The Dynamic Process Of Hydro Power Station And Its Effects On The Power System Stability

With the building and operating of large-scale hydro power stations and pumped storage plants, the water power proportion in our country is increasing year by year and the effects of hydraulic system dynamic process which includes conduit system and hydroturbine on power system stability is standing out. In the current stability computation of power system, simplified models of hydraulic system are usually used which assume rigid water hammer models of simple conduit and ideal hydroturbine model. The layout and parameters of conduit system and hydroturbine in every hydro power stations and pumped storage plants are different according to their geology and geography condition. The complex conduit system usually consists of tunnels, penstocks, surge tanks and tail pipes etc. The simplified models of hydraulic system can't fit to transient stability computation of power system and can't reflect hydraulic variables of hydro power stations in the dynamic process. It is important to establish detailed models of complex hydraulic system, to carry out dynamic simulation of hydro-electrical system and analyze rules of hydraulic variables under large disturbance and effects of hydraulic system dynamic on transient stability computation of power system.It is proposed in this thesis a dynamic emulational method of complex hydro-electrical system by power system analysis software package(PSASP). PSASP a powerful software package for power system analysis, but the hydraulic system model provided in it is a simplified one, that is rigid water hammer model of conduit and ideal hydroturbine model. In order to analyze dynamic process of hydro power station with complex hydraulic system, user-defined model function of PSASP is necessary to adopt detailed models of hydraulic system or user program interface function to call program. With these functions, a emulational method of complex hydro-electrical system under large-disturbance is proposed, especially a emulational method by user-defined model function is presented in one-conduit multi-units conduit system. Using this method ,we can analyze dynamic process of hydro power station and effects of detailed models of complex hydraulic system on transient stability of power system.In the thesis a nonlinear Bergeron model of uniform conduit is deduced and itsapplications in the hydro-electrical system simulation are carried out. In terms of thesimilarity of the water wave equations in uniform conduit to the electromagnetism wave equations in uniform transmission lines, the nonlinear Bergeron model of uniforms conduit is deduced and its equivalent circuit is established. Comparing with traditional characteristic equation arithmetic used in hydraulic transient computation of hydro power stations under large-disturbance, this model is understandable and easily used for power system stability researchers. Based on the segmental uniform conduit system, a user program of hydraulic system is made by Visual C++ software. Through the user program interface function supplied by PSASP the simulation of multi-units hydro-electrical system under large-disturbance achieve reasonable and reliable results.Firstly the linearized models of conduit system are used in simulations of the large-disturbance transient of hydro power station with complex hydraulic system. It is introduced in this thesis equivalent circuit models of hydraulic typical components, such as uniform conduit, surge tank, series connected point etc. The linearized equivalent circuit of complex conduit system can be set up straightly by using above models, block diagram also can be established subsequently. The model can describe dynamic characteristics of complex conduit system, take into account the penstock and water column elasticity and hydraulic coupling between units. It is simple and intuitionistic to use this model in large-disturbance transient simulation of hydro power station with complex hydraulic system and easily accepted for power system stability researchers.Models of hydraulic system mainly include models of conduit system and hydroturbine. The simplified analytic nonlinear model and the linear model based on the model characteristic curves of Francies' hydroturbine are introduced and analyzed. It is believed that the proper model should be selected according to the study purpose and known conditions.As an example and based on Xiaolangdi hydro power station with complex hydraulic system, different models of hydraulic system used in Henan power system transient stability analysis are established through combination of different models of conduit system and hydroturbine. Using the user-defined model function of PSASP, user-defined models of hydraulic system are set up, also the effects of different models of hydraulic system and hydraulic coupling on transient stability computation are analyzed.