Phase controlled circuit breaker can obviously improve the switching transient process of the circuit breaker according to different loads by switching or closing at optimized phase position which reduces the switching inrush current and overvoltage.However the dispersion of the circuit breaker mechanism directly affects the precision of phase selection control of the phase controlled circuit breaker.A new type of permanent magnet mechanism and closed loop position feedback control system is explained in this paper.By analyzing and simulation of mechanism and study of excitation current closed loop tracking a

lgorithm for permanent magnet mechanism

we achieve to control the percision of position and time when switching on and off.Then some type tests forphase selection acuracy of phase controlled circuit breaker are carried out under different working conditions and it shows that the percision is about ±1 ms.Finally

the test of closing switching and back-to back capacitor bank of phase coutrolled circuit breaker under load condition is carried out

it is concluded that SF

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phase-controlled circuit breaker based on closed loop control can effectively restrain closing inrush current to no more than 3 times and opening overvoltage to be no more than 2.9 times

which is suitable for the applic ation of frequent switching of reactive power compensation device.