Torsional Vibration Mechanism And Safety Analysis Of Turbo-generator Shafts

With the increase of the single-unit capacity of the steam turbine generator sets,the rotor structure is becoming more and more complex.In addition,most of the power is transmitted over distance,so series compensation is put into operation or HVDC transmission is adopted.These factors all increase the risk of torsional vibration failure of steam turbine generator sets.In addition to the power oscillation caused by the torsional vibration of the unit,the torsional fatigue damage of the shafting is caused,which threatens safety operation for power plant,.Therefore,it is of great significance to carry out the analysis of the torsional vibration failure mechanism and the safety of the shafting of the steam turbine generator set.This paper deeply studies the mechanism of torsional vibration of steam turbine generator sets,and the small signal stability and transient torque characteristics are analyzed qualitatively and quantitatively.And the on-line monitoring and protection system for torsional vibration of steam turbine are developed combining the fatigue damage calculation method of shafting system,and provide safeguard for the safe operation of the unit.Firstly,the faults are divided into impact type and resonance type fault according to the fault form,and the mechanism and fault characteristics of torsional vibration faults are studied in this paper.Transient torsional torque response characteristics of the shafting are analyzed in detail for the torsional vibration faults.Subsynchronous oscillation occurs in a complicated mechanism,various incentives and fault formation processes of subsynchronous oscillation are analyzed qualitatively.Full-band damping of systems within 50 Hz is calculated quantitatively by complex torque coefficient approach based on the system-wide linearization model of the system to be studied,mechanism of subsynchronous oscillation is lucubrated From the point of negative damping,the factors which effect the SSR are analyzed.Secondly,mechanical-electrical-network co-simulation is adopted based on multi lumped masses model to analyze transient torque characteristics in torsional vibration.The simple lumped masses which is adopted extensively can not reflect the oscillation of generator-network accurately.The simple shaft model with several masses in PSCAD is replaced with a complicated model with hundreds of masses,the transfer matrix-step by step integral method and reducing-order method are adopted to calculate the torsional response respectively,the co-simulation method is realized under the unify platform of PSCAD which makes the torsional vibration study more complete,the local torsional torque and stress can also be got.Nextly,the torsional fatigue damage of the shafting under torsional vibration is evaluated,besides the various dangerous sections of the shafting,the paper considers the key parts such as blades and coupling.For this purpose,the coupling model of rotor-blade is established,and the torsional response of blade is calculated by the transfer matrix method.The finite element method is used to calculate the torsional stress of coupling under torsional vibration,especially the stress of connecting bolts under different torsional moment.As the key for evaluating the fatigue damage,S-N curve is always affected by many factors.mean stress and stress concentration are considered when correction S-N curve is got.Finally,the torsional vibration diagnosis technology and analysis methods of the system safety are applied to engineering practice,an on-line monitoring and torsional vibration protection systems for turbo generator shafting are developped.Based on the engineering requirement of a CGNPC plant,combining the theory of fault diagnosis and safety analysis,the on-line monitoring system is developed and the B/S mode is adopted,it can judge the fault types and choose different methods to calculate the torsional response depending on it is resonance fault or impact fault,so the system can evaluate the shafting torsional vibration safety quickly and accurately.In addition,the torsional protection device,torsion stress relay(TSR)is developped,different levels of relay protection logic is made based on fatigue damage value,so it can not only provide timely protection to the unit,but also avoid unnecessary protection actions.