In case of system fault in substation，the transient recovery voltage steepness of circuit breaker connected to the system increases instantly and affects normal interruption operation of the circuit breaker. For solving this problem，a kind of protection capacitor device（“capacitor device”in short）with such functions as harmonic suppression and limit of closing inrush current of current limiting reactor on the 500 kV transmission line is designed in this paper. First of all，both operating principle and design scheme of the capacitor device are described；Then，the static strength，seismic performance and electric field simulation calculations are performed and the simulation shows that they meet the design requirement；Finally，the device passes the complete set of type test items one time and meets the requirements of related standards and technical specification.