Study On Flow Mechanism Of Transition Process Of Pump Storage Group Based On 1D-3D Coupled Method

Pumped storage power station plays a very important role in the construction of modern power grid.Its role is not limited to peak and valley filling,but also plays an important role in frequency regulation,phase regulation and emergency standby.In order to realize the regulatory role in the power grid,pumped storage power station must be converted between different working conditions several times every day,and repeatedly undergo the transition process.As the core component of pumped storage power station,the pump turbine will appear obvious unstable phenomenon during the transition process.In order to explore its evolution law and reveal its formation mechanism and influencing factors,this paper firstly adopts a 1D-3D coupled numerical simulation method to conduct numerical simulation and analysis of typical transition processes of a pumped storage power station,such as water pump shutdown and conductive vane closing process,turbine runaway process and turbine load rejection process.Then the time-frequency characteristics of various transient signals are analyzed by using short-time Fourier transform method,and the formation mechanism of various pressure and water thrust pulsation is explained by analyzing the internal flow field.Finally,the influence of four kinds of guide vane closing laws on the transient characteristics of hydraulic turbine load rejection process is compared.The results show that:(1)In the process of automatic closing of ball valve and guide vane after pump failure.The main instability phenomenon occurs at the moment when the flow rate of the pump condition decreases rapidly and the rotation speed direction of the unit changes,mainly in the vaneless area and the inlet area of the draft pipe,which is caused by the collision and backflow of water bodies in different directions.(2)In the process of turbine load rejection,the instability phenomenon mainly appears at the moment when the flow rate drops to zero,and obvious vortex structure appears in the vaneless area and the area between stay vane and guide vane,which leads to the complex pressure pulsation phenomenon and the uneven radial force of the runner.In the turbine runaway condition,there is an obvious low-frequency pressure pulsation near the runaway point of the turbine unit which comes from vaneless area.The unstable vortex structure formed in the va neless area leads to the low-frequency pressure pulsation inside the turbine unit,which leads to periodic fluctuations in the external characteristics of the turbine unit.(3)Different closing rules of guide vane have a great influence on the characteristics of the unit,mainly affecting the change of the speed of the unit,the pressure change of the inlet and outlet,and the frequency and amplitude of pressure pulsation.The two-stage closing law has obvious effect on improving the stability of the unit,but the selection of the two-stage closing slope and inflection point needs further analysis and research.