As an important part of high voltage switchgear

fast earthing switches（FES）usually uses spring operatingmechanism

decreasing the operating power of mechanism driven spring

can effectively reduce the impact load ofthe transmission system

and is significant to improve the reliability and stability of FES. In this article

the model ofFES is built

dynamic simulation calculation is carried out

the data of simulation is analyzed

the relationship isfound between FES closing speed and key parameters of operation spring

an optimal design method for drivingspring is proposed

and the effectiveness of the design method is proved by test on a spring. The test results show thatthe driving spring designed by this method can not only meet the requirements of closing speed

but also realize theminimization of the operating power of the driving spring.