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Research Papers: Gas Turbines: Structures and Dynamics

Rotordynamic Behavior of 225 kW (300 HP) Class PMS Motor–Generator System Supported by Gas Foil Bearings

[+] Author and Article Information
Bok Seong Choe

Center of Urban Energy System Research,
Korea Institute of Science and Technology,
39-1 Hawolgok-dong,
Seongbuk-gu, Seoul 137-791, South Korea
e-mail: bschoe@kist.re.kr

Tae Ho Kim

Assistant Professor
School of Mechanical Systems Engineering,
Kookmin University,
77 Jeongneung-ro,
Seongbuk-gu, Seoul 136-702, South Korea
e-mail: thk@kookmin.ac.kr

Chang Ho Kim

Center of Urban Energy System Research,
Korea Institute of Science and Technology,
39-1 Hawolgok-dong,
Seongbuk-gu, Seoul 137-791, South Korea
e-mail: kimch@kist.re.kr

Yong Bok Lee

Center of Urban Energy System Research,
Korea Institute of Science and Technology,
39-1 Hawolgok-dong,
Seongbuk-gu, Seoul 137-791, South Korea
e-mail: lyb@kist.re.kr

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 December 4, 2014; final manuscript received January 15, 2015; published online February 25, 2015. Editor: David Wisler.

J. Eng. Gas Turbines Power 137(9), 092505 (Sep 01, 2015) (8 pages) Paper No: GTP-14-1650; doi: 10.1115/1.4029712 History: Received December 04, 2014; Revised January 15, 2015; Online February 25, 2015

This paper presents the dynamic behavior of a 225 kW class (300 HP), 60,000 rpm, permanent magnet synchronous (PMS) motor–generator system supported on gas foil bearings (GFBs). The rotor of a 225 kW PMS motor is supported by two identical gas foil journal bearings (GFJBs) and one pair of gas foil thrust bearings (GFTBs). The total weight and axial length of the coupled rotors are 272 N and 1042 mm, respectively. During the speed-up test to 60,000 rpm, unexpected large subsynchronous rotor motions appear at around 120–130 Hz above 35,040 rpm. After disassembling the motor, an inspection of the top foils of the GFJBs reveals significant rotor rubbing. Thus, the GFJBs are redesigned to have a smaller load capacity by reducing their axial length to 45 mm. In addition, three 50 μm thick shims are installed in the GFJBs at 120 deg intervals for reducing the swirl speed of air and producing bearing preloads. The modification delays the onset speed of subsynchronous motions to 43,200 rpm and decreases the amplitude of the subsynchronous motions from 20 to 15 μm. These results indicate that the modification improves the stability margin of the high-speed rotor system with increasing stiffness and damping. In addition, the logarithmic decrement trends are in good agreement with the test results.

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References

Heshmat, H., Walowit, J. A., and Pinkus, O., 1983, “Analysis of Gas Lubricated Compliant Thrust Bearings,” ASME J. Tribol., 105(4), pp. 638–646. [CrossRef]
Agrawal, G. L., 1997, “Foil Air/Gas Bearing Technology—An Overview,” ASME Paper No. 97-GT-347. [CrossRef]
Dellacorte, C., and Valco, M. J., 2000, “Load Capacity Estimation of Foil Air Journal Bearings for Oil-Free Turbomachinery Applications,” STLE Tribol. Trans., 43(4), pp. 795–801. [CrossRef]
DellaCorte, C., Radil, K., Bruckner, R., and Howard, S., 2007, “Design, Fabrication and Performance of Open Source Generation I and II Compliant Hydrodynamic Gas Foil Bearings,” NASA Glenn Research Center, Cleveland, OH, Report No. NASA/TM-2007-214691.
Heshmat, H., 1994, “Advancements in the Performance of Aerodynamic Foil Journal Bearings: High Speed and Load Capacity,” ASME J. Tribol., 116(2), pp. 287–294. [CrossRef]
Kim, T. H., and San Andrés, L., 2007, “Analysis of Advanced Gas Foil Bearings With Piecewise Linear Elastic Supports,” Tribol. Int., 40(8), pp. 1239–1245. [CrossRef]
Kim, T. H., and San Andrés,L., 2009, “Effects of a Mechanical Preload on the Dynamic Force Response of Gas Foil Bearings: Measurements and Model Predictions,” STLE Tribol. Trans., 52(4), pp. 569–580. [CrossRef]
Heshmat, H., and Walton, J. F., 2007, “On the Coupling of Foil Bearing Supported Rotors: Part 1—Analysis,” ASME Paper No. GT2007-27821. [CrossRef]
Heshmat, H., and Walton, J. F., 2007, “On the Coupling of Foil Bearing Supported Rotors: Part 2—Experiment,” ASME Paper No. GT2007-27825. [CrossRef]
Lee, Y. B., Jo, S. B., Kim, T. Y., Kim, C. H., and Kim, T. H., 2010, “Rotordynamic Performance Measurement of an Oil-Free Turbocompressor Supported on Gas Foil Bearings,” IFToMM 8th International Conference on Rotor Dynamics, Seoul, South Korea, Sept. 12–15, pp. 372–378.
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Figures

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Fig. 1

225 kW (300 HP) class PMS motor–generator system, maximum speed = 60,000 rpm (1000 Hz)

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Fig. 2

GFBs. (a) GFJB and (b) GFTB with six top foils and bump layer.

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Fig. 3

Design geometry of GFBs

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Fig. 15

(a) Analysis: trajectory of rotor center, 0–60,000 rpm, bearing axial length = 45 mm and (b) experiment: trajectory of rotor center, 0–60,000 rpm, bearing axial length = 45 mm

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Fig. 14

Predicted minimum film thickness versus rotor speed for increasing bearing axial length. Designed GFJB with static load of 60 N.

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Fig. 13

1 × synchronous vibration amplitude of coupling (a) horizontal and (b) vertical at 0–60,000 rpm—after adjusting alignment

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Fig. 12

(a) Analysis: trajectory of rotor center, 0–54,000 rpm, bearing axial length = 60 mm and (b) experiment: trajectory of rotor center, 0–54,000 rpm, bearing axial length = 60 mm

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Fig. 11

Waterfall graph of 1 × synchronous amplitude at coupling vertical direction, bearing axial length = 60 mm (0–54,000 rpm)

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Fig. 10

1 × synchronous vibration amplitude of coupling (a) horizontal and (b) vertical at 0–54,000 rpm—before adjusting alignment

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Fig. 9

Measurement sensor (fiber optic, 750 μm/V) for amplitude of rotor vibration and data acquisition device (FFT analyzer, pulse), oscilloscope

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Fig. 7

(a) Mode shape of coupled motor–generator system for each N.F. (N.F.1–4) and (b) mode shape of coupled motor–generator system for each N.F. (N.F.5–6)

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Fig. 6

Campbell diagram of coupled motor–generator system (N.F.1–4: rigid mode, N.F.5–6: bending mode)

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Fig. 5

Free–free natural frequency analysis and impact test results of 225 kW (300 HP) coupled motor–generator system

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Fig. 4

FE model of 225 kW (300 HP) coupled motor–generator system

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Fig. 16

Waterfall graph of 1 × synchronous amplitude at coupling vertical direction, bearing axial length = 45 mm (0–60,000 rpm)

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Fig. 17

Logarithmic decrement analysis versus speed (B.W. = bearing width, N.F.4 = 240–250 Hz)

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Fig. 18

(a) GFJB synchronous direct stiffness coefficient versus speed at the G2 position (B.W. = bearing width), (b) GFJB synchronous cross coupled stiffness coefficient versus speed at the G2 position (B.W. = bearing width), (c) GFJB synchronous direct damping coefficient versus speed at the G2 position (B.W. = bearing width), and (d) GFJB synchronous cross coupled damping coefficient versus speed at the G2 position (B.W. = bearing width)

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