Damping of Power Swings in a Parallel AC and DC System

In an earlier paper, the authors presented a method of simulating a transmission system including ac and dc lines in parallel, and established the validity of the simulation. In this paper the method, which utilizes a direct and quadrature axis representation, is used to study with the aid of an analog computer the electromechanical oscillations in a system consisting of one machine tied to an infinite bus through two parallel transmission lines, one of which is ac and the other dc. Results make it clear that with proper dynamic control of power flow in the dc line, a substantial degree of damping of transient power swings may be achieved.