Self-Excitation of a Synchronous Generator During Power System Restoration

This paper analyzes synchronous generator self-excitation during power system restoration, caused by a large capacitive load and the impact of generator voltage control on the voltage rise. The paper analyzes measurements from a recent self-excitation incident in the Finnish 400-kV transmission system, models the system using an electromagnetic transient model and a linear d-axis generator model, validates the models using the measurements and analyzes the impact of generator voltage control during self-excitation. Self-excitation is rare during a normal system operation but may occur in a weak system during system restoration after a blackout. Since high voltages caused by the self-excitation may delay the restoration or even damage the equipment, self-excitation should be taken into account in restoration planning. This paper shows that the voltage controller and especially the under-excitation limiter settings of the generator have significant impact on the voltage during self-excitation. This paper also shows that details in the excitation system response influence the simulations significantly and reference measurements from the specific generator are required for detailed modeling. However, all measured incidents with digital static excitation systems are important references for simulations. In addition, special attention should be given to protection relays during the restoration.