Life Assessment Of Thermal Power Unit Shafting Considering Grid Flexibility

With the transformation of the global energy structure,it is imperative that renewable energy will access the power grid with a large scale.But considering the random volatility of renewable energy,it will bring a lot of uncertainty and affect the stability of the power system.The power system is required to have more flexibility to cope with this uncertainty.Thermal power unit is an important source of power system flexibility.When renewable energy is connected to the grid,it will be needed to track fluctuations of these distributed resources from serving the middle load.Due to the change of operating conditions,the fatigue loss of the thermal power unit is increased,and its life will be affected.The relationship between power system flexibility and renewable energy access is studied in this thesis.Flexibility is the power system's ability to respond to changes in both ends of supply and demand.The random volatility of renewable energy increases the change of the power supply side of the power system.Flexibility can be used as a criterion for renewable energy access to the grid.Power system with high flexibility can absorb more renewable energy.According to the operating characteristics of the thermal power unit,this thesis puts forward the index of evaluating the flexibility of the thermal power unit from the angle of the ramping rate.The index can evaluate not only the flexibility of a single thermal power unit in a given senario,but also the flexibility of the whole thermal power plant.By comparison,the flexible units and non-flexible units in this senario can be identified.The flexibility index is calculated by simulation,and its effectiveness is verified by the utilization rate of wind power.In this thesis,fatigue loss of thermal power unit is studied by ANSYS,the finite element analysis software,and coupled degradation model,respectively.In the ANSYS finite element analysis,the influence of the ramping rate and peak range on the torsional vibration fatigue loss is studied.It can be found that the torsional fatigue loss increases exponentially with the increase of this two factors.It is proved that the torsional vibration fatigue loss of the thermal power unit can be ignored when the peak-shaving is shallow,but it will be large at the deep peak-shaving.It also shows that the rapid fluctuation of renewable energy is the important factor that affects the life of thermal power unit.The advantage of ANSYS finite element analysis is that the established model is more accurate.It is suitable for analysing the influence of the factors on the life of thermal power unit.But it is not suitable for analysing the life change curve in a long term,which requires a lot of time and memory.According to the frequent adjustment of thermal power unit with renewable energy penetrated,this thesis uses the coupled degradation model to study the degradation process.This model coupls the dynamic model of the shafting torsional vibration with the degradation model based on the crack propagation.By analysing the relationship of the torsional vibration response,the degradation measure and the stiffness change,this model indicates that the torsional vibration affects the degradation,then the degradation causes stiffness change,and the stiffness change aggravates torsional vibration.The degradation curve of thermal power unit is obtained.An assessment method for the life of thermal power unit is obtained.