Research on overvoltage simulation and protection of the 126 kV single-break vacuum circuit breaker is conducted to ensure safe operation of the 126 kV vacuum circuit breakers in power network and overvoltage test security. First

the operation mode of the circuit breaker and the simulation data are determine. Then

a model is established based on the software EMTP to simulate the overvoltage on the main transformer and no-load power line in switching of the vacuum circuit breaker

and the simulated overvoltage on transformer is compared with the measured one. At last

according to the simulation results

an overvoltage protection scheme is proposed.Simulation results show that: 1)the switching overvoltage of the 126 kV vacuum circuit breaker is high

while the overvoltage due to switching the transformer without load is low

so overvoltage protection is unnecessary

but because the overvoltage in switching the transformer with load is high

overvoltage protection is necessary

which is consistent with the field test situation; 2)for no-load line

since the 110 kV bus is equipped with arrester protection

the damage degree of overhead line due to overvoltage is low; and 3)MOA arrester is effective in suppressing the switching overvoltage of the 126 kV vacuum circuit breaker.