| With the development of the national energy system planning and construction,the construction of pumped storage power stations has become an essential and important part.It is explicitly stated in the medium and long-term planning for pumped storage that the total scale will reach about 120 million kilowatts by 2030.Due to the strong controllability of pumped storage power generation and its ability to adapt to the changing power load demands,it can play an important role in peak shaving and frequency regulation in the power grid,while ensuring the stable operation of the power grid,thus having broad development prospects.The power house of pumped storage power station has the characteristics of complex structural forms,hydraulic,mechanical,and electrical vibration source loads coupled together.As the core site of energy cycle conversion of pumped storage engineering,the stable operation of power house structure is related to the safety of the whole project.However,the vibration response characteristics and key vibration sources of various structures of power house under various conditions are not fully understood in the hydropower industry at present.Various assumptions are required for the simulation of vibration problems in finite element numerical analysis,which greatly restricts the anti-vibration design and dynamic optimization of power house structure of pumped storage power station.In this paper,the underground power house structure of a pumped storage power station is taken as the research object,and the vibration response of power house structure under different conditions is collected by means of on-site vibration test method.The different conditions include stable operation conditions of power generation and pumping,and transient conditions of start-up,shutdown and load rejection.Vibration characteristics and source contribution of floor,wind cover of generator pier,stair and column structures are studied by time and frequency domain analysis.The frequency spectrum characteristics and application methods of vibration loads are studied by combining finite element numerical simulation.The main research contents and results are as follows.(1)The peak and effective value of vibration response of each structure of power house are obtained by time domain analysis.It is found that the vibration response characteristic values of each part of power house rapidly decreases from no-load to 50% output.The characteristic value of vibration response decreases slightly in the range of 75%～100% output,which indicates that the range is better for unit operation.The vibration response of the floor structure shows a pattern in which the vibration response was greater in the turbine floor than in the busbar floor and the generator floor in terms of elevation.In terms of the plan,the vibration response is greater in the open part than in the non-open part,and in terms of direction,the vibration response is greater in the vertical direction than in the water flow direction and the longitudinal axis direction.The vibration response of stair structure decreases with increasing elevation.The correlation between column vibration response of the column and the elevation is not significant.(2)Frequency-domain analysis is used to obtain the vibration source contribution of each typical component of the power house under steady-state operating conditions.The contribution of mechanical vibration sources to the vibration acceleration of each structure of the power house is relatively large under low output conditions.With the increase of output,the contribution of mechanical vibration sources gradually decreases,and the contribution of hydraulic vibration sources gradually increases,eventually occupying the dominant position.For the column structure,the electrical vibration source has a greater contribution.Under the condition of full output,the vibration acceleration of each structure of the power house is controlled by high frequency pulsating pressure(multiple frequency of turbine blade number),the vibration displacement is controlled by low frequency pulsating pressure(low frequency of draft tube),and the vibration speed is controlled by the above two kinds of frequencies.The vibration response characteristics of each structure of the power house and the contribution of the three types of vibration sources are similar for the pumping and power generation conditions,which is beneficial to the long-term pumping and power generation cycle.The test results of the two units show that setting structural joints between the powerhouse structures of each unit can effectively limit the vibration superposition effect.(3)Based on the vibration acceleration time-domain diagram of transient operating conditions,the peak value and relative time of vibration acceleration of each structure of the power house are comprehensively analyzed,and two main transmission paths of vibration energy are obtained.Path one is that the pulsating pressure in inside the turbine is transmitted to the stator foundation,the lower frame foundation and the top of the wind cover through the main shaft and thrust bearing of the hydro-generator.Path two is that the pulsating pressure in the spiral case and draft tube is transmitted to the floor of the turbine floor,the busbar floor and the generator floor successively through the concrete outside the spiral case,the wind cover and generator pier,the column and the wall.(4)The finite element numerical simulation combined with on-site data is used to analyze the dynamic load of the unit.The amplitude of the dynamic load of the unit under the frequency and twice the frequency of rotor blades is obtained.The results show that the dynamic load amplitude of the unit is significantly smaller than that specified in the plant design code.A refined numerical model including the head cover structure was established for vibration analysis under pulsating pressure and dynamic load of the unit,and then compared with on-site measured data.The results show that the pulsating pressure application scheme for establishing a fine model of the head cover structure is closer to the measured results,and it is necessary to establish a fine model including the head cover structure or consider the pulsating pressure effect at the head cover when using finite element numerical simulation. |
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