A static excitation system that can eliminate shaft vibrations of a generator and overvoltage when it is underexited is provided. The static excitation system includes an initial excitation equipment; a step-down transformer; a 3-phase diode bridge; a boost chopper provided with a transistor and a resister, and maintaining DC voltage to be constant; a DC chopper provided with a plurality of transistors and diodes, and supplying DC power to a rotor of a generator; a boost controller for controlling the boost chopper; and a DC chopper controller for controlling the DC chopper, wherein, overvoltage applied on the excitation system when underexcited is eliminated owing to the boost chopper preventing any changes at an output terminal of the generator from being transferred to the excitation system, and maintaining the excitation DC voltage to be constant; and also owing to the DC chopper which is capable of 4 quadrant operation, hereby pole slipping of the generator can be prevented.