Research On Non-contact On-line Detection Method And Technology For Vibration Of Shrouded Blades In Steam Turbines

Steam turbine is one of the key equipments in the field of energy power in China.As the core work element,blade directly determines the operation safety and efficiency of steam turbine.Statistics show that about 30% of turbine faults are caused by the blade vibration.Therefore,on-line detection of blade vibration in steam turbine is of great significance.Traditional Blade Tip Timing(BTT)technology can be used for noncontact vibration measurement of high-speed rotating blades,but it is mainly used for measuring the circumferential vibration of free blades and is not suitable for turbine shrouded blades dominated by axial vibration.Secondly,the high-speed steam flow environment of steam turbine imposes strict requirements on sensor reliability.In addition,few research results focus on the on-line vibration detection equipment and data processing algorithm for shrouded blades under actual operating conditions of power plant.In this paper,the shrouded blades of steam turbine are taken as the main research object.From the aspects of the measuring method for shrouded blades’ vibrations,sensor design,vibration parameter identification algorithm and other aspects,the non-contact on-line vibration detection method of shrouded blades in steam turbines is developed and the vibration detection system is developed.The main work is summarized as follows:(1)The structural characteristics of blade’s shroud and the vibration characteristics of shrouded blades in steam turbines are analyzed.Combining with the technical characteristics of tip timing,a vibration detection scheme for converting axial vibration at interlock of blade’s shroud into circumferential timing signal is proposed and the integral vibration detection scheme for shrouded blade-disc based on variable area of the eddy current sensor is developed.The schemes meet the requirements of noncontact vibration detection of shrouded blades in steam medium environment.(2)A vibration measurement method for shrouded blades based on improved BTT is proposed.Aiming at the shrouded blades with protruding edges,the vibration in axial direction is converted into circumferential timing signal by utilizing the edge and corner characteristics to realize vibration measurement of blades.An optical fiber tip timing sensor based on inclined lens is designed.The inclined angle of the lens is calculated according to the parameters of the lens and the installation position of the optical fiber,which improves the signal-to-noise ratio and meets the requirements of high-precision and long-distance tip timing vibration measurement.The eddy current tip timing sensor based on parallel resonance and three-coaxial cable is designed to reduce the influence of series resistance and distributed capacitance on the bandwidth,improve the response and meet the requirements of high tip rotating speed and steam environment.(3)A blade vibration event identification algorithm based on Included Angle Distribution(IAD)is proposed.The characteristics of the angle distribution between the blades are extracted by timing data,and the vibration event identification evaluation index is constructed by utilizing the correlation coefficient of the angle distribution characteristics of adjacent two-circle blades.Compared with the traditional algorithm,the proposed algorithm only needs one sensor to judge the vibration event of the blade and locate the vibration blade accurately,which meets the requirements of automatic and real-time identification of the vibration event of the blade.The rotor test results show that the proposed algorithm can effectively identify and locate synchronous vibration signals of blades using one sensor data.(4)A detection method of shrouded blade-disc’s integrated vibration based on eddy current area-varied type is proposed.A characteristic signal model of the shrouded blade with regular edge is established.Based on the modulation relationship between the vibration signal of the blade and the characteristic signal of the shroud,the vibration parameters such as frequency,amplitude and nodal diameter are identified accurately by means of spectrum analysis technology.The proposed method can continuously detect the vibration signal of shrouded blades,overcome the under-sampling problem of BTT,and meet the requirements of overall vibration measurement of shrouded bladediscs.(5)An on-line vibration detection system for shrouded blades of steam turbines was developed,a blade vibration verification platform in steam turbine balancing chamber was established.A vibration measurement test for shrouded blade tip was carried out.The test results show that,compared with strain gauge measuring system,the developed optical fiber tip timing sensor and system have better consistency.The frequency’s relative error is less than 0.35% and the amplitude’s relative error is less than 10%.The developed eddy current sensor and system can meet the requirement of670m/s blade tip linear speed.The overall vibration monitoring test of shrouded bladedisc by eddy rheological area method was further carried out.The measurement results agree with the design values.The systems had been installed in several power plant units and operated for a long time,showing that it meets the working requirements of steam turbines.