Research And Application On Steam Excited Vibration Characteristics Of 1000MW Ultra-Supercritical Steam Turbine

With the rapid development of China’s electric power industry,supercritical,ultra supercritical thermal power unit with large capacity has become the main force in the grid,There are 97 units of 1000MW steam turbine sets in service and including the building units are nearly 68(by the end of 2016),which ranked the first place in the world.At the same time,the proportion of large capacity units of ultra super-critical in the power grid are increasing constantly.Therefore,the safe and reliable operation is an important guarantee for the safe operation of power grid.The problem of steam excited vibration has appeared in different steam turbine sets at home and abroad.The main manifestation is the low-frequency vibration of high pressure rotor and valve with the large load operation of turbine.According to the mechanism of steam excited vibration and the operation experience of large capacity units,it has been confirmed that the steam excited vibration fault is more likely to occur in the high pressure(or high and middle pressure)rotor of high parameter and large capacity steam turbine.It has appeared in some of the 1000MW ultra super-critical units in China,which affects the safe operation of the turbine seriously.From the mechanism of steam excited vibration we know that the eccentricity of the rotor leads to the uneven leakage of the circumferential clearance.The tangential excitation force perpendicular to the axis is generated in the circumferential direction of the rotor which makes the rotor be an asynchronous vortex.There are many factors that cause the gap excitation force due to the impeller eccentricity,which brings certain difficulties to the theoretical analysis and the experimental research.In the present study,different emphases are placed on the theory,the experimental platform,mathematical description,numerical analysis and other aspects.In the actual engineering application research,qualitative analysis is more emphasized than quantitative analysis.In view of the above situation,this paper will take a 1000MW steam turbine vibration excitation case as the research object,and study the following aspects:First of all,the mechanism of steam flow excited vibration generated is analyzed.According to the analysis of steam excited vibration of a 1000MW steam turbine,the vibration data of the unit is extracted;the vibration characteristics are analyzed;the vibration type is judged;and the possible factors of steam excited vibration are analyzed.Secondly,in different operating conditions,the formation of the static steam force and the governing stage impeller vortex excitation force are analyzed.The calculation results show that the static steam force and the weight of the rotor in the same magnitude,static steam force has a great influence on the vibration.The vortex induced vibration force of the impeller is about 20%of the rotor weight,which is the second to the exciting force.Besides,a 3D model is consistent with the parameters of seal and governing stage blade tip seal.By using the axis orbit diagram of tripping as a dynamic eccentric basis,the numerical simulation of vortex induced vibration force is carried out.The results show that the excitation force is not large,but the vapor film cross stiffness magnitude reaches 106 and 107,and the damping is small,or negative.Although it is less than the bearing oil film that the cross stiffness magnitude reaches 109,the stability of the system is adversely affected because of its negative damping.When the original system stability margin is not enough,this part of the steam excitation may affect the stability of the turbine,especially at high load area.Finally,according to the results of the analysis and the research,the corresponding steam flow excitation control scheme is formulated:(1)The field test uses a new valve opening sequence so that the turbine successfully crosses the original load limit from 928MW to 961 MW.The vibration situation can be improved but the problem still exists.The regulation mode of steam turbine caused by steam is the static steam force which can not be completely eliminated;(2)By increasing bearing capacity,balance the bearing load and adjust to the bearing clearance to reduce the eccentric.The steam excitation force is further treated.The turbine reaches 1028MW successfully,and the vibration values are within the normal range;(3)Replace the anti-rotation seal at the first two stages of high pressure and the first ring of high pressure front shaft high to improve the stability of the steam film.So,the load raises up to 1083MW,close to the maximum rated power,and the vibration in normal range.This research is a presentation of practical engineering example:from the sets tripping due to vibration,to the analysis of the vibration characteristics which determine the type of vibration,to the analysis the reasons of vibration and calculation one by one,and test scheme is determined,the implementation of the corresponding control measures,so that the unit steam-induced vibration force is gradually improved and basically eliminated in the end.At the same time,the accuracy of the results is verified by the effective control of the unit vibration,and it offers the experience to the same type units with the value of engineering application.