基于原型振动测试的水轮机顶盖螺栓疲劳分析

以国内一大型高水头水电站为例,对水轮机顶盖振动展开变负荷稳定工况、开停机工况以及甩负荷极端工况下的原型测试和分析;建立顶盖及螺栓的有限元模型,结合实测振动数据与有限元动力分析,反演了顶盖水压脉动荷载;运用线性疲劳累积损伤理论和雨流计数法,结合机组一年内的实际运行方式,分别进行了年正常运行工况和甩负荷极端工况下顶盖螺栓的疲劳分析.计算结果表明:100 MW稳定负荷工况时顶盖水压脉动荷载双幅值约为19.3 m水头,为机组额定出力工况(600 MW)的5.6倍;同一工况下顶盖螺栓的破坏循环次数随存活率增大而出现较大程度降低,100 MW稳定负荷工况下存活率由95%增大至99%时,顶盖螺栓的破坏循环次数则由6.488×10⁷次降低到2.415×10⁷次,降幅为62.8%;考虑99%的存活率标准,甩负荷工况下的顶盖螺栓破坏循环次数为7.494×10⁵次,仅为各稳定工况下螺栓疲劳寿命的3%~5%.

Fatigue analysis of hydro-turbine head cover bolts based on prototype vibration measurement

Taking a high-head hydropower plant in China as an example,vibration of the head cover in a real hydro-turbine was mearued and analyzed under steady variable load,startup and shutdown,load-rejection conditions.A fininte element model was established for the head cover and connecting bolts,the fluctuating presure load on the head cover was detemiend inversely by making using finite element dynamic analysis base on the measured data.Fatigue of the bolts was anlayzed under normal ope-rating and load-rejection conditions by utilizing linear fatigue cumulative damage theory and rainfall counting method and by adopting actual operation modes of the turine in one year.The results indicate that the pressure fluctuating double amplitude is about 19.3 m on the head cover under 100 MW steady operating condition,which is 5.6 times that under 600 MW condition.Fatigue life of the bolts decreases sharply along with increase of survival rate.When the survival rate is increased from 95%to 99%under 100 MW condition,the fatigue life is decreased to 2.415×107 from 6.488×107,and the reduction is 62.8%.Taking 99%as a survival rate criteria,the fatigue life of the bolts is 7.494×105 under load-rejection condition,which accounts for only 3%-5%of that under various steady load conditions.