部分进汽下汽轮机不稳定振动及抑制方法

Turbine Unstable Vibration and Its Reduction Method under Partial Admission Mode

汽轮机组在部分进汽模式下运行时容易出现不稳定振动。以某台大型汽轮机组为例,应用计算流体力学(Computational fluid dynamics,CFD)技术,建立调节级叶片不均衡汽流力计算模型,给出不同阀序下汽流力变化情况。不同进汽工况下不均衡汽流力大小和方向相差很大,汽流力作用到转子上后改变轴颈在轴承内的偏心率和偏位角,从而改变轴承动力特性。建立转子-轴承系统动力特性有限元模型,分析阀序切换过程中不平衡响应和稳定性变化情况,从剩余汽流力角度解释阀序切换过程中所出现的不稳定振动机理。实例说明,部分进汽状态下所出现的不稳定振动受调节级侧轴承所承受载荷的影响较大,轻载轴承特别容易出现不稳定振动。从轴承标高调整角度提出不稳定振动抑制方法。在瓦温不超标的前提下,应适当抬高调节级侧轴承标高。

Unstable vibration is likely to occur on turbine unit under partial admission mode. The computational fluid dynamics （CFD） model to calculate the uneven steam force of governor stage for a turbine unit is set up. Steam force at different valve sequence case is given. It is shown that difference of the magnitude and the angle of the uneven steam force at different partial admission mode is large. Journal eccentricity and load angle in bearing and bearing dynamics are changed a lot under the influence of steam force acting on rotor. Rotor bearing dynamic model to calculate the unbalance response and system stability during valve change process is set up using the finite element method. Rotor unbalance response and stability at difference partial admission mode is researched. The mechanism of the unstable vibration is explained on the base of the influence of uneven steam force. It is found that the unstable vibration under partial admission is influenced by the load of bearing near governor stage largely. The unstable vibration is likely to occur on lightly loaded bearing. A method to reduce the influence of partial admission is put forward. Elevation of bearing near governor stage should be raised properly on the premise that bearing temperature is not high.