Optimization Of Economic Tunnel Diameter Of Pumped Storage Power Station

In the initial stage of designning on the water conveyance tunnel of the pumped storage power station,the tunnel radius is one of the key parameters,and its value directly affects the economic benefits of the power station.The diameter of the water channel is small,the work amount is small,the construction period is short and the investment is small,but the power generation power of the power station is small,the head loss and the output of the power station are large,so the economic benefits are reduced;on the contrary,the diameter of the water channel is large,the work amount and investment are large,and the construction period is long,but the head loss and the output of the power station are small,and the economic benefits are large.The traditional economic tunnel diameter selection of water diversion and power generation tunnel usually adopts the empirical formula method,engineering analogy method and the minimum cost present value method.According to the empirical formula,it is proposed in the code for design of hydraulic tunnels(DL/t5195-2004)that the tunnel diameter value is preliminarily determined,in which the economic velocity V is generally 4-5m/s based on experience,and then the optimal value is selected through kinetic energy economic comparison.However,it should be noted that the maximum discharge of water turbine of large and medium-sized pumped storage power station is larger than that of General Hydropower Station.Under the condition of the same discharge area,the flow velocity increases and the head loss increases,which leads to the reduction of economic benefits.T he theoretical basis for the range of tunnel diameter in the design specification of raw water power station is insufficient.Therefore,further study is needed for the range of tunnel diameter in pumped storage power station.In view of the problems existing in the existing calculation methods,this paper,combined with the economic velocity method and the minimum annual cost value method,expands the tunnel diameter range on the basis of the tunnel diameter calculated by the economic velocity method,compares the economic benefit changes caused by the construction cost and head loss of the tunnel,obtains the economic velocity corresponding to the minimum scheme of the total cost,summarizes and sums up the tunnel diameter when the economic benefit of multiple engineering cases is maximum The results are as follows:(1)The design of the hole diameter scheme is empirical.Based on the empirical formula,this paper combines the mechanics,structure,materials and other factors to conduct mathematical model research and establish the current value model of the hole diameter cost-benefit loss.(2)The Calculation results about relationship between the total present value of the water conveyance tunnel and the diameter of the tunnel is a concave continuous function.The method of directly seeking the extreme value of the function can be used to calculate the economic diameter of the tunnel.Hole diameter calculation provides a new method.(3)According to the comparison and selection results of various surrounding rock characteristic schemes,the economic velocity can be concentrated between 3.7-4.1m/s,which is further narrowed than the range of 4-5m/s in the code for design of hydraulic tunnels.Therefore,for the tunnel diameter design scheme of pumped storage power station with large flow and high head,it is suggested that the relevant codes can reduce the economic velocity and adjust the economic velocity according to the actual engineering situation The value range is 3.7-4.1m/s to adapt to the actual situation of the project and provide reference for the value range of economic velocity of pumped storage power station.