A hydrogen-cooled turbogenerator operating at 3600 rpm showed the phenomenon of spiral vibration with a forward rotating unbalance vector. The relative shaft vibration measured at the non-driven end-bearing was close to the trip level. Spiral vibration is observed at various types of rotating machinery with both rotation directions of the unbalance vector, i.e., forward and backward. Spiral vibration is caused by a vibration-induced hot spot on the shaft surface generated by friction. The turbogenerator has three bearings: two main bearings and the brush gear bearing. The carbon brushes sliding on the slip rings were identified as the hot spot location. Potential modifications were studied using hot spot stability analyses with a rotor dynamic model of the generator rotor on three journal bearings. The applied method, introduced by Schmied (1987, “Spiral Vibrations of Rotors” Proc. 11th Biennial ASME Design Engineering Div. Conf., Vib. Noise, DE-Vol. 2, Rotating Machinery Dynamics, Boston, MA, ASME H0400B, pp. 449–456), allows the handling of general systems. The hot spot model is based on the theory of Kellenberger (1978, Ingenieur-Archiv, 47, pp. 223–229; 1980, Journal of Mechanical Design, 102, pp. 177–184) using a thermal equation between the shaft’s thermal deflection and the shaft displacement at the hot spot location. Three different relations between the heat input and the shaft vibration were modeled: heat input proportional to the shaft displacement, to the shaft velocity, and to the shaft acceleration. The model, in which the heat input is proportional to the velocity, is the most suitable variant for slip rings. This was confirmed by comparison with the measured vibration behavior. A modification of the shaft line was selected based on the calculation results and was successfully implemented. This generator and other generators with the same modified brush gear unit have been in operation for more than four years.

Issue Section:
Gas Turbines: Structures and Dynamics
Keywords:
turbogenerators, shafts, vibrations, machine bearings, rotors, Newkirk effect, vector turning, rotating unbalance vector, rub, hot spot phenomenon
Topics:
Heat, Stability, Vibration, Turbogenerators, Rotors, Displacement, Bearings
1.
Newkirk
,
B. L.
, 1926, “
Shaft Rubbing. Relative Freedom of Rotor Shafts From Sensitiveness to Rubbing Contact When Running Above Their Critical Speeds
,”
Mech. Eng. (Am. Soc. Mech. Eng.)
0025-6501,
48
(
8
), pp.
830
–
832
.
2.
Adams
,
M. L.
, 2001, “
Vector Turning From Synchronously Modulated Rubs
,” in
Rotating Machinery Vibration from Analysis to Troubleshooting
,
Marcel Dekker, Inc.
, New York, Chap. 12.3, pp.
312
–
318
.
3.
Balbahadur
,
A. C.
, 2001, “
A Thermoelastohydrodynamic Model of the Morton Effect Operating in Overhung Rotors Supported by Plain or Tilting Pad Journal Bearings
,” Ph.D. thesis, Faculty of the Virginia Polytechnic Institute and State University, Blacksburg, Virginia.
4.
Balbahadur
,
A. C.
, and
Kirk
,
R. G.
, 2004, “
Part I—Theoretical Model for a Synchronous. Thermal Instability Operating in Overhung Rotors
,”
Int. J. Rotating Mach.
1023-621X,
10
(
6
), pp.
469
–
475
.
Crossref
Search ADS
 
5.
Kirk
,
R. G.
,
Guo
,
Z.
, and
Balbahadur
,
A. C.
, “
Synchronous Thermal Instability Prediction for Overhung Rotors
,”
Proceedings of the Thirty-Second Turbomachinery Symposium
,
Texas A&M University
, Houston, Texas, September 8–11, pp.
121
–
135
.
6.
De Jongh
,
F. M.
, and
Morton
,
P. G.
, 1996, “
The Synchronous Instability of a Compressor Rotor Due to Bearing Journal Differential Heating
,”
ASME J. Eng. Gas Turbines Power
0742-4795,
118
, pp.
816
–
824
.
Crossref
Search ADS
 
7.
Keogh
,
P. S.
, and
Morton
,
P. G.
, 1993, “
Journal Bearing Differential Heating Evaluation With Influence on Rotor Dynamic Behaviour
,”
Proc. R. Soc. London, Ser. A
1364-5021
441
, pp.
527
–
548
.
Crossref
Search ADS
 
8.
Muszynska
,
A.
, 1989, “
Rotor-to-Stationary Element Rub-Related Vibration Phenomena in Rotating Machinery-Literature Survey
,”
Shock Vib. Dig.
0583-1024,
21
(
3
), pp.
3
–
11
.
Crossref
Search ADS
 
9.
Gasch
,
R.
,
Nordmann
,
R.
, and
Pfützer
,
H.
, 2002, “
Der sanft anstreifende Rotor
,” in
Rotordynamik
, 2nd ed.,
Springer-Verlag
, Berlin, Chap. 26, pp.
537
–
554
.
10.
Bastow
,
P.
, and
Fenner
,
R.
, 1993, “
The Practical Application of On-Line Systems To the Diagnosis of Machine Problems
,” CISM Courses and Lecture No. 352,
Proceedings of the CISM/IFToMM Symposium “Diagnostics of Rotating Machines in Power Plants
,” October 27-29, Udine, Italy,
G.
Diana
, ed.,
Springer-Verlag
,
Berlin
, pp.
49
–
73
.
11.
Kellenberger
,
W.
, 1978, “
Das Streifen einer rotierenden Welle an einem federnden Hindernis—Spiralschwingungen
,”
Ing.-Arch.
0020-1154,
47
, pp.
223
–
229
.
Crossref
Search ADS
 
12.
Kellenberger
,
W.
, 1980, “
Spiral Vibrations Due to the Seal Rings in Turbogenerators Thermally Induced Interaction Between Rotor and Stator
,”
ASME J. Mech. Des.
0161-8458,
102
, pp.
177
–
184
.
13.
Schmied
,
J.
, 1987, “
Spiral Vibrations of Rotors
,”
Proc. 11th Biennial ASME Design Engineering Div. Conf., Vib. Noise, DE-Vol. 2, Rotating Machinery Dynamics
, Boston MA, ASME H0400B, pp.
449
–
456
.
14.
Eckert
,
L.
,
Schmied
,
J.
, and
Ziegler
,
A.
, 2006, “
Case History and Analysis of the Spiral Vibration of a Large Turbogenerator Using Three Different Heat Input Models
,”
7th IFToMM International Conference on Rotor Dynamics
, Vienna, Austria, September 25–28, Paper-ID 161, pp.
1
–
10
.
15.
ISO 7919-2
, 2001, “
Mechanical Vibration—Evaluation of Machine Vibration by Measurements on Rotating Shafts. Part2: Land-Based Steam Turbines and Generators in Excess of 50MW With Normal Operation Speeds of 1500r∕min, 1800r∕min, 3000r∕min, and 3600r∕min
,” 2nd ed.,
ISO (International Organization for Standardization)
, pp.
11
–
15
.
16.
Klement
,
H. D.
, 1997,
Manuals of MADYN
, Version 4.2, Program System for Machine Dynamics,
Ingenieur-Büro Klement
, Troyesstr. 4,
Darmstadt, Germany
.
Copyright © 2008
 by ALSTOM
You do not currently have access to this content.