Research On Transmission Shafts And Breaking System Of Megawatt Vertical Axis Wind Turbine

As an important part of the high power vertical axis wind turbines,transmission system and braking system plays a vital role for the entire wind turbine operation and safety.At present,the market share of large power vertical axis wind turbine is very small.There is no fixed design system for the transmission system of large power vertical axis wind turbines,and the majority of vertical axis wind turbines do not have variable pitch systems,which results that the required mechanical braking torque is very large.To resolve this problem,the transmission system and braking system of megawatt vertical axis wind turbine were studied in this paper.In this paper,the aerodynamic characteristics of the stroke wheel were calculated by fluent numerical simulation method,and the loads under different working conditions were determined.The different transmission schemes of wind turbines were compared,and an optimal structural scheme was selected.This structural scheme was that the whole machine is driven by semi direct drive,and the speeder and generator were arranged near the ground.The three stage bearings were mounted on the drive shaft.And the main bearing(class I bearing)is slewing bearing,upper guide bearing(class II bearing)is spherical roller bearings,bearing(class III bearing)is thrust roller bearings.For the convenient of installation,the upper and lower guide bearings were split bearing.According to the load,the structural dimensions of each shaft of the drive shaft were determined,and static fatigue analysis and dynamic modal analysis were carried out.Than the critical speed of the shafting structure was obtained to ensure that resonance can be effectively avoided.In order to study the wind turbine braking system,the model of the braking system was established firstly and the force analysis of the arrester installed in different positions was carried out.According to the different braking conditions,the braking torque and braking time of the mechanical braking system were calculated.The braking scheme was finally determined,which is break was mounted both on high speed shaft and low speed shaft.And the numerical calculation of temperature field and stress field was carried out by ANSYS.In the paper,cyclic loading heat flux was used at equal time intervals,the temperature field of friction pair of low speed shaft and high speed shaft were simulated respectively under the condition of normal wind speed and rated wind speed.The results showed that the temperature distribution of the brake disc is inhomogeneous,and the high temperature zone was mainly on the friction contact surface.The brake lining temperature was much higher than the brake disc,and the surface temperature distribution was more uniform.Under the two conditions,the temperature distribution of the brake disc and brake lining was similar,and the temperature in the emergency condition was relatively high.It will cause the internal stress of the structure when the temperature rises too much.In this paper,the mechanical stress analysis and the thermal stress analysis were carried out respectively when the temperature rise are considered or not.The result showed that the thermal stress caused by temperature rise plays a leading role in the stress field of the brake,and the variation law of thermal stress was similar with that of temperature field,but there were also some differences Through the stress field analysis,it could be judged whether the brake disc will cause thermal crack or failure,which provides reference for the improved design of the brake disc.