CA1079313A - Torsional oscillation damper - Google Patents

Abstract

TORSIONAL OSCILLATION DAMPER
ABSTRACT OF THE DISCLOSURE
A pair of concentric, rotatable shaft members which are assembled together in a shrink fit relationship.
When one of the shafts is subjected to torsional oscilla-tions, the other twists therewith until the frictional forces therebetween which cause simultaneousjrotation of both rotatable shafts is overcome by elastic torque accumu-lated in the other shaft causing relative motion between the two shafts and resulting in energy being dissipated by dynamic fiction thus limiting the amplitude of the torsional oscillations. To prevent fretting between the adjacent, slippable surfaces, one on each shaft, a coating of non-fretting material is disposed on at least one of the two slippable surfaces, A thin sleeve of non-fretting material can also be assembled in a shrink fit relationship between the adjacent, slippable surfaces.

Description

C ICGR'OUND' ~ =
I' This ln~enti~n relates to tor~s:}onal oscillation . .. .
dan~per and mo~e p~rticularly to two concentric sha:Ft mem-20 bers, one o~ which acts as a d~mper for the torslonal 08eil-i,',' ~ lat;ons impoæed upon the ~t~er~ shaft.
., ~. Tn the past, ~at~gue :Pailure of turbine~ generator :",: .
6hafts h~s been ~are, ~t the pre~ent time, howe~re~ in ce~tain ~geographlcaI regions such as ~he Southwes~ern United atès, power~ trarlsmisoion l~nes a~e be~ng ~trung over vast 7 extended di~tances . Subs~nchronous re~E;onan~e~ 'd`~ e-e' o êffii~L phe'~o~mena''~n.'1s'u;~ x'~iended`~
tr~ al ~ power d~stribut~n s~stems can induoe large torsional ~"~
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oscillations in turbine generator rotors causing ,laccom-panying s~esses therein which can result in fatigue failures and bring abou-t forced outages of the -turbine-generator unit.
A simple, universal torsional oscillation damper is desired to reduce the chance of shaft fatigue failure while providing the characteristics of ease of manuacturing, simple installation, and low maintenance.
SUMMARY OF THE INVENTION
In general, a torsional oscillation damper, when made in accordacne with this invention, comprises a pair of concentrically arranged shaft members having radially adja-cent surfaces on the inner and outer shafts, with those surfaces being engaged by radially directed forces thereon which cause torsional oscillations which are exerted on one shaft to be frictionally transmi-tted to the second shaft and damped b~ frictional forces resulting from relative motion occurring between the adjacent, engaged shaft surfaces. The frictional forces acting at the adjacent shaft surfaces ~0 during relative movement therebetween reduces the amplitude of the torsional oscillations which results ;n a longer life for the concentr~c sha~ts.
BRIEF DESCR~Pl`ION OF THE DRAWINGS
The ob~ec-ts and advantages of this invention will becomeemore apparent from reading t~e following detailed description in c~nnection with the accompanying drawings, in which cor~asponding reference characters indicate corres-ponding port~ns thr~ughout the drawings and ln which:
Figure 1 is a partial sectional view of a turbine-generator unit whosle connect~ng shaft is made in accordance . :

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~7~ 3 with this invention;
Figure 2 is a sectional view taken on line II II
of Figure l;
Figure 3 is an additional sectional view embodi-ment of the appar~tus shown in Figure 2; and Figures 4A-4E are end views of the concentric shaft arrangement ~uring one cycle o~ a torsional oscillation.
DESCRIPTION OF THE PREFERRED EMBODIMENT
-Referring now to the draw;ngs in detail~ Figure 1 shows generator 10 being connected to and driven by turbine 12 by mPans of shaft 14.
Figure 2 illustrates a jacksha~t portion 16 and insert portion 18 of sectioned shaft 14. Jackshaft portion 16, as illustrated, is th~ torque carrying member between the generator 10 and turbine 12 while insert 18 provides the frictional damping effect on jackshaft 16 when it is tor-sionally oscillated ~y forces whose origins are immaterial for the purposes of this in~ention. When torsional oscil-lations are exerted on jackshaft 16 through either end 20 adjacent to the turbine 12 or end 22 ad~acent to generator 10, a relative twisting between ends 20 and 22 of the jack-shaft will occur. Since jackshaf-t 16 is shrunk onto insert 18, insert 18 will twist with jackshaft 16 until the relative angle of twist as measured between ends 20 and 22 exceed the value where the elastic torque accumulated in insert 18 is equal to the f~ict~on torque exerted across interface 24 ~; where the outside surface of insert 18 contacts the inside : surface of jackshaXt 22. Slîpping occurs at innerface 24 when the elastic torque of the insert surpasses that of the frictional torque holdîng jacksha~t 16 to insert 18, causing ~

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3~3 energy to be dissipated by the sliding friction which, in turn, provides damping and limlts the amplitude of the torsional oscillations which are exerted on jackshaft 16.
The threshold value of torsional stress at which slipping starts and the degree of damping caused by -that slipping both vary as a ~unc-tion of the contact pressure holding jackshaft 16 and insert 18 together. The contac-t pressure i9 selected to optimize damping at an aceeptable level of torsional stress while retaining jackshaft shrink fit stresses within permissible limits. Acceptable values of torsional and shrink fit stresses in the jacksh~ft 16 and insert 18 respectively, can be adjusted by judicious choices of material, correct selection of relative æizes, and an al-teration of appropriate material propertles such as hy heat treating jackshaft 16 and insert 18.
Figure 3 illustretes an alternative embodiment to that shown in Figure 2 and has a non-fretting substance such as a Stellite material disp~sed ~t~ erface~24 to prevent fretting~tween the` engaged~s-ur-~aces when slipping occurs therebetween. The stellite ~5 disposed as a coating on either or bot~ o~ the engaged sur~aces ~e~ore jacksha~t 16 is shrunk flt onto insert 18. An alternative disposition of the non-~rett~ng ma-terial is assembling a thin sleeve of it on insert 18 ~efore shrink fitting the jackshaft thereon.
The oscillation sequence from an axial view of jackshaft 16 and insert 18 is illustrated in Figures 4A, 4B, 4C, 4D, and 4E. While the illustrated sequence only shows -oscillatory motlon in the direetions indicated by the arrows, the two shafts usually experîence con':inuous~ one directional ro-tation superimposled on the oscillator~ motion. Figure 4A

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shows the relative positioning of radial marks 16' and 18' respectively on jackshaft 16 and insert 18 at the star-t of a clockwise oscillation exerted on jackshaft 16. Figure 4B
illustrates the maximum simultaneous rotational displacemPnt of jackshaft 16 and insert 18. Beyond this point, relative slippigg between the two shaft members will will occur. The oscillation's maximum amplitude is shown in Figure 4C. The time span between Figures 4B and 4C provides the interval for slipping between the shaft members and the resulting frictional damping of the clockwise torsional oscillation.
Figure 4D illu~trates the maximum simultaneous counterclock wise rotational displacement of the two shaft members7 Figure 4E shows the maximum counterclockwiæe oscillatory amplitude and relative pos~tioning of jack~ha~t mark 16' and insert mark 18'. Figure ~ is not meant to indicate typical oscillatory rotation angles, but is to be treated as a schematic which illustrateæ one cycle o~ torsional oscillation and the intermovement between concentric shaft m~bers. It is also to be noted that while Figures 2, 3, and 4 show solid inse~t sha~t members 18~ cylindrical inserts or other suitable shapes could also be utilized.
It i5 to be understood that while shaft 14 has been illustrated as connecting turbine 12 and generator 10, this invention can be utilized to connect any power source to a driven load or betwaen cooperating power sources such as different pressure turbines or turbine sections. Also, whlle certain pre~erred materials have been described, other equivalent or otherwise suitable materials may ~e substituted therefor.

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Claims (6)

Claims:

1. A torsional oscillation damper comprising:
a pair of concentrically arranged shaft members having radially adjacent surfaces on the inner and outer shafts, said adjacent surfaces being engaged by radially directed, friction promoting forces wherein torsional oscil-lations exerted on one shaft are frictionally transmitted to the second shaft and have their amplitude damped by fric-tional forces resulting from relative motion occurring between said adjacent shaft surfaces.

2. The torsional oscillation damper of claim 1, wherein one of said shaft members is relatively more rigid and relatively less resilient than the other.

3. The torsional oscillation damper of claim 1, wherein said radially directed friction promoting forces and degree of frictional damping resulting therefrom can be selectively varied by shrink fitting the concentric shafts together so as to provide a predictable extent of inter-ference therebetween.

4. The torsional oscillation damper of claim 1, wherein at least one of said engaged surfaces comprises non-fretting material.

5. The torsional oscillation damper of claim 1, wherein a sleeve of non-fretting material is disposed between said radially adjacent surfaces.

6. In combination:
a turbine;
aagenerator; and the torsional oscillation damper of claim 1 through which said turbine drives said generator.