PREVENTION OF LOW-FREQUENCY VIBRATION OF HIGH-CAPACITY STEAM-TURBINE UNITS BY SQUEEZE-FILM DAMPER

The cause of the low-frequency vibration (subsynchronous vibration) of a high-pressure turbine was investigated by the analytical study and vibration exciting lest for the actual machine in operation. From the results, it is found that the low-frequency vibration is caused by the decrease of the rotor system damping at high-loading operating condit ions. As a countermeasure, a squeeze-film damper is designed in order to increase the damping of the rotor system. After the verification te st of the squeeze-film damper's capability in the workshop, it was ins talled on the actual turbine. Vibration exciting tests for the high-pr essure turbine under the actual operating conditions were carried out. These field tests confirmed that the damping of the rotor system was increased as expected in the design and consequently the low-frequency vibrations disappeared completely under all operating conditions.