Improving Transient Stability of AC System by Joint Usage of DC System

Studies of stability problems are expected to be developed in parallel ac-dc systems. Results obtained by the experiment on the artificial ac and dc transmission facilities were: the more the dc power of steady state compared with the ac power, the more the transient stability is improved. The transient stability is improved if the dc power is rapidly increased in case of faults in the ac system. The 3-phase short circuit at the sending ac system results in a serious decrease of the dc power. This decrease causes the generator to accelerate at the sending end. Two control methods for the countermeasure are presented.