THEEFFECTOFHYSTERETICDAMPING ON TURBOGENERATOR SHAFTTORSIONAL OSCILLATIONS

damping associated with thevarious steamturbine stages [3], andshafts, should beincluded intheformulation. Theprincipal aimofthepresent Electromechanical interaction between anelectrical system and paper concerns thedevelopment ofamethod toaccount fortheeffect of turbogenerator units may,incertain circumstances, leadtoshafthysteretic material damping andtoenhance thetorsional modelformuoscillatory behaviour which hasanonerous effect onthelife expenditure lation toinclude theeffective variation indamping this produces. Inthe oftheshaft. Therate ofdecay oftheoscillations produced asaresult ofa paper, theeffect ofthis strain-amplitude related damping isillustrated by system disturbance isdetermined byboththeelectrical andmechanical comparing theturbogenerator shaft torques whenincluding these effects components ofdamping. Duetotheadvances madeinthemodelling of withthose obtained using theconventional constant viscous damping electrical machines overthepastfifty years theeffect oftheelectrical coefficient model. component ofdamping iswell understood andeasily incorporated into a system model. Themechanical components ofdamping areknown tobe Inthefollowing, theconfiguration oftheshaft arrangement hasbeen variable, butnevertheless areusually represented asconstant viscousretained soastobedirectly applicable andcommensurate with thewell coefficients intheshaft system equations ofmotion. Thepresent papertried andproven methods for theoverall analysis ofasystem. Theoverall proposes amethod fortheevaluation ofavariable damping coefficient representation ofthetypical practical system configuration usedinthe which depends ontheproperty oftheshaft material whenundergoing highstudy includes aphase coordinate modelforthesynchronous generator stress cyclic variations. Theeffect ofthis termistomorerapidly reducecombined with theequation ofthenetwork [13] andthetorsional lumpedthehigh torque oscillations andreduce lowtorque oscillations less rapidly. parameter modeloftheshaft arrangement. Theseequations arethen Thiseffect hasbeenobserved inpractice andhitherto notpredicted from arranged forsolution infirst-order differential form. Thesimulation model simulation studies. Theinvestigation relies onprevious workwhentakingusedinthestudies undertaken issummarised andthepaper isillustrated account oftheeffects ofvarious steamconditions. Emphasis isplaced on byresults which showtheeffect ofthevariable material parameter onthe thederivation ofashaft model which includes equivalent variable viscousshaft response. damping andrepresentative results arecollected toshowtheeffect ofthis important parameter onthepattern ofderived shaft torques based ona representative 600MW turbo-generator. 2.MECHANICALSYSTEMMODEL