| As the main power machinery of the power station,steam turbine plays a vital role in the safe and economic operation of the power station.At present,static and dynamic rubbing is a common fault in the actual operation of steam turbines,and the probability of rubbing at the end of low pressure(LP)casing is higher than that at the end of high and intermediate pressure(HIP)casing,which causes serious damage to the safe operation of steam turbines.Therefore,it is necessary to analyze the deformation and mechanism of gland seal housing at LP casing end,to determine the cause of gland seal housing rubbing,and to put forward measures to avoid rubbing fault.In this paper,based on the finite element method(FEM),the numerical analysis of the deformation of the LP inner casing and the gland seal housing on a nuclear steam turbine under different working conditions,the cause and specific location of rubbing are carried out.Firstly,the geometric model and finite element mathematical model of the LP inner casing of a 1000 MW high-power nuclear steam turbine are established,and the boundary conditions are determined.Secondly,the deformation distribution of LP inner casing and gland seal housing under different working conditions(vacuum pumping condition,full load working condition and whole start-up stage)are calculated in detail.Combining with the finite element calculation results,the cause and location of rubbing are found out.Then,several sensitive factors affecting gland seal housing deformation are analyzed in detail.The effects of the temperature of exhaust hood,gland seal housing and bearing housing,vacuum pressure,friction force and gland seal housing supply extraction pressure on the gland seal housing deformation are studied respectively.Finally,the measures to improve the rubbing of gland seal housing at LP casing end of nuclear steam turbine are put forward.The calculation results show that rubbing is most likely to occur in the gland seal housing at LP casing end of nuclear steam turbine under vacuum pumping condition before start-up,and the rubbing position occurs at the bottom of the outer side of the gland seal.The gland seal housing is upward and inclined inward,and the bottom clearance is reduced(the bottom of the gland seal housing is upward 0.5～1.2mm,the top is upward 1～2mm),which is highly consistent with the actual situation on site.During the start-up process,when the unit is rushed to low-load operation,the gland seal housing first presents the sinking trend,the bottom clearence increases(maximum value is 1.6mm),and the inward inclination is significantly weakened;during the load-lifting process,due to the action of thermal stress and steam pressure,the expansion of the LP casing increases rapidly,which drives the gland seal housing upward gradually.Although the bottom clearance is slightly reduced and the inclination degree of the gland seal is slightly increased,it is basically stable.Based on the calculation results,this paper proposes rubbing improvement schemes from the aspects of LP casing structure optimization and on-site commissioning operation.From the perspective of the structural optimization of LP casing,firstly,strengthening the structural strength of the top of the exhaust hood will effectively reduce the inclined deformation of the gland seal housing;secondly,strengthening the strength of the inner vertical plate of the exhaust hood will reduce the lifting of the bottom of the gland seal housing,thus effectively avoiding the occurrence of rubbing.In the on-site commissioning operation,cooling the junction area of vertical plate and inclined plate on the outermost side of the exhaust hood will effectively avoid gland seal housing rubbing.Finally,a rubbing improvement scheme that comprehensively considers the strength and cooling of the exhaust hood is proposed. |
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