The test tesearch on hydraulic transient process inside the changing topaltitude tailrace tunnel of TGP'sunderground power plant was conducted for the firsttime in our country by use of a model generating set.Adopting the piece wise linear closure for guide vanes of turbine,the best inflection point of twostepclosure (i.e.closed in two kinds of uniform speed)was found,and it was verfiedthat the method of twostep closure has obvious effect for decreasing negative pressures and the rising rates of rotational speed of generating set.Through the measurement of hydraulicparameters,it was regarded that the changing topaltitude tailraee tunnel scheme can meet all the technical reqirements,and it is anewtype design scheme benificial for decreasing rock excavation and saving engineering investment.It can be widely applied in underground plant.
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