Research Papers: Gas Turbines: Structures and Dynamics

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

[+] Author and Article Information
Bugra Ertas

Mechanical Systems Organization,
GE Global Research Center,
Niskayuna, NY 12309

Vaclav Cerny

Head of Operational Analysis,
Doosan Skoda Power,
Pizen 30614, Czech Republic

Jongsoo Kim

Engineering and Research,
Waukesha Bearings Corporation,
Pewaukee, WI 53072

Vaclav Polreich

Measurement and Diagnostics,
Doosan Skoda Power,
Pizen 30614, Czech Republic

1Corresponding author.

Contributed by the Structures and Dynamics Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 9, 2014; final manuscript received August 20, 2014; published online December 2, 2014. Editor: David Wisler.

J. Eng. Gas Turbines Power 137(5), 052506 (May 01, 2015) (11 pages) Paper No: GTP-14-1349; doi: 10.1115/1.4028715 History: Received July 09, 2014; Revised August 20, 2014; Online December 02, 2014

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.

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Fig. 1

Past applications of SFD in multistage steam turbines. (a) Ball-socket TPJ bearing with O-ring SFD [6], (b) ball-socket TPJ bearing with an arc centering spring and O-ring SFD [7], and (c) rocker-back TPJ bearing with “pin” bearing support centering spring and SFD [9].

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Fig. 2

46 MW multistage utility steam turbine

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Fig. 3

Turbine power versus rotor vibration at the bearings

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Fig. 4

Waterfall spectrum 0-peak: five pad LOP bearings

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Fig. 6

Damping mechanism: conventional SFD versus ISFD

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Fig. 7

NDE four pad LBP ISFD TPJ bearing: 200 mm

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Fig. 8

DE four pad LBP ISFD TPJ bearing: 220 mm

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Fig. 9

Synchronously reduced bearing and damper coefficients

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Fig. 10

Rotordynamic models

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Fig. 11

Damped eigenvalue frequency map

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Fig. 12

First mode log dec using ISFD: damper optimization

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Fig. 13

Effective seal damping and stiffness at 5500 rpm

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Fig. 14

First mode damped eigenvalue: five pad LOP TPJ

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Fig. 15

First mode damped eigenvalue: four pad LBP ISFD

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Fig. 16

Field vibration measurements: synchronous response

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Fig. 17

Predicted synchronous vibration response

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Fig. 18

Rotor midspan vibration and deflected rotor shapes

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Fig. 19

Waterfall spectrum 0-peak: four pad LBP ISFD bearings




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