Sealing Ring Performance Analysis Of Large Hydrogen-cooled Turbo-generator And Its Influence On Vibration

Sealing ring is an important component of large hydrogen-cooled turbo-generator.Its induced unstable vibration often occurs in engineering.In this paper,single-flow and doubleflow sealing rings are taken as research objects.The performances of sealing ring and its influence on vibration are studied.Firstly,performance analysis of sealing ring is carried out by using the Ocvirk model based on infinitely short bearing theory and the CFD model.Meanwhile,a force analysis model of sealing ring is established.Results show that,in a case of small eccentricity ratio(less than 0.6),the calculation results of the Ocvirk model is basically consistent with those of the CFD model.Eccentricity ratio,rotational speed,radius clearance and sealing oil temperature have different effects on buoyancy force and leakage.When radius clearance is too large or sealing oil temperature is too high,the buoyancy force is low,and it is prone to jamming for sealing ring.When radius clearance is too small or sealing oil temperature is too low,it is helpful for the floating of sealing ring and the sealing of hydrogen.However,it is prone to rubbing.Besides,sealing ring will jam under large pressure difference between hydrogen side and air side.The single-flow sealing ring has greater buoyancy force(oil film force)and lower leakage than double-flow one.When the buoyancy force of sealing ring is below the sum of its gravity and friction force,it will jam,and sealing ring will rub against with rotor.The rotor suffers from unstable vibration fault induced by the coupled heat and force impact due to rubbing of sealing ring.Based on the force analysis model of sealing ring,the jamming condition is analyzed.The vibration analysis model of rotor system under rubbing thermal shock caused by sealing ring is established.The rubbing vibration and its influencing factors are studied.Results show that,the rubbing thermal shock due to sealing ring causes rotor thermal bending.When the generator is running below the critical speed,the rotor system vibration diverges.The vibration frequency is rich,and the axis orbit is irregular.It is easy to develop from local rubbing to full-circle rubbing.When the generator is running above the critical speed,the rotor system vibration fluctuates periodically.The synchronous component(1X)is extremely dominant in frequency spectrum.The axis orbit is disordered during rubbing,and is regular in thermal bending recovery period.Generally,sealing ring rubs against rotor slightly,which is difficult to cause divergence of vibration.Reducing initial unbalance of rotor,increasing sealing clearance and sealing oil temperature can reduce rubbing of sealing ring.Therefore,the vibration induced by rubbing of sealing ring can be reduced or prevented by increasing sealing clearance properly during design or installation of sealing ring,increasing sealing oil temperature properly during operation of generator,and reducing initial unbalance of rotor by dynamic balance technology.There is another kind of unstable vibration fault which is similar to rubbing of sealing ring in engineering,and it is easy to be misdiagnosed as rubbing of sealing ring.Some previous studies show that it is related to thermal effect caused by rotor whirls in a small gap.The viscous shearing within oil film in the small gaps between sealing ring,bearing and rotor may cause rotor surface circumferential temperature difference.The rotor surface temperature difference results in temporary rotor thermal bending,which leads to a rotor vibration fault.To investigate the thermal unstable vibration caused by rotor whirls in a small gap,an analysis model of rotor surface temperature distribution is established.The rotor surface circumferential temperature difference and its influencing factors are studied.Meanwhile,its influence on rotor vibration is analyzed.Results show that,the rotor surface circumferential temperature difference is caused by viscous shearing within oil film under rotor whirls in a small gap.The rotor surface temperature difference under large static eccentricity ratio,large whirl amplitude,high rotational speed and small radius clearance is larger.The influence of rotor surface temperature difference on rotor vibration is determined by working and critical rotational speed.Reducing the initial(mechanical)unbalance not only reduces the shaft vibrations,but also decreases the rotor surface circumferential temperature difference.Finally,in order to prevent the sealing ring from jamming,arranging shallow grooves on the sealing surface of sealing ring is proposed to promote the buoyancy force.CFD models of shallow-groove sealing rings are established.Comparative analysis between sealing rings with shallow grooves and smooth sealing surface is carried out.Results show that,the maximum pressure in the dynamic pressure area can be effectively raised after shallow grooves arranged on sealing surface.The buoyancy force of shallow-groove sealing ring is larger than that of sealing ring with smooth sealing surface.It can effectively prevent the occurrence of jamming fault.Its leakage is also larger.It is necessary to increase the amount of sealing oil to seal the hydrogen in generator.Compared with shallow-groove sealing ring without dam area,the shallow-groove sealing ring with dam area has higher buoyancy force and lower leakage,however its structure is relatively complex.during the design and engineering application process,it is necessary to comprehensively analyze the performance,processing difficulty and dam area width.