Reducing impulse grounding impedance of grounding devices can effectively heighten lightning prevention level of transmission lines

while the reduction of the impulse grounding resistance extremely depends on the increase of the impulse current leakage efficiency of the concentrated grounding device. In this study

based on the research of the impulse current leakage characteristics of a concentrated grounding device

and from the aspect of enhancing spark effect to raise the efficiency of impulse current leakage

simulation experiment was conducted on four kinds of commonly used concentrated grounding devices with additional outlet terminals at proper position. Experiment results show that the additional terminals significantly improve local electric field and enhance local spark effect

so the efficiency of impulse current leakage is raised. Consequently

the impulse grounding resistance can be reduced. Furthermore

the vertical arrangement of the outlet terminals can achieve larger resistance reduction than the horizontal arrangement.