Thefeaturesofunsteadyflowsuchaspressurevariationandfluctuationinalargehydraulicturbineusuallyleadtotheinstabilityofoperation.Thisarticlereportstherecentinsiteinvestigationconcerningthecharacteristicfrequenciesinpressurefluctuation,shafttorsionaloscillationandstructuralvibrationofaprototype700MWFrancisturbineunit.Theinvestigationwascarriedoutforawideloadrangeof200MW-700MWintheconditionofwaterhead57m-90m.Anextensiveanalysisofbothtime-historyandfrequencydataoftheseunsteadyhydraulicbehaviourswasconducted.Itwasobservedthatthepressurefluctuationinadrafttubeisstrongerthanthatinupstreamflowpassage.Thelowfrequencywithaboutonethirdofrotationfrequencyisdominativeforthepressurefluctuationinpartloadrange.Alsotheunsteadyfeaturesofvibrationofheadcoverandtorsionaloscillationofshaftexhibitedthesimilarfeatures.Numericalanalysisshowedthatthevibrationandoscillationarecausedbyvortexropeinthedrafttube.Inaddition,astrongvibrationwithspecialcharacteristicfrequencywasobservedfortheheadcoverinmiddleloadrange.Thepressurefluctuationinthedrafttubewiththesamefrequencywasalsorecorded.Becausethisspecialvibrationhasappearedinthedesignednormalrunningcondition,itshouldbeavoidedbycarefullyallocatingpowerloadinthefutureoperation.
