This paper presents the theory of generating secondary arc current in ultra-high-voltage（UHV） power transmission system.The mathematic representations of recovery voltage and secondary arc current can be obtained based on circuit principle

and the values can also be obtained by using MATLAB.Based on SIMULINK the whole circuit has been simulated

thus

the waveshapes of recovery voltage and secondary arc current are obtained.The effect of secondary arc suppression is studied when the high speed grounding switch（HSGS） is adopted.The mechanism of secondary arc restriction by HSGS is analyzed.Motor-driven spring operating mechanism has been used to enhance breaking velocity of HSGS.The magnitude of the secondary arc current and recovery voltage in arc path are obviously reduced after using HSGS on line.Then it reduces the extinction time of the secondary arc and assures successful single-phase auto reclosure.