Short circuit current of power system seriously affects the safe and reliable operation of the transformer.In order to limit the short-circuit current of the transformer

variable impedance transformer is proposed. This transformer can reduce the impact of short-circuit current and also take the economy into account. The structure and principle of variable impedance transformer are introduced

PSCAD simulation software is used to analyze the distribution of overvoltage of variable impedance transformer. Researches indicate that the transient overvoltage would be generated in the process of impedance adjustment

the amplitude and frequency of transient overvoltage could be suppressed effectively with the existence of shunt capacitor

and the voltage of the reactor winding could be distributed evenly because of the shunt capacitor. The use of variable impedance transformer is benefit to improve the security and reliability of power system.