To solve SCR over voltage breakdown problem

this paper analyzes process of switching capacitor bank by thyristors in 3-phase power lines.The analysis results show that through two times current alternating the same polarity or reversed polarity voltage superposition on capacitor bank could be formed.If the same polarity voltage added the capacitor bank’s residual voltage up to 1.366 times of peak voltage of power network

thus will cause 2.366 times peak voltage of power network on first off thyristor.While reversed polarity voltage is added

the capacitor bank’s residual voltage is 0.366 times of peak voltage of power network.So

the reversed polarity control method of TSC switching off for positive-sequence or negative-sequence connecting is obtained.Analysis and application verify its validity.