Model Test And Investigation On Draft Tube Mid-pier Modification Of The Qingtong-Gorge Hydropower Station

A large number of hydropower stations had been built up during the 50 and 60'sin the last century. These hydropower stations had been making great action on Chineseeconomic progress. There are many problems in these old hydropower stations afteroperation for so many year, such as crack, vibration and so on . It should bedemonstrated that how to make the old hydropower stations more efficient and how tocarry out the technical improvement.In this article, taking the Qingtonggorge hydropower station as an example, thetechnical feasibility to the improvement of the old hydropower stations was demonst-rated.Although the study was a special case , the approaches and means were common,Because of the modification and the replacement of the water turbine, the effects to thestructure and the fluid were roundly analyzed by building up the physical,FEM andfluid model. Also eighteen kinds of vibration source from the hydraulic, mechanic andelectrical factors were analyzed. According to the analytical results, the resonance wascalibrated and the effects to resonance brought by the modification was analyzed . Afew pieces of suggestion were put forward in the light of the problems occurred duringthe resonance calibration. In addition, the balance water tank which was the uniquestructure of the Qingtonggorge hydropower station was studied again. The thoughts ofthe design were analyzed and the researching results during the past years weregeneralized. The main conclusions were drawn as follows:(1) According to the results of the test and calculation , the mostly affectedposition was the draft tube, especially the location which would be removed. Theamount of reinforcement bar in the bottom and upper plates was not affected by themodification. Calculated through the current standards, the amount of the reinforcementbar in the bottom plate of the tail pipe was not enough. By simulating the rapidconstruction method, the test to the body stress was successful.(2) The resonance between the powerhouse structure and the centrifugal forcewhich is induced by the poor manufacture of the thrust bushing and the non-uniformpotential field in the scroll case is easily provoked, which should be paid attentionespecially when the output of the power station needs to be changed frequently andgreatly. Improving the design, manufacture and installation of the power generator andthe flow path of scroll case could solve this problem. At the same time, it is better toavoid the operation in the region where strong vibrations are possible to happen. Thereis some effect to the resonance brought by the modification, but the degree isn't large.By comparison, the replacement of the water turbine easily widen the scope of theresonance, which should be paid attention to.(3)The balance water tank could improved the state of the stress in somelocations, but the effect was not agreed with what the design had expected. It wasreasonable to strengthen the field measurement combining with the FEM calculationand the model test.(4)Through numerical simulation, the non-uniform of the draft tube flow wasimproved. The modification of the draft tube mid-pier made the flow smoother. But theeffect was not evident and the degree to the two holes was different.