Cause Analysis and Mitigation Measures of Vertical Vibration of Head-Cover of a Pump-Turbine

Abstract The abnormal vertical vibration of the head cover of a 306 MW pump-turbine was found in the 150 to 240 MW part load region of generating condition. To reveal the causes and find mitigation measures, field tests on vibration and pressure pulsations, and the ODS (Operational Deflection Shape) analysis of the head cover were conducted. It was found that the vibration of the head-cover is transferred by means of the clearance water body from the runner vibration, which in induced by pressure pulsations. Several vibration reduction measures were analysed and injecting compressed-air into the clearance between the head-cover and the runner-crown was proposed. The field test showed that the abnormal vibration was effectively eliminated because the fluid characteristics between the head-cover and the runner can be changed by just adding a small amount of compressed-air, which destroys the critical conditions of inducing vibration. This first attempt is of reference values, because it is a simple, effective, and economical.