TECHNICAL PAPERS: Gas Turbines: Structures and Dynamics

Test Results and Analytical Predictions for Rotor Drop Testing of an Active Magnetic Bearing Expander/Generator

[+] Author and Article Information
Lawrence Hawkins

 Calnetix, Inc., Cerritos, CA 90703larry@calnetix.com

Alexei Filatov, Shamim Imani

 Calnetix, Inc., Cerritos, CA 90703

Darren Prosser

 Air Products, Allentown, PA 18195

J. Eng. Gas Turbines Power 129(2), 522-529 (Sep 14, 2006) (8 pages) doi:10.1115/1.2436549 History: Received June 15, 2006; Revised September 14, 2006

A cryogenic gas expander system that incorporates a high-performance, high-speed permanent magnet, direct-drive generator and low loss magnetic bearings is described. Flow loop testing to 30,000rpm was completed at the system manufacturer’s facility in January 2005, and field installation is scheduled for October 2005. As part of the system testing, the rotor was dropped onto the backup bearings multiple times at an intermediate speed and at 30,000rpm. Orbit and time-history data from a full speed drop and spin down are presented and discussed in detail. A transient, nonlinear rotordynamic analysis simulation model was developed for the machine to provide insight into the dynamic behavior. The model includes the dead band clearance, the flexible backup bearing support, and hard stop. Model predictions are discussed relative to the test data.

Copyright © 2007 by American Society of Mechanical Engineers
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Figure 1

Crosssection of expander generator with nominal 114mm(4.5in) wheel

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Figure 2

Crosssection showing radial/thrust backup bearing

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Figure 3

Undamped critical speed map for the rotor supported at the backup bearings

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Figure 4

Displacement and speed versus time during rotor drop and spin down

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Figure 5

Displacement orbit at expander end during rotor drop and spin down: (a) 1.28–1.43sec; (b) 1.43–1.83sec; and (c) 1.83–6.0sec

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Figure 6

Displacement time history at expander end: (a) 1.28–1.43sec; (b) 1.4–1.6sec; (c) 3.2–3.9sec

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Figure 7

Predicted drop response for nominal model: (a) orbit at expander end; (b) Fourier transform of x axis; and (c) expander end backup brg load mag and phase

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Figure 8

Predicted displacement orbit for unbalanced Case 2

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Figure 9

Predicted displacement orbit for unbalanced Case 3

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Figure 10

Predicted displacement orbit for unbalanced Case 4



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