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Research Papers: Gas Turbines: Structures and Dynamics

Torsional Vibrations Caused by Geared Coupling in a Shaft Train Driven by a Steam Turbine

[+] Author and Article Information
Paolo Pennacchi1

Department of Mechanical Engineering, Politecnico di Milano, Via La Masa 1, I-20156 Milan, Italypaolo.pennacchi@polimi.it

Andrea Vania

Department of Mechanical Engineering, Politecnico di Milano, Via La Masa 1, I-20156 Milan, Italy

Franco Frattaroli

Service Engineering, Franco Tosi Meccanica S.p.A., Piazza Monumento 12, I-20025 Legnano (MI), Italy

1

Corresponding author.

J. Eng. Gas Turbines Power 133(1), 012501 (Sep 27, 2010) (8 pages) doi:10.1115/1.4001830 History: Received April 09, 2010; Revised April 23, 2010; Published September 27, 2010; Online September 27, 2010

Rotating machines that include geared shaft-trains can be affected by a dynamic behavior that is influenced by coupling effects between lateral and torsional vibrations. These latter vibrations are rarely measured by means of permanent probes in industrial machines; therefore, these phenomena can be often pointed out only by detecting abnormal harmonic components in the frequency spectrum of the lateral vibrations measured during common monitoring activities. Then, the diagnosis of the occurrence of coupling effects between torsional and lateral vibrations can be supported by the results provided by model-based techniques. In this paper, the results of the analysis of the dynamic behavior of a small power unit that was affected by abnormal lateral vibrations caused by the excitation of torsional normal modes of the geared shaft-train are shown and discussed.

Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Machine-train diagram and bearing numbers

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Figure 2

Position of the proximity probes mounted on the supports of generator and steam turbine

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Figure 3

Angular position of the proximity probes mounted on the supports of the fast and slow gear shafts of the gearbox

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Figure 4

Historic trend of the overall amplitude of the gear shaft vibrations measured on bearing Nos. 3 and 6 during a load rise. Historic trend of the megawatt load (scale on the diagram right side).

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Figure 5

Octave band analysis of the acoustic emission measured in the vicinity of the gearbox in the FSNL condition, as well as with 16 MW

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Figure 6

Close up of gear teeth affected by wear

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Figure 7

Waveform of the vibration signal measured at bearing No. 3 in the Y direction in operating conditions associated with different loads ranging from 2–16 MW

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Figure 8

Waveform of the vibration signal measured at bearing No. 6 in the Y direction in operating conditions associated with different loads ranging from 2–16 MW

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Figure 9

12.3X filtered orbits measured on bearing Nos. 5 and 6 of the slow gear shaft with a megawatt load of 16 MW

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Figure 10

Finite element model of the fast shaft-train composed of steam turbine, flexible coupling, and fast gear shaft

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Figure 11

Finite element model of the slow shaft-train composed of slow gear shaft, flexible coupling and generator

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Figure 12

Theoretical torsional normal modes of the fast shaft-train associated with the third and fourth natural frequencies of the geared machines (266.15 Hz and 309.9 Hz)

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Figure 13

Theoretical torsional normal modes of the slow shaft-train associated with the third and fourth natural frequencies of the geared machines (266.15 Hz and 309.9 Hz)

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Figure 14

Overall amplitude of the vibrations measured on bearing No. 6 during a machine run-up

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Figure 15

Waveform of the vibration measured on bearing No. 6, in the Y direction, at 1063 rpm

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Figure 16

Waveform of the vibration measured on bearing No. 6, in the Y direction, at 1173 rpm

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Figure 17

Bode plot of the 1X transient vibrations measured on bearing No. 2 of the steam turbine

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Figure 18

Overall amplitude of the transient vibrations measured on bearing No. 3 during a machine run-up

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Figure 19

Theoretical torsional normal mode, of the fast and slow shaft-trains, associated with the second natural frequency of the geared machines (68.6 Hz)

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Figure 20

Filtered orbits measured on bearing Nos. 3 and 6 of gear shafts when the generator rotational speed was 1063 rpm

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