6.1　Selection of Turbine and Generator

6.1　Selection of Turbine and Generator

6.1.1　The type，capacity and number of hydraulic turbines shall be selected after techno-economic comparison based on project layout，range and characteristics of working heads，and technical features，economic indicators and operating reliability of the hydropower station，while the current design and manufacturing technology of turbines shall be taken into account.

6.1.2　The main target parameters of turbines such as diameter，rotation speed，output，efficiency，and suction head shall be finalized according to the range of working head and the runner characteristics.

6.1.3　For a hydropower station located on a sediment-laden river，the specific speed of turbine shall be appropriately reduced according to the sediment volume passing through the turbines and the characteristics of sediment.The parts with flows passing through should be made of anti-corrosion materials or applied with a protection coating.

6.1.4　For the double-nozzle impulse unit with its runner nominal diameter larger than 1.4m，it should be vertically installed.

6.1.5　The maximum runaway speed of Kaplan turbines shall be calculated based on the hypothesis that coordinated operation of the guide vane and the runner blade causes damages.The maximum runaway speed of radial-axial flow turbines or propeller turbines shall be determined according to the maximum net water head of the hydropower station and the maximum unit runaway speed.The maximum runaway speed of impulse turbines shall be determined according to the maximum net water head of the hydropower station.

6.1.6　The installation elevation of turbines shall be determined based on the necessary suction head and the corresponding tailrace water level under various kinds of operating conditions of the turbines，and shall comply with the following requirements:

1　If more than two units are installed，the requirement for one unit′s suction head and the corresponding tailrace water level at the maximum output under various water heads should be met.(https://www.daowen.com)

2　If one or two units are installed，the requirement for one unit′s suction head and the corresponding tailrace water level at 50% of the maximum output under various water heads should be met.

3　The installation elevation of Kaplan turbines should be determined through calculation based on the actual combined working conditions of water head，flow volume and output of the hydropower station，and cavitation coefficient of the runner，and shall meet the requirement that the submergence of the top of the draft tube outlet is more than 0.5m.

4　The installation elevation of impulse turbines shall be determined according to the maximum tailrace water level for power generation，and meet the requirements for an aeration height no less than 0.3m.

5　The outlet edge of draft tube of vertical turbines shall be 0.5m lower than the minimum tailrace water level；and the submergence of the outlet of draft tube of horizontal turbines shall be more than 0.3m.

6.1.7　The types and sizes of spiral case and draft tube of hydraulic turbines should be designed as recommended by the manufacturer，and the base slab of the diffuser section of elbow draft tubes should be at an angle of 0°-12° to the horizontal plane.Metal internal liner shall be applied to the conical part of vertical shaft turbine draft tube，and the elbow part as well.Metal liner shall also be used if the mean flow velocity is higher than 6m/s in the diffuser section of draft tubes.

6.1.8　The predominant parameters，structural types and general layout of hydraulic turbine-generator shall meet the operational requirements of the electric power system and the hydropower station.