Stabilizing a 46 MW Multistage Utility Steam Turbine Using Integral Squeeze Film Bearing Support Dampers

Abstract

A 46 MW 5500 rpm multistage single casing utility steam turbine experienced strong subsynchronous rotordynamic vibration of the first rotor mode; preventing full load operation of the unit. The root cause of the vibration stemmed from steam whirl forces generated at secondary sealing locations in combination with a flexible rotor-bearing system. Several attempts were made to eliminate the subsynchronous vibration by modifying bearing geometry and clearances, which came short of enabling full load operation. The following paper presents experimental tests and analytical results focused on stabilizing a 46 MW 6230 kg utility steam turbine experiencing subsynchronous rotordynamic instability. The paper advances an integral squeeze film damper (ISFD) solution, which was implemented to resolve the subsynchronous vibration and allow full load and full speed operation of the machine. The present work addresses the bearing-damper analysis, rotordynamic analysis, and experimental validation through waterfall plots, and synchronous vibration data of the steam turbine rotor. Analytical and experimental results show that using ISFD improved the stability margin by a factor of 12 eliminating the subsynchronous instability and significantly reducing critical speed amplification factors. Additionally, by using ISFD the analysis showed significant reduction in interstage clearance closures during critical speed transitions in comparison to the hard mounted tilting pad bearing configuration.

A computational fluid dynamics investigation of the segmented integral squeeze film damper

“…1b) design allows partition of the thin layer of the oil film between the inner and outer damper ring into the circumferentially partitioned segments. Partitioning of the squeeze film offers the advantage of a precise damping as well as the stiffness controlled by flow resistance at the end seal clearances as well as the oil supply nozzle [23,24]. Therefore, the ISFD can produce damping by the squeezing thin oil film and by the piston/dashpot effect.…”

“…The relatively long axial length, the complicated assembling of the squirrel cage spring, and the difficult adjustment of the damper due to the elimination of the deflection of the rotor weight are the main drawbacks of the traditional SFDs. The utilization of the manufacturing process of wire electrical discharge machining has enabled the design of a new segmented integral squeeze film damper (ISFD) [20][21][22][23][24].…”

A modeling method for a rotor system with an active floating ring squeeze film damper

“…For unsupported dampers, if there is a steady-state solution, there are synchronous, subharmonic, and superharmonic components. An integral squeeze film damper (ISFD) solution was advanced by Ertas et al, 5 which was implemented to resolve the sub-synchronous vibration and allow full load and full speed operation of the machine. Ertas et al 6 also advanced experimental results and analytical predictions on dynamic performance of an ISFD for application in high-speed supercritical CO 2 expander.…”

Dynamic characteristics of elastic ring squeeze film damper

“…In spite of the successful implementation on steam turbine (Ertas et al, 2015) and supercritical CO 2 expander (Ertas et al, 2018), the complex structure of the ISFD raises challenges for its manufacturing and assembly. The elastic ring squeeze film damper (ERSFD) combines the design of dual clearances with the scheme of laying the elastic support in the gap between the journal and the housing.…”