Synchronous Machine Damping by Excitation Control with Direct and Quadrature Axis Field Windings

Damping of synchronous machines by means of rapid response excitation control is analyzed for a one-field and two-field machine connected through a line impedance to an infinite bus. Emphasis is placed on the influence of the control parameters upon the damping characteristics of a conventional one-field machine. Regions of instability which may occur due to improper controller design or adjustment are established. Optimization of controller parameters and the effect of controller compensation are considered. Also, the damping characteristics of a two-field machine are presented and compared with those of a one-field machine. The application of the two-field machine to damp frequency oscillations in power systems has the potential of being of practical importance. Damping by excitation control ("forced" damping) is compared to damping due to the action of damper windings. The advantages of forced damping are clearly established; particularly in systems where long line lengths exist between large generating units.