CST05 - Fluid-Film Bearing Damage Detection Based on Vibration Data�

Abstract

This case occurred during startup after outage on a steam turbine generator. Vibration reached over full scale of 20 mil pp at generator drive end bearing and therefore tripped the unit. The major vibration component that tripped the unit was 0.5X sub-synchronous in a level of over 20 mil pp. 1X vibration excursions existed at constant speed before the trip event. Abnormal shaft centerline positions were observed. Shaft bow reached 10 mil pp at low speeds during coast-down. Bearing metal temperature reading was invalid. After an in-depth data review, diagnostic conclusions and recommendations were made, followed by correct actions. Inspection and findings confirmed bearing damage and rubs. If the vibration issue had simply be treated as rub, followed by re-start without opening the casing, further catastrophic damages would have occurred.