Analysis On Hydraulic Transition Process Of Combined Differential Surge Chamber

In the development of hydropower industry in China,Some projects make full use of its terrain conditions to build a long water diversion tunnel with high head.Because of it's long diversion tunnel,this kind of hydropower station will produce large water flow inertia,which brings great threat to the system.It is necessary to set up upstream surge chamber to reflect water hammer wave and reduce water hammer pressure.At the same time,the research and analysis of-hydraulic transition process can effectively reveal the dynamic characteristics of the system between the parameters under different working conditions,and ensure the safe and stable operation of hydropower stations.In this dissertation,the combined differential surge chamber is the key research object.Based on the existing research results,the simulation model is established based on the actual engineering.The surge water level,unit parameters and water hammer pressure are systematically studied,and the following research results were obtained:(1)Compared with the straight-line closing rule;when the guide vane adopts the two-stage closing rule,the maximum pressure value at the end of the volute and the increase rate of the maximum speed of the unit can be effective ly reduced.And the choice of the closing tire of each section and the inflection point opening all affect the results of the adjustment guarantee calculation.(2)Under large fluctuation conditions,the ratio of joint pipe size to shaft size can effectively improve the regulation guarantee parameters within a certain range,and the increase of section size of surge chamber is beneficial to reduce the Maximum surge water level.At the same time,the rotary inertia GD2 of the unit should be selected in combination with the safe operation of the unit and the engineering cost.The combination of flow coefficient in and out of differential hole has great influence on the performance of the combined differential surge chamber.(3)Under small fluctuation conditions,The increase of shaft size and rotary inertia GD2 of the unit within a certain range is conducive to the stability of-small fluctuations.In addition,the increase of connecting pipe size will make the regulating quality and the surge water level in the surge chamber worse.What's more,the selection of the roughness of the diversion tunnel should be determined by combining the stability of small fluctuations and the power supply quality of the unit.(4)Under the condition of hydraulic disturbance,The increase of shaft section size is beneficial to the output stability of the unit and the water level attenuation of the surge chamber.But the increase of the section size of the joint pipe is not conducive to the stability of the hydraulic disturbance transition condition,when the joint pipe diameter exceeds 60%of the shaft diameter,the sensitivity is reduced.In addition,in the allowable value range of roughness of diversion tunnel,the larger value can effectively reduce the output swing of the unit.