Great grounding devices are important measures of thundering prevention of wind turbine generator systems and the impulse characteristics is major index to judge if the grounding devices good or not.In this paper

using the high impulse current generate to simulate the lightning impulse current

conducting impulse characteristics test to the typical grounding conductors of wind turbine generator systems-annulus grounding conductors and its improvements.The concept of the rate of change impulse characteristics is proposed

to quantitatively describe the common affects of spark effect and other impulse properties on the impulse grounding resistance

its value reacts the size of the strength

its symbol reacts the trend.Considering the rate of change impulse characteristics

the results discover that when the soil have two levels that the upper resistance is higher than the lower

adding vertical grounding conductors reaching to the lower soil lever can decrease the impulse grounding resistance apparently

and change the rate of impulse characteristics from -0.36 Ω/kA to-0.07 Ω/kA; When the length of the grounding conductors is stationary

replacing the annulus grounding conductors by the annulus conductors with level branch can decrease the impulse grounding resistance

but more significant is the rate of impulse characteristics change to -0.8Ω/kA.The results have some guidance for the wind turbine grounding device selection.