Influence Of Different Tailrace Systems On Stability Of Hydro-power Station System

In the design and construction of hydroelectric station,according to different topographic and geological conditions,there will be obvious differences in length and structure of the tailrace system,which will have different effects on the operation and the stability of hydroelectric station.Furthermore,during the operation of a hydroelectric generating unit,there are some factors,such as power load disturbance and time-delay effect of hydraulic servo system,which will affect the stable operation of the system.As the core component of hydroelectric station,the hydropower generation system plays an important role in the stable operation of the unit and guarantee of power supply quality.Therefore,it is necessary to establish a nonlinear mathematical model which can accurately reflect the structure and operation characteristics of the hydroelectric station in different tailrace system and the unstable factors existing in the operation of the system.Then we focused on the influence of these factors on the stability of the system,and exploring the dynamic mechanism of system instability.Finally,the above research can provide some theoretical guidance for the stable operation of hydroelectric station.The main contents and conclusions of this paper are included below:（1）Considering the characteristics of free surface-pressurized flow has reciprocating interface motion and free surface flow has water level fluctuation in the inclined ceiling tailrace tunnel.Furthermore,electric load disturbance and stochastic change of hydro-turbine speed may exist during the operation.We establish a stochastic nonlinear mathematical model of hydropower generation system with inclined ceiling tailrace tunnel by using Fourier series expansion and Chebyshev orthogonal polynomial approximation theory.Based on a real hydroelectric station,we obtain the stable region of system parameter by using stability theory and MATLAB numerical simulation,then the influence of stochastic intensity and load disturbance on the stable region of are studied.The results show that the increase of stochastic intensity reduces the area of stability region,and when the stochastic intensity is greater than 0,the load disturbance has little effect on the stability region.Then,we study the effects of load disturbance,stochastic intensity and inclination angle on the dynamic response characteristics of the system.The numerical results indicate that under the conditions in this paper,the reasonable inclination angle is not more than 4%.（2）Considering the interrelation between the units in the hydroelectric station with sharing tailrace surge tank,the not controlled characteristics of surge tank in the process of regulation,and the time lag of the hydraulic servo system,then the corresponding nonlinear mathematical model of hydropower generation system with time-delay is established.Based on Hopf bifurcation theory,the stable regions of the system with different k_d1 values are obtained.Then the bifurcation characteristics of the system with different time-delay are obtained by numerical simulation and the corresponding stable intervals of k_{p 1} are counted.We easily get that k_d1and time-delay will affect the stable interval of k_{p 1},and when k_d1 changes,the influence of time-delay on the stable interval is different.Moreover,the influence of pipeline asymmetry on system dynamic response characteristics and stability is studied by changing the length of water diversion pipeline,and the results show that the shortening of the diversion pipeline is beneficial to the stability of the system.（3）Considering the poor stability of hydropower generation system with upstream and downstream surge tanks in single unit under disturbance,and the adjustment effect of traditional PID control strategy is not ideal,we apply nonlinear state feedback control strategy to hydropower generation system.Then,considering the influence of stochastic change of hydro-turbine speed,a nonlinear mathematical model of stochastic hydropower generation system is established.Moreover,based on numerical simulation,the stable region of system parameters,the influence of control parameters on the system dynamic response characteristics and the surge tank water level are obtained.Further,the simulation results are compared with the PID control strategy and the results show that the nonlinear state feedback control strategy obvious advantages over PID control strategy in regulating quality and response speed,but the fluctuation of water level in surge tank is more severe.Then,considering the stochastic change of hydro-turbine speed,the sensitivity of two control strategies to stochastic intensity is analyzed.It turned out that the stable region of the system under PID control is greatly affected by the stochastic intensity,but the change of the stable domain is not obvious under the state feedback control.In addition,in the stable region,the dynamic response characteristics of the system almost coincides with each other under different control parameters.