Study On Vribration Characteristics Of Bulb Tubular Generator Shafting

A bulb turbine generator is a device that converts water energy into electrical energy.Its working environment is complicated,It will vibrate during operation because it is affected by mechanical force,electromagnetic force,hydraulic force and other force.The shafting is the core component of energy conversion,and its vibration characteristics are important indicators for evaluating whether the unit is safe to operate.Therefore,it is necessary to conduct an in-depth study on the vibration characteristics of the shafting.This thesis took the shafting of 24 MW bulb turbine generator of Chaijiaxia Hydropower Station as the research object,and studied its self-vibration characteristics and transient response law.The progress of the research obtained is as follows :(1)An analytical model for the self-vibration characteristics of the shafting is established based on Riccati transfer matrix method.During the modeling process,according to the particularity of the bulb turbine generator shafting,it was proposed to add the angular stiffness of the thrust bearing to the transfer relationship of state quantity,the non-negligibility of the thrust bearing in the model was verified by calculating the critical speed of the shafting.Based on the model,the influence of the stiffness of the guide bearing and the negative stiffness of the unbalanced magnetic pull force on the first-order critical speed of the shafting is analyzed.The results show that the increase of the stiffness of the guide bearing will lead to the increase of the first-order critical speed of the shafting,however,critical speed value has a limit value;the negative stiffness of the unbalanced magnetic pull will reduce the first-order critical speed of the shafting.(2)In order to reveal the unbalanced response characteristics of the shafting,the influence of the unbalanced mass on the important part of the shafting system was studied by applying the unbalanced mass throughout the shafting system.The results show that,under the same conditions,when there is unbalanced mass at the runner,the displacement response of the whole shafting system is the largest;near the critical speed,the displacement response value of the shafting system will increa se sharply;the displacement response value is proportional to the unbalanced mass.(3)The transient dynamics analysis model of the shafting was established,and the boundary conditions of the shafting and the common unbalanced loads under actual working conditions were modeled.Based on the Riccati transfer matrix method and the Wilson-? method,the theoretical process of calculating the transient response of the shafting was derived and the corresponding calculation program was compiled.The transient response law of the shafting under typical load was studied.The results shows that when the unit is in actual operation,due to various unbalanced loads,the running track of the shafting is not always stable at the origin,because of the anisotropic characteristics of the oil film force,the trajectory of its stable operation is an ellipse;the runner is subjected to the unstable impact load and results in a sharp increase in the displacement response of the shafting and an irregular operation state for a period of time,because it is directly contacted with the water flow,the shafting of the unit will eventually converge to a stable operating state because of the damping effect of the oil film force,however,when the impact load is too large,the shafting is prone to excessive vibration.The research work in this paper is of great significance for the optimal design of the bulb turbine generator shafting and the fault state monitoring of the unit during actual operation.