiments show that the branches have an effective use of length, the box and radiation have an optimal proportion, over length radiation or improper proportion will render the resistance reduction ineffective. According to the results of the experiments, we have gotten the optimal length rays add branch and put forward an impulse characteristics features better tower grounding structure which is named T2-15-25&H2-15. There are some references for engineering.