Vibration Testing And Analysis Of Underground Powerhouse Of Large Pumped Storage Power Station

High head and bidirectional frequent start-up are the main operating characteristics of pumped storage power station,so the vibration problem inevitably exists in the structure of powerhouse.Since a large domestic pumped storage power station put into full operation eight units,the vibration problem of workshop structure has appeared in varying degrees,especially in the weak part of stairwell.Entrusted by the Pumped Storage Power Station Construction Bureau,the project team of Wuhan University undertook the project of "Vibration Research on Underground Powerhouse Structure of a Large Pumped Storage Power Station in China".Based on the project of structural vibration research of underground powerhouse of Large Pumped Storage Power station,the vibration performance of underground powerhouse of this power station is systematically studied by combining field vibration test with finite element numerical simulation analysis.The main research results are as follows.(1)Using finite element software ANSYS,the vibration performance of underground powerhouse structure of a large pumped storage power station in China is simulated and analyzed by finite element method.Four kinds of finite element models are established considering different connection forms between upstream and downstream side walls and surrounding rocks.Among them,model 1 is the calculation model of underground powerhouse structure without considering the effect of surrounding rock,model 2~4 is the calculation model of underground powerhouse structure with different action of surrounding rock.Through the comparison and analysis of the calculated and measured natural frequencies of underground powerhouse structures,it can be seen that except model 1,the calculated frequencies of model 2~4 calculated by dynamic elastic modulus are close to the measured values,and the measured frequencies are in the middle of the calculated frequencies of model 2~4.Therefore,it can be considered that the finite element modal analysis results and field modal test results of the underground powerhouse structure of pumped storage power station in this paper are reasonable and credible.The calculated frequencies of model 3 based on dynamic elastic modulus are close to the measured values in order 1-6.It can be concluded that the assumption of boundary conditions and the calculation method based on dynamic elastic modulus of model 3 may be closer to the actual situation of the underground powerhouse structure of the pumped storage power station.Based on the actual site conditions of this project,it is reasonable to select the factory building structure and surrounding rock model of model 3 in the finite element modal analysis.(2)The results of finite element analysis reveal the distribution of large vibration displacement in underground powerhouse structure,which provides a theoretical basis for the layout of measurement points for field vibration testing of underground powerhouse structure.The larger vibration displacement mainly occurs at the top of wind shield of generator floor,ball valve suspension hole of generator floor,rectangular long hole of upstream of generator floor,outer side of staircase opening of intermediate floor,top of intermediate pier,suspension hole of ball valve of intermediate floor and stator foundation plate above dismantling hole of machine pier.In the field detection,vibration displacement measurement points should be arranged near the displacement calculation points of these parts,and the emphasis should be placed on the placement of vibration displacement measurement points at the entrances of suspension holes,staircases and other holes.(3)Through the field vibration source test,it is found that the main vibration source of the pumped storage power plant unit is the uneven flow(vibration frequency is 75Hz)generated by the runner blade in the volute,and the secondary vibration source is the harmonic load(vibration frequency is 8.33 Hz or its multiple).Other vibration sources include the hydraulic vibration(vibration frequency is 0.5Hz,0.75 Hz,etc.)generated by the tailrace vortex belt and the multiple frequency vibration component of the frequency conversion of some units generated by the operation of the unit.It is also found that the vibration displacement of underground powerhouse structure of pumped storage power station is mainly caused by tailrace vortex band and unit frequency conversion;the vibration energy produced by pump turbine is relatively large,while the vibration energy produced by generator is relatively small;pumping or power start-up conditions is a disadvantageous condition of structural vibration of underground powerhouse under normal operation of pumped storage power station.The results of field vibration source test and finite element calculation show that the main frequency components produced by vibration sources are avoided in the design of building A and B structures,and no "resonance" occurs.(4)Through the dynamic response test of a single unit on site,it is found that the maximum vibration displacement of underground powerhouse distributes along the floor as follows: the vibration displacement of the hydraulic turbine layer is the largest,and the vibration displacement of the intermediate layer is close to that of the generator layer,but is obviously smaller than that of the hydraulic turbine layer.The difference of the dynamic response along the floor is consistent with the vibration energy produced by the generator and the turbine.Hydraulic turbine floor in storage power station is a component with weak stiffness and strength in underground powerhouse structure,and it is most vulnerable to induced vibration.(5)Through the dynamic response test of load rejection of two units on site,it is found that the load rejection condition is more disadvantageous than the disadvantageous condition of the structure vibration of underground powerhouse under normal operation.It can be considered that the load rejection condition is the most disadvantageous condition for the vibration of underground powerhouse during the operation of pumped storage power station(normal and abnormal operation).The emergency measures for vibration reduction of pumped storage power station when sudden load rejection occurs should be studied based on the field measured data.(6)Through the analysis of field vibration test results,it is found that the setting of structural joints between units has a good energy dissipation effect on the vibration energy generated by the operation of adjacent units,thus the vibration reduction effect on the powerhouse structure is very obvious.It shows that the structure of underground powerhouse of this pumped storage power station adopts a series of vibration reduction measures,such as "one machine and one joint" structural arrangement,1 m thick concrete wall for side wall and pouring into a whole by connecting anchor rod and surrounding rock,as well as large column,deep beam and thick plate structure,which are reasonable and effective for the anti-vibration design of underground powerhouse structure.(7)Suggestions on evaluation criteria for structural vibration control of underground powerhouse of pumped storage power station are put forward.The recommended values of the traditional vibration control evaluation criteria are not reasonable and lack of pertinence.The proposed scheme for the vibration control evaluation criteria of the underground powerhouse structure of pumped storage power station is aimed at the floor and pier of the underground powerhouse.The recommended values of vibration control evaluation criteria for vibration displacement and acceleration under steady and transient conditions are given respectively,which can be used for future revision of relevant codes,engineering design and operation of power plants.(8)The revised formulas for calculating dynamic coefficients are put forward,and two parameters,peak-shaving and frequency-regulating coefficients and the number of turbine runner blades,are introduced to better control the vibration amplitude of pier structure,so as to achieve the purpose of controlling the overall vibration of underground powerhouse structure of pumped storage power station.It is suggested that in the finite element calculation of the anti-vibration design of the underground powerhouse structure of pumped storage power station,the standard values of dynamic loads should be calculated by the manufacturer according to the steady and transient conditions respectively.In this way,the vibration of underground powerhouse structure of Pumped Storage Power Station can be analyzed more comprehensively under the transient conditions of peak-shaving and frequency-regulating including pumping or power generation start-up,shutdown and mutual conversion,so that the corresponding adjustment can be made for the vibration control of underground powerhouse structure in the design stage.(9)Suggestions for vibration reduction of underground powerhouse structure of pumped storage power station are put forward from three aspects: active control of vibration source,passive reinforcement of underground powerhouse structure and optimization of operation scheme of power station.These suggestions can be used for future revision of relevant codes and selection and reference in engineering design and operation of power station: 1)Control vibration source,increase the number of turbine runner blades or reduce the overall height of the unit;2)Reinforcement of underground powerhouse structure,add mass blocks to the floor to reduce the natural vibration frequency or improve the design scheme of concrete structure,pier or support structure of spiral case to restrict vibration energy transmission;3)Optimizing the operation plan of the power plant,reduce the vibration of pumping unit and power generation unit during the transition process,or stagger the start-up and shutdown transition process of multiple units through unit design and research.