| With the development of human society,the demand for energy is increasing.The conventional energy such as oil and coal is limited and non-renewable,and the environmental pollution caused by conventional energy sources is becoming increasingly serious.With the increasing pressure from energy and the environment,it is imperative to seek new energy sources for development and utilization.Wind energy,as a kind of clean energy which is easy to be developed,has received more and more attention.In 2015,Chinese has installed a capacity of wind power has reaching 129 GW,the first in the world.But the failure frequency of wind power equipment servicing currently is high.Gearbox is a key component of the wind turbine,its failure accounts for 19.4% downtime of wind turbine,and about 60% failure of gearbox is caused by gear.The thesis regards the power split type 2.5MW wind turbine gearbox as object,The FMECA and FTA were completed based on the load spectrum obtained by monitoring for years on Wind Farm and the result of finite element analysis,then the main failure modes and mechanisms were determined.Study the reliability of gear in gearbox based on Monte Carlo method with the randomness of load and parameter considered.During fulfill this work,the main research includes:Firstly,briefly state the background and meaning of the dissertation,the development status of wind power.The current research status of load calculation in wind turbine gearbox,gear transmission system,planetary gear transmission and the reliability of gear transmission system was summarized.Introduce the main contents of the dissertation.Secondly,Finite element software was used to analyze the stress and deformation of the gearbox based on the structure,material,working mode and environment of 2.5MW wind turbine gearbox and the relationship between the spindle torque and the number of revolutions in20 years acquired by monitoring for years on Wind Farm,that is,the LDD(Lord Duration Distribution).Combined the results of finite element analysis with the failure data of existing wind generator gearbox in the same or similar working environment,then the detailed FMECA and FTA of 2.5MW wind turbine gearbox were completed based on the above results.The analysis results show that the main failure modes of 2.5MW wind turbine gearbox are pitting and breaking of gear,another called contact fatigue and bending fatigue failure,As well as contact fatigue failure of bearing.The weakest parts are the secondary planetary and tertiary helical gears,as well as the bearings installed at output shaft and the secondary planetary shaft,which provides the basis for the reliability evaluation.Thirdly,according to the transmission principle of power split type 2.5MW wind turbine gearbox,the calculating formulas of the tangential force were established based on the torqueand power balance theory of planetary differential gear train,the distributions of the tangential forces of the gear pairs were obtained by calculating with the LDD spectrum.The result provides the basis for calculation the fatigue reliability of gears.Fourthly,According to the main failure mode and mechanism of 2.5MW wind turbine gearbox,regarding the contact fatigue and bending fatigue reliability of each gear are ensured as the design criterion.The reliability calculation model was established by using the stress-strength model theory.The formulas to calculate contact stress and bending stress of gears were established.The randomness of parameters in the formulas was studied.The distributions of contact stress and bending stress of gears were obtained by Monte Carlo simulation with the distribution of load and the randomness of each parameter considered.According to the materials of gears,manufacturing and heat treatment processes,and working condition,the distribution of contact fatigue strength and bending fatigue strength of gears were obtained by Monte Carlo simulations with the randomness of parameters considered.The contact fatigue and bending fatigue reliability of the gears for 20 years were obtained by Monte Carlo simulation based on the stress-strength model.Fifthly,the fatigue reliability model of gears was established with the correlation of the two failure modes considered,the fatigue reliability of gears were obtained.The fatigue reliability of the gear was analyzed and calculated with the strength degradation considered.The reliability model of gear transmission in wind 2.5MW turbine gearbox in service period of 20 years was established with the correlation of the gear failure considered,and the reliability model of gear transmission in 2.5MW wind turbine gearbox was obtained.Finally,the research work of this thesis was summarized and the future research about this topic was briefly presented. |
