| The reversible pump-turbine has two functions of pump and turbine at the same time and been in a wide range of applications in pumped storage power station.Because of the starting and stopping quickly and changing working conditions flexibly of the pump-turbine,the pumped storage power station can make rapid response and tracking the load change,and can play an efficient role in peak load shifting and ensuring the stability of the power system operation and so on.In recent years,with the emergence of the pump-turbine of large capacity and high head,a series of problems occur frequently such as start and stop accident of the unit,workshop vibration,noise,network difficulties,blade crack and so on.According to the literature research we can know that the pressure fluctuation is one of the main reasons these problems.Therefore,it is necessary to study the amplitude frequency characteristics and propagation mechanism of pressure fluctuation in the flow passage of the pump turbine unit,and provide a reliable reference for the hydraulic design and safe operation of the pump turbine.In order to study the vibration law of pump-turbine and workshop of a pumped storage power station in our country,we have carried out two times variable load experiments in the turbine working condition,with the average water head is 326.01 m and 316.23 m.During the experiments,four pressure pulse measurement points were arranged,one in the spiral case inlet,one in the top cover and two in the vaneless space.Subsequently,the pressure fluctuation signals were collected by the pressure sensor.This paper mainly analyzes the characteristics of pressure fluctuation,and the contents are as follows.Firstly,we analyzed the pressure signal in time domain of the first experiment,compared the difference of pressure fluctuation at different measuring points with the increasing of the load.The analysis results are as follows: The maximum relative amplitude of pressure fluctuation appears in the vaneless space,and along the channel extending to upstream the farther the distance,the smaller the amplitude;the relative amplitude of pressure fluctuation at each measuring point decreased firstly and then increased with the increasing of the load,and the minimum value appears when it reaches 80% of rated load where the flow is relatively good and the operation is relatively safe and stable.Secondly,we performed Fast Fourier Transform(FFT)on the pressure signal of first experiment,and analyzed its frequency domain characteristics.The analysis results are as follows: 9 times and 18 times of rotating frequency component of pressure fluctuation signals are in the dominant,which producing in vaneless space,and at the same time the two pressure pulsation frequency is the main cause for the unit and building vibration;with the improvement of the load,the two component above have different features,the pressure fluctuation with 9 times of the rotating frequency decreases constantly with the increasing of the load and the other pressure fluctuation decreases firstly decreases and then increases with the improvement of the load.Thirdly,we analyzed the amplitude and frequency characteristics of the pressure fluctuation signal of the second experiment and then compared them with the first data.Subsequently we discussed the relationship between the pressure fluctuation and the operating head of the pump-turbine.The analysis results are as follows: the relative amplitude of pressure fluctuation at the spiral case inlet and top cover is smaller under the operating conditions of higher water head,in which the internal flow is relatively good;the relative amplitude of fluctuation at vaneless space is smaller under the operating conditions of lower water head,in which the internal flow is relatively good;it is worth noting that The frequency of pressure fluctuation is not affected by the change of head. |
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