Turbine generator synchronization - two case studies

Abstract

This article presents two case studies of increased vibrations associated with load dispatch and removal from gas turbine-driven synchronous generators during electrical supply synchronization. The first case involves a classical uneven air gap fault due to a loose foot on the generator. Such faults are readily detected from the 2x line frequency associated with an electrical defect source. Another case involves unusually high transient vibrations during synchronization and not widely reported in the literature. Vibration levels increased during synchronization which, under full load conditions, remained high and resulted in a unit trip due to excessive vibration levels. At partial-load conditions, the high-transient vibrations dropped back down to pre-synchronization levels. Dominant vibration frequency was at lx synchronous frequency (and not the classical 2x line frequency). This fault was not due to the generators themselves but due to defects involving the synchronization process with likely out-of-phase synchronization.