As for such faults of 500 k V series capacitor compensation devices（Fengtun to Yimin series compensation in short）in operation such bypass circuit breaker due to the fault of power supply board of valve base electronic equipment（VBE）

protection mal-operation sub-synchronous resonance（SSR）

threephase inconsistence protection of circuit breaker and circuit breaker close due to protection action of metal oxidization varistor（MOV）

the reason of the fault is analyzed in accordance with the principle and structural feature of Yimin-Fengtun series compensation and with combination of operation and record data of the compensation

the interference-resistance ability and operation stability are improved by way of replacing the faulty parts

optimizing protection procedure

modifying protection operation logic and strengthening manufacturing process and maintenance etc. of the equipment. It is shown by the operation at site that the existed hidden faults in the Yimin-Fengtun series compensation can be eliminated completely by the adopted modification measures and

at the same time

the correctness and validity of the preventive measures are proved.